It is assumed the reader is familiar with bencoding, as described in
the BitTorrent protocol specification at
http://www.bittorrent.org/protocol.html

Dictionary keys used below will be enclosed in quotation marks, these
are used for clarity and are not part of the actual key.

The IPC protocol is used to allow processes to control or retrieve
information from Transmission frontend, such as transmission-daemon,
or the GTK+ or Mac OS X frontends.  This communication is done
over a unix-domain socket file such as
~/.transmission/daemon/socket. In this document the Transmission
frontend will be referred to as the server and the process connecting
to it as the client.

Once a client connects to the server's socket, messages may be
exchanged until either end closes the connection. Messages contain an
32-bit payload length, encoded as 8 bytes of ASCII hexadecimal,
followed by the payload. Upper, lower, or mixed case for the length
are all acceptable and must be handled correctly. Payload lengths
greater than 2^31 - 8 (ie: 2147483640 decimal, 7FFFFFF8 hex) are not
allowed.

Bencoded messages will additionally be shown in the following format
for better readability:
str  - "this is a string"
num  - 38795
list - ("wheeee", 435, "writing docs is boring")
dict - {"name": "Josh", "beverage": "coffee", "quantity": "too damn much" }

For version 1, the message payload is a bencoded dictionary, the
valid keys and value formats for which are described below. Multiple
keys may be used in one message.

An example version 1 message:

0000000Ed4:porti9090ee
        {"port": 9090}

For version 2 the message payload is a bencoded list containing a
message id string followed by a bencoded value, the format of which is
the same for version 1. The value may be followed by an optional
bencoded integer, this is a message tag and is described in more
detail below.

An example version 2 message:

0000001El12:get-info-alll4:hashee
        ("get-info-all", ("hash"))

The same message with a tag:

00000021l12:get-info-alll4:hashei5ee
        ("get-info-all", ("hash"), 5)

Once the connection is made both the client and server must send a
version 1 style message (ie: the payload is a dictionary and may not
contain a tag) with the dictionary key "version" and a value formatted
as described below. The version should be the first but not
necessarily only key in the dictionary. Any other keys should be
ignored and not processed as messages. Neither the client nor the
server should wait to receive a version message before sending one, it
must be sent immediately. No other messages should be sent until the
version is received.

The version value should be a bencoded dictionary containing two keys,
"max" and "min". These are the minimum and maximum supported protocol
versions, respectively. Communication will take place using the
highest protocol version supported by both the client and the server,
and is not possible at all if there is no common version. A client may
receive a version value that is an integer instead of a dictionary
with "min" and "max" keys. This deprecated version format indicates
the only version supported by the server.

The version dictionary may optionally contain a key "label". This is a
human-readable name for the software, it is not machine-readable and
neither servers nor clients should attempt to parse it.

An example message containing minimum and maximum versions 1 and 2:

0000001Dd7:versiond3:mini1e3:maxi2eee
        {"version": {"min": 1, "max": 2}}

Tagged messages, only supported in version 2, allow a client to tag a
message with a positive non-zero integer. The server is then required
to send a response to the message even if none would normally be
required, and to tag the response with the same integer. When the
server receives a tagged message it must send exactly one message back
with the same tag. The client is allowed to use the same tag for
multiple messages, even if a response to the first is not received
before the second it sent. If a tagged message does not normally
require a response then a "succeeded", "failed", "not-supported" or
"bad-format" message will be sent back.

An example tagged message and response:

00000010l5:startli8eei15ee
        ("start", (8), 15)
00000011l8:succeeded0:i15ee
        ("succeeded", "", 15)

Some example sessions, including version handshake, are found at the
end of this file.

Dictionary keys are encoded in UTF-8 and case sensitive. Any character
except a NUL (0x00) is valid. A server or client need not support
every possible key and should silently ignore any that it does not
understand.

If a reference to a boolean is seen, it should be taken to mean an
integer with a value of 0 representing false, 1 representing true, and
any other value undefined.

Individual torrents are identified by a unique integer. This integer
is only valid for the current connection and may be invalid or refer
to another torrent in a future connection. If a torrent is closed it's
ID will never be reused to refer to another torrent for at least the
duration of the connection. Negative integers or 0 are not valid IDs.

A list of keys and the format of their values follows. Also listed is
the minimum protocol version that the key may be used with.


Key:     "addfiles"
Version: 1
Format:  list of strings
Replies: "succeeded", "failed", "not-supported", "bad-format", "info"
Example: 8:addfilesl21:/torrents/foo.torrent20:/home/me/bar.torrente
         "addfiles", ("/torrents/foo.torrent", /home/me/bar.torrent")
Details: Each string is the absolute path to a torrent metainfo file
         for the server to add. Note that whether or not the torrent
         metainfo file is copied (allowing the original to be moved or
         deleted safely) is implementation dependent and may not
         currently be known or changed with this protocol.

Key:     "addfile-detailed"
Version: 2
Format:  dict
Replies: "succeeded", "failed", "not-supported", "bad-format", "info"
Example: 16:addfile-detailedd4:file19:/tor/wooble.torrente
         "addfile-detailed", {"file": "/tor/wooble.torrent"}
Details: Dictionary containing information about a torrent for the
         server to add. Valid keys include:
           "file"       string, filename of torrent metainfo file
           "data"       string, contents of a torrent metainfo file
           "directory"  string, directory for data files for the torrent
           "autostart"  boolean, start the torrent automatically
         Either "file" or "data" is required, but both are not allowed.

Key:     "automap"
Version: 2
Format:  boolean
Replies: "succeeded", "failed", "not-supported", "bad-format"
Example: 7:automapi1e
         "automap", 1
Details: Enable (1) or disable (0) automatic port mapping on the server.

Key:     "autostart"
Version: 2
Format:  boolean
Replies: "succeeded", "failed", "not-supported", "bad-format"
Example: 9:autostarti0e
         "autostart", 0
Details: Enable (1) or disable (0) automatic starting of new torrents
         added via "addfiles" or "addfiles-detailed" messages.

Key:     "bad-format"
Version: 2
Format:  value is ignored
Replies: N/A
Example: 10:bad-format0:
         "bad-format", ""
Details: Sent in response to a tagged message which was structured
         incorrectly. For example, an "autostart" message with a
         string value might cause this message to be returned.

Key:     "directory"
Version: 2
Format:  string
Replies: "succeeded", "failed", "not-supported", "bad-format"
Example: 9:directory21:/home/roger/downloads
         "directory", "/home/roger/downloads"
Details: Set the default directory used for any torrents added in the future.

Key:     "downlimit"
Version: 2
Format:  int
Replies: "succeeded", "failed", "not-supported", "bad-format"
Example: 9:downlimiti100e
         "downlimit", 100
Details: Set the server's download limit in kilobytes per second.
         Negative values are interpreted as no limit.

Key:     "encryption"
Version: 2
Format:  string
Replies: "succeeded", "failed", "not-supported", "bad-format"
Example: 10:encryption8:required
         "encryption", "required"
Details: Set the encryption mode for peer connections. Valid values
         are "required" and "preferred".

Key:     "failed"
Version: 2
Format:  string
Replies: N/A
Example: 6:failed17:permission denied
         "failed", "permission denied"
Details: Sent in response to a tagged message to indicate failure.

Key:     "get-automap"
Version: 2
Format:  value is ignored
Replies: "failed", "not-supported", "bad-format", "automap"
Example: 11:get-automap0:
         "get-automap", ""
Details: Requests that an "automap" message be sent back.

Key:     "get-autostart"
Version: 2
Format:  value is ignored
Replies: "failed", "not-supported", "bad-format", "autostart"
Example: 13:get-autostart0:
         "get-autostart", ""
Details: Requests that an "autostart" message be sent back.

Key:     "get-directory"
Version: 2
Format:  value is ignored
Replies: "failed", "not-supported", "bad-format", "directory"
Example: 13:get-directory0:
         "get-directory", ""
Details: Requests that an "directory" message be sent back.

Key:     "get-downlimit"
Version: 2
Format:  value is ignored
Replies: "failed", "not-supported", "bad-format", "downlimit"
Example: 13:get-downlimit0:
         "get-downlimit", ""
Details: Requests that a "downlimit" message be sent back.

Key:     "get-encryption"
Version: 2
Format:  value is ignored
Replies: "failed", "not-supported", "bad-format", "encryption"
Example: 14:get-encryption0:
         "get-encryption", ""
Details: Requests that an "encryption" message be sent back.

Key:     "get-info"
Version: 2
Format:  dict with keys "id" and "type" for lists of ints and strings
Replies: "failed", "not-supported", "bad-format", "info"
Example: 8:get-infod2:idli4ei7ei2ee4:typel4:hash4:nameee
         "get-info", {"id": (4, 7, 2), "type": ("hash", "name")}
Details: Requests that the server send back an "info" message with
         info on all the torrent IDs in "id". The "type" key requests
         what info will be returned. See below for valid values to use
         here. Since the torrent ID is always included in an "info"
         message an empty or missing "type" key will cause only the ID
         to be returned. An "info" message will always be sent back,
         even if it is empty.

Key:     "get-info-all"
Version: 2
Format:  list of strings
Replies: "failed", "not-supported", "bad-format", "info"
Example: 12:get-info-alll4:hash4:namee
         "get-info-all", ("hash", "name")
Details: Same as "getinfo" message with all torrent IDs specified.

Key:     "get-pex"
Version: 2
Format:  value is ignored
Replies: "failed", "not-supported", "bad-format", "pex"
Example: 7:get-pex0:
         "get-pex", ""
Details: Requests that a "pex" message be sent back.

Key:     "get-port"
Version: 2
Format:  value is ignored
Replies: "failed", "not-supported", "bad-format", "port"
Example: 8:get-port0:
         "get-port", ""
Details: Requests that a "port" message be sent back.

Key:     "get-status"
Version: 2
Format:  dict with keys "id" and "type" for lists of ints and strings
Replies: "failed", "not-supported", "bad-format", "status"
Example: 10:get-statusd2:idli4ei7ei2ee4:typel5:state9:completedee
         "get-status", {"id": (4, 7, 4), "type": ("state", "completed")}
Details: Same as "get-info" message except status type strings are used
         instead and the server sends back a "status" message.

Key:     "get-status-all"
Version: 2
Format:  list of strings
Replies: "failed", "not-supported", "bad-format", "status"
Example: 14:get-status-alll5:state9:completede
         "get-status-all", ("state", "completed")
Details: Same as "get-status" message with all torrent IDs specified.

Key:     "get-supported"
Version: 2
Format:  list of strings
Replies: "failed", "not-supported", "bad-format", "supported"
Example: 13:get-supportedl6:lookup8:get-port16:addfile-detailede
         "get-supported", ("lookup", "get-port", "addfile-detailed")
Details: Request that a "supported" message be returned with whichever
         of the given message keys are supported.

Key:     "get-uplimit"
Version: 2
Format:  value is ignored
Replies: "failed", "not-supported", "bad-format", "uplimit"
Example: 11:get-uplimit0:
         "get-uplimit", ""
Details: Requests that an "uplimit" message be sent back.

Key:     "lookup"
Version: 2
Format:  list of strings
Replies: "failed", "not-supported", "bad-format", "info"
Example: 6:lookupl40:0f16ea6965ee5133ea4dbb1e7f516e9fcf3d899ee
         "lookup", ("0f16ea6965ee5133ea4dbb1e7f516e9fcf3d899e")
Details: Request that the server send back an "info" message with "id"
         and "hash" keys for any torrents with the given hashes.

Key:     "info"
Version: 2
Format:  list of dictionaries
Replies: N/A
Example: 4:infold2:idi3e4:name3:fooed2:idi9e4:name3:baree
         "info", ({"id": 4, "name": "foo"}, {"id": 9, "name": "bar"})
Details: A list containing information for several torrents. The
         dictionaries always contain at least an "id" key with the
         integer ID for the torrent, other possible values are listed
         below.

Key:     "noop"
Version: 2
Format:  value is ignored
Replies: "succeeded", "failed", "not-supported", "bad-format"
Example: 4:noop0:
         "noop", ""
Details: This does nothing but keep the connection alive. With a tag
         it may be used as a ping.

Key:     "not-supported"
Version: 2
Format:  value is ignored
Replies: N/A
Example: 13:not-supported0:
         "not-supported", ""
Details: Sent in response to a tagged message to indicated that the
         message was not supported.

Key:     "pex"
Version: 2
Format:  boolean
Replies: "succeeded", "failed", "not-supported", "bad-format"
Example: 3:pexi0e
         "pex", 0
Details: Enables or disables peer exchange.

Key:     "port"
Version: 2
Format:  int between 0 and 65535
Replies: "succeeded", "failed", "not-supported", "bad-format"
Example: 4:porti9090e
         "port", 9090
Details: Change the port the server uses to listen for incoming peer
         connections.

Key:     "quit"
Version: 1
Format:  value is ignored
Replies: "succeeded", "failed", "not-supported", "bad-format"
Example: 4:quit0:
         "quit", ""
Details: Cause the server to quit. Note that the connection might be
         closed without a response being sent.

Key:     "remove"
Version: 2
Format:  list of torrent ID ints
Replies: "succeeded", "failed", "not-supported", "bad-format"
Example: 5:removeli3ei8ei6ee
         "remove", (3, 8, 6)
Details: Stop and remove the specified torrents. Note that whether or
         not the downloaded data or the original torrent files will be
         removed is implementation dependent and may not currently be
         known or changed with this protocol. If a saved copy of the
         torrent file has been made then it will always be deleted.

Key:     "remove-all"
Version: 2
Format:  value is ignored
Replies: "succeeded", "failed", "not-supported", "bad-format"
Example: 10:remove-all0:
         "remove-all", ""
Details: Like "remove" with all torrent IDs specified.

Key:     "start"
Version: 2
Format:  list of torrent ID ints
Replies: "succeeded", "failed", "not-supported", "bad-format"
Example: 5:startli3ei8ei6ee
         "start", (3, 8, 6)
Details: List of torrent IDs to start.

Key:     "start-all"
Version: 2
Format:  value is ignored
Replies: "succeeded", "failed", "not-supported", "bad-format"
Example: 9:start-all0:
         "start-all", ""
Details: Start all torrents.

Key:     "status"
Version: 2
Format:  list of dictionaries
Replies: N/A
Example: 4:infold2:idi3e5:state7:seedinged2:idi9e5:state6:pausedee
         "info", ({"id": 3, "state": "seeding"}, {"id": 9, "state" : "paused"})
Details: Same as "info" message except status type keys are used.

Key:     "stop"
Version: 2
Format:  list of torrent ID ints
Replies: "succeeded", "failed", "not-supported", "bad-format"
Example: 4:stopli3ei8ei6ee
         "stop", (3, 8, 6)
Details: List of torrent IDs to stop.

Key:     "stop-all"
Version: 2
Format:  value is ignored
Replies: "succeeded", "failed", "not-supported", "bad-format"
Example: 8:stop-all0:
         "stop-all", ""
Details: Stop all torrents.

Key:     "succeeded"
Version: 2
Format:  value is ignored
Replies: N/A
Example: 8:succeeded0:
         "succeeded", ""
Details: This is used to indicate that a tagged message was processed
         successfully.

Key:     "supported"
Version: 2
Format:  list of strings
Replies: N/A
Example: 9:supportedl8:get-port6:lookupe
         "supported", ("get-port", "lookup")
Details: Sent in response to a "get-supported" message, indicates that
         the given messages ate supported.

Key:     "uplimit"
Version: 2
Format:  int
Replies: "succeeded", "failed", "not-supported", "bad-format"
Example: 7:uplimiti20e
         "uplimit", 20
Details: Set the server's upload limit in kilobytes per second.
         Negative values are interpreted as no limit.


Info types for "get-info" and "info" messages. The only type for which
support is mandatory is "id".

"id"       integer, torrent's ID for this connection
"hash"     SHA-1 info hash as a 40-char hex string
"name"     string, torrent name
"path"     string, path to .torrent file
"saved"    boolean, true if a copy of this torrent was saved
"private"  boolean, true if the torrent is private
"trackers" a list of lists of dictionaries containing tracker info:
             "address"  string, hostname or ip address of tracker
             "port"     integer, port for tracker
             "announce" string, announce url on tracker
             "scrape"   string, scrape url on tracker, may be absent
"comment"  string, comment from torrent file
"creator"  string, creator of torrent file
"date"     integer, date of torrent creation (unix time_t format)
"size"     integer, total size of all files in bytes
"files"    list of dictionaries for the files in this torrent:
             "name" string, name of file
             "size" integer, size of file in bytes


Status types for "get-status" and "status" messages. The only type for
which support is mandatory is "id".

"completed"         integer, bytes of data downloaded and verified
"download-speed"    integer, download speed in bytes per second
"download-total"    integer, total bytes downloaded so far
"error"             string, one of the following:
                      "assert"          something happened that shouldn't
                      "io-parent"       missing parent directory
                      "io-permissions"  filesystem permission error
                      "io-space"        not enough free space in filesystem
                      "io-resource"     insufficient resources
                      "io-other"        other filesystem i/o error
                      "tracker-error"   tracker returned error message
                      "tracker-warning" tracker returned warning message
                      "other"           other error
                      zero-length or missing string indicates no error
"error-message"     string, printable error message
"eta"               integer, estimated seconds until downloading is finished
"id"                integer, torrent's ID for this connection
"peers-downloading" integer, peers downloading from us
"peers-from"        dict with the following int keys, peer connection sources:
                      "incoming"    peers connected to our listening port
                      "tracker"     peers discovered from tracker
                      "cache"       peers retrieved from on-disk cache
                      "pex"         peers discovered via peer exchange
"peers-total"       integer, total connected peers
"peers-uploading"   integer, peers uploading to us
"running"           boolean, false if torrent is stopped or stopping
"state"             string, one of the following:
                      "checking"    performing hash check on file data
                      "downloading" downloading file data
                      "seeding"     seeding file data to peers
                      "stopping"    contacting tracker to send 'stopped' event
                      "paused"      torrent is not active
                      "waiting to checking"
                                    torrent is queued for hash check.
                                    yes, this it really is called that.
"swarm-speed"       integer, swarm speed in bytes per second
"tracker"           dict with the following keys, current active tracker
                      "address"     string, hostname or ip address of tracker
                      "port"        integer, port for tracker
                      "announce"    string, tracker announce url
                      "scrape"      string, tracker scrape url, may be absent
"scrape-completed"  integer, total completed peers as reported by tracker
"scrape-leechers"   integer, current leechers as reported by tracker
"scrape-seeders"    integer, current, seeders as reported by tracker
"upload-speed"      integer, upload speed in bytes per second
"upload-total"      integer, total bytes uploaded so far


Examples:

Data from the client to the server is prefixed with >>> and from
server to client with <<<. These prefixes and newlines are added for
clarity, they are not actually sent over the socket.

Quit the server. Note that this is a version 1 client and so version 1
messages are used.
>>> 0000001Dd7:versiond3:mini1e3:maxi1eee
            {"version", {"min": 1, "max": 1"}}
<<< 0000001Dd7:versiond3:mini1e3:maxi2eee
            {"version", {"min": 1, "max": 2"}}
>>> 0000000Bd4:quit0:e
            {"quit": ""}

Pause all torrents and disable automapping. Note the server happens to
have sent it's version before the client. The value for the stop-all
message here is 5:fnord instead of 0: as used above, since the value
is unused anything is allowed.
<<< 0000001Dd7:versiond3:mini1e3:maxi2eee
            {"version", {"min": 1, "max": 2"}}
>>> 0000001Dd7:versiond3:mini1e3:maxi2eee
            {"version", {"min": 1, "max": 2"}}
>>> 0000000El8:stop-all5:fnorde
            ("stop-all", "fnord")

Change upload and download limits with tagged responses.
>>> 0000001Dd7:versiond3:mini1e3:maxi2eee
            {"version", {"min": 1, "max": 2"}}
<<< 0000001Dd7:versiond3:mini1e3:maxi2eee
            {"version", {"min": 1, "max": 2"}}
>>> 00000017l9:downlimiti100ei47el
            ("downlimit", 100, 47)
>>> 00000017l9:uplimiti20ei48ee
            ("uplimit", 20, 48)
<<< 00000014l8:succeeded0:i47ee
            ("succeeded", "", 47)
<<< 00000014l8:succeeded0:i48ee
            (succeeded"", "", 48)

Retrieve the upload and download limits. Note that the server has
returned the responses in a different order than the requests were
sent. The server is allowed to do this, a client should use tags if
this is a concern.
>>> 0000001Dd7:versiond3:mini1e3:maxi2eee
            {"version", {"min": 1, "max": 2"}}
<<< 0000001Dd7:versiond3:mini1e3:maxi2eee
            {"version", {"min": 1, "max": 2"}}
>>> 00000015l13:get-downlimiti0ee00000013l13:get-uplimiti0ee
            ("get-downlimit", 0)
            ("get-uplimit", 0)
<<< 0000000Fl9:uplimiti20ee00000012l9:downlimiti100ee
            ("uplimit", 20)
            ("downlimit", 100)