455 lines
17 KiB
Text
455 lines
17 KiB
Text
Git Wire Protocol, Version 2
|
|
============================
|
|
|
|
This document presents a specification for a version 2 of Git's wire
|
|
protocol. Protocol v2 will improve upon v1 in the following ways:
|
|
|
|
* Instead of multiple service names, multiple commands will be
|
|
supported by a single service
|
|
* Easily extendable as capabilities are moved into their own section
|
|
of the protocol, no longer being hidden behind a NUL byte and
|
|
limited by the size of a pkt-line
|
|
* Separate out other information hidden behind NUL bytes (e.g. agent
|
|
string as a capability and symrefs can be requested using 'ls-refs')
|
|
* Reference advertisement will be omitted unless explicitly requested
|
|
* ls-refs command to explicitly request some refs
|
|
* Designed with http and stateless-rpc in mind. With clear flush
|
|
semantics the http remote helper can simply act as a proxy
|
|
|
|
In protocol v2 communication is command oriented. When first contacting a
|
|
server a list of capabilities will advertised. Some of these capabilities
|
|
will be commands which a client can request be executed. Once a command
|
|
has completed, a client can reuse the connection and request that other
|
|
commands be executed.
|
|
|
|
Packet-Line Framing
|
|
-------------------
|
|
|
|
All communication is done using packet-line framing, just as in v1. See
|
|
`Documentation/technical/pack-protocol.txt` and
|
|
`Documentation/technical/protocol-common.txt` for more information.
|
|
|
|
In protocol v2 these special packets will have the following semantics:
|
|
|
|
* '0000' Flush Packet (flush-pkt) - indicates the end of a message
|
|
* '0001' Delimiter Packet (delim-pkt) - separates sections of a message
|
|
|
|
Initial Client Request
|
|
----------------------
|
|
|
|
In general a client can request to speak protocol v2 by sending
|
|
`version=2` through the respective side-channel for the transport being
|
|
used which inevitably sets `GIT_PROTOCOL`. More information can be
|
|
found in `pack-protocol.txt` and `http-protocol.txt`. In all cases the
|
|
response from the server is the capability advertisement.
|
|
|
|
Git Transport
|
|
~~~~~~~~~~~~~
|
|
|
|
When using the git:// transport, you can request to use protocol v2 by
|
|
sending "version=2" as an extra parameter:
|
|
|
|
003egit-upload-pack /project.git\0host=myserver.com\0\0version=2\0
|
|
|
|
SSH and File Transport
|
|
~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
When using either the ssh:// or file:// transport, the GIT_PROTOCOL
|
|
environment variable must be set explicitly to include "version=2".
|
|
|
|
HTTP Transport
|
|
~~~~~~~~~~~~~~
|
|
|
|
When using the http:// or https:// transport a client makes a "smart"
|
|
info/refs request as described in `http-protocol.txt` and requests that
|
|
v2 be used by supplying "version=2" in the `Git-Protocol` header.
|
|
|
|
C: GET $GIT_URL/info/refs?service=git-upload-pack HTTP/1.0
|
|
C: Git-Protocol: version=2
|
|
|
|
A v2 server would reply:
|
|
|
|
S: 200 OK
|
|
S: <Some headers>
|
|
S: ...
|
|
S:
|
|
S: 000eversion 2\n
|
|
S: <capability-advertisement>
|
|
|
|
Subsequent requests are then made directly to the service
|
|
`$GIT_URL/git-upload-pack`. (This works the same for git-receive-pack).
|
|
|
|
Capability Advertisement
|
|
------------------------
|
|
|
|
A server which decides to communicate (based on a request from a client)
|
|
using protocol version 2, notifies the client by sending a version string
|
|
in its initial response followed by an advertisement of its capabilities.
|
|
Each capability is a key with an optional value. Clients must ignore all
|
|
unknown keys. Semantics of unknown values are left to the definition of
|
|
each key. Some capabilities will describe commands which can be requested
|
|
to be executed by the client.
|
|
|
|
capability-advertisement = protocol-version
|
|
capability-list
|
|
flush-pkt
|
|
|
|
protocol-version = PKT-LINE("version 2" LF)
|
|
capability-list = *capability
|
|
capability = PKT-LINE(key[=value] LF)
|
|
|
|
key = 1*(ALPHA | DIGIT | "-_")
|
|
value = 1*(ALPHA | DIGIT | " -_.,?\/{}[]()<>!@#$%^&*+=:;")
|
|
|
|
Command Request
|
|
---------------
|
|
|
|
After receiving the capability advertisement, a client can then issue a
|
|
request to select the command it wants with any particular capabilities
|
|
or arguments. There is then an optional section where the client can
|
|
provide any command specific parameters or queries. Only a single
|
|
command can be requested at a time.
|
|
|
|
request = empty-request | command-request
|
|
empty-request = flush-pkt
|
|
command-request = command
|
|
capability-list
|
|
[command-args]
|
|
flush-pkt
|
|
command = PKT-LINE("command=" key LF)
|
|
command-args = delim-pkt
|
|
*command-specific-arg
|
|
|
|
command-specific-args are packet line framed arguments defined by
|
|
each individual command.
|
|
|
|
The server will then check to ensure that the client's request is
|
|
comprised of a valid command as well as valid capabilities which were
|
|
advertised. If the request is valid the server will then execute the
|
|
command. A server MUST wait till it has received the client's entire
|
|
request before issuing a response. The format of the response is
|
|
determined by the command being executed, but in all cases a flush-pkt
|
|
indicates the end of the response.
|
|
|
|
When a command has finished, and the client has received the entire
|
|
response from the server, a client can either request that another
|
|
command be executed or can terminate the connection. A client may
|
|
optionally send an empty request consisting of just a flush-pkt to
|
|
indicate that no more requests will be made.
|
|
|
|
Capabilities
|
|
------------
|
|
|
|
There are two different types of capabilities: normal capabilities,
|
|
which can be used to convey information or alter the behavior of a
|
|
request, and commands, which are the core actions that a client wants to
|
|
perform (fetch, push, etc).
|
|
|
|
Protocol version 2 is stateless by default. This means that all commands
|
|
must only last a single round and be stateless from the perspective of the
|
|
server side, unless the client has requested a capability indicating that
|
|
state should be maintained by the server. Clients MUST NOT require state
|
|
management on the server side in order to function correctly. This
|
|
permits simple round-robin load-balancing on the server side, without
|
|
needing to worry about state management.
|
|
|
|
agent
|
|
~~~~~
|
|
|
|
The server can advertise the `agent` capability with a value `X` (in the
|
|
form `agent=X`) to notify the client that the server is running version
|
|
`X`. The client may optionally send its own agent string by including
|
|
the `agent` capability with a value `Y` (in the form `agent=Y`) in its
|
|
request to the server (but it MUST NOT do so if the server did not
|
|
advertise the agent capability). The `X` and `Y` strings may contain any
|
|
printable ASCII characters except space (i.e., the byte range 32 < x <
|
|
127), and are typically of the form "package/version" (e.g.,
|
|
"git/1.8.3.1"). The agent strings are purely informative for statistics
|
|
and debugging purposes, and MUST NOT be used to programmatically assume
|
|
the presence or absence of particular features.
|
|
|
|
ls-refs
|
|
~~~~~~~
|
|
|
|
`ls-refs` is the command used to request a reference advertisement in v2.
|
|
Unlike the current reference advertisement, ls-refs takes in arguments
|
|
which can be used to limit the refs sent from the server.
|
|
|
|
Additional features not supported in the base command will be advertised
|
|
as the value of the command in the capability advertisement in the form
|
|
of a space separated list of features: "<command>=<feature 1> <feature 2>"
|
|
|
|
ls-refs takes in the following arguments:
|
|
|
|
symrefs
|
|
In addition to the object pointed by it, show the underlying ref
|
|
pointed by it when showing a symbolic ref.
|
|
peel
|
|
Show peeled tags.
|
|
ref-prefix <prefix>
|
|
When specified, only references having a prefix matching one of
|
|
the provided prefixes are displayed.
|
|
|
|
The output of ls-refs is as follows:
|
|
|
|
output = *ref
|
|
flush-pkt
|
|
ref = PKT-LINE(obj-id SP refname *(SP ref-attribute) LF)
|
|
ref-attribute = (symref | peeled)
|
|
symref = "symref-target:" symref-target
|
|
peeled = "peeled:" obj-id
|
|
|
|
fetch
|
|
~~~~~
|
|
|
|
`fetch` is the command used to fetch a packfile in v2. It can be looked
|
|
at as a modified version of the v1 fetch where the ref-advertisement is
|
|
stripped out (since the `ls-refs` command fills that role) and the
|
|
message format is tweaked to eliminate redundancies and permit easy
|
|
addition of future extensions.
|
|
|
|
Additional features not supported in the base command will be advertised
|
|
as the value of the command in the capability advertisement in the form
|
|
of a space separated list of features: "<command>=<feature 1> <feature 2>"
|
|
|
|
A `fetch` request can take the following arguments:
|
|
|
|
want <oid>
|
|
Indicates to the server an object which the client wants to
|
|
retrieve. Wants can be anything and are not limited to
|
|
advertised objects.
|
|
|
|
have <oid>
|
|
Indicates to the server an object which the client has locally.
|
|
This allows the server to make a packfile which only contains
|
|
the objects that the client needs. Multiple 'have' lines can be
|
|
supplied.
|
|
|
|
done
|
|
Indicates to the server that negotiation should terminate (or
|
|
not even begin if performing a clone) and that the server should
|
|
use the information supplied in the request to construct the
|
|
packfile.
|
|
|
|
thin-pack
|
|
Request that a thin pack be sent, which is a pack with deltas
|
|
which reference base objects not contained within the pack (but
|
|
are known to exist at the receiving end). This can reduce the
|
|
network traffic significantly, but it requires the receiving end
|
|
to know how to "thicken" these packs by adding the missing bases
|
|
to the pack.
|
|
|
|
no-progress
|
|
Request that progress information that would normally be sent on
|
|
side-band channel 2, during the packfile transfer, should not be
|
|
sent. However, the side-band channel 3 is still used for error
|
|
responses.
|
|
|
|
include-tag
|
|
Request that annotated tags should be sent if the objects they
|
|
point to are being sent.
|
|
|
|
ofs-delta
|
|
Indicate that the client understands PACKv2 with delta referring
|
|
to its base by position in pack rather than by an oid. That is,
|
|
they can read OBJ_OFS_DELTA (aka type 6) in a packfile.
|
|
|
|
If the 'shallow' feature is advertised the following arguments can be
|
|
included in the clients request as well as the potential addition of the
|
|
'shallow-info' section in the server's response as explained below.
|
|
|
|
shallow <oid>
|
|
A client must notify the server of all commits for which it only
|
|
has shallow copies (meaning that it doesn't have the parents of
|
|
a commit) by supplying a 'shallow <oid>' line for each such
|
|
object so that the server is aware of the limitations of the
|
|
client's history. This is so that the server is aware that the
|
|
client may not have all objects reachable from such commits.
|
|
|
|
deepen <depth>
|
|
Requests that the fetch/clone should be shallow having a commit
|
|
depth of <depth> relative to the remote side.
|
|
|
|
deepen-relative
|
|
Requests that the semantics of the "deepen" command be changed
|
|
to indicate that the depth requested is relative to the client's
|
|
current shallow boundary, instead of relative to the requested
|
|
commits.
|
|
|
|
deepen-since <timestamp>
|
|
Requests that the shallow clone/fetch should be cut at a
|
|
specific time, instead of depth. Internally it's equivalent to
|
|
doing "git rev-list --max-age=<timestamp>". Cannot be used with
|
|
"deepen".
|
|
|
|
deepen-not <rev>
|
|
Requests that the shallow clone/fetch should be cut at a
|
|
specific revision specified by '<rev>', instead of a depth.
|
|
Internally it's equivalent of doing "git rev-list --not <rev>".
|
|
Cannot be used with "deepen", but can be used with
|
|
"deepen-since".
|
|
|
|
If the 'filter' feature is advertised, the following argument can be
|
|
included in the client's request:
|
|
|
|
filter <filter-spec>
|
|
Request that various objects from the packfile be omitted
|
|
using one of several filtering techniques. These are intended
|
|
for use with partial clone and partial fetch operations. See
|
|
`rev-list` for possible "filter-spec" values. When communicating
|
|
with other processes, senders SHOULD translate scaled integers
|
|
(e.g. "1k") into a fully-expanded form (e.g. "1024") to aid
|
|
interoperability with older receivers that may not understand
|
|
newly-invented scaling suffixes. However, receivers SHOULD
|
|
accept the following suffixes: 'k', 'm', and 'g' for 1024,
|
|
1048576, and 1073741824, respectively.
|
|
|
|
If the 'ref-in-want' feature is advertised, the following argument can
|
|
be included in the client's request as well as the potential addition of
|
|
the 'wanted-refs' section in the server's response as explained below.
|
|
|
|
want-ref <ref>
|
|
Indicates to the server that the client wants to retrieve a
|
|
particular ref, where <ref> is the full name of a ref on the
|
|
server.
|
|
|
|
If the 'sideband-all' feature is advertised, the following argument can be
|
|
included in the client's request:
|
|
|
|
sideband-all
|
|
Instruct the server to send the whole response multiplexed, not just
|
|
the packfile section. All non-flush and non-delim PKT-LINE in the
|
|
response (not only in the packfile section) will then start with a byte
|
|
indicating its sideband (1, 2, or 3), and the server may send "0005\2"
|
|
(a PKT-LINE of sideband 2 with no payload) as a keepalive packet.
|
|
|
|
The response of `fetch` is broken into a number of sections separated by
|
|
delimiter packets (0001), with each section beginning with its section
|
|
header.
|
|
|
|
output = *section
|
|
section = (acknowledgments | shallow-info | wanted-refs | packfile)
|
|
(flush-pkt | delim-pkt)
|
|
|
|
acknowledgments = PKT-LINE("acknowledgments" LF)
|
|
(nak | *ack)
|
|
(ready)
|
|
ready = PKT-LINE("ready" LF)
|
|
nak = PKT-LINE("NAK" LF)
|
|
ack = PKT-LINE("ACK" SP obj-id LF)
|
|
|
|
shallow-info = PKT-LINE("shallow-info" LF)
|
|
*PKT-LINE((shallow | unshallow) LF)
|
|
shallow = "shallow" SP obj-id
|
|
unshallow = "unshallow" SP obj-id
|
|
|
|
wanted-refs = PKT-LINE("wanted-refs" LF)
|
|
*PKT-LINE(wanted-ref LF)
|
|
wanted-ref = obj-id SP refname
|
|
|
|
packfile = PKT-LINE("packfile" LF)
|
|
*PKT-LINE(%x01-03 *%x00-ff)
|
|
|
|
acknowledgments section
|
|
* If the client determines that it is finished with negotiations
|
|
by sending a "done" line, the acknowledgments sections MUST be
|
|
omitted from the server's response.
|
|
|
|
* Always begins with the section header "acknowledgments"
|
|
|
|
* The server will respond with "NAK" if none of the object ids sent
|
|
as have lines were common.
|
|
|
|
* The server will respond with "ACK obj-id" for all of the
|
|
object ids sent as have lines which are common.
|
|
|
|
* A response cannot have both "ACK" lines as well as a "NAK"
|
|
line.
|
|
|
|
* The server will respond with a "ready" line indicating that
|
|
the server has found an acceptable common base and is ready to
|
|
make and send a packfile (which will be found in the packfile
|
|
section of the same response)
|
|
|
|
* If the server has found a suitable cut point and has decided
|
|
to send a "ready" line, then the server can decide to (as an
|
|
optimization) omit any "ACK" lines it would have sent during
|
|
its response. This is because the server will have already
|
|
determined the objects it plans to send to the client and no
|
|
further negotiation is needed.
|
|
|
|
shallow-info section
|
|
* If the client has requested a shallow fetch/clone, a shallow
|
|
client requests a fetch or the server is shallow then the
|
|
server's response may include a shallow-info section. The
|
|
shallow-info section will be included if (due to one of the
|
|
above conditions) the server needs to inform the client of any
|
|
shallow boundaries or adjustments to the clients already
|
|
existing shallow boundaries.
|
|
|
|
* Always begins with the section header "shallow-info"
|
|
|
|
* If a positive depth is requested, the server will compute the
|
|
set of commits which are no deeper than the desired depth.
|
|
|
|
* The server sends a "shallow obj-id" line for each commit whose
|
|
parents will not be sent in the following packfile.
|
|
|
|
* The server sends an "unshallow obj-id" line for each commit
|
|
which the client has indicated is shallow, but is no longer
|
|
shallow as a result of the fetch (due to its parents being
|
|
sent in the following packfile).
|
|
|
|
* The server MUST NOT send any "unshallow" lines for anything
|
|
which the client has not indicated was shallow as a part of
|
|
its request.
|
|
|
|
* This section is only included if a packfile section is also
|
|
included in the response.
|
|
|
|
wanted-refs section
|
|
* This section is only included if the client has requested a
|
|
ref using a 'want-ref' line and if a packfile section is also
|
|
included in the response.
|
|
|
|
* Always begins with the section header "wanted-refs".
|
|
|
|
* The server will send a ref listing ("<oid> <refname>") for
|
|
each reference requested using 'want-ref' lines.
|
|
|
|
* The server MUST NOT send any refs which were not requested
|
|
using 'want-ref' lines.
|
|
|
|
packfile section
|
|
* This section is only included if the client has sent 'want'
|
|
lines in its request and either requested that no more
|
|
negotiation be done by sending 'done' or if the server has
|
|
decided it has found a sufficient cut point to produce a
|
|
packfile.
|
|
|
|
* Always begins with the section header "packfile"
|
|
|
|
* The transmission of the packfile begins immediately after the
|
|
section header
|
|
|
|
* The data transfer of the packfile is always multiplexed, using
|
|
the same semantics of the 'side-band-64k' capability from
|
|
protocol version 1. This means that each packet, during the
|
|
packfile data stream, is made up of a leading 4-byte pkt-line
|
|
length (typical of the pkt-line format), followed by a 1-byte
|
|
stream code, followed by the actual data.
|
|
|
|
The stream code can be one of:
|
|
1 - pack data
|
|
2 - progress messages
|
|
3 - fatal error message just before stream aborts
|
|
|
|
server-option
|
|
~~~~~~~~~~~~~
|
|
|
|
If advertised, indicates that any number of server specific options can be
|
|
included in a request. This is done by sending each option as a
|
|
"server-option=<option>" capability line in the capability-list section of
|
|
a request.
|
|
|
|
The provided options must not contain a NUL or LF character.
|