annotate mercurial/help/internals/wireprotocolv2.txt @ 40178:46a40bce3ae0

wireprotov2: define and implement "filesdata" command

Previously, the only way to access file revision data was the
"filedata" command. This command is useful to have. But, it only
allowed resolving revision data for a single file. This meant that
clients needed to send 1 command for each tracked path they were
seeking data on. Furthermore, those commands would need to enumerate
the exact file nodes they wanted data for.

This approach meant that clients were sending a lot of data to
remotes in order to request file data. e.g. if there were 1M
file revisions, we'd need at least 20,000,000 bytes just to encode
file nodes! Many clients on the internet don't have that kind of
upload capacity.

In order to limit the amount of data that clients must send, we'll
need more efficient ways to request repository data.

This commit defines and implements a new "filesdata" command. This
command allows the retrieval of data for multiple files by specifying
changeset revisions and optional file patterns. The command figures
out what file revisions are "relevant" and sends them in bulk.

The logic around choosing which file revisions to send in the case of
haveparents not being set is overly simple and will over-send files. We
will need more smarts here eventually. (Specifically, the client will
need to tell the server which revisions it knows about.) This work
is deferred until a later time.

Differential Revision: https://phab.mercurial-scm.org/D4981

**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
         (map) Describes arguments accepted by the command.

         Keys are bytestrings denoting the argument name.

         Values are maps describing the argument. The map has the following
         bytestring keys:

         default
            (varied) The default value for this argument if not specified. Only
            present if ``required`` is not true.

         required
            (boolean) Whether the argument must be specified. Failure to send
            required arguments will result in an error executing the command.

         type
            (bytestring) The type of the argument. e.g. ``bytes`` or ``bool``.

         validvalues
            (set) Values that are recognized for this argument. Some arguments
            only allow a fixed set of values to be specified. These arguments
            may advertise that set in this key. If this set is advertised and
            a value not in this set is specified, the command should result
            in error.

      permissions
         An array of permissions required to execute this command.

      *
         (various) Individual commands may define extra keys that supplement
         generic command metadata. See the command definition for more.

framingmediatypes
   An array of bytestrings defining the supported framing protocol
   media types. Servers will not accept media types not in this list.

pathfilterprefixes
   (set of bytestring) Matcher prefixes that are recognized when performing
   path filtering. Specifying a path filter whose type/prefix does not
   match one in this set will likely be rejected by the server.

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.

redirect
   A map declaring potential *content redirects* that may be used by this
   server. Contains the following bytestring keys:

   targets
      (array of maps) Potential redirect targets. Values are maps describing
      this target in more detail. Each map has the following bytestring keys:

      name
         (bytestring) Identifier for this target. The identifier will be used
         by clients to uniquely identify this target.

      protocol
         (bytestring) High-level network protocol. Values can be
         ``http``, ```https``, ``ssh``, etc.

      uris
          (array of bytestrings) Representative URIs for this target.

      snirequired (optional)
          (boolean) Indicates whether Server Name Indication is required
          to use this target. Defaults to False.

      tlsversions (optional)
          (array of bytestring) Indicates which TLS versions are supported by
          this target. Values are ``1.1``, ``1.2``, ``1.3``, etc.

   hashes
      (array of bytestring) Indicates support for hashing algorithms that are
      used to ensure content integrity. Values include ``sha1``, ``sha256``,
      etc.

changesetdata
-------------

Obtain various data related to changesets.

The command accepts the following arguments:

revisions
   (array of maps) Specifies revisions whose data is being requested. Each
   value in the array is a map describing revisions. See the
   *Revisions Specifiers* section below for the format of this map.

   Data will be sent for the union of all revisions resolved by all
   revision specifiers.

   Only revision specifiers operating on changeset revisions are allowed.

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 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 the ``fieldsfollowing`` key is present, the map will immediately be followed
by N CBOR bytestring values, where N is the number of elements in
``fieldsfollowing``. Each bytestring value corresponds to a field denoted
by ``fieldsfollowing``.

Following the optional bytestring field values is the next revision descriptor
map, or end of stream.

Each revision descriptor 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.

fieldsfollowing (optional)
   (array of 2-array) Denotes what fields immediately follow this map. Each
   value is an array with 2 elements: the bytestring field name and an unsigned
   integer describing the length of the data, in bytes.

   If this key isn't present, no special fields will follow this map.

   The following fields may be present:

   revision
      Raw, revision data for the changelog entry. 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 the ``revision`` field was requested.

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.

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 hgtagsfnodes cache / tags data
TODO support branch heads cache
TODO consider unify query mechanism. e.g. as an array of "query descriptors"
rather than a set of top-level arguments that have semantics when combined.

filedata
--------

Obtain various data related to an individual tracked file.

The command accepts the following arguments:

fields
   (set of bytestring) Which data associated with a file to fetch.
   The following values are recognized:

   parents
      Parent nodes for the revision.

   revision
      The raw revision data for a file.

haveparents
   (bool) Whether the client has the parent revisions of all requested
   nodes. If set, the server may emit revision data as deltas against
   any parent revision. If not set, the server MUST only emit deltas for
   revisions previously emitted by this command.

   False is assumed in the absence of any value.

nodes
   (array of bytestrings) File nodes whose data to retrieve.

path
   (bytestring) Path of the tracked file whose data to retrieve.

TODO allow specifying revisions via alternate means (such as from
changeset revisions or ranges)

The response bytestream starts with a CBOR map describing the data that
follows. It has the following bytestream keys:

totalitems
   (unsigned integer) Total number of file revisions whose data is
   being returned.

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 the ``fieldsfollowing`` key is present, the map will immediately be followed
by N CBOR bytestring values, where N is the number of elements in
``fieldsfollowing``. Each bytestring value corresponds to a field denoted
by ``fieldsfollowing``.

Following the optional bytestring field values is the next revision descriptor
map, or end of stream.

Each revision descriptor map has the following bytestring keys:

Each map has the following bytestring keys:

node
   (bytestring) The node of the file revision whose data is represented.

deltabasenode
   (bytestring) Node of the file revision the following delta is against.

   Only present if the ``revision`` field is requested and delta data
   follows this map.

fieldsfollowing
   (array of 2-array) Denotes extra bytestring fields that following this map.
   See the documentation for ``changesetdata`` for semantics.

   The following named fields may be present:

   ``delta``
      The delta data to use to construct the fulltext revision.

      Only present if the ``revision`` field is requested and a delta is
      being emitted. The ``deltabasenode`` top-level key will also be
      present if this field is being emitted.

   ``revision``
      The fulltext revision data for this manifest. Only present if the
      ``revision`` field is requested and a fulltext revision is being emitted.

parents
   (array of bytestring) The nodes of the parents of this file revision.

   Only present if the ``parents`` field is requested.

When ``revision`` data is requested, the server chooses to emit either fulltext
revision data or a delta. What the server decides can be inferred by looking
for the presence of the ``delta`` or ``revision`` keys in the
``fieldsfollowing`` array.

filesdata
---------

Obtain various data related to multiple tracked files for specific changesets.

This command is similar to ``filedata`` with the main difference being that
individual requests operate on multiple file paths. This allows clients to
request data for multiple paths by issuing a single command.

The command accepts the following arguments:

fields
   (set of bytestring) Which data associated with a file to fetch.
   The following values are recognized:

   parents
      Parent nodes for the revision.

   revision
      The raw revision data for a file.

haveparents
   (bool) Whether the client has the parent revisions of all requested
   nodes.

pathfilter
   (map) Defines a filter that determines what file paths are relevant.

   See the *Path Filters* section for more.

   If the argument is omitted, it is assumed that all paths are relevant.

revisions
   (array of maps) Specifies revisions whose data is being requested. Each value
   in the array is a map describing revisions. See the *Revisions Specifiers*
   section below for the format of this map.

   Data will be sent for the union of all revisions resolved by all revision
   specifiers.

   Only revision specifiers operating on changeset revisions are allowed.

The response bytestream starts with a CBOR map describing the data that
follows. This map has the following bytestring keys:

totalpaths
   (unsigned integer) Total number of paths whose data is being transferred.

totalitems
   (unsigned integer) Total number of file revisions whose data is being
   transferred.

Following the map header are 0 or more sequences of CBOR values. Each sequence
represents data for a specific tracked path. Each sequence begins with a CBOR
map describing the file data that follows. Following that map is N CBOR values
describing file revision data. The format of this data is identical to that
returned by the ``filedata`` command.

Each sequence's map header has the following bytestring keys:

path
   (bytestring) The tracked file path whose data follows.

totalitems
   (unsigned integer) Total number of file revisions whose data is being
   transferred.

The ``haveparents`` argument has significant implications on the data
transferred.

When ``haveparents`` is true, the command MAY only emit data for file
revisions introduced by the set of changeset revisions whose data is being
requested. In other words, the command may assume that all file revisions
for all relevant paths for ancestors of the requested changeset revisions
are present on the receiver.

When ``haveparents`` is false, the command MUST assume that the receiver
has no file revisions data. This means that all referenced file revisions
in the queried set of changeset revisions will be sent.

TODO we'll probably want a more complicated mechanism for the client to
specify which ancestor revisions are known.

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.

manifestdata
------------

Obtain various data related to manifests (which are lists of files in
a revision).

The command accepts the following arguments:

fields
   (set of bytestring) Which data associated with manifests to fetch.
   The following values are recognized:

   parents
      Parent nodes for the manifest.

   revision
      The raw revision data for the manifest.

haveparents
   (bool) Whether the client has the parent revisions of all requested
   nodes. If set, the server may emit revision data as deltas against
   any parent revision. If not set, the server MUST only emit deltas for
   revisions previously emitted by this command.

   False is assumed in the absence of any value.

nodes
   (array of bytestring) Manifest nodes whose data to retrieve.

tree
   (bytestring) Path to manifest to retrieve. The empty bytestring represents
   the root manifest. All other values represent directories/trees within
   the repository.

TODO allow specifying revisions via alternate means (such as from changeset
revisions or ranges)
TODO consider recursive expansion of manifests (with path filtering for
narrow use cases)

The response bytestream starts with a CBOR map describing the data that
follows. It has the following bytestring keys:

totalitems
   (unsigned integer) Total number of manifest revisions whose data is
   being returned.

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 manifest
revision.

If the ``fieldsfollowing`` key is present, the map will immediately be followed
by N CBOR bytestring values, where N is the number of elements in
``fieldsfollowing``. Each bytestring value corresponds to a field denoted
by ``fieldsfollowing``.

Following the optional bytestring field values is the next revision descriptor
map, or end of stream.

Each revision descriptor map has the following bytestring keys:

node
   (bytestring) The node of the manifest revision whose data is represented.

deltabasenode
   (bytestring) The node that the delta representation of this revision is
   computed against. Only present if the ``revision`` field is requested and
   a delta is being emitted.

fieldsfollowing
   (array of 2-array) Denotes extra bytestring fields that following this map.
   See the documentation for ``changesetdata`` for semantics.

   The following named fields may be present:

   ``delta``
      The delta data to use to construct the fulltext revision.

      Only present if the ``revision`` field is requested and a delta is
      being emitted. The ``deltabasenode`` top-level key will also be
      present if this field is being emitted.

   ``revision``
      The fulltext revision data for this manifest. Only present if the
      ``revision`` field is requested and a fulltext revision is being emitted.

parents
   (array of bytestring) The nodes of the parents of this manifest revision.
   Only present if the ``parents`` field is requested.

When ``revision`` data is requested, the server chooses to emit either fulltext
revision data or a delta. What the server decides can be inferred by looking
for the presence of ``delta`` or ``revision`` in the ``fieldsfollowing`` array.

Servers MAY advertise the following extra fields in the capabilities
descriptor for this command:

recommendedbatchsize
   (unsigned integer) Number of revisions the server recommends as a batch
   query size. If defined, clients needing to issue multiple ``manifestdata``
   commands to obtain needed data SHOULD construct their commands to have
   this many revisions per request.

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.

Revision Specifiers
===================

A *revision specifier* is a map that evaluates to a set of revisions.

A *revision specifier* has a ``type`` key that defines the revision
selection type to perform. Other keys in the map are used in a
type-specific manner.

The following types are defined:

changesetexplicit
   An explicit set of enumerated changeset revisions.

   The ``nodes`` key MUST contain an array of full binary nodes, expressed
   as bytestrings.

changesetexplicitdepth
   Like ``changesetexplicit``, but contains a ``depth`` key defining the
   unsigned integer number of ancestor revisions to also resolve. For each
   value in ``nodes``, DAG ancestors will be walked until up to N total
   revisions from that ancestry walk are present in the final resolved set.

changesetdagrange
   Defines revisions via a DAG range of changesets on the changelog.

   The ``roots`` key MUST contain an array of full, binary node values
   representing the *root* revisions.

   The ``heads`` key MUST contain an array of full, binary nodes values
   representing the *head* revisions.

   The DAG range between ``roots`` and ``heads`` will be resolved and all
   revisions between will be used. Nodes in ``roots`` are not part of the
   resolved set. Nodes in ``heads`` are. The ``roots`` array may be empty.
   The ``heads`` array MUST be defined.

Path Filters
============

Various commands accept a *path filter* argument that defines the set of file
paths relevant to the request.

A *path filter* is defined as a map with the bytestring keys ``include`` and
``exclude``. Each is an array of bytestring values. Each value defines a pattern
rule (see :hg:`help patterns`) that is used to match file paths.

A path matches the path filter if it is matched by a rule in the ``include``
set but doesn't match a rule in the ``exclude`` set. In other words, a path
matcher takes the union of all ``include`` patterns and then substracts the
union of all ``exclude`` patterns.

Patterns MUST be prefixed with their pattern type. Only the following pattern
types are allowed: ``path:``, ``rootfilesin:``.

If the ``include`` key is omitted, it is assumed that all paths are
relevant. The patterns from ``exclude`` will still be used, if defined.

An example value is ``path:tests/foo``, which would match a file named
``tests/foo`` or a directory ``tests/foo`` and all files under it.