help: document wire protocol commands

mercurial/help/internals/wireprotocol.txt

@@ -1,417 +1,773 b''
 The Mercurial wire protocol is a request-response based protocol
 with multiple wire representations.
 
 Each request is modeled as a command name, a dictionary of arguments, and
 optional raw input. Command arguments and their types are intrinsic
 properties of commands. So is the response type of the command. This means
 clients can't always send arbitrary arguments to servers and servers can't
 return multiple response types.
 
 The protocol is synchronous and does not support multiplexing (concurrent
 commands).
 
 Transport Protocols
 ===================
 
 HTTP Transport
 --------------
 
 Commands are issued as HTTP/1.0 or HTTP/1.1 requests. Commands are
 sent to the base URL of the repository with the command name sent in
 the ``cmd`` query string parameter. e.g.
 ``https://example.com/repo?cmd=capabilities``. The HTTP method is ``GET``
 or ``POST`` depending on the command and whether there is a request
 body.
 
 Command arguments can be sent multiple ways.
 
 The simplest is part of the URL query string using ``x-www-form-urlencoded``
 encoding (see Python's ``urllib.urlencode()``. However, many servers impose
 length limitations on the URL. So this mechanism is typically only used if
 the server doesn't support other mechanisms.
 
 If the server supports the ``httpheader`` capability, command arguments can
 be sent in HTTP request headers named ``X-HgArg-<N>`` where ``<N>`` is an
 integer starting at 1. A ``x-www-form-urlencoded`` representation of the
 arguments is obtained. This full string is then split into chunks and sent
 in numbered ``X-HgArg-<N>`` headers. The maximum length of each HTTP header
 is defined by the server in the ``httpheader`` capability value, which defaults
 to ``1024``. The server reassembles the encoded arguments string by
 concatenating the ``X-HgArg-<N>`` headers then URL decodes them into a
 dictionary.
 
 The list of ``X-HgArg-<N>`` headers should be added to the ``Vary`` request
 header to instruct caches to take these headers into consideration when caching
 requests.
 
 If the server supports the ``httppostargs`` capability, the client
 may send command arguments in the HTTP request body as part of an
 HTTP POST request. The command arguments will be URL encoded just like
 they would for sending them via HTTP headers. However, no splitting is
 performed: the raw arguments are included in the HTTP request body.
 
 The client sends a ``X-HgArgs-Post`` header with the string length of the
 encoded arguments data. Additional data may be included in the HTTP
 request body immediately following the argument data. The offset of the
 non-argument data is defined by the ``X-HgArgs-Post`` header. The
 ``X-HgArgs-Post`` header is not required if there is no argument data.
 
 Additional command data can be sent as part of the HTTP request body. The
 default ``Content-Type`` when sending data is ``application/mercurial-0.1``.
 A ``Content-Length`` header is currently always sent.
 
 Example HTTP requests::
 
     GET /repo?cmd=capabilities
     X-HgArg-1: foo=bar&baz=hello%20world
 
 The ``Content-Type`` HTTP response header identifies the response as coming
 from Mercurial and can also be used to signal an error has occurred.
 
 The ``application/mercurial-0.1`` media type indicates a generic Mercurial
 response. It matches the media type sent by the client.
 
 The ``application/hg-error`` media type indicates a generic error occurred.
 The content of the HTTP response body typically holds text describing the
 error.
 
 The ``application/hg-changegroup`` media type indicates a changegroup response
 type.
 
 Clients also accept the ``text/plain`` media type. All other media
 types should cause the client to error.
 
 Clients should issue a ``User-Agent`` request header that identifies the client.
 The server should not use the ``User-Agent`` for feature detection.
 
 A command returning a ``string`` response issues the
 ``application/mercurial-0.1`` media type and the HTTP response body contains
 the raw string value. A ``Content-Length`` header is typically issued.
 
 A command returning a ``stream`` response issues the
 ``application/mercurial-0.1`` media type and the HTTP response is typically
 using *chunked transfer* (``Transfer-Encoding: chunked``).
 
 SSH Transport
 =============
 
 The SSH transport is a custom text-based protocol suitable for use over any
 bi-directional stream transport. It is most commonly used with SSH.
 
 A SSH transport server can be started with ``hg serve --stdio``. The stdin,
 stderr, and stdout file descriptors of the started process are used to exchange
 data. When Mercurial connects to a remote server over SSH, it actually starts
 a ``hg serve --stdio`` process on the remote server.
 
 Commands are issued by sending the command name followed by a trailing newline
 ``\n`` to the server. e.g. ``capabilities\n``.
 
 Command arguments are sent in the following format::
 
     <argument> <length>\n<value>
 
 That is, the argument string name followed by a space followed by the
 integer length of the value (expressed as a string) followed by a newline
 (``\n``) followed by the raw argument value.
 
 Dictionary arguments are encoded differently::
 
     <argument> <# elements>\n
     <key1> <length1>\n<value1>
     <key2> <length2>\n<value2>
     ...
 
 Non-argument data is sent immediately after the final argument value. It is
 encoded in chunks::
 
     <length>\n<data>
 
 Each command declares a list of supported arguments and their types. If a
 client sends an unknown argument to the server, the server should abort
 immediately. The special argument ``*`` in a command's definition indicates
 that all argument names are allowed.
 
 The definition of supported arguments and types is initially made when a
 new command is implemented. The client and server must initially independently
 agree on the arguments and their types. This initial set of arguments can be
 supplemented through the presence of *capabilities* advertised by the server.
 
 Each command has a defined expected response type.
 
 A ``string`` response type is a length framed value. The response consists of
 the string encoded integer length of a value followed by a newline (``\n``)
 followed by the value. Empty values are allowed (and are represented as
 ``0\n``).
 
 A ``stream`` response type consists of raw bytes of data. There is no framing.
 
 A generic error response type is also supported. It consists of a an error
 message written to ``stderr`` followed by ``\n-\n``. In addition, ``\n`` is
 written to ``stdout``.
 
 If the server receives an unknown command, it will send an empty ``string``
 response.
 
 The server terminates if it receives an empty command (a ``\n`` character).
 
 Capabilities
 ============
 
 Servers advertise supported wire protocol features. This allows clients to
 probe for server features before blindly calling a command or passing a
 specific argument.
 
 The server's features are exposed via a *capabilities* string. This is a
 space-delimited string of tokens/features. Some features are single words
 like ``lookup`` or ``batch``. Others are complicated key-value pairs
 advertising sub-features. e.g. ``httpheader=2048``. When complex, non-word
 values are used, each feature name can define its own encoding of sub-values.
 Comma-delimited and ``x-www-form-urlencoded`` values are common.
 
 The following document capabilities defined by the canonical Mercurial server
 implementation.
 
 batch
 -----
 
 Whether the server supports the ``batch`` command.
 
 This capability/command was introduced in Mercurial 1.9 (released July 2011).
 
 branchmap
 ---------
 
 Whether the server supports the ``branchmap`` command.
 
 This capability/command was introduced in Mercurial 1.3 (released July 2009).
 
 bundle2-exp
 -----------
 
 Precursor to ``bundle2`` capability that was used before bundle2 was a
 stable feature.
 
 This capability was introduced in Mercurial 3.0 behind an experimental
 flag. This capability should not be observed in the wild.
 
 bundle2
 -------
 
 Indicates whether the server supports the ``bundle2`` data exchange format.
 
 The value of the capability is a URL quoted, newline (``\n``) delimited
 list of keys or key-value pairs.
 
 A key is simply a URL encoded string.
 
 A key-value pair is a URL encoded key separated from a URL encoded value by
 an ``=``. If the value is a list, elements are delimited by a ``,`` after
 URL encoding.
 
 For example, say we have the values::
 
   {'HG20': [], 'changegroup': ['01', '02'], 'digests': ['sha1', 'sha512']}
 
 We would first construct a string::
 
   HG20\nchangegroup=01,02\ndigests=sha1,sha512
 
 We would then URL quote this string::
 
   HG20%0Achangegroup%3D01%2C02%0Adigests%3Dsha1%2Csha512
 
 This capability was introduced in Mercurial 3.4 (released May 2015).
 
 changegroupsubset
 -----------------
 
 Whether the server supports the ``changegroupsubset`` command.
 
 This capability was introduced in Mercurial 0.9.2 (released December
 2006).
 
 This capability was introduced at the same time as the ``lookup``
 capability/command.
 
 getbundle
 ---------
 
 Whether the server supports the ``getbundle`` command.
 
 This capability was introduced in Mercurial 1.9 (released July 2011).
 
 httpheader
 ----------
 
 Whether the server supports receiving command arguments via HTTP request
 headers.
 
 The value of the capability is an integer describing the max header
 length that clients should send. Clients should ignore any content after a
 comma in the value, as this is reserved for future use.
 
 This capability was introduced in Mercurial 1.9 (released July 2011).
 
 httppostargs
 ------------
 
 **Experimental**
 
 Indicates that the server supports and prefers clients send command arguments
 via a HTTP POST request as part of the request body.
 
 This capability was introduced in Mercurial 3.8 (released May 2016).
 
 known
 -----
 
 Whether the server supports the ``known`` command.
 
 This capability/command was introduced in Mercurial 1.9 (released July 2011).
 
 lookup
 ------
 
 Whether the server supports the ``lookup`` command.
 
 This capability was introduced in Mercurial 0.9.2 (released December
 2006).
 
 This capability was introduced at the same time as the ``changegroupsubset``
 capability/command.
 
 pushkey
 -------
 
 Whether the server supports the ``pushkey`` and ``listkeys`` commands.
 
 This capability was introduced in Mercurial 1.6 (released July 2010).
 
 standardbundle
 --------------
 
 **Unsupported**
 
 This capability was introduced during the Mercurial 0.9.2 development cycle in
 2006. It was never present in a release, as it was replaced by the ``unbundle``
 capability. This capability should not be encountered in the wild.
 
 stream-preferred
 ----------------
 
 If present the server prefers that clients clone using the streaming clone
 protocol (``hg clone --uncompressed``) rather than the standard
 changegroup/bundle based protocol.
 
 This capability was introduced in Mercurial 2.2 (released May 2012).
 
 streamreqs
 ----------
 
 Indicates whether the server supports *streaming clones* and the *requirements*
 that clients must support to receive it.
 
 If present, the server supports the ``stream_out`` command, which transmits
 raw revlogs from the repository instead of changegroups. This provides a faster
 cloning mechanism at the expense of more bandwidth used.
 
 The value of this capability is a comma-delimited list of repo format
 *requirements*. These are requirements that impact the reading of data in
 the ``.hg/store`` directory. An example value is
 ``streamreqs=generaldelta,revlogv1`` indicating the server repo requires
 the ``revlogv1`` and ``generaldelta`` requirements.
 
 If the only format requirement is ``revlogv1``, the server may expose the
 ``stream`` capability instead of the ``streamreqs`` capability.
 
 This capability was introduced in Mercurial 1.7 (released November 2010).
 
 stream
 ------
 
 Whether the server supports *streaming clones* from ``revlogv1`` repos.
 
 If present, the server supports the ``stream_out`` command, which transmits
 raw revlogs from the repository instead of changegroups. This provides a faster
 cloning mechanism at the expense of more bandwidth used.
 
 This capability was introduced in Mercurial 0.9.1 (released July 2006).
 
 When initially introduced, the value of the capability was the numeric
 revlog revision. e.g. ``stream=1``. This indicates the changegroup is using
 ``revlogv1``. This simple integer value wasn't powerful enough, so the
 ``streamreqs`` capability was invented to handle cases where the repo
 requirements have more than just ``revlogv1``. Newer servers omit the
 ``=1`` since it was the only value supported and the value of ``1`` can
 be implied by clients.
 
 unbundlehash
 ------------
 
 Whether the ``unbundle`` commands supports receiving a hash of all the
 heads instead of a list.
 
 For more, see the documentation for the ``unbundle`` command.
 
 This capability was introduced in Mercurial 1.9 (released July 2011).
 
 unbundle
 --------
 
 Whether the server supports pushing via the ``unbundle`` command.
 
 This capability/command has been present since Mercurial 0.9.1 (released
 July 2006).
 
 Mercurial 0.9.2 (released December 2006) added values to the capability
 indicating which bundle types the server supports receiving. This value is a
 comma-delimited list. e.g. ``HG10GZ,HG10BZ,HG10UN``. The order of values
 reflects the priority/preference of that type, where the first value is the
 most preferred type.
 
 Handshake Protocol
 ==================
 
 While not explicitly required, it is common for clients to perform a
 *handshake* when connecting to a server. The handshake accomplishes 2 things:
 
 * Obtaining capabilities and other server features
 * Flushing extra server output (e.g. SSH servers may print extra text
   when connecting that may confuse the wire protocol)
 
 This isn't a traditional *handshake* as far as network protocols go because
 there is no persistent state as a result of the handshake: the handshake is
 simply the issuing of commands and commands are stateless.
 
 The canonical clients perform a capabilities lookup at connection establishment
 time. This is because clients must assume a server only supports the features
 of the original Mercurial server implementation until proven otherwise (from
 advertised capabilities). Nearly every server running today supports features
 that weren't present in the original Mercurial server implementation. Rather
 than wait for a client to perform functionality that needs to consult
 capabilities, it issues the lookup at connection start to avoid any delay later.
 
 For HTTP servers, the client sends a ``capabilities`` command request as
 soon as the connection is established. The server responds with a capabilities
 string, which the client parses.
 
 For SSH servers, the client sends the ``hello`` command (no arguments)
 and a ``between`` command with the ``pairs`` argument having the value
 ``0000000000000000000000000000000000000000-0000000000000000000000000000000000000000``.
 
 The ``between`` command has been supported since the original Mercurial
 server. Requesting the empty range will return a ``\n`` string response,
 which will be encoded as ``1\n\n`` (value length of ``1`` followed by a newline
 followed by the value, which happens to  be a newline).
 
 The ``hello`` command was later introduced. Servers supporting it will issue
 a response to that command before sending the ``1\n\n`` response to the
 ``between`` command. Servers not supporting ``hello`` will send an empty
 response (``0\n``).
 
 In addition to the expected output from the ``hello`` and ``between`` commands,
 servers may also send other output, such as *message of the day (MOTD)*
 announcements. Clients assume servers will send this output before the
 Mercurial server replies to the client-issued commands. So any server output
 not conforming to the expected command responses is assumed to be not related
 to Mercurial and can be ignored.
+
+Commands
+========
+
+This section contains a list of all wire protocol commands implemented by
+the canonical Mercurial server.
+
+batch
+-----
+
+Issue multiple commands while sending a single command request. The purpose
+of this command is to allow a client to issue multiple commands while avoiding
+multiple round trips to the server therefore enabling commands to complete
+quicker.
+
+The command accepts a ``cmds`` argument that contains a list of commands to
+execute.
+
+The value of ``cmds`` is a ``;`` delimited list of strings. Each string has the
+form ``<command> <arguments>``. That is, the command name followed by a space
+followed by an argument string.
+
+The argument string is a ``,`` delimited list of ``<key>=<value>`` values
+corresponding to command arguments. Both the argument name and value are
+escaped using a special substitution map::
+
+   : -> :c
+   , -> :o
+   ; -> :s
+   = -> :e
+
+The response type for this command is ``string``. The value contains a
+``;`` delimited list of responses for each requested command. Each value
+in this list is escaped using the same substitution map used for arguments.
+
+If an error occurs, the generic error response may be sent.
+
+between
+-------
+
+(Legacy command used for discovery in old clients)
+
+Obtain nodes between pairs of nodes.
+
+The ``pairs`` arguments contains a space-delimited list of ``-`` delimited
+hex node pairs. e.g.::
+
+   a072279d3f7fd3a4aa7ffa1a5af8efc573e1c896-6dc58916e7c070f678682bfe404d2e2d68291a18
+
+Return type is a ``string``. Value consists of lines corresponding to each
+requested range. Each line contains a space-delimited list of hex nodes.
+A newline ``\n`` terminates each line, including the last one.
+
+branchmap
+---------
+
+Obtain heads in named branches.
+
+Accepts no arguments. Return type is a ``string``.
+
+Return value contains lines with URL encoded branch names followed by a space
+followed by a space-delimited list of hex nodes of heads on that branch.
+e.g.::
+
+    default a072279d3f7fd3a4aa7ffa1a5af8efc573e1c896 6dc58916e7c070f678682bfe404d2e2d68291a18
+    stable baae3bf31522f41dd5e6d7377d0edd8d1cf3fccc
+
+There is no trailing newline.
+
+branches
+--------
+
+Obtain ancestor changesets of specific nodes back to a branch point.
+
+Despite the name, this command has nothing to do with Mercurial named branches.
+Instead, it is related to DAG branches.
+
+The command accepts a ``nodes`` argument, which is a string of space-delimited
+hex nodes.
+
+For each node requested, the server will find the first ancestor node that is
+a DAG root or is a merge.
+
+Return type is a ``string``. Return value contains lines with result data for
+each requested node. Each line contains space-delimited nodes followed by a
+newline (``\n``). The 4 nodes reported on each line correspond to the requested
+node, the ancestor node found, and its 2 parent nodes (which may be the null
+node).
+
+capabilities
+------------
+
+Obtain the capabilities string for the repo.
+
+Unlike the ``hello`` command, the capabilities string is not prefixed.
+There is no trailing newline.
+
+This command does not accept any arguments. Return type is a ``string``.
+
+changegroup
+-----------
+
+(Legacy command: use ``getbundle`` instead)
+
+Obtain a changegroup version 1 with data for changesets that are
+descendants of client-specified changesets.
+
+The ``roots`` arguments contains a list of space-delimited hex nodes.
+
+The server responds with a changegroup version 1 containing all
+changesets between the requested root/base nodes and the repo's head nodes
+at the time of the request.
+
+The return type is a ``stream``.
+
+changegroupsubset
+-----------------
+
+(Legacy command: use ``getbundle`` instead)
+
+Obtain a changegroup version 1 with data for changesetsets between
+client specified base and head nodes.
+
+The ``bases`` argument contains a list of space-delimited hex nodes.
+The ``heads`` argument contains a list of space-delimited hex nodes.
+
+The server responds with a changegroup version 1 containing all
+changesets between the requested base and head nodes at the time of the
+request.
+
+The return type is a ``stream``.
+
+clonebundles
+------------
+
+Obtains a manifest of bundle URLs available to seed clones.
+
+Each returned line contains a URL followed by metadata. See the
+documentation in the ``clonebundles`` extension for more.
+
+The return type is a ``string``.
+
+getbundle
+---------
+
+Obtain a bundle containing repository data.
+
+This command accepts the following arguments:
+
+heads
+   List of space-delimited hex nodes of heads to retrieve.
+common
+   List of space-delimited hex nodes that the client has in common with the
+   server.
+obsmarkers
+   Boolean indicating whether to include obsolescence markers as part
+   of the response. Only works with bundle2.
+bundlecaps
+   Comma-delimited set of strings defining client bundle capabilities.
+listkeys
+   Comma-delimited list of strings of ``pushkey`` namespaces. For each
+   namespace listed, a bundle2 part will be included with the content of
+   that namespace.
+cg
+   Boolean indicating whether changegroup data is requested.
+cbattempted
+   Boolean indicating whether the client attempted to use the *clone bundles*
+   feature before performing this request.
+
+The return type on success is a ``stream`` where the value is bundle.
+On the HTTP transport, the response is zlib compressed.
+
+If an error occurs, a generic error response can be sent.
+
+Unless the client sends a false value for the ``cg`` argument, the returned
+bundle contains a changegroup with the nodes between the specified ``common``
+and ``heads`` nodes. Depending on the command arguments, the type and content
+of the returned bundle can vary significantly.
+
+The default behavior is for the server to send a raw changegroup version
+``01`` response.
+
+If the ``bundlecaps`` provided by the client contain a value beginning
+with ``HG2``, a bundle2 will be returned. The bundle2 data may contain
+additional repository data, such as ``pushkey`` namespace values.
+
+heads
+-----
+
+Returns a list of space-delimited hex nodes of repository heads followed
+by a newline. e.g.
+``a9eeb3adc7ddb5006c088e9eda61791c777cbf7c 31f91a3da534dc849f0d6bfc00a395a97cf218a1\n``
+
+This command does not accept any arguments. The return type is a ``string``.
+
+hello
+-----
+
+Returns lines describing interesting things about the server in an RFC-822
+like format.
+
+Currently, the only line defines the server capabilities. It has the form::
+
+    capabilities: <value>
+
+See above for more about the capabilities string.
+
+SSH clients typically issue this command as soon as a connection is
+established.
+
+This command does not accept any arguments. The return type is a ``string``.
+
+listkeys
+--------
+
+List values in a specified ``pushkey`` namespace.
+
+The ``namespace`` argument defines the pushkey namespace to operate on.
+
+The return type is a ``string``. The value is an encoded dictionary of keys.
+
+Key-value pairs are delimited by newlines (``\n``). Within each line, keys and
+values are separated by a tab (``\t``). Keys and values are both strings.
+
+lookup
+------
+
+Try to resolve a value to a known repository revision.
+
+The ``key`` argument is converted from bytes to an
+``encoding.localstr`` instance then passed into
+``localrepository.__getitem__`` in an attempt to resolve it.
+
+The return type is a ``string``.
+
+Upon successful resolution, returns ``1 <hex node>\n``. On failure,
+returns ``0 <error string>\n``. e.g.::
+
+   1 273ce12ad8f155317b2c078ec75a4eba507f1fba\n
+
+   0 unknown revision 'foo'\n
+
+known
+-----
+
+Determine whether multiple nodes are known.
+
+The ``nodes`` argument is a list of space-delimited hex nodes to check
+for existence.
+
+The return type is ``string``.
+
+Returns a string consisting of ``0``s and ``1``s indicating whether nodes
+are known. If the Nth node specified in the ``nodes`` argument is known,
+a ``1`` will be returned at byte offset N. If the node isn't known, ``0``
+will be present at byte offset N.
+
+There is no trailing newline.
+
+pushkey
+-------
+
+Set a value using the ``pushkey`` protocol.
+
+Accepts arguments ``namespace``, ``key``, ``old``, and ``new``, which
+correspond to the pushkey namespace to operate on, the key within that
+namespace to change, the old value (which may be empty), and the new value.
+All arguments are string types.
+
+The return type is a ``string``. The value depends on the transport protocol.
+
+The SSH transport sends a string encoded integer followed by a newline
+(``\n``) which indicates operation result. The server may send additional
+output on the ``stderr`` stream that should be displayed to the user.
+
+The HTTP transport sends a string encoded integer followed by a newline
+followed by additional server output that should be displayed to the user.
+This may include output from hooks, etc.
+
+The integer result varies by namespace. ``0`` means an error has occurred
+and there should be additional output to display to the user.
+
+stream_out
+----------
+
+Obtain *streaming clone* data.
+
+The return type is either a ``string`` or a ``stream``, depending on
+whether the request was fulfilled properly.
+
+A return value of ``1\n`` indicates the server is not configured to serve
+this data. If this is seen by the client, they may not have verified the
+``stream`` capability is set before making the request.
+
+A return value of ``2\n`` indicates the server was unable to lock the
+repository to generate data.
+
+All other responses are a ``stream`` of bytes. The first line of this data
+contains 2 space-delimited integers corresponding to the path count and
+payload size, respectively::
+
+    <path count> <payload size>\n
+
+The ``<payload size>`` is the total size of path data: it does not include
+the size of the per-path header lines.
+
+Following that header are ``<path count>`` entries. Each entry consists of a
+line with metadata followed by raw revlog data. The line consists of::
+
+    <store path>\0<size>\n
+
+The ``<store path>`` is the encoded store path of the data that follows.
+``<size>`` is the amount of data for this store path/revlog that follows the
+newline.
+
+There is no trailer to indicate end of data. Instead, the client should stop
+reading after ``<path count>`` entries are consumed.
+
+unbundle
+--------
+
+Send a bundle containing data (usually changegroup data) to the server.
+
+Accepts the argument ``heads``, which is a space-delimited list of hex nodes
+corresponding to server repository heads observed by the client. This is used
+to detect race conditions and abort push operations before a server performs
+too much work or a client transfers too much data.
+
+The request payload consists of a bundle to be applied to the repository,
+similarly to as if :hg:`unbundle` were called.
+
+In most scenarios, a special ``push response`` type is returned. This type
+contains an integer describing the change in heads as a result of the
+operation. A value of ``0`` indicates nothing changed. ``1`` means the number
+of heads remained the same. Values ``2`` and larger indicate the number of
+added heads minus 1. e.g. ``3`` means 2 heads were added. Negative values
+indicate the number of fewer heads, also off by 1. e.g. ``-2`` means there
+is 1 fewer head.
+
+The encoding of the ``push response`` type varies by transport.
+
+For the SSH transport, this type is composed of 2 ``string`` responses: an
+empty response (``0\n``) followed by the integer result value. e.g.
+``1\n2``. So the full response might be ``0\n1\n2``.
+
+For the HTTP transport, the response is a ``string`` type composed of an
+integer result value followed by a newline (``\n``) followed by string
+content holding server output that should be displayed on the client (output
+hooks, etc).
+
+In some cases, the server may respond with a ``bundle2`` bundle. In this
+case, the response type is ``stream``. For the HTTP transport, the response
+is zlib compressed.
+
+The server may also respond with a generic error type, which contains a string
+indicating the failure.