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NAME | SYNOPSIS | DESCRIPTION | PACKET-LINE FRAMING | INITIAL CLIENT REQUEST | CAPABILITY ADVERTISEMENT | COMMAND REQUEST | CAPABILITIES | GIT | NOTES | COLOPHON |
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GITPROTOCOL-V2(5) Git Manual GITPROTOCOL-V2(5)
gitprotocol-v2 - Git Wire Protocol, Version 2
<over-the-wire-protocol>
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.
All communication is done using packet-line framing, just as in
v1. See gitprotocol-pack(5) and gitprotocol-common(5) 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
• 0002 Response End Packet (response-end-pkt) - indicates the
end of a response for stateless connections
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 gitprotocol-pack(5) and gitprotocol-http(5), as
well as the GIT_PROTOCOL definition in git.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". The server may need to be configured to
allow this environment variable to pass.
HTTP Transport
When using the http:// or https:// transport a client makes a
"smart" info/refs request as described in gitprotocol-http(5) 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
$GIT_URL/git-upload-pack. (This works the same for
git-receive-pack).
Uses the --http-backend-info-refs option to git-upload-pack(1).
The server may need to be configured to pass this header’s
contents via the GIT_PROTOCOL variable. See the discussion in
git-http-backend.txt.
A server which decides to communicate (based on a request from a
client) using protocol version 2, notifies the client by sending
a version string in its initial response followed by an
advertisement of its capabilities. Each capability is a key with
an optional value. Clients must ignore all unknown keys.
Semantics of unknown values are left to the definition of each
key. Some capabilities will describe commands which can be
requested to be executed by the client.
capability-advertisement = protocol-version
capability-list
flush-pkt
protocol-version = PKT-LINE("version 2" LF)
capability-list = *capability
capability = PKT-LINE(key[=value] LF)
key = 1*(ALPHA | DIGIT | "-_")
value = 1*(ALPHA | DIGIT | " -_.,?\/{}[]()<>!@#$%^&*+=:;")
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
delim-pkt
command-args
flush-pkt
command = PKT-LINE("command=" key LF)
command-args = *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.
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. Multiple instances may be
given, in which case references matching any prefix will be
shown. Note that this is purely for optimization; a server MAY
show refs not matching the prefix if it chooses, and clients
should filter the result themselves.
If the unborn feature is advertised the following argument can be
included in the client’s request.
unborn
The server will send information about HEAD even if it is a symref
pointing to an unborn branch in the form "unborn HEAD
symref-target:<target>".
The output of ls-refs is as follows:
output = *ref
flush-pkt
obj-id-or-unborn = (obj-id | "unborn")
ref = PKT-LINE(obj-id-or-unborn 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.
If the packfile-uris feature is advertised, the following
argument can be included in the client’s request as well as the
potential addition of the packfile-uris section in the server’s
response as explained below.
packfile-uris <comma-separated list of protocols>
Indicates to the server that the client is willing to receive
URIs of any of the given protocols in place of objects in the
sent packfile. Before performing the connectivity check, the
client should download from all given URIs. Currently, the
protocols supported are "http" and "https".
If the wait-for-done feature is advertised, the following
argument can be included in the client’s request.
wait-for-done
Indicates to the server that it should never send "ready", but
should wait for the client to say "done" before sending the
packfile.
The response of fetch is broken into a number of sections
separated by delimiter packets (0001), with each section
beginning with its section header. Most sections are sent only
when the packfile is sent.
output = acknowledgements flush-pkt |
[acknowledgments delim-pkt] [shallow-info delim-pkt]
[wanted-refs delim-pkt] [packfile-uris delim-pkt]
packfile flush-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-uris = PKT-LINE("packfile-uris" LF) *packfile-uri
packfile-uri = PKT-LINE(40*(HEXDIGIT) SP *%x20-ff LF)
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 (thus requiring the server to send a packfile),
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.
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-uris section
* This section is only included if the client sent
'packfile-uris' and the server has at least one such URI to
send.
• Always begins with the section header "packfile-uris".
• For each URI the server sends, it sends a hash of the pack’s
contents (as output by git index-pack) followed by the URI.
• The hashes are 40 hex characters long. When Git upgrades to a
new hash algorithm, this might need to be updated. (It should
match whatever index-pack outputs after "pack\t" or "keep\t".
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.
object-format
The server can advertise the object-format capability with a
value X (in the form object-format=X) to notify the client that
the server is able to deal with objects using hash algorithm X.
If not specified, the server is assumed to only handle SHA-1. If
the client would like to use a hash algorithm other than SHA-1,
it should specify its object-format string.
session-id=<session id>
The server may advertise a session ID that can be used to
identify this process across multiple requests. The client may
advertise its own session ID back to the server as well.
Session IDs should be unique to a given process. They must fit
within a packet-line, and must not contain non-printable or
whitespace characters. The current implementation uses trace2
session IDs (see api-trace2[1] for details), but this may change
and users of the session ID should not rely on this fact.
object-info
object-info is the command to retrieve information about one or
more objects. Its main purpose is to allow a client to make
decisions based on this information without having to fully fetch
objects. Object size is the only information that is currently
supported.
An object-info request takes the following arguments:
size
Requests size information to be returned for each listed object id.
oid <oid>
Indicates to the server an object which the client wants to obtain
information for.
The response of object-info is a list of the requested object ids
and associated requested information, each separated by a single
space.
output = info flush-pkt
info = PKT-LINE(attrs) LF)
*PKT-LINE(obj-info LF)
attrs = attr | attrs SP attrs
attr = "size"
obj-info = obj-id SP obj-size
Part of the git(1) suite
1. api-trace2
file:///home/mtk/share/doc/git-doc/technical/api-trace2.html
This page is part of the git (Git distributed version control
system) project. Information about the project can be found at
⟨http://git-scm.com/⟩. If you have a bug report for this manual
page, see ⟨http://git-scm.com/community⟩. This page was obtained
from the project's upstream Git repository
⟨https://github.com/git/git.git⟩ on 2022-12-17. (At that time,
the date of the most recent commit that was found in the
repository was 2022-12-14.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
Git 2.39.0.56.g57e2c6e 12/15/2022 GITPROTOCOL-V2(5)
Pages that refer to this page: git(1), git-config(1), git-upload-pack(1), gitformat-pack(5), gitprotocol-capabilities(5), gitprotocol-pack(5)
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