Ticket #118: webapi-new.txt

This document has six sections:

1.  the basic API for how to programmatically control your tahoe node
2.  convenience methods
3.  safety and security issues
4.  features for controlling your tahoe node from a standard web browser
5.  debugging and testing features
6.  XML-RPC (coming soon)


1. the basic API for how to programmatically control your tahoe node

a. connecting to the tahoe node

Writing "8011" into $NODEDIR/webport causes the node to run a webserver on
port 8011. Writing "tcp:8011:interface=127.0.0.1" into $NODEDIR/webport does
the same but binds to the loopback interface, ensuring that only the programs
on the local host can connect. Using
"ssl:8011:privateKey=mykey.pem:certKey=cert.pem" would run an SSL server. See
twisted.application.strports for more details.

If $NODEDIR/webpassword exists, it will be used (somehow) to require HTTP
Digest Authentication for all webserver connections.  XXX specify how

b. file names

The node provides some small number of "virtual drives". In the 0.5
release, this number is two: the first is the global shared vdrive, the
second is the private non-shared vdrive. We will call these "global" and
"private".

For the purpose of this document, let us assume that the vdrives currently
contain the following directories and files:

global/
global/Documents/
global/Documents/notes.txt

private/
private/Pictures/
private/Pictures/tractors.jpg
private/Pictures/family/
private/Pictures/family/bobby.jpg

Within the webserver, there is a tree of resources. The top-level "vdrive"
resource gives access to files and directories in all of the user's virtual
drives. For example, the URL that corresponds to notes.txt would be:

http://localhost:8011/vdrive/global/Documents/notes.txt

and the URL for tractors.jpg would be:

http://localhost:8011/vdrive/private/Pictures/tractors.jpg

In addition, each directory has a corresponding URL. The Pictures URL is:

http://localhost:8011/vdrive/private/Pictures

c. URIs

A separate top-level namespace ("uri/" instead of "vdrive/") is used to
access to files and directories directly by URI, rather than by going through
the vdrive.

For example, this identifies a file or directory:

http://localhost:8011/uri/$URI

And this identifies a file or directory named "tractors.jpg" in a
subdirectory "Pictures" of the identified directory:

http://localhost:8011/uri/$URI/Pictures/tractors.jpg

In the following examples, "$URL" is a shorthand for a URL like the ones
above, either with "vdrive/" as the top level and a sequence of
slash-separated pathnames following, or with "uri/" as the top level,
followed by a URI, optionally followed by a sequence of slash-separated
pathnames.

Now, what can we do with these URLs? By varying the HTTP method
(GET/PUT/POST/DELETE) and by appending a type-indicating query argument, we
control what we want to do with the data and how it should be presented.

d. examining files or directories

  GET $URL?t=json

  This returns machine-parseable information about the indicated file or
  directory in the HTTP response body. This information contains a flag that
  indicates whether the thing is a file or a directory.

  If it is a file, then the information includes file size and URI, like
  this:

   [ 'filenode', { 'ro_uri': file_uri,
                   'size': bytes } ]

  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 metadata about the
  child (the same data that would appear in a corresponding GET?t=json of the
  child itself). Like this:

   [ 'dirnode', { 'rw_uri': read_write_uri,
                  'ro_uri': read_only_uri,
                  'children': children } ]

  In the above example, '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:

   'foo.txt': [ 'filenode', { 'ro_uri': uri, 'size': bytes } ]
   'subdir':  [ 'dirnode', { 'rw_uri': rwuri, 'ro_uri': rouri } ]

  note that the value is the same as the JSON representation of the child
  object (except that directories do not recurse -- the "children" entry of
  the child is omitted).

  Then 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,

e. downloading a file

  GET $URL

  If the indicated object is a file, then this simply retrieves the contents
  of the file. The file's contents are provided in the body of the HTTP
  response.

  If the indicated object a directory, then this returns an HTML page,
  intended to be used by humans, 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
  delete files and directories. These forms use POST methods to do their job.

  You can add the "save=true" argument, which adds a 'Content-Disposition:
  attachment' header to prompt most web browsers to save the file to disk
  rather than attempting to display it.

  A filename (from which a MIME type can be derived) can be specified using a
  'filename=' query argument. This is especially useful if the $URL does not
  end with the name of the file (because it instead ends with the identifier
  of the file). This filename is also the one used if the 'save=true'
  argument is set. For example:

   GET http://localhost:8011/uri/$TRACTORS_URI?filename=tractors.jpg

f. uploading a file

  PUT http://localhost:8011/uri

  Upload a file, returning its URI as the HTTP response body. This does not
  make the file visible from the virtual drive -- to do that, see section
  1.h. below, or the convenience method in section 2.a..

g. creating a new directory

  PUT http://localhost:8011/uri?t=mkdir

  Create a new empty directory and return its URI as the HTTP response body.
  This does not make the newly created directory visible from the virtual
  drive, but you can use section 1.h. to attach it, or the convenience method
  in section 2.XXX.

h. attaching a file or directory as the child of an extant directory

  PUT $URL?t=uri

  This attaches a child (either a file or a directory) to the given directory
  $URL is required to indicate a directory as the second-to-last element and
  the desired filename as the last element, for example:

   PUT http://localhost:8011/uri/$URI_OF_SOME_DIR/Pictures/tractors.jpg
   PUT http://localhost:8011/uri/$URI_OF_SOME_DIR/tractors.jpg
   PUT http://localhost:8011/vdrive/private/Pictures/tractors.jpg

  The URI of the child is provided in the body of the HTTP request.

  There is an optional "?overwrite=" param whose value can be "true", "t",
  "1", "false", "f", or "0" (case-insensitive), and which defaults to "true".
  If the indicated directory already contains the given child name, then if
  overwrite is true then the value of that name is changed to be the new URI.
  If overwrite is false then an error is returned. XXX specify the error

  This can be used to attach a shared directory (a directory that other
  people can read or write) to the vdrive. Intermediate directories, if any,
  are created on-demand.

i. removing a name from a directory

  DELETE $URL

  This removes the given name from the given directory. $URL is required to
  indicate a directory as the second-to-last element and the name to remove
  from that directory as the last element, just as in section 1.g..

  Note that this does not actually delete the resource that the name points
  to from the tahoe grid -- it only removes this name in 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 resource are removed from their parent
  directories, then if someone is in possession of the URI of this resource
  they can continue to access the resource through the URI. Only if a person
  is not in possession of the URI, and they do not have access to any
  directories which contain names pointing to this resource, are they
  prevented from accessing the resource.

2. convenience methods

a. uploading a file and attaching it to the vdrive

  PUT $URI

  Upload a file and link it into the the vdrive at the location specified by
  $URI. The last item in the $URI must be a filename, and the second-to-last
  item must identify a directory.

  It will create intermediate directories as necessary. The file's contents
  are taken from the body of the HTTP request. For convenience, the HTTP
  response contains the URI that results from uploading the file, although
  the client is not obligated to do anything with the URI. According to the
  HTTP/1.1 specification (rfc2616), this should return a 200 (OK) code when
  modifying an existing file, and a 201 (Created) code when creating a new
  file.

  To use this, run 'curl -T localfile http://localhost:8011/vdrive/global/newfile'

3. safety and security issues -- names vs. URIs

The vdrive provides a mutable filesystem, but the ways that the filesystem
can change are limited. The only thing that can change is that the mapping
from child names to child objects that each directory contains can be changed
by adding a new child name pointing to an object, removing an existing child
name, or changing an existing child name to point to a different object.

Obviously if you query tahoe for information about the filesystem and then
act upon the filesystem (such as by getting a listing of the contents of a
directory and then adding a file to the directory), then the filesystem 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 the only change that can happen is when the object is a
directory then the set of child names it has might be different. 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 sub-directory 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 and the file
would be skipped), or a child name that pointed to a file when you listed the
directory might now point to a sub-directory (in which case your attempt to
download the child would result in a file containing HTML text describing the
sub-directory!).

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 harder to use the URI for this purpose.

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".

4. features for controlling your tahoe node from a standard web browser

a. uri redirect

  GET http://localhost:8011/uri?uri=$URI

  This causes a redirect to /uri/$URI, 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 URI (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 URI: unlike the GET /uri/$URI form, you cannot traverse to
  children by appending additional path segments to the URL.

b. web page offering rename

  GET $URL?t=rename-form&name=$CHILDNAME

  This provides a useful facility to browser-based user interfaces. It
  returns a page containing a form targetting the "POST $URL t=rename"
  functionality described below, 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.

c. POST forms

  POST $URL
  t=upload
  name=childname  (optional)
  file=newfile
  This instructs the node to upload a file into the given directory. We need
  this because forms are the only way for a web browser to upload a file
  (browsers do not know how to do PUT or DELETE). The file's contents and the
  new child name will be included in the form's arguments. This can only be
  used to upload a single file at a time. To avoid confusion, name= is not
  allowed to contain a slash (a 400 Bad Request error will result).

  POST $URL
  t=mkdir
  name=childname

  This instructs the node to create a new empty directory. The name of the
  new child directory will be included in the form's arguments.

  POST $URL
  t=uri
  name=childname
  uri=newuri

  This instructs the node to attach a child that is referenced by URI (just
  like the PUT $URL?t=uri method). The name and URI of the new child
  will be included in the form's arguments.

  POST $URL
  t=delete
  name=childname

  This instructs the node to delete a file from the given directory. The name
  of the child to be deleted will be included in the form's arguments.

  POST $URL
  t=rename
  from_name=oldchildname
  to_name=newchildname

  This instructs the node to rename a child within the given directory. The
  child specified by 'from_name' is removed, and reattached as a child named
  for 'to_name'. This is unconditional and will replace any child already
  present under 'to_name', akin to 'mv -f' in unix parlance.

5. debugging and testing features

GET $URL?t=download&localfile=$LOCALPATH
GET $URL?t=download&localdir=$LOCALPATH

  The localfile= form instructs the node to download the given file and write
  it into the local filesystem at $LOCALPATH. The localdir= form instructs
  the node to recursively download everything from the given directory and
  below into the local filesystem. To avoid surprises, the localfile= form
  will signal an error if $URL actually refers to a directory, likewise if
  localdir= is used with a $URL that refers to a file.

  This request will only be accepted from an HTTP client connection
  originating at 127.0.0.1 . This request is most useful when the client node
  and the HTTP client are operated by the same user. $LOCALPATH should be an
  absolute pathname.

  This form is only implemented for testing purposes, because of a trivially
  easy attack: any web server that the local browser visits could serve an
  IMG tag that causes the local node to modify the local filesystem.
  Therefore this form is only enabled if you create a file named
  'webport_allow_localfile' in the node's base directory.

PUT $NEWURL?t=upload&localfile=$LOCALPATH
PUT $NEWURL?t=upload&localdir=$LOCALPATH

  This uploads a file or directory from the node's local filesystem to the
  vdrive. As with "GET $URL?t=download&localfile=$LOCALPATH", this request
  will only be accepted from an HTTP connection originating from 127.0.0.1 .

  The localfile= form expects that $LOCALPATH will point to a file on the
  node's local filesystem, and causes the node to upload that one file into
  the vdrive at the given location. Any parent directories will be created in
  the vdrive as necessary.

  The localdir= form expects that $LOCALPATH will point to a directory on the
  node's local filesystem, and it causes the node to perform a recursive
  upload of the directory into the vdrive at the given location, creating
  parent directories as necessary. When the operation is complete, the
  directory referenced by $NEWURL will contain all of the files and
  directories that were present in $LOCALPATH, so this is equivalent to the
  unix commands:

   mkdir -p $NEWURL; cp -r $LOCALPATH/* $NEWURL/

  Note that the "curl" utility can be used to provoke this sort of recursive
  upload, since the -T option will make it use an HTTP 'PUT':

   curl -T /dev/null 'http://localhost:8011/vdrive/global/newdir?t=upload&localdir=/home/user/directory-to-upload'

  This form is only implemented for testing purposes, because any attacker's
  web server that a local browser visits could serve an IMG tag that causes
  the local node to modify the local filesystem. Therefore this form is only
  enabled if you create a file named 'webport_allow_localfile' in the node's
  base directory.

GET $URL?t=manifest

  Return an HTML-formatted manifest of the given directory, for debugging.

6. XMLRPC (coming soon)

  http://localhost:8011/xmlrpc

  This resource provides an XMLRPC server on which all of the previous
  operations can be expressed as function calls taking a "pathname" argument.
  This is provided for applications that want to think of everything in terms
  of XMLRPC.

   listdir(vdrivename, path) -> dict of (childname -> (stuff))
   put(vdrivename, path, contents) -> URI
   get(vdrivename, path) -> contents
   mkdir(vdrivename, path) -> URI
   put_localfile(vdrivename, path, localfilename) -> URI
   get_localfile(vdrivename, path, localfilename)
   put_localdir(vdrivename, path, localdirname)   # recursive
   get_localdir(vdrivename, path, localdirname)   # recursive
   put_uri(vdrivename, path, URI)

   etc..