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<body class="manpage"> | |
<div id="header"> | |
<h1> | |
gitprotocol-pack(5) Manual Page | |
</h1> | |
<h2>NAME</h2> | |
<div class="sectionbody"> | |
<p>gitprotocol-pack - | |
How packs are transferred over-the-wire | |
</p> | |
</div> | |
</div> | |
<div id="content"> | |
<div class="sect1"> | |
<h2 id="_synopsis">SYNOPSIS</h2> | |
<div class="sectionbody"> | |
<div class="verseblock"> | |
<pre class="content"><over-the-wire-protocol></pre> | |
<div class="attribution"> | |
</div></div> | |
</div> | |
</div> | |
<div class="sect1"> | |
<h2 id="_description">DESCRIPTION</h2> | |
<div class="sectionbody"> | |
<div class="paragraph"><p>Git supports transferring data in packfiles over the ssh://, git://, http:// and | |
file:// transports. There exist two sets of protocols, one for pushing | |
data from a client to a server and another for fetching data from a | |
server to a client. The three transports (ssh, git, file) use the same | |
protocol to transfer data. http is documented in <a href="gitprotocol-http.html">gitprotocol-http(5)</a>.</p></div> | |
<div class="paragraph"><p>The processes invoked in the canonical Git implementation are <em>upload-pack</em> | |
on the server side and <em>fetch-pack</em> on the client side for fetching data; | |
then <em>receive-pack</em> on the server and <em>send-pack</em> on the client for pushing | |
data. The protocol functions to have a server tell a client what is | |
currently on the server, then for the two to negotiate the smallest amount | |
of data to send in order to fully update one or the other.</p></div> | |
</div> | |
</div> | |
<div class="sect1"> | |
<h2 id="_pkt_line_format">pkt-line Format</h2> | |
<div class="sectionbody"> | |
<div class="paragraph"><p>The descriptions below build on the pkt-line format described in | |
<a href="gitprotocol-common.html">gitprotocol-common(5)</a>. When the grammar indicates <code>PKT-LINE(...)</code>, unless | |
otherwise noted the usual pkt-line LF rules apply: the sender SHOULD | |
include a LF, but the receiver MUST NOT complain if it is not present.</p></div> | |
<div class="paragraph"><p>An error packet is a special pkt-line that contains an error string.</p></div> | |
<div class="listingblock"> | |
<div class="content"> | |
<pre><code> error-line = PKT-LINE("ERR" SP explanation-text)</code></pre> | |
</div></div> | |
<div class="paragraph"><p>Throughout the protocol, where <code>PKT-LINE(...)</code> is expected, an error packet MAY | |
be sent. Once this packet is sent by a client or a server, the data transfer | |
process defined in this protocol is terminated.</p></div> | |
</div> | |
</div> | |
<div class="sect1"> | |
<h2 id="_transports">Transports</h2> | |
<div class="sectionbody"> | |
<div class="paragraph"><p>There are three transports over which the packfile protocol is | |
initiated. The Git transport is a simple, unauthenticated server that | |
takes the command (almost always <em>upload-pack</em>, though Git | |
servers can be configured to be globally writable, in which <em>receive- | |
pack</em> initiation is also allowed) with which the client wishes to | |
communicate and executes it and connects it to the requesting | |
process.</p></div> | |
<div class="paragraph"><p>In the SSH transport, the client just runs the <em>upload-pack</em> | |
or <em>receive-pack</em> process on the server over the SSH protocol and then | |
communicates with that invoked process over the SSH connection.</p></div> | |
<div class="paragraph"><p>The file:// transport runs the <em>upload-pack</em> or <em>receive-pack</em> | |
process locally and communicates with it over a pipe.</p></div> | |
</div> | |
</div> | |
<div class="sect1"> | |
<h2 id="_extra_parameters">Extra Parameters</h2> | |
<div class="sectionbody"> | |
<div class="paragraph"><p>The protocol provides a mechanism in which clients can send additional | |
information in its first message to the server. These are called "Extra | |
Parameters", and are supported by the Git, SSH, and HTTP protocols.</p></div> | |
<div class="paragraph"><p>Each Extra Parameter takes the form of <code><key>=<value></code> or <code><key></code>.</p></div> | |
<div class="paragraph"><p>Servers that receive any such Extra Parameters MUST ignore all | |
unrecognized keys. Currently, the only Extra Parameter recognized is | |
"version" with a value of <em>1</em> or <em>2</em>. See <a href="gitprotocol-v2.html">gitprotocol-v2(5)</a> for more | |
information on protocol version 2.</p></div> | |
</div> | |
</div> | |
<div class="sect1"> | |
<h2 id="_git_transport">Git Transport</h2> | |
<div class="sectionbody"> | |
<div class="paragraph"><p>The Git transport starts off by sending the command and repository | |
on the wire using the pkt-line format, followed by a NUL byte and a | |
hostname parameter, terminated by a NUL byte.</p></div> | |
<div class="literalblock"> | |
<div class="content"> | |
<pre><code>0033git-upload-pack /project.git\0host=myserver.com\0</code></pre> | |
</div></div> | |
<div class="paragraph"><p>The transport may send Extra Parameters by adding an additional NUL | |
byte, and then adding one or more NUL-terminated strings:</p></div> | |
<div class="literalblock"> | |
<div class="content"> | |
<pre><code>003egit-upload-pack /project.git\0host=myserver.com\0\0version=1\0</code></pre> | |
</div></div> | |
<div class="openblock"> | |
<div class="content"> | |
<div class="literalblock"> | |
<div class="content"> | |
<pre><code>git-proto-request = request-command SP pathname NUL | |
[ host-parameter NUL ] [ NUL extra-parameters ] | |
request-command = "git-upload-pack" / "git-receive-pack" / | |
"git-upload-archive" ; case sensitive | |
pathname = *( %x01-ff ) ; exclude NUL | |
host-parameter = "host=" hostname [ ":" port ] | |
extra-parameters = 1*extra-parameter | |
extra-parameter = 1*( %x01-ff ) NUL</code></pre> | |
</div></div> | |
</div></div> | |
<div class="paragraph"><p>host-parameter is used for the | |
git-daemon name based virtual hosting. See --interpolated-path | |
option to git daemon, with the %H/%CH format characters.</p></div> | |
<div class="paragraph"><p>Basically what the Git client is doing to connect to an <em>upload-pack</em> | |
process on the server side over the Git protocol is this:</p></div> | |
<div class="literalblock"> | |
<div class="content"> | |
<pre><code>$ echo -e -n \ | |
"003agit-upload-pack /schacon/gitbook.git\0host=example.com\0" | | |
nc -v example.com 9418</code></pre> | |
</div></div> | |
</div> | |
</div> | |
<div class="sect1"> | |
<h2 id="_ssh_transport">SSH Transport</h2> | |
<div class="sectionbody"> | |
<div class="paragraph"><p>Initiating the upload-pack or receive-pack processes over SSH is | |
executing the binary on the server via SSH remote execution. | |
It is basically equivalent to running this:</p></div> | |
<div class="literalblock"> | |
<div class="content"> | |
<pre><code>$ ssh git.example.com "git-upload-pack '/project.git'"</code></pre> | |
</div></div> | |
<div class="paragraph"><p>For a server to support Git pushing and pulling for a given user over | |
SSH, that user needs to be able to execute one or both of those | |
commands via the SSH shell that they are provided on login. On some | |
systems, that shell access is limited to only being able to run those | |
two commands, or even just one of them.</p></div> | |
<div class="paragraph"><p>In an ssh:// format URI, it’s absolute in the URI, so the <em>/</em> after | |
the host name (or port number) is sent as an argument, which is then | |
read by the remote git-upload-pack exactly as is, so it’s effectively | |
an absolute path in the remote filesystem.</p></div> | |
<div class="literalblock"> | |
<div class="content"> | |
<pre><code> git clone ssh://user@example.com/project.git | |
| | |
v | |
ssh user@example.com "git-upload-pack '/project.git'"</code></pre> | |
</div></div> | |
<div class="paragraph"><p>In a "user@host:path" format URI, it’s relative to the user’s home | |
directory, because the Git client will run:</p></div> | |
<div class="literalblock"> | |
<div class="content"> | |
<pre><code> git clone user@example.com:project.git | |
| | |
v | |
ssh user@example.com "git-upload-pack 'project.git'"</code></pre> | |
</div></div> | |
<div class="paragraph"><p>The exception is if a <em>~</em> is used, in which case | |
we execute it without the leading <em>/</em>.</p></div> | |
<div class="literalblock"> | |
<div class="content"> | |
<pre><code> ssh://user@example.com/~alice/project.git, | |
| | |
v | |
ssh user@example.com "git-upload-pack '~alice/project.git'"</code></pre> | |
</div></div> | |
<div class="paragraph"><p>Depending on the value of the <code>protocol.version</code> configuration variable, | |
Git may attempt to send Extra Parameters as a colon-separated string in | |
the GIT_PROTOCOL environment variable. This is done only if | |
the <code>ssh.variant</code> configuration variable indicates that the ssh command | |
supports passing environment variables as an argument.</p></div> | |
<div class="paragraph"><p>A few things to remember here:</p></div> | |
<div class="ulist"><ul> | |
<li> | |
<p> | |
The "command name" is spelled with dash (e.g. git-upload-pack), but | |
this can be overridden by the client; | |
</p> | |
</li> | |
<li> | |
<p> | |
The repository path is always quoted with single quotes. | |
</p> | |
</li> | |
</ul></div> | |
</div> | |
</div> | |
<div class="sect1"> | |
<h2 id="_fetching_data_from_a_server">Fetching Data From a Server</h2> | |
<div class="sectionbody"> | |
<div class="paragraph"><p>When one Git repository wants to get data that a second repository | |
has, the first can <em>fetch</em> from the second. This operation determines | |
what data the server has that the client does not then streams that | |
data down to the client in packfile format.</p></div> | |
</div> | |
</div> | |
<div class="sect1"> | |
<h2 id="_reference_discovery">Reference Discovery</h2> | |
<div class="sectionbody"> | |
<div class="paragraph"><p>When the client initially connects the server will immediately respond | |
with a version number (if "version=1" is sent as an Extra Parameter), | |
and a listing of each reference it has (all branches and tags) along | |
with the object name that each reference currently points to.</p></div> | |
<div class="literalblock"> | |
<div class="content"> | |
<pre><code>$ echo -e -n "0045git-upload-pack /schacon/gitbook.git\0host=example.com\0\0version=1\0" | | |
nc -v example.com 9418 | |
000eversion 1 | |
00887217a7c7e582c46cec22a130adf4b9d7d950fba0 HEAD\0multi_ack thin-pack | |
side-band side-band-64k ofs-delta shallow no-progress include-tag | |
00441d3fcd5ced445d1abc402225c0b8a1299641f497 refs/heads/integration | |
003f7217a7c7e582c46cec22a130adf4b9d7d950fba0 refs/heads/master | |
003cb88d2441cac0977faf98efc80305012112238d9d refs/tags/v0.9 | |
003c525128480b96c89e6418b1e40909bf6c5b2d580f refs/tags/v1.0 | |
003fe92df48743b7bc7d26bcaabfddde0a1e20cae47c refs/tags/v1.0^{} | |
0000</code></pre> | |
</div></div> | |
<div class="paragraph"><p>The returned response is a pkt-line stream describing each ref and | |
its current value. The stream MUST be sorted by name according to | |
the C locale ordering.</p></div> | |
<div class="paragraph"><p>If HEAD is a valid ref, HEAD MUST appear as the first advertised | |
ref. If HEAD is not a valid ref, HEAD MUST NOT appear in the | |
advertisement list at all, but other refs may still appear.</p></div> | |
<div class="paragraph"><p>The stream MUST include capability declarations behind a NUL on the | |
first ref. The peeled value of a ref (that is "ref^{}") MUST be | |
immediately after the ref itself, if presented. A conforming server | |
MUST peel the ref if it’s an annotated tag.</p></div> | |
<div class="listingblock"> | |
<div class="content"> | |
<pre><code> advertised-refs = *1("version 1") | |
(no-refs / list-of-refs) | |
*shallow | |
flush-pkt | |
no-refs = PKT-LINE(zero-id SP "capabilities^{}" | |
NUL capability-list) | |
list-of-refs = first-ref *other-ref | |
first-ref = PKT-LINE(obj-id SP refname | |
NUL capability-list) | |
other-ref = PKT-LINE(other-tip / other-peeled) | |
other-tip = obj-id SP refname | |
other-peeled = obj-id SP refname "^{}" | |
shallow = PKT-LINE("shallow" SP obj-id) | |
capability-list = capability *(SP capability) | |
capability = 1*(LC_ALPHA / DIGIT / "-" / "_") | |
LC_ALPHA = %x61-7A</code></pre> | |
</div></div> | |
<div class="paragraph"><p>Server and client MUST use lowercase for obj-id, both MUST treat obj-id | |
as case-insensitive.</p></div> | |
<div class="paragraph"><p>See protocol-capabilities.txt for a list of allowed server capabilities | |
and descriptions.</p></div> | |
</div> | |
</div> | |
<div class="sect1"> | |
<h2 id="_packfile_negotiation">Packfile Negotiation</h2> | |
<div class="sectionbody"> | |
<div class="paragraph"><p>After reference and capabilities discovery, the client can decide to | |
terminate the connection by sending a flush-pkt, telling the server it can | |
now gracefully terminate, and disconnect, when it does not need any pack | |
data. This can happen with the ls-remote command, and also can happen when | |
the client already is up to date.</p></div> | |
<div class="paragraph"><p>Otherwise, it enters the negotiation phase, where the client and | |
server determine what the minimal packfile necessary for transport is, | |
by telling the server what objects it wants, its shallow objects | |
(if any), and the maximum commit depth it wants (if any). The client | |
will also send a list of the capabilities it wants to be in effect, | |
out of what the server said it could do with the first <em>want</em> line.</p></div> | |
<div class="listingblock"> | |
<div class="content"> | |
<pre><code> upload-request = want-list | |
*shallow-line | |
*1depth-request | |
[filter-request] | |
flush-pkt | |
want-list = first-want | |
*additional-want | |
shallow-line = PKT-LINE("shallow" SP obj-id) | |
depth-request = PKT-LINE("deepen" SP depth) / | |
PKT-LINE("deepen-since" SP timestamp) / | |
PKT-LINE("deepen-not" SP ref) | |
first-want = PKT-LINE("want" SP obj-id SP capability-list) | |
additional-want = PKT-LINE("want" SP obj-id) | |
depth = 1*DIGIT | |
filter-request = PKT-LINE("filter" SP filter-spec)</code></pre> | |
</div></div> | |
<div class="paragraph"><p>Clients MUST send all the obj-ids it wants from the reference | |
discovery phase as <em>want</em> lines. Clients MUST send at least one | |
<em>want</em> command in the request body. Clients MUST NOT mention an | |
obj-id in a <em>want</em> command which did not appear in the response | |
obtained through ref discovery.</p></div> | |
<div class="paragraph"><p>The client MUST write all obj-ids which it only has shallow copies | |
of (meaning that it does not have the parents of a commit) as | |
<em>shallow</em> lines so that the server is aware of the limitations of | |
the client’s history.</p></div> | |
<div class="paragraph"><p>The client now sends the maximum commit history depth it wants for | |
this transaction, which is the number of commits it wants from the | |
tip of the history, if any, as a <em>deepen</em> line. A depth of 0 is the | |
same as not making a depth request. The client does not want to receive | |
any commits beyond this depth, nor does it want objects needed only to | |
complete those commits. Commits whose parents are not received as a | |
result are defined as shallow and marked as such in the server. This | |
information is sent back to the client in the next step.</p></div> | |
<div class="paragraph"><p>The client can optionally request that pack-objects omit various | |
objects from the packfile using one of several filtering techniques. | |
These are intended for use with partial clone and partial fetch | |
operations. An object that does not meet a filter-spec value is | |
omitted unless explicitly requested in a <em>want</em> line. See <code>rev-list</code> | |
for possible filter-spec values.</p></div> | |
<div class="paragraph"><p>Once all the <em>want’s and 'shallow’s (and optional 'deepen</em>) are | |
transferred, clients MUST send a flush-pkt, to tell the server side | |
that it is done sending the list.</p></div> | |
<div class="paragraph"><p>Otherwise, if the client sent a positive depth request, the server | |
will determine which commits will and will not be shallow and | |
send this information to the client. If the client did not request | |
a positive depth, this step is skipped.</p></div> | |
<div class="listingblock"> | |
<div class="content"> | |
<pre><code> shallow-update = *shallow-line | |
*unshallow-line | |
flush-pkt | |
shallow-line = PKT-LINE("shallow" SP obj-id) | |
unshallow-line = PKT-LINE("unshallow" SP obj-id)</code></pre> | |
</div></div> | |
<div class="paragraph"><p>If the client has requested a positive depth, the server will compute | |
the set of commits which are no deeper than the desired depth. The set | |
of commits starts at the client’s wants.</p></div> | |
<div class="paragraph"><p>The server writes <em>shallow</em> lines for each | |
commit whose parents will not be sent as a result. The server writes | |
an <em>unshallow</em> line for each commit which the client has indicated is | |
shallow, but is no longer shallow at the currently requested depth | |
(that is, its parents will now be sent). The server MUST NOT mark | |
as unshallow anything which the client has not indicated was shallow.</p></div> | |
<div class="paragraph"><p>Now the client will send a list of the obj-ids it has using <em>have</em> | |
lines, so the server can make a packfile that only contains the objects | |
that the client needs. In multi_ack mode, the canonical implementation | |
will send up to 32 of these at a time, then will send a flush-pkt. The | |
canonical implementation will skip ahead and send the next 32 immediately, | |
so that there is always a block of 32 "in-flight on the wire" at a time.</p></div> | |
<div class="listingblock"> | |
<div class="content"> | |
<pre><code> upload-haves = have-list | |
compute-end | |
have-list = *have-line | |
have-line = PKT-LINE("have" SP obj-id) | |
compute-end = flush-pkt / PKT-LINE("done")</code></pre> | |
</div></div> | |
<div class="paragraph"><p>If the server reads <em>have</em> lines, it then will respond by ACKing any | |
of the obj-ids the client said it had that the server also has. The | |
server will ACK obj-ids differently depending on which ack mode is | |
chosen by the client.</p></div> | |
<div class="paragraph"><p>In multi_ack mode:</p></div> | |
<div class="ulist"><ul> | |
<li> | |
<p> | |
the server will respond with <em>ACK obj-id continue</em> for any common | |
commits. | |
</p> | |
</li> | |
<li> | |
<p> | |
once the server has found an acceptable common base commit and is | |
ready to make a packfile, it will blindly ACK all <em>have</em> obj-ids | |
back to the client. | |
</p> | |
</li> | |
<li> | |
<p> | |
the server will then send a <em>NAK</em> and then wait for another response | |
from the client - either a <em>done</em> or another list of <em>have</em> lines. | |
</p> | |
</li> | |
</ul></div> | |
<div class="paragraph"><p>In multi_ack_detailed mode:</p></div> | |
<div class="ulist"><ul> | |
<li> | |
<p> | |
the server will differentiate the ACKs where it is signaling | |
that it is ready to send data with <em>ACK obj-id ready</em> lines, and | |
signals the identified common commits with <em>ACK obj-id common</em> lines. | |
</p> | |
</li> | |
</ul></div> | |
<div class="paragraph"><p>Without either multi_ack or multi_ack_detailed:</p></div> | |
<div class="ulist"><ul> | |
<li> | |
<p> | |
upload-pack sends "ACK obj-id" on the first common object it finds. | |
After that it says nothing until the client gives it a "done". | |
</p> | |
</li> | |
<li> | |
<p> | |
upload-pack sends "NAK" on a flush-pkt if no common object | |
has been found yet. If one has been found, and thus an ACK | |
was already sent, it’s silent on the flush-pkt. | |
</p> | |
</li> | |
</ul></div> | |
<div class="paragraph"><p>After the client has gotten enough ACK responses that it can determine | |
that the server has enough information to send an efficient packfile | |
(in the canonical implementation, this is determined when it has received | |
enough ACKs that it can color everything left in the --date-order queue | |
as common with the server, or the --date-order queue is empty), or the | |
client determines that it wants to give up (in the canonical implementation, | |
this is determined when the client sends 256 <em>have</em> lines without getting | |
any of them ACKed by the server - meaning there is nothing in common and | |
the server should just send all of its objects), then the client will send | |
a <em>done</em> command. The <em>done</em> command signals to the server that the client | |
is ready to receive its packfile data.</p></div> | |
<div class="paragraph"><p>However, the 256 limit <strong>only</strong> turns on in the canonical client | |
implementation if we have received at least one "ACK %s continue" | |
during a prior round. This helps to ensure that at least one common | |
ancestor is found before we give up entirely.</p></div> | |
<div class="paragraph"><p>Once the <em>done</em> line is read from the client, the server will either | |
send a final <em>ACK obj-id</em> or it will send a <em>NAK</em>. <em>obj-id</em> is the object | |
name of the last commit determined to be common. The server only sends | |
ACK after <em>done</em> if there is at least one common base and multi_ack or | |
multi_ack_detailed is enabled. The server always sends NAK after <em>done</em> | |
if there is no common base found.</p></div> | |
<div class="paragraph"><p>Instead of <em>ACK</em> or <em>NAK</em>, the server may send an error message (for | |
example, if it does not recognize an object in a <em>want</em> line received | |
from the client).</p></div> | |
<div class="paragraph"><p>Then the server will start sending its packfile data.</p></div> | |
<div class="listingblock"> | |
<div class="content"> | |
<pre><code> server-response = *ack_multi ack / nak | |
ack_multi = PKT-LINE("ACK" SP obj-id ack_status) | |
ack_status = "continue" / "common" / "ready" | |
ack = PKT-LINE("ACK" SP obj-id) | |
nak = PKT-LINE("NAK")</code></pre> | |
</div></div> | |
<div class="paragraph"><p>A simple clone may look like this (with no <em>have</em> lines):</p></div> | |
<div class="listingblock"> | |
<div class="content"> | |
<pre><code> C: 0054want 74730d410fcb6603ace96f1dc55ea6196122532d multi_ack \ | |
side-band-64k ofs-delta\n | |
C: 0032want 7d1665144a3a975c05f1f43902ddaf084e784dbe\n | |
C: 0032want 5a3f6be755bbb7deae50065988cbfa1ffa9ab68a\n | |
C: 0032want 7e47fe2bd8d01d481f44d7af0531bd93d3b21c01\n | |
C: 0032want 74730d410fcb6603ace96f1dc55ea6196122532d\n | |
C: 0000 | |
C: 0009done\n | |
S: 0008NAK\n | |
S: [PACKFILE]</code></pre> | |
</div></div> | |
<div class="paragraph"><p>An incremental update (fetch) response might look like this:</p></div> | |
<div class="listingblock"> | |
<div class="content"> | |
<pre><code> C: 0054want 74730d410fcb6603ace96f1dc55ea6196122532d multi_ack \ | |
side-band-64k ofs-delta\n | |
C: 0032want 7d1665144a3a975c05f1f43902ddaf084e784dbe\n | |
C: 0032want 5a3f6be755bbb7deae50065988cbfa1ffa9ab68a\n | |
C: 0000 | |
C: 0032have 7e47fe2bd8d01d481f44d7af0531bd93d3b21c01\n | |
C: [30 more have lines] | |
C: 0032have 74730d410fcb6603ace96f1dc55ea6196122532d\n | |
C: 0000 | |
S: 003aACK 7e47fe2bd8d01d481f44d7af0531bd93d3b21c01 continue\n | |
S: 003aACK 74730d410fcb6603ace96f1dc55ea6196122532d continue\n | |
S: 0008NAK\n | |
C: 0009done\n | |
S: 0031ACK 74730d410fcb6603ace96f1dc55ea6196122532d\n | |
S: [PACKFILE]</code></pre> | |
</div></div> | |
</div> | |
</div> | |
<div class="sect1"> | |
<h2 id="_packfile_data">Packfile Data</h2> | |
<div class="sectionbody"> | |
<div class="paragraph"><p>Now that the client and server have finished negotiation about what | |
the minimal amount of data that needs to be sent to the client is, the server | |
will construct and send the required data in packfile format.</p></div> | |
<div class="paragraph"><p>See <a href="gitformat-pack.html">gitformat-pack(5)</a> for what the packfile itself actually looks like.</p></div> | |
<div class="paragraph"><p>If <em>side-band</em> or <em>side-band-64k</em> capabilities have been specified by | |
the client, the server will send the packfile data multiplexed.</p></div> | |
<div class="paragraph"><p>Each packet starting with the packet-line length of the amount of data | |
that follows, followed by a single byte specifying the sideband the | |
following data is coming in on.</p></div> | |
<div class="paragraph"><p>In <em>side-band</em> mode, it will send up to 999 data bytes plus 1 control | |
code, for a total of up to 1000 bytes in a pkt-line. In <em>side-band-64k</em> | |
mode it will send up to 65519 data bytes plus 1 control code, for a | |
total of up to 65520 bytes in a pkt-line.</p></div> | |
<div class="paragraph"><p>The sideband byte will be a <em>1</em>, <em>2</em> or a <em>3</em>. Sideband <em>1</em> will contain | |
packfile data, sideband <em>2</em> will be used for progress information that the | |
client will generally print to stderr and sideband <em>3</em> is used for error | |
information.</p></div> | |
<div class="paragraph"><p>If no <em>side-band</em> capability was specified, the server will stream the | |
entire packfile without multiplexing.</p></div> | |
</div> | |
</div> | |
<div class="sect1"> | |
<h2 id="_pushing_data_to_a_server">Pushing Data To a Server</h2> | |
<div class="sectionbody"> | |
<div class="paragraph"><p>Pushing data to a server will invoke the <em>receive-pack</em> process on the | |
server, which will allow the client to tell it which references it should | |
update and then send all the data the server will need for those new | |
references to be complete. Once all the data is received and validated, | |
the server will then update its references to what the client specified.</p></div> | |
</div> | |
</div> | |
<div class="sect1"> | |
<h2 id="_authentication">Authentication</h2> | |
<div class="sectionbody"> | |
<div class="paragraph"><p>The protocol itself contains no authentication mechanisms. That is to be | |
handled by the transport, such as SSH, before the <em>receive-pack</em> process is | |
invoked. If <em>receive-pack</em> is configured over the Git transport, those | |
repositories will be writable by anyone who can access that port (9418) as | |
that transport is unauthenticated.</p></div> | |
</div> | |
</div> | |
<div class="sect1"> | |
<h2 id="_reference_discovery_2">Reference Discovery</h2> | |
<div class="sectionbody"> | |
<div class="paragraph"><p>The reference discovery phase is done nearly the same way as it is in the | |
fetching protocol. Each reference obj-id and name on the server is sent | |
in packet-line format to the client, followed by a flush-pkt. The only | |
real difference is that the capability listing is different - the only | |
possible values are <em>report-status</em>, <em>report-status-v2</em>, <em>delete-refs</em>, | |
<em>ofs-delta</em>, <em>atomic</em> and <em>push-options</em>.</p></div> | |
</div> | |
</div> | |
<div class="sect1"> | |
<h2 id="_reference_update_request_and_packfile_transfer">Reference Update Request and Packfile Transfer</h2> | |
<div class="sectionbody"> | |
<div class="paragraph"><p>Once the client knows what references the server is at, it can send a | |
list of reference update requests. For each reference on the server | |
that it wants to update, it sends a line listing the obj-id currently on | |
the server, the obj-id the client would like to update it to and the name | |
of the reference.</p></div> | |
<div class="paragraph"><p>This list is followed by a flush-pkt.</p></div> | |
<div class="listingblock"> | |
<div class="content"> | |
<pre><code> update-requests = *shallow ( command-list | push-cert ) | |
shallow = PKT-LINE("shallow" SP obj-id) | |
command-list = PKT-LINE(command NUL capability-list) | |
*PKT-LINE(command) | |
flush-pkt | |
command = create / delete / update | |
create = zero-id SP new-id SP name | |
delete = old-id SP zero-id SP name | |
update = old-id SP new-id SP name | |
old-id = obj-id | |
new-id = obj-id | |
push-cert = PKT-LINE("push-cert" NUL capability-list LF) | |
PKT-LINE("certificate version 0.1" LF) | |
PKT-LINE("pusher" SP ident LF) | |
PKT-LINE("pushee" SP url LF) | |
PKT-LINE("nonce" SP nonce LF) | |
*PKT-LINE("push-option" SP push-option LF) | |
PKT-LINE(LF) | |
*PKT-LINE(command LF) | |
*PKT-LINE(gpg-signature-lines LF) | |
PKT-LINE("push-cert-end" LF) | |
push-option = 1*( VCHAR | SP )</code></pre> | |
</div></div> | |
<div class="paragraph"><p>If the server has advertised the <em>push-options</em> capability and the client has | |
specified <em>push-options</em> as part of the capability list above, the client then | |
sends its push options followed by a flush-pkt.</p></div> | |
<div class="listingblock"> | |
<div class="content"> | |
<pre><code> push-options = *PKT-LINE(push-option) flush-pkt</code></pre> | |
</div></div> | |
<div class="paragraph"><p>For backwards compatibility with older Git servers, if the client sends a push | |
cert and push options, it MUST send its push options both embedded within the | |
push cert and after the push cert. (Note that the push options within the cert | |
are prefixed, but the push options after the cert are not.) Both these lists | |
MUST be the same, modulo the prefix.</p></div> | |
<div class="paragraph"><p>After that the packfile that | |
should contain all the objects that the server will need to complete the new | |
references will be sent.</p></div> | |
<div class="listingblock"> | |
<div class="content"> | |
<pre><code> packfile = "PACK" 28*(OCTET)</code></pre> | |
</div></div> | |
<div class="paragraph"><p>If the receiving end does not support delete-refs, the sending end MUST | |
NOT ask for delete command.</p></div> | |
<div class="paragraph"><p>If the receiving end does not support push-cert, the sending end | |
MUST NOT send a push-cert command. When a push-cert command is | |
sent, command-list MUST NOT be sent; the commands recorded in the | |
push certificate is used instead.</p></div> | |
<div class="paragraph"><p>The packfile MUST NOT be sent if the only command used is <em>delete</em>.</p></div> | |
<div class="paragraph"><p>A packfile MUST be sent if either create or update command is used, | |
even if the server already has all the necessary objects. In this | |
case the client MUST send an empty packfile. The only time this | |
is likely to happen is if the client is creating | |
a new branch or a tag that points to an existing obj-id.</p></div> | |
<div class="paragraph"><p>The server will receive the packfile, unpack it, then validate each | |
reference that is being updated that it hasn’t changed while the request | |
was being processed (the obj-id is still the same as the old-id), and | |
it will run any update hooks to make sure that the update is acceptable. | |
If all of that is fine, the server will then update the references.</p></div> | |
</div> | |
</div> | |
<div class="sect1"> | |
<h2 id="_push_certificate">Push Certificate</h2> | |
<div class="sectionbody"> | |
<div class="paragraph"><p>A push certificate begins with a set of header lines. After the | |
header and an empty line, the protocol commands follow, one per | |
line. Note that the trailing LF in push-cert PKT-LINEs is <em>not</em> | |
optional; it must be present.</p></div> | |
<div class="paragraph"><p>Currently, the following header fields are defined:</p></div> | |
<div class="dlist"><dl> | |
<dt class="hdlist1"> | |
<code>pusher</code> ident | |
</dt> | |
<dd> | |
<p> | |
Identify the GPG key in "Human Readable Name <<a href="mailto:email@address">email@address</a>>" | |
format. | |
</p> | |
</dd> | |
<dt class="hdlist1"> | |
<code>pushee</code> url | |
</dt> | |
<dd> | |
<p> | |
The repository URL (anonymized, if the URL contains | |
authentication material) the user who ran <code>git push</code> | |
intended to push into. | |
</p> | |
</dd> | |
<dt class="hdlist1"> | |
<code>nonce</code> nonce | |
</dt> | |
<dd> | |
<p> | |
The <em>nonce</em> string the receiving repository asked the | |
pushing user to include in the certificate, to prevent | |
replay attacks. | |
</p> | |
</dd> | |
</dl></div> | |
<div class="paragraph"><p>The GPG signature lines are a detached signature for the contents | |
recorded in the push certificate before the signature block begins. | |
The detached signature is used to certify that the commands were | |
given by the pusher, who must be the signer.</p></div> | |
</div> | |
</div> | |
<div class="sect1"> | |
<h2 id="_report_status">Report Status</h2> | |
<div class="sectionbody"> | |
<div class="paragraph"><p>After receiving the pack data from the sender, the receiver sends a | |
report if <em>report-status</em> or <em>report-status-v2</em> capability is in effect. | |
It is a short listing of what happened in that update. It will first | |
list the status of the packfile unpacking as either <em>unpack ok</em> or | |
<em>unpack [error]</em>. Then it will list the status for each of the references | |
that it tried to update. Each line is either <em>ok [refname]</em> if the | |
update was successful, or <em>ng [refname] [error]</em> if the update was not.</p></div> | |
<div class="listingblock"> | |
<div class="content"> | |
<pre><code> report-status = unpack-status | |
1*(command-status) | |
flush-pkt | |
unpack-status = PKT-LINE("unpack" SP unpack-result) | |
unpack-result = "ok" / error-msg | |
command-status = command-ok / command-fail | |
command-ok = PKT-LINE("ok" SP refname) | |
command-fail = PKT-LINE("ng" SP refname SP error-msg) | |
error-msg = 1*(OCTET) ; where not "ok"</code></pre> | |
</div></div> | |
<div class="paragraph"><p>The <em>report-status-v2</em> capability extends the protocol by adding new option | |
lines in order to support reporting of reference rewritten by the | |
<em>proc-receive</em> hook. The <em>proc-receive</em> hook may handle a command for a | |
pseudo-reference which may create or update one or more references, and each | |
reference may have different name, different new-oid, and different old-oid.</p></div> | |
<div class="listingblock"> | |
<div class="content"> | |
<pre><code> report-status-v2 = unpack-status | |
1*(command-status-v2) | |
flush-pkt | |
unpack-status = PKT-LINE("unpack" SP unpack-result) | |
unpack-result = "ok" / error-msg | |
command-status-v2 = command-ok-v2 / command-fail | |
command-ok-v2 = command-ok | |
*option-line | |
command-ok = PKT-LINE("ok" SP refname) | |
command-fail = PKT-LINE("ng" SP refname SP error-msg) | |
error-msg = 1*(OCTET) ; where not "ok" | |
option-line = *1(option-refname) | |
*1(option-old-oid) | |
*1(option-new-oid) | |
*1(option-forced-update) | |
option-refname = PKT-LINE("option" SP "refname" SP refname) | |
option-old-oid = PKT-LINE("option" SP "old-oid" SP obj-id) | |
option-new-oid = PKT-LINE("option" SP "new-oid" SP obj-id) | |
option-force = PKT-LINE("option" SP "forced-update")</code></pre> | |
</div></div> | |
<div class="paragraph"><p>Updates can be unsuccessful for a number of reasons. The reference can have | |
changed since the reference discovery phase was originally sent, meaning | |
someone pushed in the meantime. The reference being pushed could be a | |
non-fast-forward reference and the update hooks or configuration could be | |
set to not allow that, etc. Also, some references can be updated while others | |
can be rejected.</p></div> | |
<div class="paragraph"><p>An example client/server communication might look like this:</p></div> | |
<div class="listingblock"> | |
<div class="content"> | |
<pre><code> S: 006274730d410fcb6603ace96f1dc55ea6196122532d refs/heads/local\0report-status delete-refs ofs-delta\n | |
S: 003e7d1665144a3a975c05f1f43902ddaf084e784dbe refs/heads/debug\n | |
S: 003f74730d410fcb6603ace96f1dc55ea6196122532d refs/heads/master\n | |
S: 003d74730d410fcb6603ace96f1dc55ea6196122532d refs/heads/team\n | |
S: 0000 | |
C: 00677d1665144a3a975c05f1f43902ddaf084e784dbe 74730d410fcb6603ace96f1dc55ea6196122532d refs/heads/debug\n | |
C: 006874730d410fcb6603ace96f1dc55ea6196122532d 5a3f6be755bbb7deae50065988cbfa1ffa9ab68a refs/heads/master\n | |
C: 0000 | |
C: [PACKDATA] | |
S: 000eunpack ok\n | |
S: 0018ok refs/heads/debug\n | |
S: 002ang refs/heads/master non-fast-forward\n</code></pre> | |
</div></div> | |
</div> | |
</div> | |
<div class="sect1"> | |
<h2 id="_git">GIT</h2> | |
<div class="sectionbody"> | |
<div class="paragraph"><p>Part of the <a href="git.html">git(1)</a> suite</p></div> | |
</div> | |
</div> | |
</div> | |
<div id="footnotes"><hr /></div> | |
<div id="footer"> | |
<div id="footer-text"> | |
Last updated | |
2023-10-23 14:43:46 PDT | |
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