# The Tahoe REST-ful Web API

1. Enabling the web-API port
2. Basic Concepts: GET, PUT, DELETE, POST
3. URLs
   1. Child Lookup
4. Slow Operations, Progress, and Cancelling
5. Programmatic Operations
   1. Reading a file
   2. Writing/Uploading a File
   3. Creating a New Directory
   4. Getting Information About a File Or Directory (as JSON)
   5. Attaching an Existing File or Directory by its read- or write-cap
   6. Adding Multiple Files or Directories to a Parent Directory at Once
   7. Unlinking a File or Directory
6. Browser Operations: Human-Oriented Interfaces
   1. Viewing a Directory (as HTML)
   2. Viewing/Downloading a File
   3. Getting Information About a File Or Directory (as HTML)
   4. Creating a Directory
   5. Uploading a File
   6. Attaching an Existing File Or Directory (by URI)
   7. Unlinking a Child
   8. Renaming a Child
   9. Relinking (“Moving”) a Child
   10. Other Utilities
   11. Debugging and Testing Features
7. Other Useful Pages
8. Static Files in /public_html
9. Safety and Security Issues – Names vs. URIs
10. Concurrency Issues
11. Access Blacklist

## Enabling the web-API port

Every Tahoe node is capable of running a built-in HTTP server. To enable this, just write a port number into the “[node]web.port” line of your node’s tahoe.cfg file. For example, writing “web.port = 3456” into the “[node]” section of $NODEDIR/tahoe.cfg will cause the node to run a webserver on port 3456.

This string is actually a Twisted “strports” specification, meaning you can get more control over the interface to which the server binds by supplying additional arguments. For more details, see the documentation on twisted.application.strports.

Writing “tcp:3456:interface=127.0.0.1” into the web.port line does the same but binds to the loopback interface, ensuring that only the programs on the local host can connect. Using “ssl:3456:privateKey=mykey.pem:certKey=cert.pem” runs an SSL server.

This webport can be set when the node is created by passing a –webport option to the ‘tahoe create-node’ command. By default, the node listens on port 3456, on the loopback (127.0.0.1) interface.

## Basic Concepts: GET, PUT, DELETE, POST

As described in Tahoe-LAFS Architecture, each file and directory in a Tahoe-LAFS file store is referenced by an identifier that combines the designation of the object with the authority to do something with it (such as read or modify the contents). This identifier is called a “read-cap” or “write-cap”, depending upon whether it enables read-only or read-write access. These “caps” are also referred to as URIs (which may be confusing because they are not currently RFC3986-compliant URIs).

The Tahoe web-based API is “REST-ful”, meaning it implements the concepts of “REpresentational State Transfer”: the original scheme by which the World Wide Web was intended to work. Each object (file or directory) is referenced by a URL that includes the read- or write- cap. HTTP methods (GET, PUT, and DELETE) are used to manipulate these objects. You can think of the URL as a noun, and the method as a verb.

In REST, the GET method is used to retrieve information about an object, or to retrieve some representation of the object itself. When the object is a file, the basic GET method will simply return the contents of that file. Other variations (generally implemented by adding query parameters to the URL) will return information about the object, such as metadata. GET operations are required to have no side-effects.

PUT is used to upload new objects into the file store, or to replace an existing link or the contents of a mutable file. DELETE is used to unlink objects from directories. Both PUT and DELETE are required to be idempotent: performing the same operation multiple times must have the same side-effects as only performing it once.

POST is used for more complicated actions that cannot be expressed as a GET, PUT, or DELETE. POST operations can be thought of as a method call: sending some message to the object referenced by the URL. In Tahoe, POST is also used for operations that must be triggered by an HTML form (including upload and unlinking), because otherwise a regular web browser has no way to accomplish these tasks. In general, everything that can be done with a PUT or DELETE can also be done with a POST.

Tahoe-LAFS’ web API is designed for two different kinds of consumer. The first is a program that needs to manipulate the file store. Such programs are expected to use the RESTful interface described above. The second is a human using a standard web browser to work with the file store. This user is presented with a series of HTML pages with links to download files, and forms that use POST actions to upload, rename, and unlink files.

When an error occurs, the HTTP response code will be set to an appropriate 400-series code (like 404 Not Found for an unknown childname, or 400 Bad Request when the parameters to a web-API operation are invalid), and the HTTP response body will usually contain a few lines of explanation as to the cause of the error and possible responses. Unusual exceptions may result in a 500 Internal Server Error as a catch-all, with a default response body containing a Nevow-generated HTML-ized representation of the Python exception stack trace that caused the problem. CLI programs which want to copy the response body to stderr should provide an “Accept: text/plain” header to their requests to get a plain text stack trace instead. If the Accept header contains `*/*`, or `text/*`, or text/html (or if there is no Accept header), HTML tracebacks will be generated.

## URLs

Tahoe uses a variety of read- and write- caps to identify files and directories. The most common of these is the “immutable file read-cap”, which is used for most uploaded files. These read-caps look like the following:

    URI:CHK:ime6pvkaxuetdfah2p2f35pe54:4btz54xk3tew6nd4y2ojpxj4m6wxjqqlwnztgre6gnjgtucd5r4a:3:10:202

The next most common is a “directory write-cap”, which provides both read and write access to a directory, and look like this:

    URI:DIR2:djrdkfawoqihigoett4g6auz6a:jx5mplfpwexnoqff7y5e4zjus4lidm76dcuarpct7cckorh2dpgq

There are also “directory read-caps”, which start with “URI:DIR2-RO:”, and give read-only access to a directory. Finally there are also mutable file read- and write- caps, which start with “URI:SSK”, and give access to mutable files.

(Later versions of Tahoe will make these strings shorter, and will remove the unfortunate colons, which must be escaped when these caps are embedded in URLs.)

To refer to any Tahoe object through the web API, you simply need to combine a prefix (which indicates the HTTP server to use) with the cap (which indicates which object inside that server to access). Since the default Tahoe webport is 3456, the most common prefix is one that will use a local node listening on this port:

    http://127.0.0.1:3456/uri/ + $CAP

So, to access the directory named above, the URL would be:

    http://127.0.0.1:3456/uri/URI%3ADIR2%3Adjrdkfawoqihigoett4g6auz6a%3Ajx5mplfpwexnoqff7y5e4zjus4lidm76dcuarpct7cckorh2dpgq/

(note that the colons in the directory-cap are url-encoded into “%3A” sequences).

Likewise, to access the file named above, use:

    http://127.0.0.1:3456/uri/URI%3ACHK%3Aime6pvkaxuetdfah2p2f35pe54%3A4btz54xk3tew6nd4y2ojpxj4m6wxjqqlwnztgre6gnjgtucd5r4a%3A3%3A10%3A202

In the rest of this document, we’ll use “$DIRCAP” as shorthand for a read-cap or write-cap that refers to a directory, and “$FILECAP” to abbreviate a cap that refers to a file (whether mutable or immutable). So those URLs above can be abbreviated as:

    http://127.0.0.1:3456/uri/$DIRCAP/
    http://127.0.0.1:3456/uri/$FILECAP

The operation summaries below will abbreviate these further, by eliding the server prefix. They will be displayed like this:

    /uri/$DIRCAP/
    /uri/$FILECAP

/cap can be used as a synonym for /uri. If interoperability with older web-API servers is required, /uri should be used.

### Child Lookup

Tahoe directories contain named child entries, just like directories in a regular local filesystem. These child entries, called “dirnodes”, consist of a name, metadata, a write slot, and a read slot. The write and read slots normally contain a write-cap and read-cap referring to the same object, which can be either a file or a subdirectory. The write slot may be empty (actually, both may be empty, but that is unusual).

If you have a Tahoe URL that refers to a directory, and want to reference a named child inside it, just append the child name to the URL. For example, if our sample directory contains a file named “welcome.txt”, we can refer to that file with:

    http://127.0.0.1:3456/uri/$DIRCAP/welcome.txt

(or http://127.0.0.1:3456/uri/URI%3ADIR2%3Adjrdkfawoqihigoett4g6auz6a%3Ajx5mplfpwexnoqff7y5e4zjus4lidm76dcuarpct7cckorh2dpgq/welcome.txt)

Multiple levels of subdirectories can be handled this way:

    http://127.0.0.1:3456/uri/$DIRCAP/tahoe-source/docs/architecture.rst

In this document, when we need to refer to a URL that references a file using this child-of-some-directory format, we’ll use the following string:

    /uri/$DIRCAP/[SUBDIRS../]FILENAME

The “[SUBDIRS../]” part means that there are zero or more (optional) subdirectory names in the middle of the URL. The “FILENAME” at the end means that this whole URL refers to a file of some sort, rather than to a directory.

When we need to refer specifically to a directory in this way, we’ll write:

    /uri/$DIRCAP/[SUBDIRS../]SUBDIR

Note that all components of pathnames in URLs are required to be UTF-8 encoded, so “resume.doc” (with an acute accent on both E’s) would be accessed with:

    http://127.0.0.1:3456/uri/$DIRCAP/r%C3%A9sum%C3%A9.doc

Also note that the filenames inside upload POST forms are interpreted using whatever character set was provided in the conventional ‘_charset’ field, and defaults to UTF-8 if not otherwise specified. The JSON representation of each directory contains native Unicode strings. Tahoe directories are specified to contain Unicode filenames, and cannot contain binary strings that are not representable as such.

All Tahoe operations that refer to existing files or directories must include a suitable read- or write- cap in the URL: the web-API server won’t add one for you. If you don’t know the cap, you can’t access the file. This allows the security properties of Tahoe caps to be extended across the web-API interface.

## Slow Operations, Progress, and Cancelling

Certain operations can be expected to take a long time. The “t=deep-check”, described below, will recursively visit every file and directory reachable from a given starting point, which can take minutes or even hours for extremely large directory structures. A single long-running HTTP request is a fragile thing: proxies, NAT boxes, browsers, and users may all grow impatient with waiting and give up on the connection.

For this reason, long-running operations have an “operation handle”, which can be used to poll for status/progress messages while the operation proceeds. This handle can also be used to cancel the operation. These handles are created by the client, and passed in as a an “ophandle=” query argument to the POST or PUT request which starts the operation. The following operations can then be used to retrieve status:

`GET /operations/$HANDLE?output=HTML (with or without t=status)`

`GET /operations/$HANDLE?output=JSON (same)`

> These two retrieve the current status of the given operation. Each operation presents a different sort of information, but in general the page retrieved will indicate:

> - whether the operation is complete, or if it is still running
> - how much of the operation is complete, and how much is left, if possible

> Note that the final status output can be quite large: a deep-manifest of a directory structure with 300k directories and 200k unique files is about 275MB of JSON, and might take two minutes to generate. For this reason, the full status is not provided until the operation has completed.

> The HTML form will include a meta-refresh tag, which will cause a regular web browser to reload the status page about 60 seconds later. This tag will be removed once the operation has completed.

> There may be more status information available under /operations/$HANDLE/$ETC : i.e., the handle forms the root of a URL space.

`POST /operations/$HANDLE?t=cancel`

> This terminates the operation, and returns an HTML page explaining what was cancelled. If the operation handle has already expired (see below), this POST will return a 404, which indicates that the operation is no longer running (either it was completed or terminated). The response body will be the same as a GET /operations/$HANDLE on this operation handle, and the handle will be expired immediately afterwards.

The operation handle will eventually expire, to avoid consuming an unbounded amount of memory. The handle’s time-to-live can be reset at any time, by passing a retain-for= argument (with a count of seconds) to either the initial POST that starts the operation, or the subsequent GET request which asks about the operation. For example, if a ‘GET /operations/$HANDLE?output=JSON&retain-for=600’ query is performed, the handle will remain active for 600 seconds (10 minutes) after the GET was received.

In addition, if the GET includes a release-after-complete=True argument, and the operation has completed, the operation handle will be released immediately.

If a retain-for= argument is not used, the default handle lifetimes are:

> - handles will remain valid at least until their operation finishes
> - uncollected handles for finished operations (i.e. handles for operations that have finished but for which the GET page has not been accessed since completion) will remain valid for four days, or for the total time consumed by the operation, whichever is greater.
> - collected handles (i.e. the GET page has been retrieved at least once since the operation completed) will remain valid for one day.

Many “slow” operations can begin to use unacceptable amounts of memory when operating on large directory structures. The memory usage increases when the ophandle is polled, as the results must be copied into a JSON string, sent over the wire, then parsed by a client. So, as an alternative, many “slow” operations have streaming equivalents. These equivalents do not use operation handles. Instead, they emit line-oriented status results immediately. Client code can cancel the operation by simply closing the HTTP connection.

## Programmatic Operations

Now that we know how to build URLs that refer to files and directories in a Tahoe-LAFS file store, what sorts of operations can we do with those URLs? This section contains a catalog of GET, PUT, DELETE, and POST operations that can be performed on these URLs. This set of operations are aimed at programs that use HTTP to communicate with a Tahoe node. A later section describes operations that are intended for web browsers.

### Reading a File

`GET /uri/$FILECAP`

`GET /uri/$DIRCAP/[SUBDIRS../]FILENAME`

> This will retrieve the contents of the given file. The HTTP response body will contain the sequence of bytes that make up the file.

> The “Range:” header can be used to restrict which portions of the file are returned (see RFC 2616 section 14.35.1 “Byte Ranges”), however Tahoe only supports a single “bytes” range and never provides a `multipart/byteranges` response. An attempt to begin a read past the end of the file will provoke a 416 Requested Range Not Satisfiable error, but normal overruns (reads which start at the beginning or middle and go beyond the end) are simply truncated.

> To view files in a web browser, you may want more control over the Content-Type and Content-Disposition headers. Please see the next section “Browser Operations”, for details on how to modify these URLs for that purpose.

### Writing/Uploading a File

`PUT /uri/$FILECAP`

`PUT /uri/$DIRCAP/[SUBDIRS../]FILENAME`

> Upload a file, using the data from the HTTP request body, and add whatever child links and subdirectories are necessary to make the file available at the given location. Once this operation succeeds, a GET on the same URL will retrieve the same contents that were just uploaded. This will create any necessary intermediate subdirectories.

> To use the /uri/$FILECAP form, $FILECAP must be a write-cap for a mutable file.

> In the /uri/$DIRCAP/[SUBDIRS../]FILENAME form, if the target file is a writeable mutable file, that file’s contents will be overwritten in-place. If it is a read-cap for a mutable file, an error will occur. If it is an immutable file, the old file will be discarded, and a new one will be put in its place. If the target file is a writable mutable file, you may also specify an “offset” parameter – a byte offset that determines where in the mutable file the data from the HTTP request body is placed. This operation is relatively efficient for MDMF mutable files, and is relatively inefficient (but still supported) for SDMF mutable files. If no offset parameter is specified, then the entire file is replaced with the data from the HTTP request body. For an immutable file, the “offset” parameter is not valid.

> When creating a new file, you can control the type of file created by specifying a format= argument in the query string. format=MDMF creates an MDMF mutable file. format=SDMF creates an SDMF mutable file. format=CHK creates an immutable file. The value of the format argument is case-insensitive. If no format is specified, the newly-created file will be immutable (but see below).

> For compatibility with previous versions of Tahoe-LAFS, the web-API will also accept a mutable=true argument in the query string. If mutable=true is given, then the new file will be mutable, and its format will be the default mutable file format, as configured by the [client]mutable.format option of tahoe.cfg on the Tahoe-LAFS node hosting the webapi server. Use of mutable=true is discouraged; new code should use format= instead of mutable=true (unless it needs to be compatible with web-API servers older than v1.9.0). If neither format= nor mutable=true are given, the newly-created file will be immutable.

> This returns the file-cap of the resulting file. If a new file was created by this method, the HTTP response code (as dictated by rfc2616) will be set to 201 CREATED. If an existing file was replaced or modified, the response code will be 200 OK.

> Note that the ‘curl -T localfile http://127.0.0.1:3456/uri/$DIRCAP/foo.txt’ command can be used to invoke this operation.

`PUT /uri`

> This uploads a file, and produces a file-cap for the contents, but does not attach the file into the file store. No directories will be modified by this operation. The file-cap is returned as the body of the HTTP response.

> This method accepts format= and mutable=true as query string arguments, and interprets those arguments in the same way as the linked forms of PUT described immediately above.

### Creating a New Directory

`POST /uri?t=mkdir`

`PUT /uri?t=mkdir`

> Create a new empty directory and return its write-cap as the HTTP response body. This does not make the newly created directory visible from the file store. The “PUT” operation is provided for backwards compatibility: new code should use POST.

> This supports a format= argument in the query string. The format= argument, if specified, controls the format of the directory. format=MDMF indicates that the directory should be stored as an MDMF file; format=SDMF indicates that the directory should be stored as an SDMF file. The value of the format= argument is case-insensitive. If no format= argument is given, the directory’s format is determined by the default mutable file format, as configured on the Tahoe-LAFS node responding to the request.

`POST /uri?t=mkdir-with-children`

> Create a new directory, populated with a set of child nodes, and return its write-cap as the HTTP response body. The new directory is not attached to any other directory: the returned write-cap is the only reference to it.

> The format of the directory can be controlled with the format= argument in the query string, as described above.

> Initial children are provided as the body of the POST form (this is more efficient than doing separate mkdir and set_children operations). If the body is empty, the new directory will be empty. If not empty, the body will be interpreted as a UTF-8 JSON-encoded dictionary of children with which the new directory should be populated, using the same format as would be returned in the ‘children’ value of the t=json GET request, described below. Each dictionary key should be a child name, and each value should be a list of [TYPE, PROPDICT], where PROPDICT contains “rw_uri”, “ro_uri”, and “metadata” keys (all others are ignored). For example, the PUT request body could be:

>     {
>       "Fran\u00e7ais": [ "filenode", {
>           "ro_uri": "URI:CHK:...",
>           "metadata": {
>             "ctime": 1202777696.7564139,
>             "mtime": 1202777696.7564139,
>             "tahoe": {
>               "linkcrtime": 1202777696.7564139,
>               "linkmotime": 1202777696.7564139
>               } } } ],
>       "subdir":  [ "dirnode", {
>           "rw_uri": "URI:DIR2:...",
>           "ro_uri": "URI:DIR2-RO:...",
>           "metadata": {
>             "ctime": 1202778102.7589991,
>             "mtime": 1202778111.2160511,
>             "tahoe": {
>               "linkcrtime": 1202777696.7564139,
>               "linkmotime": 1202777696.7564139
>             } } } ]
>     }

> For forward-compatibility, a mutable directory can also contain caps in a format that is unknown to the web-API server. When such caps are retrieved from a mutable directory in a “ro_uri” field, they will be prefixed with the string “ro.”, indicating that they must not be decoded without checking that they are read-only. The “ro.” prefix must not be stripped off without performing this check. (Future versions of the web-API server will perform it where necessary.)

> If both the “rw_uri” and “ro_uri” fields are present in a given PROPDICT, and the web-API server recognizes the rw_uri as a write cap, then it will reset the ro_uri to the corresponding read cap and discard the original contents of ro_uri (in order to ensure that the two caps correspond to the same object and that the ro_uri is in fact read-only). However this may not happen for caps in a format unknown to the web-API server. Therefore, when writing a directory the web-API client should ensure that the contents of “rw_uri” and “ro_uri” for a given PROPDICT are a consistent (write cap, read cap) pair if possible. If the web-API client only has one cap and does not know whether it is a write cap or read cap, then it is acceptable to set “rw_uri” to that cap and omit “ro_uri”. The client must not put a write cap into a “ro_uri” field.

> The metadata may have a “no-write” field. If this is set to true in the metadata of a link, it will not be possible to open that link for writing via the SFTP frontend; see Tahoe-LAFS SFTP and FTP Frontends for details. Also, if the “no-write” field is set to true in the metadata of a link to a mutable child, it will cause the link to be diminished to read-only.

> Note that the web-API-using client application must not provide the “Content-Type: multipart/form-data” header that usually accompanies HTML form submissions, since the body is not formatted this way. Doing so will cause a server error as the lower-level code misparses the request body.

> Child file names should each be expressed as a Unicode string, then used as keys of the dictionary. The dictionary should then be converted into JSON, and the resulting string encoded into UTF-8. This UTF-8 bytestring should then be used as the POST body.

`POST /uri?t=mkdir-immutable`

> Like t=mkdir-with-children above, but the new directory will be deep-immutable. This means that the directory itself is immutable, and that it can only contain objects that are treated as being deep-immutable, like immutable files, literal files, and deep-immutable directories.

> For forward-compatibility, a deep-immutable directory can also contain caps in a format that is unknown to the web-API server. When such caps are retrieved from a deep-immutable directory in a “ro_uri” field, they will be prefixed with the string “imm.”, indicating that they must not be decoded without checking that they are immutable. The “imm.” prefix must not be stripped off without performing this check. (Future versions of the web-API server will perform it where necessary.)

> The cap for each child may be given either in the “rw_uri” or “ro_uri” field of the PROPDICT (not both). If a cap is given in the “rw_uri” field, then the web-API server will check that it is an immutable read-cap of a known format, and give an error if it is not. If a cap is given in the “ro_uri” field, then the web-API server will still check whether known caps are immutable, but for unknown caps it will simply assume that the cap can be stored, as described above. Note that an attacker would be able to store any cap in an immutable directory, so this check when creating the directory is only to help non-malicious clients to avoid accidentally giving away more authority than intended.

> A non-empty request body is mandatory, since after the directory is created, it will not be possible to add more children to it.

`POST /uri/$DIRCAP/[SUBDIRS../]SUBDIR?t=mkdir`

`PUT /uri/$DIRCAP/[SUBDIRS../]SUBDIR?t=mkdir`

> Create new directories as necessary to make sure that the named target ($DIRCAP/SUBDIRS../SUBDIR) is a directory. This will create additional intermediate mutable directories as necessary. If the named target directory already exists, this will make no changes to it.

> If the final directory is created, it will be empty.

> This accepts a format= argument in the query string, which controls the format of the named target directory, if it does not already exist. format= is interpreted in the same way as in the POST /uri?t=mkdir form. Note that format= only controls the format of the named target directory; intermediate directories, if created, are created based on the default mutable type, as configured on the Tahoe-LAFS server responding to the request.

> This operation will return an error if a blocking file is present at any of the parent names, preventing the server from creating the necessary parent directory; or if it would require changing an immutable directory.

> The write-cap of the new directory will be returned as the HTTP response body.

`POST /uri/$DIRCAP/[SUBDIRS../]SUBDIR?t=mkdir-with-children`

> Like /uri?t=mkdir-with-children, but the final directory is created as a child of an existing mutable directory. This will create additional intermediate mutable directories as necessary. If the final directory is created, it will be populated with initial children from the POST request body, as described above.

> This accepts a format= argument in the query string, which controls the format of the target directory, if the target directory is created as part of the operation. format= is interpreted in the same way as in the POST/ uri?t=mkdir-with-children operation. Note that format= only controls the format of the named target directory; intermediate directories, if created, are created using the default mutable type setting, as configured on the Tahoe-LAFS server responding to the request.

> This operation will return an error if a blocking file is present at any of the parent names, preventing the server from creating the necessary parent directory; or if it would require changing an immutable directory; or if the immediate parent directory already has a a child named SUBDIR.

`POST /uri/$DIRCAP/[SUBDIRS../]SUBDIR?t=mkdir-immutable`

> Like /uri?t=mkdir-immutable, but the final directory is created as a child of an existing mutable directory. The final directory will be deep-immutable, and will be populated with the children specified as a JSON dictionary in the POST request body.

> In Tahoe 1.6 this operation creates intermediate mutable directories if necessary, but that behaviour should not be relied on; see ticket #920.

> This operation will return an error if the parent directory is immutable, or already has a child named SUBDIR.

`POST /uri/$DIRCAP/[SUBDIRS../]?t=mkdir&name=NAME`

> Create a new empty mutable directory and attach it to the given existing directory. This will create additional intermediate directories as necessary.

> This accepts a format= argument in the query string, which controls the format of the named target directory, if it does not already exist. format= is interpreted in the same way as in the POST /uri?t=mkdir form. Note that format= only controls the format of the named target directory; intermediate directories, if created, are created based on the default mutable type, as configured on the Tahoe-LAFS server responding to the request.

> This operation will return an error if a blocking file is present at any of the parent names, preventing the server from creating the necessary parent directory, or if it would require changing any immutable directory.

> The URL of this operation points to the parent of the bottommost new directory, whereas the /uri/$DIRCAP/[SUBDIRS../]SUBDIR?t=mkdir operation above has a URL that points directly to the bottommost new directory.

`POST /uri/$DIRCAP/[SUBDIRS../]?t=mkdir-with-children&name=NAME`

> Like /uri/$DIRCAP/[SUBDIRS../]?t=mkdir&name=NAME, but the new directory will be populated with initial children via the POST request body. This command will create additional intermediate mutable directories as necessary.

> This accepts a format= argument in the query string, which controls the format of the target directory, if the target directory is created as part of the operation. format= is interpreted in the same way as in the POST/ uri?t=mkdir-with-children operation. Note that format= only controls the format of the named target directory; intermediate directories, if created, are created using the default mutable type setting, as configured on the Tahoe-LAFS server responding to the request.

> This operation will return an error if a blocking file is present at any of the parent names, preventing the server from creating the necessary parent directory; or if it would require changing an immutable directory; or if the immediate parent directory already has a a child named NAME.

> Note that the name= argument must be passed as a queryarg, because the POST request body is used for the initial children JSON.

`POST /uri/$DIRCAP/[SUBDIRS../]?t=mkdir-immutable&name=NAME`

> Like /uri/$DIRCAP/[SUBDIRS../]?t=mkdir-with-children&name=NAME, but the final directory will be deep-immutable. The children are specified as a JSON dictionary in the POST request body. Again, the name= argument must be passed as a queryarg.

> In Tahoe 1.6 this operation creates intermediate mutable directories if necessary, but that behaviour should not be relied on; see ticket #920.

> This operation will return an error if the parent directory is immutable, or already has a child named NAME.

### Getting Information About a File Or Directory (as JSON)

`GET /uri/$FILECAP?t=json`

`GET /uri/$DIRCAP?t=json`

`GET /uri/$DIRCAP/[SUBDIRS../]SUBDIR?t=json`

`GET /uri/$DIRCAP/[SUBDIRS../]FILENAME?t=json`

> This returns a machine-parseable JSON-encoded description of the given object. The JSON always contains a list, and the first element of the list is always a flag that indicates whether the referenced object is a file or a directory. If it is a capability to a file, then the information includes file size and URI, like this:

>     GET /uri/$FILECAP?t=json :

>      [ "filenode", {
>         "ro_uri": file_uri,
>         "verify_uri": verify_uri,
>         "size": bytes,
>         "mutable": false,
>         "format": "CHK"
>        } ]

> If it is a capability to a directory followed by a path from that directory to a file, then the information also includes metadata from the link to the file in the parent directory, like this:

>     GET /uri/$DIRCAP/[SUBDIRS../]FILENAME?t=json

>      [ "filenode", {
>         "ro_uri": file_uri,
>         "verify_uri": verify_uri,
>         "size": bytes,
>         "mutable": false,
>         "format": "CHK",
>         "metadata": {
>          "ctime": 1202777696.7564139,
>          "mtime": 1202777696.7564139,
>          "tahoe": {
>           "linkcrtime": 1202777696.7564139,
>           "linkmotime": 1202777696.7564139
>          } } } ]

> If it is a directory, then it includes information about the children of this directory, as a mapping from child name to a set of data about the child (the same data that would appear in a corresponding GET?t=json of the child itself). The child entries also include metadata about each child, including link-creation- and link-change- timestamps. The output looks like this:

>     GET /uri/$DIRCAP?t=json :
>     GET /uri/$DIRCAP/[SUBDIRS../]SUBDIR?t=json :

>      [ "dirnode", {
>        "rw_uri": read_write_uri,
>        "ro_uri": read_only_uri,
>        "verify_uri": verify_uri,
>        "mutable": true,
>        "format": "SDMF",
>        "children": {
>         "foo.txt": [ "filenode",
>                      {
>                        "ro_uri": uri,
>                        "size": bytes,
>                        "metadata": {
>                          "ctime": 1202777696.7564139,
>                          "mtime": 1202777696.7564139,
>                          "tahoe": {
>                            "linkcrtime": 1202777696.7564139,
>                            "linkmotime": 1202777696.7564139
>                          } } } ],
>         "subdir":  [ "dirnode",
>                      {
>                        "rw_uri": rwuri,
>                        "ro_uri": rouri,
>                        "metadata": {
>                          "ctime": 1202778102.7589991,
>                          "mtime": 1202778111.2160511,
>                          "tahoe": {
>                            "linkcrtime": 1202777696.7564139,
>                            "linkmotime": 1202777696.7564139
>                          } } } ]
>         } } ]

> In the above example, note how ‘children’ is a dictionary in which the keys are child names and the values depend upon whether the child is a file or a directory. The value is mostly the same as the JSON representation of the child object (except that directories do not recurse – the “children” entry of the child is omitted, and the directory view includes the metadata that is stored on the directory edge).

> The rw_uri field will be present in the information about a directory if and only if you have read-write access to that directory. The verify_uri field will be present if and only if the object has a verify-cap (non-distributed LIT files do not have verify-caps).

> If the cap is of an unknown format, then the file size and verify_uri will not be available:

>     GET /uri/$UNKNOWNCAP?t=json :

>      [ "unknown", {
>          "ro_uri": unknown_read_uri
>          } ]

>     GET /uri/$DIRCAP/[SUBDIRS../]UNKNOWNCHILDNAME?t=json :

>      [ "unknown", {
>          "rw_uri": unknown_write_uri,
>          "ro_uri": unknown_read_uri,
>          "mutable": true,
>          "metadata": {
>            "ctime": 1202777696.7564139,
>            "mtime": 1202777696.7564139,
>            "tahoe": {
>              "linkcrtime": 1202777696.7564139,
>              "linkmotime": 1202777696.7564139
>            } } } ]

> As in the case of file nodes, the metadata will only be present when the capability is to a directory followed by a path. The “mutable” field is also not always present; when it is absent, the mutability of the object is not known.

#### About the metadata

The value of the ‘tahoe’:’linkmotime’ key is updated whenever a link to a child is set. The value of the ‘tahoe’:’linkcrtime’ key is updated whenever a link to a child is created – i.e. when there was not previously a link under that name.

Note however, that if the edge in the Tahoe-LAFS file store points to a mutable file and the contents of that mutable file is changed, then the ‘tahoe’:’linkmotime’ value on that edge will not be updated, since the edge itself wasn’t updated – only the mutable file was.

The timestamps are represented as a number of seconds since the UNIX epoch (1970-01-01 00:00:00 UTC), with leap seconds not being counted in the long term.

In Tahoe earlier than v1.4.0, ‘mtime’ and ‘ctime’ keys were populated instead of the ‘tahoe’:’linkmotime’ and ‘tahoe’:’linkcrtime’ keys. Starting in Tahoe v1.4.0, the ‘linkmotime’/’linkcrtime’ keys in the ‘tahoe’ sub-dict are populated. However, prior to Tahoe v1.7beta, a bug caused the ‘tahoe’ sub-dict to be deleted by web-API requests in which new metadata is specified, and not to be added to existing child links that lack it.

From Tahoe v1.7.0 onward, the ‘mtime’ and ‘ctime’ fields are no longer populated or updated (see ticket #924), except by “tahoe backup” as explained below. For backward compatibility, when an existing link is updated and ‘tahoe’:’linkcrtime’ is not present in the previous metadata but ‘ctime’ is, the old value of ‘ctime’ is used as the new value of ‘tahoe’:’linkcrtime’.

The reason we added the new fields in Tahoe v1.4.0 is that there is a “set_children” API (described below) which you can use to overwrite the values of the ‘mtime’/’ctime’ pair, and this API is used by the “tahoe backup” command (in Tahoe v1.3.0 and later) to set the ‘mtime’ and ‘ctime’ values when backing up files from a local filesystem into the Tahoe-LAFS file store. As of Tahoe v1.4.0, the set_children API cannot be used to set anything under the ‘tahoe’ key of the metadata dict – if you include ‘tahoe’ keys in your ‘metadata’ arguments then it will silently ignore those keys.

Therefore, if the ‘tahoe’ sub-dict is present, you can rely on the ‘linkcrtime’ and ‘linkmotime’ values therein to have the semantics described above. (This is assuming that only official Tahoe clients have been used to write those links, and that their system clocks were set to what you expected – there is nothing preventing someone from editing their Tahoe client or writing their own Tahoe client which would overwrite those values however they like, and there is nothing to constrain their system clock from taking any value.)

When an edge is created or updated by “tahoe backup”, the ‘mtime’ and ‘ctime’ keys on that edge are set as follows:

- ‘mtime’ is set to the timestamp read from the local filesystem for the “mtime” of the local file in question, which means the last time the contents of that file were changed.
- On Windows, ‘ctime’ is set to the creation timestamp for the file read from the local filesystem. On other platforms, ‘ctime’ is set to the UNIX “ctime” of the local file, which means the last time that either the contents or the metadata of the local file was changed.

There are several ways that the ‘ctime’ field could be confusing:

1. You might be confused about whether it reflects the time of the creation of a link in the Tahoe-LAFS file store (by a version of Tahoe < v1.7.0) or a timestamp copied in by “tahoe backup” from a local filesystem.
2. You might be confused about whether it is a copy of the file creation time (if “tahoe backup” was run on a Windows system) or of the last contents-or-metadata change (if “tahoe backup” was run on a different operating system).
3. You might be confused by the fact that changing the contents of a mutable file in Tahoe doesn’t have any effect on any links pointing at that file in any directories, although “tahoe backup” sets the link ‘ctime’/’mtime’ to reflect timestamps about the local file corresponding to the Tahoe file to which the link points.
4. Also, quite apart from Tahoe, you might be confused about the meaning of the “ctime” in UNIX local filesystems, which people sometimes think means file creation time, but which actually means, in UNIX local filesystems, the most recent time that the file contents or the file metadata (such as owner, permission bits, extended attributes, etc.) has changed. Note that although “ctime” does not mean file creation time in UNIX, links created by a version of Tahoe prior to v1.7.0, and never written by “tahoe backup”, will have ‘ctime’ set to the link creation time.

### Attaching an Existing File or Directory by its read- or write-cap

`PUT /uri/$DIRCAP/[SUBDIRS../]CHILDNAME?t=uri`

> This attaches a child object (either a file or directory) to a specified location in the Tahoe-LAFS file store. The child object is referenced by its read- or write- cap, as provided in the HTTP request body. This will create intermediate directories as necessary.

> This is similar to a UNIX hardlink: by referencing a previously-uploaded file (or previously-created directory) instead of uploading/creating a new one, you can create two references to the same object.

> The read- or write- cap of the child is provided in the body of the HTTP request, and this same cap is returned in the response body.

> The default behavior is to overwrite any existing object at the same location. To prevent this (and make the operation return an error instead of overwriting), add a “replace=false” argument, as “?t=uri&replace=false”. With replace=false, this operation will return an HTTP 409 “Conflict” error if there is already an object at the given location, rather than overwriting the existing object. To allow the operation to overwrite a file, but return an error when trying to overwrite a directory, use “replace=only-files” (this behavior is closer to the traditional UNIX “mv” command). Note that “true”, “t”, and “1” are all synonyms for “True”, and “false”, “f”, and “0” are synonyms for “False”, and the parameter is case-insensitive.

> Note that this operation does not take its child cap in the form of separate “rw_uri” and “ro_uri” fields. Therefore, it cannot accept a child cap in a format unknown to the web-API server, unless its URI starts with “ro.” or “imm.”. This restriction is necessary because the server is not able to attenuate an unknown write cap to a read cap. Unknown URIs starting with “ro.” or “imm.”, on the other hand, are assumed to represent read caps. The client should not prefix a write cap with “ro.” or “imm.” and pass it to this operation, since that would result in granting the cap’s write authority to holders of the directory read cap.

### Adding Multiple Files or Directories to a Parent Directory at Once

`POST /uri/$DIRCAP/[SUBDIRS..]?t=set_children`

`POST /uri/$DIRCAP/[SUBDIRS..]?t=set-children` (Tahoe >= v1.6)

> This command adds multiple children to a directory in a single operation. It reads the request body and interprets it as a JSON-encoded description of the child names and read/write-caps that should be added.

> The body should be a JSON-encoded dictionary, in the same format as the “children” value returned by the “GET /uri/$DIRCAP?t=json” operation described above. In this format, each key is a child names, and the corresponding value is a tuple of (type, childinfo). “type” is ignored, and “childinfo” is a dictionary that contains “rw_uri”, “ro_uri”, and “metadata” keys. You can take the output of “GET /uri/$DIRCAP1?t=json” and use it as the input to “POST /uri/$DIRCAP2?t=set_children” to make DIR2 look very much like DIR1 (except for any existing children of DIR2 that were not overwritten, and any existing “tahoe” metadata keys as described below).

> When the set_children request contains a child name that already exists in the target directory, this command defaults to overwriting that child with the new value (both child cap and metadata, but if the JSON data does not contain a “metadata” key, the old child’s metadata is preserved). The command takes a boolean “overwrite=” query argument to control this behavior. If you use “?t=set_children&overwrite=false”, then an attempt to replace an existing child will instead cause an error.

> Any “tahoe” key in the new child’s “metadata” value is ignored. Any existing “tahoe” metadata is preserved. The metadata[“tahoe”] value is reserved for metadata generated by the tahoe node itself. The only two keys currently placed here are “linkcrtime” and “linkmotime”. For details, see the section above entitled “Getting Information About a File Or Directory (as JSON)”, in the “About the metadata” subsection.

> Note that this command was introduced with the name “set_children”, which uses an underscore rather than a hyphen as other multi-word command names do. The variant with a hyphen is now accepted, but clients that desire backward compatibility should continue to use “set_children”.

### Unlinking a File or Directory

`DELETE /uri/$DIRCAP/[SUBDIRS../]CHILDNAME`

> This removes the given name from its parent directory. CHILDNAME is the name to be removed, and $DIRCAP/SUBDIRS.. indicates the directory that will be modified.

> Note that this does not actually delete the file or directory that the name points to from the tahoe grid – it only unlinks the named reference from this directory. If there are other names in this directory or in other directories that point to the resource, then it will remain accessible through those paths. Even if all names pointing to this object are removed from their parent directories, then someone with possession of its read-cap can continue to access the object through that cap.

> The object will only become completely unreachable once 1: there are no reachable directories that reference it, and 2: nobody is holding a read- or write- cap to the object. (This behavior is very similar to the way hardlinks and anonymous files work in traditional UNIX filesystems).

> This operation will not modify more than a single directory. Intermediate directories which were implicitly created by PUT or POST methods will not be automatically removed by DELETE.

> This method returns the file- or directory- cap of the object that was just removed.

## Browser Operations: Human-oriented interfaces

This section describes the HTTP operations that provide support for humans running a web browser. Most of these operations use HTML forms that use POST to drive the Tahoe-LAFS node. This section is intended for HTML authors who want to write web pages containing user interfaces for manipulating the Tahoe-LAFS file store.

Note that for all POST operations, the arguments listed can be provided either as URL query arguments or as form body fields. URL query arguments are separated from the main URL by “?”, and from each other by “&”. For example, “POST /uri/$DIRCAP?t=upload&mutable=true”. Form body fields are usually specified by using <input type=”hidden”> elements. For clarity, the descriptions below display the most significant arguments as URL query args.

### Viewing a Directory (as HTML)

`GET /uri/$DIRCAP/[SUBDIRS../]`

> This returns an HTML page, intended to be displayed to a human by a web browser, which contains HREF links to all files and directories reachable from this directory. These HREF links do not have a t= argument, meaning that a human who follows them will get pages also meant for a human. It also contains forms to upload new files, and to unlink files and directories from their parent directory. Those forms use POST methods to do their job.

### Viewing/Downloading a File

`GET /uri/$FILECAP`

`GET /uri/$DIRCAP/[SUBDIRS../]FILENAME`

`GET /named/$FILECAP/FILENAME`

> These will retrieve the contents of the given file. The HTTP response body will contain the sequence of bytes that make up the file.

> The `/named/` form is an alternative to `/uri/$FILECAP` which makes it easier to get the correct filename. The Tahoe server will provide the contents of the given file, with a Content-Type header derived from the given filename. This form is used to get browsers to use the “Save Link As” feature correctly, and also helps command-line tools like “wget” and “curl” use the right filename. Note that this form can only be used with file caps; it is an error to use a directory cap after the /named/ prefix.

> URLs may also use /file/$FILECAP/FILENAME as a synonym for /named/$FILECAP/FILENAME. The use of “/file/” is deprecated in favor of “/named/” and support for “/file/” will be removed in a future release of Tahoe-LAFS.

> If you use the first form (`/uri/$FILECAP`) and want the HTTP response to include a useful Content-Type header, add a “filename=foo” query argument, like “GET /uri/$FILECAP?filename=foo.jpg”. The bare “GET /uri/$FILECAP” does not give the Tahoe node enough information to determine a Content-Type (since LAFS immutable files are merely sequences of bytes, not typed and named file objects).

> If the URL has both filename= and “save=true” in the query arguments, then the server to add a “Content-Disposition: attachment” header, along with a filename= parameter. When a user clicks on such a link, most browsers will offer to let the user save the file instead of displaying it inline (indeed, most browsers will refuse to display it inline). “true”, “t”, “1”, and other case-insensitive equivalents are all treated the same.

> Character-set handling in URLs and HTTP headers is a dubious art. For maximum compatibility, Tahoe simply copies the bytes from the filename= argument into the Content-Disposition header’s filename= parameter, without trying to interpret them in any particular way.

### Getting Information About a File Or Directory (as HTML)

`GET /uri/$FILECAP?t=info`

`GET /uri/$DIRCAP/?t=info`

`GET /uri/$DIRCAP/[SUBDIRS../]SUBDIR/?t=info`

`GET /uri/$DIRCAP/[SUBDIRS../]FILENAME?t=info`

> This returns a human-oriented HTML page with more detail about the selected file or directory object. This page contains the following items:

> - object size
> - storage index
> - JSON representation
> - raw contents (text/plain)
> - access caps (URIs): verify-cap, read-cap, write-cap (for mutable objects)
> - check/verify/repair form
> - deep-check/deep-size/deep-stats/manifest (for directories)
> - replace-contents form (for mutable files)

### Creating a Directory

`POST /uri?t=mkdir`

> This creates a new empty directory, but does not attach it to any other directory in the Tahoe-LAFS file store.

> If a “redirect_to_result=true” argument is provided, then the HTTP response will cause the web browser to be redirected to a /uri/$DIRCAP page that gives access to the newly-created directory. If you bookmark this page, you’ll be able to get back to the directory again in the future. This is the recommended way to start working with a Tahoe server: create a new unlinked directory (using redirect_to_result=true), then bookmark the resulting /uri/$DIRCAP page. There is a “create directory” button on the Welcome page to invoke this action.

> This accepts a format= argument in the query string. Refer to the documentation of the PUT /uri?t=mkdir operation in Creating A New Directory for information on the behavior of the format= argument.

> If “redirect_to_result=true” is not provided (or is given a value of “false”), then the HTTP response body will simply be the write-cap of the new directory.

`POST /uri/$DIRCAP/[SUBDIRS../]?t=mkdir&name=CHILDNAME`

> This creates a new empty directory as a child of the designated SUBDIR. This will create additional intermediate directories as necessary.

> This accepts a format= argument in the query string. Refer to the documentation of POST /uri/$DIRCAP/[SUBDIRS../]?t=mkdir&name=CHILDNAME in Creating a New Directory for information on the behavior of the format= argument.

> If a “when_done=URL” argument is provided, the HTTP response will cause the web browser to redirect to the given URL. This provides a convenient way to return the browser to the directory that was just modified. Without a when_done= argument, the HTTP response will simply contain the write-cap of the directory that was just created.

### Uploading a File

`POST /uri?t=upload`

> This uploads a file, and produces a file-cap for the contents, but does not attach the file to any directory in the Tahoe-LAFS file store. That is, no directories will be modified by this operation.

> The file must be provided as the “file” field of an HTML encoded form body, produced in response to an HTML form like this:

>     <form action="/uri" method="POST" enctype="multipart/form-data">
>      <input type="hidden" name="t" value="upload" />
>      <input type="file" name="file" />
>      <input type="submit" value="Upload Unlinked" />
>     </form>

> If a “when_done=URL” argument is provided, the response body will cause the browser to redirect to the given URL. If the when_done= URL has the string “%(uri)s” in it, that string will be replaced by a URL-escaped form of the newly created file-cap. (Note that without this substitution, there is no way to access the file that was just uploaded).

> The default (in the absence of when_done=) is to return an HTML page that describes the results of the upload. This page will contain information about which storage servers were used for the upload, how long each operation took, etc.

> This accepts format= and mutable=true query string arguments. Refer to Writing/Uploading a File for information on the behavior of format= and mutable=true.

`POST /uri/$DIRCAP/[SUBDIRS../]?t=upload`

> This uploads a file, and attaches it as a new child of the given directory, which must be mutable. The file must be provided as the “file” field of an HTML-encoded form body, produced in response to an HTML form like this:

>     <form action="." method="POST" enctype="multipart/form-data">
>      <input type="hidden" name="t" value="upload" />
>      <input type="file" name="file" />
>      <input type="submit" value="Upload" />
>     </form>

> A “name=” argument can be provided to specify the new child’s name, otherwise it will be taken from the “filename” field of the upload form (most web browsers will copy the last component of the original file’s pathname into this field). To avoid confusion, name= is not allowed to contain a slash.

> If there is already a child with that name, and it is a mutable file, then its contents are replaced with the data being uploaded. If it is not a mutable file, the default behavior is to remove the existing child before creating a new one. To prevent this (and make the operation return an error instead of overwriting the old child), add a “replace=false” argument, as “?t=upload&replace=false”. With replace=false, this operation will return an HTTP 409 “Conflict” error if there is already an object at the given location, rather than overwriting the existing object. Note that “true”, “t”, and “1” are all synonyms for “True”, and “false”, “f”, and “0” are synonyms for “False”. the parameter is case-insensitive.

> This will create additional intermediate directories as necessary, although since it is expected to be triggered by a form that was retrieved by “GET /uri/$DIRCAP/[SUBDIRS../]”, it is likely that the parent directory will already exist.

> This accepts format= and mutable=true query string arguments. Refer to Writing/Uploading a File for information on the behavior of format= and mutable=true.

> If a “when_done=URL” argument is provided, the HTTP response will cause the web browser to redirect to the given URL. This provides a convenient way to return the browser to the directory that was just modified. Without a when_done= argument, the HTTP response will simply contain the file-cap of the file that was just uploaded (a write-cap for mutable files, or a read-cap for immutable files).

`POST /uri/$DIRCAP/[SUBDIRS../]FILENAME?t=upload`

> This also uploads a file and attaches it as a new child of the given directory, which must be mutable. It is a slight variant of the previous operation, as the URL refers to the target file rather than the parent directory. It is otherwise identical: this accepts mutable= and when_done= arguments too.

`POST /uri/$FILECAP?t=upload`

> This modifies the contents of an existing mutable file in-place. An error is signalled if $FILECAP does not refer to a mutable file. It behaves just like the “PUT /uri/$FILECAP” form, but uses a POST for the benefit of HTML forms in a web browser.

### Attaching An Existing File Or Directory (by URI)

`POST /uri/$DIRCAP/[SUBDIRS../]?t=uri&name=CHILDNAME&uri=CHILDCAP`

> This attaches a given read- or write- cap “CHILDCAP” to the designated directory, with a specified child name. This behaves much like the PUT t=uri operation, and is a lot like a UNIX hardlink. It is subject to the same restrictions as that operation on the use of cap formats unknown to the web-API server.

> This will create additional intermediate directories as necessary, although since it is expected to be triggered by a form that was retrieved by “GET /uri/$DIRCAP/[SUBDIRS../]”, it is likely that the parent directory will already exist.

> This accepts the same replace= argument as POST t=upload.

### Unlinking a Child

`POST /uri/$DIRCAP/[SUBDIRS../]?t=delete&name=CHILDNAME`

`POST /uri/$DIRCAP/[SUBDIRS../]?t=unlink&name=CHILDNAME` (Tahoe >= v1.9)

> This instructs the node to remove a child object (file or subdirectory) from the given directory, which must be mutable. Note that the entire subtree is unlinked from the parent. Unlike deleting a subdirectory in a UNIX local filesystem, the subtree need not be empty; if it isn’t, then other references into the subtree will see that the child subdirectories are not modified by this operation. Only the link from the given directory to its child is severed.

> In Tahoe-LAFS v1.9.0 and later, t=unlink can be used as a synonym for t=delete. If interoperability with older web-API servers is required, t=delete should be used.

### Renaming a Child

`POST /uri/$DIRCAP/[SUBDIRS../]?t=rename&from_name=OLD&to_name=NEW`

> This instructs the node to rename a child of the given directory, which must be mutable. This has a similar effect to removing the child, then adding the same child-cap under the new name, except that it preserves metadata. This operation cannot move the child to a different directory.

> The default behavior is to overwrite any existing link at the destination (replace=true). To prevent this (and make the operation return an error instead of overwriting), add a “replace=false” argument. With replace=false, this operation will return an HTTP 409 “Conflict” error if the destination is not the same link as the source and there is already a link at the destination, rather than overwriting the existing link. To allow the operation to overwrite a link to a file, but return an HTTP 409 error when trying to overwrite a link to a directory, use “replace=only-files” (this behavior is closer to the traditional UNIX “mv” command). Note that “true”, “t”, and “1” are all synonyms for “True”; “false”, “f”, and “0” are synonyms for “False”; and the parameter is case-insensitive.

### Relinking (“Moving”) a Child

`POST /uri/$DIRCAP/[SUBDIRS../]?t=relink&from_name=OLD&to_dir=$NEWDIRCAP/[NEWSUBDIRS../]&to_name=NEW`

  `[&replace=true|false|only-files]` (Tahoe >= v1.10)

  This instructs the node to move a child of the given source directory, into a different directory and/or to a different name. The command is named `relink` because what it does is add a new link to the child from the new location, then remove the old link. Nothing is actually “moved”: the child is still reachable through any path from which it was formerly reachable, and the storage space occupied by its ciphertext is not affected.

  The source and destination directories must be writeable. If `to_dir` is not present, the child link is renamed within the same directory. If `to_name` is not present then it defaults to `from_name`. If the destination link (directory and name) is the same as the source link, the operation has no effect.

  Metadata from the source directory entry is preserved. Multiple levels of descent in the source and destination paths are supported.

  This operation will return an HTTP 404 “Not Found” error if `$DIRCAP/[SUBDIRS../]`, the child being moved, or the destination directory does not exist. It will return an HTTP 400 “Bad Request” error if any entry in the source or destination paths is not a directory.

  The default behavior is to overwrite any existing link at the destination (replace=true). To prevent this (and make the operation return an error instead of overwriting), add a “replace=false” argument. With replace=false, this operation will return an HTTP 409 “Conflict” error if the destination is not the same link as the source and there is already a link at the destination, rather than overwriting the existing link. To allow the operation to overwrite a link to a file, but return an HTTP 409 error when trying to overwrite a link to a directory, use “replace=only-files” (this behavior is closer to the traditional UNIX “mv” command). Note that “true”, “t”, and “1” are all synonyms for “True”; “false”, “f”, and “0” are synonyms for “False”; and the parameter is case-insensitive.

  When relinking into a different directory, for safety, the child link is not removed from the old directory until it has been successfully added to the new directory. This implies that in case of a crash or failure, the link to the child will not be lost, but it could be linked at both the old and new locations.

  The source link should not be the same as any link (directory and child name) in the `to_dir` path. This restriction is not enforced, but it may be enforced in a future version. If it were violated then the result would be to create a cycle in the directory structure that is not necessarily reachable from the root of the destination path (`$NEWDIRCAP`), which could result in data loss, as described in ticket #943.

### Other Utilities

`GET /uri?uri=$CAP`

> This causes a redirect to /uri/$CAP, and retains any additional query arguments (like filename= or save=). This is for the convenience of web forms which allow the user to paste in a read- or write- cap (obtained through some out-of-band channel, like IM or email).

> Note that this form merely redirects to the specific file or directory indicated by the $CAP: unlike the GET /uri/$DIRCAP form, you cannot traverse to children by appending additional path segments to the URL.

`GET /uri/$DIRCAP/[SUBDIRS../]?t=rename-form&name=$CHILDNAME`

> This provides a useful facility to browser-based user interfaces. It returns a page containing a form targetting the “POST $DIRCAP t=rename” functionality described above, with the provided $CHILDNAME present in the ‘from_name’ field of that form. I.e. this presents a form offering to rename $CHILDNAME, requesting the new name, and submitting POST rename. This same URL format can also be used with “move-form” with the expected results.

`GET /uri/$DIRCAP/[SUBDIRS../]CHILDNAME?t=uri`

> This returns the file- or directory- cap for the specified object.

`GET /uri/$DIRCAP/[SUBDIRS../]CHILDNAME?t=readonly-uri`

> This returns a read-only file- or directory- cap for the specified object. If the object is an immutable file, this will return the same value as t=uri.

### Debugging and Testing Features

These URLs are less-likely to be helpful to the casual Tahoe user, and are mainly intended for developers.

`POST $URL?t=check`

> This triggers the FileChecker to determine the current “health” of the given file or directory, by counting how many shares are available. The page that is returned will display the results. This can be used as a “show me detailed information about this file” page.

> If a verify=true argument is provided, the node will perform a more intensive check, downloading and verifying every single bit of every share.

> If an add-lease=true argument is provided, the node will also add (or renew) a lease to every share it encounters. Each lease will keep the share alive for a certain period of time (one month by default). Once the last lease expires or is explicitly cancelled, the storage server is allowed to delete the share.

> If an output=JSON argument is provided, the response will be machine-readable JSON instead of human-oriented HTML. The data is a dictionary with the following keys:

>     storage-index: a base32-encoded string with the objects's storage index,
>                    or an empty string for LIT files
>     summary: a string, with a one-line summary of the stats of the file
>     results: a dictionary that describes the state of the file. For LIT files,
>              this dictionary has only the 'healthy' key, which will always be
>              True. For distributed files, this dictionary has the following
>              keys:
>       count-happiness: the servers-of-happiness level of the file, as
>                        defined in doc/specifications/servers-of-happiness.
>       count-shares-good: the number of good shares that were found
>       count-shares-needed: 'k', the number of shares required for recovery
>       count-shares-expected: 'N', the number of total shares generated
>       count-good-share-hosts: the number of distinct storage servers with
>                               good shares. Note that a high value does not
>                               necessarily imply good share distribution,
>                               because some of these servers may only hold
>                               duplicate shares.
>       count-wrong-shares: for mutable files, the number of shares for
>                           versions other than the 'best' one (highest
>                           sequence number, highest roothash). These are
>                           either old, or created by an uncoordinated or
>                           not fully successful write.
>       count-recoverable-versions: for mutable files, the number of
>                                   recoverable versions of the file. For
>                                   a healthy file, this will equal 1.
>       count-unrecoverable-versions: for mutable files, the number of
>                                     unrecoverable versions of the file.
>                                     For a healthy file, this will be 0.
>       count-corrupt-shares: the number of shares with integrity failures
>       list-corrupt-shares: a list of "share locators", one for each share
>                            that was found to be corrupt. Each share locator
>                            is a list of (serverid, storage_index, sharenum).
>       servers-responding: list of base32-encoded storage server identifiers,
>                           one for each server which responded to the share
>                           query.
>       healthy: (bool) True if the file is completely healthy, False otherwise.
>                Healthy files have at least N good shares. Overlapping shares
>                do not currently cause a file to be marked unhealthy. If there
>                are at least N good shares, then corrupt shares do not cause the
>                file to be marked unhealthy, although the corrupt shares will be
>                listed in the results (list-corrupt-shares) and should be manually
>                removed to wasting time in subsequent downloads (as the
>                downloader rediscovers the corruption and uses alternate shares).
>                Future compatibility: the meaning of this field may change to
>                reflect whether the servers-of-happiness criterion is met
>                (see ticket #614).
>       sharemap: dict mapping share identifier to list of serverids
>                 (base32-encoded strings). This indicates which servers are
>                 holding which shares. For immutable files, the shareid is
>                 an integer (the share number, from 0 to N-1). For
>                 immutable files, it is a string of the form
>                 'seq%d-%s-sh%d', containing the sequence number, the
>                 roothash, and the share number.

Before Tahoe-LAFS v1.11, the `results` dictionary also had a `needs-rebalancing` field, but that has been removed since it was computed incorrectly.

`POST $URL?t=start-deep-check` (must add &ophandle=XYZ)

> This initiates a recursive walk of all files and directories reachable from the target, performing a check on each one just like t=check. The result page will contain a summary of the results, including details on any file/directory that was not fully healthy.

> t=start-deep-check can only be invoked on a directory. An error (400 BAD_REQUEST) will be signalled if it is invoked on a file. The recursive walker will deal with loops safely.

> This accepts the same verify= and add-lease= arguments as t=check.

> Since this operation can take a long time (perhaps a second per object), the ophandle= argument is required (see “Slow Operations, Progress, and Cancelling” above). The response to this POST will be a redirect to the corresponding /operations/$HANDLE page (with output=HTML or output=JSON to match the output= argument given to the POST). The deep-check operation will continue to run in the background, and the /operations page should be used to find out when the operation is done.

> Detailed check results for non-healthy files and directories will be available under /operations/$HANDLE/$STORAGEINDEX, and the HTML status will contain links to these detailed results.

> The HTML /operations/$HANDLE page for incomplete operations will contain a meta-refresh tag, set to 60 seconds, so that a browser which uses deep-check will automatically poll until the operation has completed.

> The JSON page (/options/$HANDLE?output=JSON) will contain a machine-readable JSON dictionary with the following keys:

>     finished: a boolean, True if the operation is complete, else False. Some
>               of the remaining keys may not be present until the operation
>               is complete.
>     root-storage-index: a base32-encoded string with the storage index of the
>                         starting point of the deep-check operation
>     count-objects-checked: count of how many objects were checked. Note that
>                            non-distributed objects (i.e. small immutable LIT
>                            files) are not checked, since for these objects,
>                            the data is contained entirely in the URI.
>     count-objects-healthy: how many of those objects were completely healthy
>     count-objects-unhealthy: how many were damaged in some way
>     count-corrupt-shares: how many shares were found to have corruption,
>                           summed over all objects examined
>     list-corrupt-shares: a list of "share identifiers", one for each share
>                          that was found to be corrupt. Each share identifier
>                          is a list of (serverid, storage_index, sharenum).
>     list-unhealthy-files: a list of (pathname, check-results) tuples, for
>                           each file that was not fully healthy. 'pathname' is
>                           a list of strings (which can be joined by "/"
>                           characters to turn it into a single string),
>                           relative to the directory on which deep-check was
>                           invoked. The 'check-results' field is the same as
>                           that returned by t=check&output=JSON, described
>                           above.
>     stats: a dictionary with the same keys as the t=start-deep-stats command
>            (described below)

`POST $URL?t=stream-deep-check`

> This initiates a recursive walk of all files and directories reachable from the target, performing a check on each one just like t=check. For each unique object (duplicates are skipped), a single line of JSON is emitted to the HTTP response channel (or an error indication, see below). When the walk is complete, a final line of JSON is emitted which contains the accumulated file-size/count “deep-stats” data.

> This command takes the same arguments as t=start-deep-check.

> A CLI tool can split the response stream on newlines into “response units”, and parse each response unit as JSON. Each such parsed unit will be a dictionary, and will contain at least the “type” key: a string, one of “file”, “directory”, or “stats”.

> For all units that have a type of “file” or “directory”, the dictionary will contain the following keys:

>     "path": a list of strings, with the path that is traversed to reach the
>             object
>     "cap": a write-cap URI for the file or directory, if available, else a
>            read-cap URI
>     "verifycap": a verify-cap URI for the file or directory
>     "repaircap": an URI for the weakest cap that can still be used to repair
>                  the object
>     "storage-index": a base32 storage index for the object
>     "check-results": a copy of the dictionary which would be returned by
>                      t=check&output=json, with three top-level keys:
>                      "storage-index", "summary", and "results", and a variety
>                      of counts and sharemaps in the "results" value.

> Note that non-distributed files (i.e. LIT files) will have values of None for verifycap, repaircap, and storage-index, since these files can neither be verified nor repaired, and are not stored on the storage servers. Likewise the check-results dictionary will be limited: an empty string for storage-index, and a results dictionary with only the “healthy” key.

> The last unit in the stream will have a type of “stats”, and will contain the keys described in the “start-deep-stats” operation, below.

> If any errors occur during the traversal (specifically if a directory is unrecoverable, such that further traversal is not possible), an error indication is written to the response body, instead of the usual line of JSON. This error indication line will begin with the string “ERROR:” (in all caps), and contain a summary of the error on the rest of the line. The remaining lines of the response body will be a python exception. The client application should look for the ERROR: and stop processing JSON as soon as it is seen. Note that neither a file being unrecoverable nor a directory merely being unhealthy will cause traversal to stop. The line just before the ERROR: will describe the directory that was untraversable, since the unit is emitted to the HTTP response body before the child is traversed.

`POST $URL?t=check&repair=true`

> This performs a health check of the given file or directory, and if the checker determines that the object is not healthy (some shares are missing or corrupted), it will perform a “repair”. During repair, any missing shares will be regenerated and uploaded to new servers.

> This accepts the same verify=true and add-lease= arguments as t=check. When an output=JSON argument is provided, the machine-readable JSON response will contain the following keys:

>     storage-index: a base32-encoded string with the objects's storage index,
>                    or an empty string for LIT files
>     repair-attempted: (bool) True if repair was attempted
>     repair-successful: (bool) True if repair was attempted and the file was
>                        fully healthy afterwards. False if no repair was
>                        attempted, or if a repair attempt failed.
>     pre-repair-results: a dictionary that describes the state of the file
>                         before any repair was performed. This contains exactly
>                         the same keys as the 'results' value of the t=check
>                         response, described above.
>     post-repair-results: a dictionary that describes the state of the file
>                          after any repair was performed. If no repair was
>                          performed, post-repair-results and pre-repair-results
>                          will be the same. This contains exactly the same keys
>                          as the 'results' value of the t=check response,
>                          described above.

`POST $URL?t=start-deep-check&repair=true` (must add &ophandle=XYZ)

> This triggers a recursive walk of all files and directories, performing a t=check&repair=true on each one.

> Like t=start-deep-check without the repair= argument, this can only be invoked on a directory. An error (400 BAD_REQUEST) will be signalled if it is invoked on a file. The recursive walker will deal with loops safely.

> This accepts the same verify= and add-lease= arguments as t=start-deep-check. It uses the same ophandle= mechanism as start-deep-check. When an output=JSON argument is provided, the response will contain the following keys:

>     finished: (bool) True if the operation has completed, else False
>     root-storage-index: a base32-encoded string with the storage index of the
>                         starting point of the deep-check operation
>     count-objects-checked: count of how many objects were checked

>     count-objects-healthy-pre-repair: how many of those objects were completely
>                                       healthy, before any repair
>     count-objects-unhealthy-pre-repair: how many were damaged in some way
>     count-objects-healthy-post-repair: how many of those objects were completely
>                                         healthy, after any repair
>     count-objects-unhealthy-post-repair: how many were damaged in some way

>     count-repairs-attempted: repairs were attempted on this many objects.
>     count-repairs-successful: how many repairs resulted in healthy objects
>     count-repairs-unsuccessful: how many repairs resulted did not results in
>                                 completely healthy objects
>     count-corrupt-shares-pre-repair: how many shares were found to have
>                                      corruption, summed over all objects
>                                      examined, before any repair
>     count-corrupt-shares-post-repair: how many shares were found to have
>                                       corruption, summed over all objects
>                                       examined, after any repair
>     list-corrupt-shares: a list of "share identifiers", one for each share
>                          that was found to be corrupt (before any repair).
>                          Each share identifier is a list of (serverid,
>                          storage_index, sharenum).
>     list-remaining-corrupt-shares: like list-corrupt-shares, but mutable shares
>                                    that were successfully repaired are not
>                                    included. These are shares that need
>                                    manual processing. Since immutable shares
>                                    cannot be modified by clients, all corruption
>                                    in immutable shares will be listed here.
>     list-unhealthy-files: a list of (pathname, check-results) tuples, for
>                           each file that was not fully healthy. 'pathname' is
>                           relative to the directory on which deep-check was
>                           invoked. The 'check-results' field is the same as
>                           that returned by t=check&repair=true&output=JSON,
>                           described above.
>     stats: a dictionary with the same keys as the t=start-deep-stats command
>            (described below)

`POST $URL?t=stream-deep-check&repair=true`

> This triggers a recursive walk of all files and directories, performing a t=check&repair=true on each one. For each unique object (duplicates are skipped), a single line of JSON is emitted to the HTTP response channel (or an error indication). When the walk is complete, a final line of JSON is emitted which contains the accumulated file-size/count “deep-stats” data.

> This emits the same data as t=stream-deep-check (without the repair=true), except that the “check-results” field is replaced with a “check-and-repair-results” field, which contains the keys returned by t=check&repair=true&output=json (i.e. repair-attempted, repair-successful, pre-repair-results, and post-repair-results). The output does not contain the summary dictionary that is provied by t=start-deep-check&repair=true (the one with count-objects-checked and list-unhealthy-files), since the receiving client is expected to calculate those values itself from the stream of per-object check-and-repair-results.

> Note that the “ERROR:” indication will only be emitted if traversal stops, which will only occur if an unrecoverable directory is encountered. If a file or directory repair fails, the traversal will continue, and the repair failure will be indicated in the JSON data (in the “repair-successful” key).

`POST $DIRURL?t=start-manifest` (must add &ophandle=XYZ)

> This operation generates a “manfest” of the given directory tree, mostly for debugging. This is a table of (path, filecap/dircap), for every object reachable from the starting directory. The path will be slash-joined, and the filecap/dircap will contain a link to the object in question. This page gives immediate access to every object in the file store subtree.

> This operation uses the same ophandle= mechanism as deep-check. The corresponding /operations/$HANDLE page has three different forms. The default is output=HTML.

> If output=text is added to the query args, the results will be a text/plain list. The first line is special: it is either “finished: yes” or “finished: no”; if the operation is not finished, you must periodically reload the page until it completes. The rest of the results are a plaintext list, with one file/dir per line, slash-separated, with the filecap/dircap separated by a space.

> If output=JSON is added to the queryargs, then the results will be a JSON-formatted dictionary with six keys. Note that because large directory structures can result in very large JSON results, the full results will not be available until the operation is complete (i.e. until output[“finished”] is True):

>     finished (bool): if False then you must reload the page until True
>     origin_si (base32 str): the storage index of the starting point
>     manifest: list of (path, cap) tuples, where path is a list of strings.
>     verifycaps: list of (printable) verify cap strings
>     storage-index: list of (base32) storage index strings
>     stats: a dictionary with the same keys as the t=start-deep-stats command
>            (described below)

`POST $DIRURL?t=start-deep-size` (must add &ophandle=XYZ)

> This operation generates a number (in bytes) containing the sum of the filesize of all directories and immutable files reachable from the given directory. This is a rough lower bound of the total space consumed by this subtree. It does not include space consumed by mutable files, nor does it take expansion or encoding overhead into account. Later versions of the code may improve this estimate upwards.

> The /operations/$HANDLE status output consists of two lines of text:

>     finished: yes
>     size: 1234

`POST $DIRURL?t=start-deep-stats` (must add &ophandle=XYZ)

> This operation performs a recursive walk of all files and directories reachable from the given directory, and generates a collection of statistics about those objects.

> The result (obtained from the /operations/$OPHANDLE page) is a JSON-serialized dictionary with the following keys (note that some of these keys may be missing until ‘finished’ is True):

>     finished: (bool) True if the operation has finished, else False
>     api-version: (int), number of deep-stats API version. Will be increased every
>                  time backwards-incompatible change is introduced.
>                  Current version is 1.
>     count-immutable-files: count of how many CHK files are in the set
>     count-mutable-files: same, for mutable files (does not include directories)
>     count-literal-files: same, for LIT files (data contained inside the URI)
>     count-files: sum of the above three
>     count-directories: count of directories
>     count-unknown: count of unrecognized objects (perhaps from the future)
>     size-immutable-files: total bytes for all CHK files in the set, =deep-size
>     size-mutable-files (TODO): same, for current version of all mutable files
>     size-literal-files: same, for LIT files
>     size-directories: size of directories (includes size-literal-files)
>     size-files-histogram: list of (minsize, maxsize, count) buckets,
>                           with a histogram of filesizes, 5dB/bucket,
>                           for both literal and immutable files
>     largest-directory: number of children in the largest directory
>     largest-immutable-file: number of bytes in the largest CHK file

> size-mutable-files is not implemented, because it would require extra queries to each mutable file to get their size. This may be implemented in the future.

> Assuming no sharing, the basic space consumed by a single root directory is the sum of size-immutable-files, size-mutable-files, and size-directories. The actual disk space used by the shares is larger, because of the following sources of overhead:

>     integrity data
>     expansion due to erasure coding
>     share management data (leases)
>     backend (ext3) minimum block size

`POST $URL?t=stream-manifest`

> This operation performs a recursive walk of all files and directories reachable from the given starting point. For each such unique object (duplicates are skipped), a single line of JSON is emitted to the HTTP response channel (or an error indication, see below). When the walk is complete, a final line of JSON is emitted which contains the accumulated file-size/count “deep-stats” data.

> A CLI tool can split the response stream on newlines into “response units”, and parse each response unit as JSON. Each such parsed unit will be a dictionary, and will contain at least the “type” key: a string, one of “file”, “directory”, or “stats”.

> For all units that have a type of “file” or “directory”, the dictionary will contain the following keys:

>     "path": a list of strings, with the path that is traversed to reach the
>             object
>     "cap": a write-cap URI for the file or directory, if available, else a
>            read-cap URI
>     "verifycap": a verify-cap URI for the file or directory
>     "repaircap": an URI for the weakest cap that can still be used to repair
>                  the object
>     "storage-index": a base32 storage index for the object

> Note that non-distributed files (i.e. LIT files) will have values of None for verifycap, repaircap, and storage-index, since these files can neither be verified nor repaired, and are not stored on the storage servers.

> The last unit in the stream will have a type of “stats”, and will contain the keys described in the “start-deep-stats” operation, below.

> If any errors occur during the traversal (specifically if a directory is unrecoverable, such that further traversal is not possible), an error indication is written to the response body, instead of the usual line of JSON. This error indication line will begin with the string “ERROR:” (in all caps), and contain a summary of the error on the rest of the line. The remaining lines of the response body will be a python exception. The client application should look for the ERROR: and stop processing JSON as soon as it is seen. The line just before the ERROR: will describe the directory that was untraversable, since the manifest entry is emitted to the HTTP response body before the child is traversed.

## Other Useful Pages

The portion of the web namespace that begins with “/uri” (and “/named”) is dedicated to giving users (both humans and programs) access to the Tahoe-LAFS file store. The rest of the namespace provides status information about the state of the Tahoe-LAFS node.

`GET /` (the root page)

This is the “Welcome Page”, and contains a few distinct sections:

    Node information: library versions, local nodeid, services being provided.

    File store access forms: create a new directory, view a file/directory by
                             URI, upload a file (unlinked), download a file by
                             URI.

    Grid status: introducer information, helper information, connected storage
                 servers.

`GET /?t=json` (the json welcome page)

This is the “json Welcome Page”, and contains connectivity status of the introducer(s) and storage server(s), here’s an example:

    {
     "introducers": {
      "statuses": []
     },
     "servers": [{
       "nodeid": "other_nodeid",
       "available_space": 123456,
       "nickname": "George \u263b",
       "version": "1.0",
       "connection_status": "summary",
       "last_received_data": 1487811257
      }]
    }

The above json `introducers` section includes a list of introducer connectivity status messages.

The above json `servers` section is an array with map elements. Each map has the following properties:

1. `nodeid` - an identifier derived from the node’s public key
2. `available_space` - the available space in bytes expressed as an integer
3. `nickname` - the storage server nickname
4. `version` - the storage server Tahoe-LAFS version
5. `connection_status` - connectivity status
6. `last_received_data` - the time when data was last received, expressed in seconds since epoch

`GET /status/`

> This page lists all active uploads and downloads, and contains a short list of recent upload/download operations. Each operation has a link to a page that describes file sizes, servers that were involved, and the time consumed in each phase of the operation.

> A GET of /status/?t=json will contain a machine-readable subset of the same data. It returns a JSON-encoded dictionary. The only key defined at this time is “active”, with a value that is a list of operation dictionaries, one for each active operation. Once an operation is completed, it will no longer appear in data[“active”] .

> Each op-dict contains a “type” key, one of “upload”, “download”, “mapupdate”, “publish”, or “retrieve” (the first two are for immutable files, while the latter three are for mutable files and directories).

> The “upload” op-dict will contain the following keys:

>     type (string): "upload"
>     storage-index-string (string): a base32-encoded storage index
>     total-size (int): total size of the file
>     status (string): current status of the operation
>     progress-hash (float): 1.0 when the file has been hashed
>     progress-ciphertext (float): 1.0 when the file has been encrypted.
>     progress-encode-push (float): 1.0 when the file has been encoded and
>                                   pushed to the storage servers. For helper
>                                   uploads, the ciphertext value climbs to 1.0
>                                   first, then encoding starts. For unassisted
>                                   uploads, ciphertext and encode-push progress
>                                   will climb at the same pace.

> The “download” op-dict will contain the following keys:

>     type (string): "download"
>     storage-index-string (string): a base32-encoded storage index
>     total-size (int): total size of the file
>     status (string): current status of the operation
>     progress (float): 1.0 when the file has been fully downloaded

> Front-ends which want to report progress information are advised to simply average together all the progress-* indicators. A slightly more accurate value can be found by ignoring the progress-hash value (since the current implementation hashes synchronously, so clients will probably never see progress-hash!=1.0).

`GET /helper_status/`

> If the node is running a helper (i.e. if [helper]enabled is set to True in tahoe.cfg), then this page will provide a list of all the helper operations currently in progress. If “?t=json” is added to the URL, it will return a JSON-formatted list of helper statistics, which can then be used to produce graphs to indicate how busy the helper is.

`GET /statistics/`

> This page provides “node statistics”, which are collected from a variety of sources:

>     load_monitor: every second, the node schedules a timer for one second in
>                   the future, then measures how late the subsequent callback
>                   is. The "load_average" is this tardiness, measured in
>                   seconds, averaged over the last minute. It is an indication
>                   of a busy node, one which is doing more work than can be
>                   completed in a timely fashion. The "max_load" value is the
>                   highest value that has been seen in the last 60 seconds.

>     cpu_monitor: every minute, the node uses time.clock() to measure how much
>                  CPU time it has used, and it uses this value to produce
>                  1min/5min/15min moving averages. These values range from 0%
>                  (0.0) to 100% (1.0), and indicate what fraction of the CPU
>                  has been used by the Tahoe node. Not all operating systems
>                  provide meaningful data to time.clock(): they may report 100%
>                  CPU usage at all times.

>     uploader: this counts how many immutable files (and bytes) have been
>               uploaded since the node was started

>     downloader: this counts how many immutable files have been downloaded
>                 since the node was started

>     publishes: this counts how many mutable files (including directories) have
>                been modified since the node was started

>     retrieves: this counts how many mutable files (including directories) have
>                been read since the node was started

> There are other statistics that are tracked by the node. The “raw stats” section shows a formatted dump of all of them.

> By adding “?t=json” to the URL, the node will return a JSON-formatted dictionary of stats values, which can be used by other tools to produce graphs of node behavior. The misc/munin/ directory in the source distribution provides some tools to produce these graphs.

`GET /` (introducer status)

> For Introducer nodes, the welcome page displays information about both clients and servers which are connected to the introducer. Servers make “service announcements”, and these are listed in a table. Clients will subscribe to hear about service announcements, and these subscriptions are listed in a separate table. Both tables contain information about what version of Tahoe is being run by the remote node, their advertised and outbound IP addresses, their nodeid and nickname, and how long they have been available.

> By adding “?t=json” to the URL, the node will return a JSON-formatted dictionary of stats values, which can be used to produce graphs of connected clients over time. This dictionary has the following keys:

>     ["subscription_summary"] : a dictionary mapping service name (like
>                                "storage") to an integer with the number of
>                                clients that have subscribed to hear about that
>                                service
>     ["announcement_summary"] : a dictionary mapping service name to an integer
>                                with the number of servers which are announcing
>                                that service
>     ["announcement_distinct_hosts"] : a dictionary mapping service name to an
>                                       integer which represents the number of
>                                       distinct hosts that are providing that
>                                       service. If two servers have announced
>                                       FURLs which use the same hostnames (but
>                                       different ports and tubids), they are
>                                       considered to be on the same host.

## Static Files in /public_html

The web-API server will take any request for a URL that starts with /static and serve it from a configurable directory which defaults to $BASEDIR/public_html . This is configured by setting the “[node]web.static” value in $BASEDIR/tahoe.cfg . If this is left at the default value of “public_html”, then http://127.0.0.1:3456/static/subdir/foo.html will be served with the contents of the file $BASEDIR/public_html/subdir/foo.html .

This can be useful to serve a javascript application which provides a prettier front-end to the rest of the Tahoe web-API.

## Safety and Security Issues – Names vs. URIs

Summary: use explicit file- and dir- caps whenever possible, to reduce the potential for surprises when the file store structure is changed.

Tahoe-LAFS provides a mutable file store, but the ways that the store can change are limited. The only things that can change are:

> - the mapping from child names to child objects inside mutable directories (by adding a new child, removing an existing child, or changing an existing child to point to a different object)
> - the contents of mutable files

Obviously if you query for information about the file store and then act to change it (such as by getting a listing of the contents of a mutable directory and then adding a file to the directory), then the store might have been changed after you queried it and before you acted upon it. However, if you use the URI instead of the pathname of an object when you act upon the object, then it will be the same object; only its contents can change (if it is mutable). If, on the other hand, you act upon the object using its pathname, then a different object might be in that place, which can result in more kinds of surprises.

For example, suppose you are writing code which recursively downloads the contents of a directory. The first thing your code does is fetch the listing of the contents of the directory. For each child that it fetched, if that child is a file then it downloads the file, and if that child is a directory then it recurses into that directory. Now, if the download and the recurse actions are performed using the child’s name, then the results might be wrong, because for example a child name that pointed to a subdirectory when you listed the directory might have been changed to point to a file (in which case your attempt to recurse into it would result in an error), or a child name that pointed to a file when you listed the directory might now point to a subdirectory (in which case your attempt to download the child would result in a file containing HTML text describing the subdirectory!).

If your recursive algorithm uses the URI of the child instead of the name of the child, then those kinds of mistakes just can’t happen. Note that both the child’s name and the child’s URI are included in the results of listing the parent directory, so it isn’t any harder to use the URI for this purpose.

The read and write caps in a given directory node are separate URIs, and can’t be assumed to point to the same object even if they were retrieved in the same operation (although the web-API server attempts to ensure this in most cases). If you need to rely on that property, you should explicitly verify it. More generally, you should not make assumptions about the internal consistency of the contents of mutable directories. As a result of the signatures on mutable object versions, it is guaranteed that a given version was written in a single update, but – as in the case of a file – the contents may have been chosen by a malicious writer in a way that is designed to confuse applications that rely on their consistency.

In general, use names if you want “whatever object (whether file or directory) is found by following this name (or sequence of names) when my request reaches the server”. Use URIs if you want “this particular object”.

## Concurrency Issues

Tahoe uses both mutable and immutable files. Mutable files can be created explicitly by doing an upload with ?mutable=true added, or implicitly by creating a new directory (since a directory is just a special way to interpret a given mutable file).

Mutable files suffer from the same consistency-vs-availability tradeoff that all distributed data storage systems face. It is not possible to simultaneously achieve perfect consistency and perfect availability in the face of network partitions (servers being unreachable or faulty).

Tahoe tries to achieve a reasonable compromise, but there is a basic rule in place, known as the Prime Coordination Directive: “Don’t Do That”. What this means is that if write-access to a mutable file is available to several parties, then those parties are responsible for coordinating their activities to avoid multiple simultaneous updates. This could be achieved by having these parties talk to each other and using some sort of locking mechanism, or by serializing all changes through a single writer.

The consequences of performing uncoordinated writes can vary. Some of the writers may lose their changes, as somebody else wins the race condition. In many cases the file will be left in an “unhealthy” state, meaning that there are not as many redundant shares as we would like (reducing the reliability of the file against server failures). In the worst case, the file can be left in such an unhealthy state that no version is recoverable, even the old ones. It is this small possibility of data loss that prompts us to issue the Prime Coordination Directive.

Tahoe nodes implement internal serialization to make sure that a single Tahoe node cannot conflict with itself. For example, it is safe to issue two directory modification requests to a single tahoe node’s web-API server at the same time, because the Tahoe node will internally delay one of them until after the other has finished being applied. (This feature was introduced in Tahoe-1.1; back with Tahoe-1.0 the web client was responsible for serializing web requests themselves).

For more details, please see the “Consistency vs Availability” and “The Prime Coordination Directive” sections of Mutable Files.

## Access Blacklist

Gateway nodes may find it necessary to prohibit access to certain files. The web-API has a facility to block access to filecaps by their storage index, returning a 403 “Forbidden” error instead of the original file.

This blacklist is recorded in $NODEDIR/access.blacklist, and contains one blocked file per line. Comment lines (starting with `#`) are ignored. Each line consists of the storage-index (in the usual base32 format as displayed by the “More Info” page, or by the “tahoe debug dump-cap” command), followed by whitespace, followed by a reason string, which will be included in the 403 error message. This could hold a URL to a page that explains why the file is blocked, for example.

So for example, if you found a need to block access to a file with filecap `URI:CHK:n7r3m6wmomelk4sep3kw5cvduq:os7ijw5c3maek7pg65e5254k2fzjflavtpejjyhshpsxuqzhcwwq:3:20:14861`, you could do the following:

    tahoe debug dump-cap URI:CHK:n7r3m6wmomelk4sep3kw5cvduq:os7ijw5c3maek7pg65e5254k2fzjflavtpejjyhshpsxuqzhcwwq:3:20:14861
    -> storage index: whpepioyrnff7orecjolvbudeu
    echo "whpepioyrnff7orecjolvbudeu my puppy told me to" >>$NODEDIR/access.blacklist
    tahoe restart $NODEDIR
    tahoe get URI:CHK:n7r3m6wmomelk4sep3kw5cvduq:os7ijw5c3maek7pg65e5254k2fzjflavtpejjyhshpsxuqzhcwwq:3:20:14861
    -> error, 403 Access Prohibited: my puppy told me to

The `access.blacklist` file will be checked each time a file or directory is accessed: the file’s `mtime` is used to decide whether it need to be reloaded. Therefore no node restart is necessary when creating the initial blacklist, nor when adding second, third, or additional entries to the list. When modifying the file, be careful to update it atomically, otherwise a request may arrive while the file is only halfway written, and the partial file may be incorrectly parsed.

The blacklist is applied to all access paths (including SFTP, FTP, and CLI operations), not just the web-API. The blacklist also applies to directories. If a directory is blacklisted, the gateway will refuse access to both that directory and any child files/directories underneath it, when accessed via “DIRCAP/SUBDIR/FILENAME” -style URLs. Users who go directly to the child file/dir will bypass the blacklist.

The node will log the SI of the file being blocked, and the reason code, into the `logs/twistd.log` file.

## URLs and HTTP and UTF-8

> HTTP does not provide a mechanism to specify the character set used to encode non-ASCII names in URLs (RFC3986#2.1). We prefer the convention that the `filename=` argument shall be a URL-escaped UTF-8 encoded Unicode string. For example, suppose we want to provoke the server into using a filename of “f i a n c e-acute e” (i.e. f i a n c U+00E9 e). The UTF-8 encoding of this is 0x66 0x69 0x61 0x6e 0x63 0xc3 0xa9 0x65 (or “fianc\xC3\xA9e”, as python’s `repr()` function would show). To encode this into a URL, the non-printable characters must be escaped with the urlencode `%XX` mechanism, giving us “fianc%C3%A9e”. Thus, the first line of the HTTP request will be “`GET /uri/CAP...?save=true&filename=fianc%C3%A9e HTTP/1.1`”. Not all browsers provide this: IE7 by default uses the Latin-1 encoding, which is “fianc%E9e” (although it has a configuration option to send URLs as UTF-8).

> The response header will need to indicate a non-ASCII filename. The actual mechanism to do this is not clear. For ASCII filenames, the response header would look like:

>     Content-Disposition: attachment; filename="english.txt"

> If Tahoe were to enforce the UTF-8 convention, it would need to decode the URL argument into a Unicode string, and then encode it back into a sequence of bytes when creating the response header. One possibility would be to use unencoded UTF-8. Developers suggest that IE7 might accept this:

>     #1: Content-Disposition: attachment; filename="fianc\xC3\xA9e"
>       (note, the last four bytes of that line, not including the newline, are
>       0xC3 0xA9 0x65 0x22)

> RFC2231#4 (dated 1997): suggests that the following might work, and some developers have reported that it is supported by Firefox (but not IE7):

>     #2: Content-Disposition: attachment; filename*=utf-8''fianc%C3%A9e

> My reading of RFC2616#19.5.1 (which defines Content-Disposition) says that the filename= parameter is defined to be wrapped in quotes (presumably to allow spaces without breaking the parsing of subsequent parameters), which would give us:

>     #3: Content-Disposition: attachment; filename*=utf-8''"fianc%C3%A9e"

> However this is contrary to the examples in the email thread listed above.

> Developers report that IE7 (when it is configured for UTF-8 URL encoding, which is not the default in Asian countries), will accept:

>     #4: Content-Disposition: attachment; filename=fianc%C3%A9e

> However, for maximum compatibility, Tahoe simply copies bytes from the URL into the response header, rather than enforcing the UTF-8 convention. This means it does not try to decode the filename from the URL argument, nor does it encode the filename into the response header.