diff options
| author | Junio C Hamano <gitster@pobox.com> | 2022-08-18 14:13:08 -0700 |
|---|---|---|
| committer | Junio C Hamano <gitster@pobox.com> | 2022-08-18 14:13:08 -0700 |
| commit | 04495a1941c77d95cb6ad521f45451da4f714af2 (patch) | |
| tree | ad4d9204d5b4c2ac489f99a1051faa1bf48d6ed7 /gitprotocol-capabilities.html | |
| parent | 472c81a0f3cf8038d39479da1e3840ac33fe6ef8 (diff) | |
| download | git-htmldocs-04495a1941c77d95cb6ad521f45451da4f714af2.tar.gz | |
Autogenerated HTML docs for v2.37.2-382-g795ea
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| -rw-r--r-- | gitprotocol-capabilities.html | 1161 |
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+<div id="header">
+<h1>
+gitprotocol-capabilities(5) Manual Page
+</h1>
+<h2>NAME</h2>
+<div class="sectionbody">
+<p>gitprotocol-capabilities -
+ Protocol v0 and v1 capabilities
+</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="admonitionblock">
+<table><tr>
+<td class="icon">
+<div class="title">Note</div>
+</td>
+<td class="content">this document describes capabilities for versions 0 and 1 of the pack
+protocol. For version 2, please refer to the <a href="gitprotocol-v2.html">gitprotocol-v2(5)</a>
+doc.</td>
+</tr></table>
+</div>
+<div class="paragraph"><p>Servers SHOULD support all capabilities defined in this document.</p></div>
+<div class="paragraph"><p>On the very first line of the initial server response of either
+receive-pack and upload-pack the first reference is followed by
+a NUL byte and then a list of space delimited server capabilities.
+These allow the server to declare what it can and cannot support
+to the client.</p></div>
+<div class="paragraph"><p>Client will then send a space separated list of capabilities it wants
+to be in effect. The client MUST NOT ask for capabilities the server
+did not say it supports.</p></div>
+<div class="paragraph"><p>Server MUST diagnose and abort if capabilities it does not understand
+was sent. Server MUST NOT ignore capabilities that client requested
+and server advertised. As a consequence of these rules, server MUST
+NOT advertise capabilities it does not understand.</p></div>
+<div class="paragraph"><p>The <em>atomic</em>, <em>report-status</em>, <em>report-status-v2</em>, <em>delete-refs</em>, <em>quiet</em>,
+and <em>push-cert</em> capabilities are sent and recognized by the receive-pack
+(push to server) process.</p></div>
+<div class="paragraph"><p>The <em>ofs-delta</em> and <em>side-band-64k</em> capabilities are sent and recognized
+by both upload-pack and receive-pack protocols. The <em>agent</em> and <em>session-id</em>
+capabilities may optionally be sent in both protocols.</p></div>
+<div class="paragraph"><p>All other capabilities are only recognized by the upload-pack (fetch
+from server) process.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_multi_ack">multi_ack</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>The <em>multi_ack</em> capability allows the server to return "ACK obj-id
+continue" as soon as it finds a commit that it can use as a common
+base, between the client’s wants and the client’s have set.</p></div>
+<div class="paragraph"><p>By sending this early, the server can potentially head off the client
+from walking any further down that particular branch of the client’s
+repository history. The client may still need to walk down other
+branches, sending have lines for those, until the server has a
+complete cut across the DAG, or the client has said "done".</p></div>
+<div class="paragraph"><p>Without multi_ack, a client sends have lines in --date-order until
+the server has found a common base. That means the client will send
+have lines that are already known by the server to be common, because
+they overlap in time with another branch that the server hasn’t found
+a common base on yet.</p></div>
+<div class="paragraph"><p>For example suppose the client has commits in caps that the server
+doesn’t and the server has commits in lower case that the client
+doesn’t, as in the following diagram:</p></div>
+<div class="literalblock">
+<div class="content">
+<pre><code> +---- u ---------------------- x
+ / +----- y
+ / /
+a -- b -- c -- d -- E -- F
+ \
+ +--- Q -- R -- S</code></pre>
+</div></div>
+<div class="paragraph"><p>If the client wants x,y and starts out by saying have F,S, the server
+doesn’t know what F,S is. Eventually the client says "have d" and
+the server sends "ACK d continue" to let the client know to stop
+walking down that line (so don’t send c-b-a), but it’s not done yet,
+it needs a base for x. The client keeps going with S-R-Q, until a
+gets reached, at which point the server has a clear base and it all
+ends.</p></div>
+<div class="paragraph"><p>Without multi_ack the client would have sent that c-b-a chain anyway,
+interleaved with S-R-Q.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_multi_ack_detailed">multi_ack_detailed</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>This is an extension of multi_ack that permits client to better
+understand the server’s in-memory state. See <a href="gitprotocol-pack.html">gitprotocol-pack(5)</a>,
+section "Packfile Negotiation" for more information.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_no_done">no-done</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>This capability should only be used with the smart HTTP protocol. If
+multi_ack_detailed and no-done are both present, then the sender is
+free to immediately send a pack following its first "ACK obj-id ready"
+message.</p></div>
+<div class="paragraph"><p>Without no-done in the smart HTTP protocol, the server session would
+end and the client has to make another trip to send "done" before
+the server can send the pack. no-done removes the last round and
+thus slightly reduces latency.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_thin_pack">thin-pack</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>A thin pack is one 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.</p></div>
+<div class="paragraph"><p>The upload-pack server advertises <em>thin-pack</em> when it can generate
+and send a thin pack. A client requests the <em>thin-pack</em> capability
+when it understands how to "thicken" it, notifying the server that
+it can receive such a pack. A client MUST NOT request the
+<em>thin-pack</em> capability if it cannot turn a thin pack into a
+self-contained pack.</p></div>
+<div class="paragraph"><p>Receive-pack, on the other hand, is assumed by default to be able to
+handle thin packs, but can ask the client not to use the feature by
+advertising the <em>no-thin</em> capability. A client MUST NOT send a thin
+pack if the server advertises the <em>no-thin</em> capability.</p></div>
+<div class="paragraph"><p>The reasons for this asymmetry are historical. The receive-pack
+program did not exist until after the invention of thin packs, so
+historically the reference implementation of receive-pack always
+understood thin packs. Adding <em>no-thin</em> later allowed receive-pack
+to disable the feature in a backwards-compatible manner.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_side_band_side_band_64k">side-band, side-band-64k</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>This capability means that server can send, and client understand multiplexed
+progress reports and error info interleaved with the packfile itself.</p></div>
+<div class="paragraph"><p>These two options are mutually exclusive. A modern client always
+favors <em>side-band-64k</em>.</p></div>
+<div class="paragraph"><p>Either mode indicates that the packfile data will be streamed broken
+up into packets of up to either 1000 bytes in the case of <em>side_band</em>,
+or 65520 bytes in the case of <em>side_band_64k</em>. Each packet is made up
+of a leading 4-byte pkt-line length of how much data is in the packet,
+followed by a 1-byte stream code, followed by the actual data.</p></div>
+<div class="paragraph"><p>The stream code can be one of:</p></div>
+<div class="literalblock">
+<div class="content">
+<pre><code>1 - pack data
+2 - progress messages
+3 - fatal error message just before stream aborts</code></pre>
+</div></div>
+<div class="paragraph"><p>The "side-band-64k" capability came about as a way for newer clients
+that can handle much larger packets to request packets that are
+actually crammed nearly full, while maintaining backward compatibility
+for the older clients.</p></div>
+<div class="paragraph"><p>Further, with side-band and its up to 1000-byte messages, it’s actually
+999 bytes of payload and 1 byte for the stream code. With side-band-64k,
+same deal, you have up to 65519 bytes of data and 1 byte for the stream
+code.</p></div>
+<div class="paragraph"><p>The client MUST send only maximum of one of "side-band" and "side-
+band-64k". Server MUST diagnose it as an error if client requests
+both.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_ofs_delta">ofs-delta</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>Server can send, and client understand PACKv2 with delta referring to
+its base by position in pack rather than by an obj-id. That is, they can
+send/read OBJ_OFS_DELTA (aka type 6) in a packfile.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_agent">agent</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>The server may optionally send a capability of the form <code>agent=X</code> to
+notify the client that the server is running version <code>X</code>. The client may
+optionally return its own agent string by responding with an <code>agent=Y</code>
+capability (but it MUST NOT do so if the server did not mention the
+agent capability). The <code>X</code> and <code>Y</code> 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.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_object_format">object-format</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>This capability, which takes a hash algorithm as an argument, indicates
+that the server supports the given hash algorithms. It may be sent
+multiple times; if so, the first one given is the one used in the ref
+advertisement.</p></div>
+<div class="paragraph"><p>When provided by the client, this indicates that it intends to use the
+given hash algorithm to communicate. The algorithm provided must be one
+that the server supports.</p></div>
+<div class="paragraph"><p>If this capability is not provided, it is assumed that the only
+supported algorithm is SHA-1.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_symref">symref</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>This parameterized capability is used to inform the receiver which symbolic ref
+points to which ref; for example, "symref=HEAD:refs/heads/master" tells the
+receiver that HEAD points to master. This capability can be repeated to
+represent multiple symrefs.</p></div>
+<div class="paragraph"><p>Servers SHOULD include this capability for the HEAD symref if it is one of the
+refs being sent.</p></div>
+<div class="paragraph"><p>Clients MAY use the parameters from this capability to select the proper initial
+branch when cloning a repository.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_shallow">shallow</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>This capability adds "deepen", "shallow" and "unshallow" commands to
+the fetch-pack/upload-pack protocol so clients can request shallow
+clones.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_deepen_since">deepen-since</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>This capability adds "deepen-since" command to fetch-pack/upload-pack
+protocol so the client can request shallow clones that are cut at a
+specific time, instead of depth. Internally it’s equivalent of doing
+"rev-list --max-age=<timestamp>" on the server side. "deepen-since"
+cannot be used with "deepen".</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_deepen_not">deepen-not</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>This capability adds "deepen-not" command to fetch-pack/upload-pack
+protocol so the client can request shallow clones that are cut at a
+specific revision, instead of depth. Internally it’s equivalent of
+doing "rev-list --not <rev>" on the server side. "deepen-not"
+cannot be used with "deepen", but can be used with "deepen-since".</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_deepen_relative">deepen-relative</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>If this capability is requested by the client, the semantics of
+"deepen" command is changed. The "depth" argument is the depth from
+the current shallow boundary, instead of the depth from remote refs.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_no_progress">no-progress</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>The client was started with "git clone -q" or something, and doesn’t
+want that side band 2. Basically the client just says "I do not
+wish to receive stream 2 on sideband, so do not send it to me, and if
+you did, I will drop it on the floor anyway". However, the sideband
+channel 3 is still used for error responses.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_include_tag">include-tag</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>The <em>include-tag</em> capability is about sending annotated tags if we are
+sending objects they point to. If we pack an object to the client, and
+a tag object points exactly at that object, we pack the tag object too.
+In general this allows a client to get all new annotated tags when it
+fetches a branch, in a single network connection.</p></div>
+<div class="paragraph"><p>Clients MAY always send include-tag, hardcoding it into a request when
+the server advertises this capability. The decision for a client to
+request include-tag only has to do with the client’s desires for tag
+data, whether or not a server had advertised objects in the
+refs/tags/* namespace.</p></div>
+<div class="paragraph"><p>Servers MUST pack the tags if their referrant is packed and the client
+has requested include-tags.</p></div>
+<div class="paragraph"><p>Clients MUST be prepared for the case where a server has ignored
+include-tag and has not actually sent tags in the pack. In such
+cases the client SHOULD issue a subsequent fetch to acquire the tags
+that include-tag would have otherwise given the client.</p></div>
+<div class="paragraph"><p>The server SHOULD send include-tag, if it supports it, regardless
+of whether or not there are tags available.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_report_status">report-status</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>The receive-pack process can receive a <em>report-status</em> capability,
+which tells it that the client wants a report of what happened after
+a packfile upload and reference update. If the pushing client requests
+this capability, after unpacking and updating references the server
+will respond with whether the packfile unpacked successfully and if
+each reference was updated successfully. If any of those were not
+successful, it will send back an error message. See <a href="gitprotocol-pack.html">gitprotocol-pack(5)</a>
+for example messages.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_report_status_v2">report-status-v2</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>Capability <em>report-status-v2</em> extends capability <em>report-status</em> by
+adding new "option" directives in order to support reference rewritten by
+the "proc-receive" hook. The "proc-receive" hook may handle a command
+for a pseudo-reference which may create or update a reference with
+different name, new-oid, and old-oid. While the capability
+<em>report-status</em> cannot report for such case. See <a href="gitprotocol-pack.html">gitprotocol-pack(5)</a>
+for details.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_delete_refs">delete-refs</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>If the server sends back the <em>delete-refs</em> capability, it means that
+it is capable of accepting a zero-id value as the target
+value of a reference update. It is not sent back by the client, it
+simply informs the client that it can be sent zero-id values
+to delete references.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_quiet">quiet</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>If the receive-pack server advertises the <em>quiet</em> capability, it is
+capable of silencing human-readable progress output which otherwise may
+be shown when processing the received pack. A send-pack client should
+respond with the <em>quiet</em> capability to suppress server-side progress
+reporting if the local progress reporting is also being suppressed
+(e.g., via <code>push -q</code>, or if stderr does not go to a tty).</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_atomic">atomic</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>If the server sends the <em>atomic</em> capability it is capable of accepting
+atomic pushes. If the pushing client requests this capability, the server
+will update the refs in one atomic transaction. Either all refs are
+updated or none.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_push_options">push-options</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>If the server sends the <em>push-options</em> capability it is able to accept
+push options after the update commands have been sent, but before the
+packfile is streamed. If the pushing client requests this capability,
+the server will pass the options to the pre- and post- receive hooks
+that process this push request.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_allow_tip_sha1_in_want">allow-tip-sha1-in-want</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>If the upload-pack server advertises this capability, fetch-pack may
+send "want" lines with object names that exist at the server but are not
+advertised by upload-pack. For historical reasons, the name of this
+capability contains "sha1". Object names are always given using the
+object format negotiated through the <em>object-format</em> capability.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_allow_reachable_sha1_in_want">allow-reachable-sha1-in-want</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>If the upload-pack server advertises this capability, fetch-pack may
+send "want" lines with object names that exist at the server but are not
+advertised by upload-pack. For historical reasons, the name of this
+capability contains "sha1". Object names are always given using the
+object format negotiated through the <em>object-format</em> capability.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_push_cert_lt_nonce_gt">push-cert=<nonce></h2>
+<div class="sectionbody">
+<div class="paragraph"><p>The receive-pack server that advertises this capability is willing
+to accept a signed push certificate, and asks the <nonce> to be
+included in the push certificate. A send-pack client MUST NOT
+send a push-cert packet unless the receive-pack server advertises
+this capability.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_filter">filter</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>If the upload-pack server advertises the <em>filter</em> capability,
+fetch-pack may send "filter" commands to request a partial clone
+or partial fetch and request that the server omit various objects
+from the packfile.</p></div>
+</div>
+</div>
+<div class="sect1">
+<h2 id="_session_id_lt_session_id_gt">session-id=<session id></h2>
+<div class="sectionbody">
+<div class="paragraph"><p>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.</p></div>
+<div class="paragraph"><p>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
+<a href="api-trace2.html">api-trace2</a> for details), but this may change and users of
+the session ID should not rely on this fact.</p></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
+ 2022-08-18 14:11:07 PDT
+</div>
+</div>
+</body>
+</html>
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