**Experimental and under active development**

This section documents the wire protocol commands exposed to transports

using the frame-based protocol. The set of commands exposed through

these transports is distinct from the set of commands exposed to legacy

transports.

The frame-based protocol uses CBOR to encode command execution requests.

All command arguments must be mapped to a specific or set of CBOR data

types.

The response to many commands is also CBOR. There is no common response

format: each command defines its own response format.

TODOs

=====

* Add "node namespace" support to each command. In order to support

  SHA-1 hash transition, we want servers to be able to expose different

  "node namespaces" for the same data. Every command operating on nodes

  should specify which "node namespace" it is operating on and responses

  should encode the "node namespace" accordingly.

Commands

========

The sections below detail all commands available to wire protocol version

2.

branchmap

---------

Obtain heads in named branches.

Receives no arguments.

The response is a map with bytestring keys defining the branch name.

Values are arrays of bytestring defining raw changeset nodes.

capabilities

------------

Obtain the server's capabilities.

Receives no arguments.

This command is typically called only as part of the handshake during

initial connection establishment.

The response is a map with bytestring keys defining server information.

The defined keys are:

commands

   A map defining available wire protocol commands on this server.

   Keys in the map are the names of commands that can be invoked. Values

   are maps defining information about that command. The bytestring keys

   are:

      args

         A map of argument names and their expected types.

         Types are defined as a representative value for the expected type.

         e.g. an argument expecting a boolean type will have its value

         set to true. An integer type will have its value set to 42. The

         actual values are arbitrary and may not have meaning.

      permissions

         An array of permissions required to execute this command.

compression

   An array of maps defining available compression format support.

   The array is sorted from most preferred to least preferred.

   Each entry has the following bytestring keys:

      name

         Name of the compression engine. e.g. ``zstd`` or ``zlib``.

framingmediatypes

   An array of bytestrings defining the supported framing protocol

   media types. Servers will not accept media types not in this list.

rawrepoformats

   An array of storage formats the repository is using. This set of

   requirements can be used to determine whether a client can read a

   *raw* copy of file data available.

changesetdata

-------------

Obtain various data related to changesets.

The command accepts the following arguments:

noderange

   (array of arrays of bytestrings) An array of 2 elements, each being an

   array of node bytestrings. The first array denotes the changelog revisions

   that are already known to the client. The second array denotes the changelog

   revision DAG heads to fetch. The argument essentially defines a DAG range

   bounded by root and head nodes to fetch.

   The roots array may be empty. The heads array must be defined.

nodes

   (array of bytestrings) Changelog revisions to request explicitly.

fields

   (set of bytestring) Which data associated with changelog revisions to

   fetch. The following values are recognized:

   bookmarks

      Bookmarks associated with a revision.

   parents

      Parent revisions.

   phase

      The phase state of a revision.

   revision

      The raw, revision data for the changelog entry. The hash of this data

      will match the revision's node value.

The server resolves the set of revisions relevant to the request by taking

the union of the ``noderange`` and ``nodes`` arguments. At least one of these

arguments must be defined.

The response bytestream starts with a CBOR map describing the data that follows.

This map has the following bytestring keys:

totalitems

   (unsigned integer) Total number of changelog revisions whose data is being

   transferred. This maps to the set of revisions in the requested node

   range, not the total number of records that follow (see below for why).

Following the map header is a series of 0 or more CBOR values. If values

are present, the first value will always be a map describing a single changeset

revision. If revision data is requested, the raw revision data (encoded as

a CBOR bytestring) will follow the map describing it. Otherwise, another CBOR

map describing the next changeset revision will occur.

Each map has the following bytestring keys:

node

   (bytestring) The node value for this revision. This is the SHA-1 hash of

   the raw revision data.

bookmarks (optional)

   (array of bytestrings) Bookmarks attached to this revision. Only present

   if ``bookmarks`` data is being requested and the revision has bookmarks

   attached.

parents (optional)

   (array of bytestrings) The nodes representing the parent revisions of this

   revision. Only present if ``parents`` data is being requested.

phase (optional)

   (bytestring) The phase that a revision is in. Recognized values are

   ``secret``, ``draft``, and ``public``. Only present if ``phase`` data

   is being requested.

revisionsize (optional)

   (unsigned integer) Indicates the size of raw revision data that follows this

   map. The following data contains a serialized form of the changeset data,

   including the author, date, commit message, set of changed files, manifest

   node, and other metadata.

   Only present if ``revision`` data was requested and the data follows this

   map.

If nodes are requested via ``noderange``, they will be emitted in DAG order,

parents always before children.

If nodes are requested via ``nodes``, they will be emitted in requested order.

Nodes from ``nodes`` are emitted before nodes from ``noderange``.

The set of changeset revisions emitted may not match the exact set of

changesets requested. Furthermore, the set of keys present on each

map may vary. This is to facilitate emitting changeset updates as well

as new revisions.

For example, if the request wants ``phase`` and ``revision`` data,

the response may contain entries for each changeset in the common nodes

set with the ``phase`` key and without the ``revision`` key in order

to reflect a phase-only update.

TODO support different revision selection mechanisms (e.g. non-public, specific

revisions)

TODO support different hash "namespaces" for revisions (e.g. sha-1 versus other)

TODO support emitting obsolescence data

TODO support filtering based on relevant paths (narrow clone)

TODO support depth limiting

TODO support hgtagsfnodes cache / tags data

TODO support branch heads cache

heads

-----

Obtain DAG heads in the repository.

The command accepts the following arguments:

publiconly (optional)

   (boolean) If set, operate on the DAG for public phase changesets only.

   Non-public (i.e. draft) phase DAG heads will not be returned.

The response is a CBOR array of bytestrings defining changeset nodes

of DAG heads. The array can be empty if the repository is empty or no

changesets satisfied the request.

TODO consider exposing phase of heads in response

known

-----

Determine whether a series of changeset nodes is known to the server.

The command accepts the following arguments:

nodes

   (array of bytestrings) List of changeset nodes whose presence to

   query.

The response is a bytestring where each byte contains a 0 or 1 for the

corresponding requested node at the same index.

TODO use a bit array for even more compact response

listkeys

--------

List values in a specified ``pushkey`` namespace.

The command receives the following arguments:

namespace

   (bytestring) Pushkey namespace to query.

The response is a map with bytestring keys and values.

TODO consider using binary to represent nodes in certain pushkey namespaces.

lookup

------

Try to resolve a value to a changeset revision.

Unlike ``known`` which operates on changeset nodes, lookup operates on

node fragments and other names that a user may use.

The command receives the following arguments:

key

   (bytestring) Value to try to resolve.

On success, returns a bytestring containing the resolved node.

pushkey

-------

Set a value using the ``pushkey`` protocol.

The command receives the following arguments:

namespace

   (bytestring) Pushkey namespace to operate on.

key

   (bytestring) The pushkey key to set.

old

   (bytestring) Old value for this key.

new

   (bytestring) New value for this key.

TODO consider using binary to represent nodes is certain pushkey namespaces.

TODO better define response type and meaning.