blob: e653f9321142010a6209cb031633a12e9635ab94 [file] [log] [blame]
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736<div id="header">
737<h1>
738gitprotocol-capabilities(5) Manual Page
739</h1>
740<h2>NAME</h2>
741<div class="sectionbody">
742<p>gitprotocol-capabilities -
743 Protocol v0 and v1 capabilities
744</p>
745</div>
746</div>
747<div id="content">
748<div class="sect1">
749<h2 id="_synopsis">SYNOPSIS</h2>
750<div class="sectionbody">
751<div class="verseblock">
752<pre class="content">&lt;over-the-wire-protocol&gt;</pre>
753<div class="attribution">
754</div></div>
755</div>
756</div>
757<div class="sect1">
758<h2 id="_description">DESCRIPTION</h2>
759<div class="sectionbody">
760<div class="admonitionblock">
761<table><tr>
762<td class="icon">
763<div class="title">Note</div>
764</td>
765<td class="content">this document describes capabilities for versions 0 and 1 of the pack
766protocol. For version 2, please refer to the <a href="gitprotocol-v2.html">gitprotocol-v2(5)</a>
767doc.</td>
768</tr></table>
769</div>
770<div class="paragraph"><p>Servers SHOULD support all capabilities defined in this document.</p></div>
771<div class="paragraph"><p>On the very first line of the initial server response of either
772receive-pack and upload-pack the first reference is followed by
773a NUL byte and then a list of space delimited server capabilities.
774These allow the server to declare what it can and cannot support
775to the client.</p></div>
776<div class="paragraph"><p>Client will then send a space separated list of capabilities it wants
777to be in effect. The client MUST NOT ask for capabilities the server
778did not say it supports.</p></div>
779<div class="paragraph"><p>Server MUST diagnose and abort if capabilities it does not understand
780was sent. Server MUST NOT ignore capabilities that client requested
781and server advertised. As a consequence of these rules, server MUST
782NOT advertise capabilities it does not understand.</p></div>
783<div class="paragraph"><p>The <em>atomic</em>, <em>report-status</em>, <em>report-status-v2</em>, <em>delete-refs</em>, <em>quiet</em>,
784and <em>push-cert</em> capabilities are sent and recognized by the receive-pack
785(push to server) process.</p></div>
786<div class="paragraph"><p>The <em>ofs-delta</em> and <em>side-band-64k</em> capabilities are sent and recognized
787by both upload-pack and receive-pack protocols. The <em>agent</em> and <em>session-id</em>
788capabilities may optionally be sent in both protocols.</p></div>
789<div class="paragraph"><p>All other capabilities are only recognized by the upload-pack (fetch
790from server) process.</p></div>
791</div>
792</div>
793<div class="sect1">
794<h2 id="_multi_ack">multi_ack</h2>
795<div class="sectionbody">
796<div class="paragraph"><p>The <em>multi_ack</em> capability allows the server to return "ACK obj-id
797continue" as soon as it finds a commit that it can use as a common
798base, between the client&#8217;s wants and the client&#8217;s have set.</p></div>
799<div class="paragraph"><p>By sending this early, the server can potentially head off the client
800from walking any further down that particular branch of the client&#8217;s
801repository history. The client may still need to walk down other
802branches, sending have lines for those, until the server has a
803complete cut across the DAG, or the client has said "done".</p></div>
804<div class="paragraph"><p>Without multi_ack, a client sends have lines in --date-order until
805the server has found a common base. That means the client will send
806have lines that are already known by the server to be common, because
807they overlap in time with another branch that the server hasn&#8217;t found
808a common base on yet.</p></div>
809<div class="paragraph"><p>For example suppose the client has commits in caps that the server
810doesn&#8217;t and the server has commits in lower case that the client
811doesn&#8217;t, as in the following diagram:</p></div>
812<div class="literalblock">
813<div class="content">
814<pre><code> +---- u ---------------------- x
815 / +----- y
816 / /
817a -- b -- c -- d -- E -- F
818 \
819 +--- Q -- R -- S</code></pre>
820</div></div>
821<div class="paragraph"><p>If the client wants x,y and starts out by saying have F,S, the server
822doesn&#8217;t know what F,S is. Eventually the client says "have d" and
823the server sends "ACK d continue" to let the client know to stop
824walking down that line (so don&#8217;t send c-b-a), but it&#8217;s not done yet,
825it needs a base for x. The client keeps going with S-R-Q, until a
826gets reached, at which point the server has a clear base and it all
827ends.</p></div>
828<div class="paragraph"><p>Without multi_ack the client would have sent that c-b-a chain anyway,
829interleaved with S-R-Q.</p></div>
830</div>
831</div>
832<div class="sect1">
833<h2 id="_multi_ack_detailed">multi_ack_detailed</h2>
834<div class="sectionbody">
835<div class="paragraph"><p>This is an extension of multi_ack that permits client to better
836understand the server&#8217;s in-memory state. See <a href="gitprotocol-pack.html">gitprotocol-pack(5)</a>,
837section "Packfile Negotiation" for more information.</p></div>
838</div>
839</div>
840<div class="sect1">
841<h2 id="_no_done">no-done</h2>
842<div class="sectionbody">
843<div class="paragraph"><p>This capability should only be used with the smart HTTP protocol. If
844multi_ack_detailed and no-done are both present, then the sender is
845free to immediately send a pack following its first "ACK obj-id ready"
846message.</p></div>
847<div class="paragraph"><p>Without no-done in the smart HTTP protocol, the server session would
848end and the client has to make another trip to send "done" before
849the server can send the pack. no-done removes the last round and
850thus slightly reduces latency.</p></div>
851</div>
852</div>
853<div class="sect1">
854<h2 id="_thin_pack">thin-pack</h2>
855<div class="sectionbody">
856<div class="paragraph"><p>A thin pack is one with deltas which reference base objects not
857contained within the pack (but are known to exist at the receiving
858end). This can reduce the network traffic significantly, but it
859requires the receiving end to know how to "thicken" these packs by
860adding the missing bases to the pack.</p></div>
861<div class="paragraph"><p>The upload-pack server advertises <em>thin-pack</em> when it can generate
862and send a thin pack. A client requests the <em>thin-pack</em> capability
863when it understands how to "thicken" it, notifying the server that
864it can receive such a pack. A client MUST NOT request the
865<em>thin-pack</em> capability if it cannot turn a thin pack into a
866self-contained pack.</p></div>
867<div class="paragraph"><p>Receive-pack, on the other hand, is assumed by default to be able to
868handle thin packs, but can ask the client not to use the feature by
869advertising the <em>no-thin</em> capability. A client MUST NOT send a thin
870pack if the server advertises the <em>no-thin</em> capability.</p></div>
871<div class="paragraph"><p>The reasons for this asymmetry are historical. The receive-pack
872program did not exist until after the invention of thin packs, so
873historically the reference implementation of receive-pack always
874understood thin packs. Adding <em>no-thin</em> later allowed receive-pack
875to disable the feature in a backwards-compatible manner.</p></div>
876</div>
877</div>
878<div class="sect1">
879<h2 id="_side_band_side_band_64k">side-band, side-band-64k</h2>
880<div class="sectionbody">
881<div class="paragraph"><p>This capability means that server can send, and client understand multiplexed
882progress reports and error info interleaved with the packfile itself.</p></div>
883<div class="paragraph"><p>These two options are mutually exclusive. A modern client always
884favors <em>side-band-64k</em>.</p></div>
885<div class="paragraph"><p>Either mode indicates that the packfile data will be streamed broken
886up into packets of up to either 1000 bytes in the case of <em>side_band</em>,
887or 65520 bytes in the case of <em>side_band_64k</em>. Each packet is made up
888of a leading 4-byte pkt-line length of how much data is in the packet,
889followed by a 1-byte stream code, followed by the actual data.</p></div>
890<div class="paragraph"><p>The stream code can be one of:</p></div>
891<div class="literalblock">
892<div class="content">
893<pre><code>1 - pack data
8942 - progress messages
8953 - fatal error message just before stream aborts</code></pre>
896</div></div>
897<div class="paragraph"><p>The "side-band-64k" capability came about as a way for newer clients
898that can handle much larger packets to request packets that are
899actually crammed nearly full, while maintaining backward compatibility
900for the older clients.</p></div>
901<div class="paragraph"><p>Further, with side-band and its up to 1000-byte messages, it&#8217;s actually
902999 bytes of payload and 1 byte for the stream code. With side-band-64k,
903same deal, you have up to 65519 bytes of data and 1 byte for the stream
904code.</p></div>
905<div class="paragraph"><p>The client MUST send only maximum of one of "side-band" and "side-
906band-64k". Server MUST diagnose it as an error if client requests
907both.</p></div>
908</div>
909</div>
910<div class="sect1">
911<h2 id="_ofs_delta">ofs-delta</h2>
912<div class="sectionbody">
913<div class="paragraph"><p>Server can send, and client understand PACKv2 with delta referring to
914its base by position in pack rather than by an obj-id. That is, they can
915send/read OBJ_OFS_DELTA (aka type 6) in a packfile.</p></div>
916</div>
917</div>
918<div class="sect1">
919<h2 id="_agent">agent</h2>
920<div class="sectionbody">
921<div class="paragraph"><p>The server may optionally send a capability of the form <code>agent=X</code> to
922notify the client that the server is running version <code>X</code>. The client may
923optionally return its own agent string by responding with an <code>agent=Y</code>
924capability (but it MUST NOT do so if the server did not mention the
925agent capability). The <code>X</code> and <code>Y</code> strings may contain any printable
926ASCII characters except space (i.e., the byte range 32 &lt; x &lt; 127), and
927are typically of the form "package/version" (e.g., "git/1.8.3.1"). The
928agent strings are purely informative for statistics and debugging
929purposes, and MUST NOT be used to programmatically assume the presence
930or absence of particular features.</p></div>
931</div>
932</div>
933<div class="sect1">
934<h2 id="_object_format">object-format</h2>
935<div class="sectionbody">
936<div class="paragraph"><p>This capability, which takes a hash algorithm as an argument, indicates
937that the server supports the given hash algorithms. It may be sent
938multiple times; if so, the first one given is the one used in the ref
939advertisement.</p></div>
940<div class="paragraph"><p>When provided by the client, this indicates that it intends to use the
941given hash algorithm to communicate. The algorithm provided must be one
942that the server supports.</p></div>
943<div class="paragraph"><p>If this capability is not provided, it is assumed that the only
944supported algorithm is SHA-1.</p></div>
945</div>
946</div>
947<div class="sect1">
948<h2 id="_symref">symref</h2>
949<div class="sectionbody">
950<div class="paragraph"><p>This parameterized capability is used to inform the receiver which symbolic ref
951points to which ref; for example, "symref=HEAD:refs/heads/master" tells the
952receiver that HEAD points to master. This capability can be repeated to
953represent multiple symrefs.</p></div>
954<div class="paragraph"><p>Servers SHOULD include this capability for the HEAD symref if it is one of the
955refs being sent.</p></div>
956<div class="paragraph"><p>Clients MAY use the parameters from this capability to select the proper initial
957branch when cloning a repository.</p></div>
958</div>
959</div>
960<div class="sect1">
961<h2 id="_shallow">shallow</h2>
962<div class="sectionbody">
963<div class="paragraph"><p>This capability adds "deepen", "shallow" and "unshallow" commands to
964the fetch-pack/upload-pack protocol so clients can request shallow
965clones.</p></div>
966</div>
967</div>
968<div class="sect1">
969<h2 id="_deepen_since">deepen-since</h2>
970<div class="sectionbody">
971<div class="paragraph"><p>This capability adds "deepen-since" command to fetch-pack/upload-pack
972protocol so the client can request shallow clones that are cut at a
973specific time, instead of depth. Internally it&#8217;s equivalent of doing
974"rev-list --max-age=&lt;timestamp&gt;" on the server side. "deepen-since"
975cannot be used with "deepen".</p></div>
976</div>
977</div>
978<div class="sect1">
979<h2 id="_deepen_not">deepen-not</h2>
980<div class="sectionbody">
981<div class="paragraph"><p>This capability adds "deepen-not" command to fetch-pack/upload-pack
982protocol so the client can request shallow clones that are cut at a
983specific revision, instead of depth. Internally it&#8217;s equivalent of
984doing "rev-list --not &lt;rev&gt;" on the server side. "deepen-not"
985cannot be used with "deepen", but can be used with "deepen-since".</p></div>
986</div>
987</div>
988<div class="sect1">
989<h2 id="_deepen_relative">deepen-relative</h2>
990<div class="sectionbody">
991<div class="paragraph"><p>If this capability is requested by the client, the semantics of
992"deepen" command is changed. The "depth" argument is the depth from
993the current shallow boundary, instead of the depth from remote refs.</p></div>
994</div>
995</div>
996<div class="sect1">
997<h2 id="_no_progress">no-progress</h2>
998<div class="sectionbody">
999<div class="paragraph"><p>The client was started with "git clone -q" or something, and doesn&#8217;t
1000want that side band 2. Basically the client just says "I do not
1001wish to receive stream 2 on sideband, so do not send it to me, and if
1002you did, I will drop it on the floor anyway". However, the sideband
1003channel 3 is still used for error responses.</p></div>
1004</div>
1005</div>
1006<div class="sect1">
1007<h2 id="_include_tag">include-tag</h2>
1008<div class="sectionbody">
1009<div class="paragraph"><p>The <em>include-tag</em> capability is about sending annotated tags if we are
1010sending objects they point to. If we pack an object to the client, and
1011a tag object points exactly at that object, we pack the tag object too.
1012In general this allows a client to get all new annotated tags when it
1013fetches a branch, in a single network connection.</p></div>
1014<div class="paragraph"><p>Clients MAY always send include-tag, hardcoding it into a request when
1015the server advertises this capability. The decision for a client to
1016request include-tag only has to do with the client&#8217;s desires for tag
1017data, whether or not a server had advertised objects in the
1018refs/tags/* namespace.</p></div>
1019<div class="paragraph"><p>Servers MUST pack the tags if their referrant is packed and the client
1020has requested include-tags.</p></div>
1021<div class="paragraph"><p>Clients MUST be prepared for the case where a server has ignored
1022include-tag and has not actually sent tags in the pack. In such
1023cases the client SHOULD issue a subsequent fetch to acquire the tags
1024that include-tag would have otherwise given the client.</p></div>
1025<div class="paragraph"><p>The server SHOULD send include-tag, if it supports it, regardless
1026of whether or not there are tags available.</p></div>
1027</div>
1028</div>
1029<div class="sect1">
1030<h2 id="_report_status">report-status</h2>
1031<div class="sectionbody">
1032<div class="paragraph"><p>The receive-pack process can receive a <em>report-status</em> capability,
1033which tells it that the client wants a report of what happened after
1034a packfile upload and reference update. If the pushing client requests
1035this capability, after unpacking and updating references the server
1036will respond with whether the packfile unpacked successfully and if
1037each reference was updated successfully. If any of those were not
1038successful, it will send back an error message. See <a href="gitprotocol-pack.html">gitprotocol-pack(5)</a>
1039for example messages.</p></div>
1040</div>
1041</div>
1042<div class="sect1">
1043<h2 id="_report_status_v2">report-status-v2</h2>
1044<div class="sectionbody">
1045<div class="paragraph"><p>Capability <em>report-status-v2</em> extends capability <em>report-status</em> by
1046adding new "option" directives in order to support reference rewritten by
1047the "proc-receive" hook. The "proc-receive" hook may handle a command
1048for a pseudo-reference which may create or update a reference with
1049different name, new-oid, and old-oid. While the capability
1050<em>report-status</em> cannot report for such case. See <a href="gitprotocol-pack.html">gitprotocol-pack(5)</a>
1051for details.</p></div>
1052</div>
1053</div>
1054<div class="sect1">
1055<h2 id="_delete_refs">delete-refs</h2>
1056<div class="sectionbody">
1057<div class="paragraph"><p>If the server sends back the <em>delete-refs</em> capability, it means that
1058it is capable of accepting a zero-id value as the target
1059value of a reference update. It is not sent back by the client, it
1060simply informs the client that it can be sent zero-id values
1061to delete references.</p></div>
1062</div>
1063</div>
1064<div class="sect1">
1065<h2 id="_quiet">quiet</h2>
1066<div class="sectionbody">
1067<div class="paragraph"><p>If the receive-pack server advertises the <em>quiet</em> capability, it is
1068capable of silencing human-readable progress output which otherwise may
1069be shown when processing the received pack. A send-pack client should
1070respond with the <em>quiet</em> capability to suppress server-side progress
1071reporting if the local progress reporting is also being suppressed
1072(e.g., via <code>push -q</code>, or if stderr does not go to a tty).</p></div>
1073</div>
1074</div>
1075<div class="sect1">
1076<h2 id="_atomic">atomic</h2>
1077<div class="sectionbody">
1078<div class="paragraph"><p>If the server sends the <em>atomic</em> capability it is capable of accepting
1079atomic pushes. If the pushing client requests this capability, the server
1080will update the refs in one atomic transaction. Either all refs are
1081updated or none.</p></div>
1082</div>
1083</div>
1084<div class="sect1">
1085<h2 id="_push_options">push-options</h2>
1086<div class="sectionbody">
1087<div class="paragraph"><p>If the server sends the <em>push-options</em> capability it is able to accept
1088push options after the update commands have been sent, but before the
1089packfile is streamed. If the pushing client requests this capability,
1090the server will pass the options to the pre- and post- receive hooks
1091that process this push request.</p></div>
1092</div>
1093</div>
1094<div class="sect1">
1095<h2 id="_allow_tip_sha1_in_want">allow-tip-sha1-in-want</h2>
1096<div class="sectionbody">
1097<div class="paragraph"><p>If the upload-pack server advertises this capability, fetch-pack may
1098send "want" lines with object names that exist at the server but are not
1099advertised by upload-pack. For historical reasons, the name of this
1100capability contains "sha1". Object names are always given using the
1101object format negotiated through the <em>object-format</em> capability.</p></div>
1102</div>
1103</div>
1104<div class="sect1">
1105<h2 id="_allow_reachable_sha1_in_want">allow-reachable-sha1-in-want</h2>
1106<div class="sectionbody">
1107<div class="paragraph"><p>If the upload-pack server advertises this capability, fetch-pack may
1108send "want" lines with object names that exist at the server but are not
1109advertised by upload-pack. For historical reasons, the name of this
1110capability contains "sha1". Object names are always given using the
1111object format negotiated through the <em>object-format</em> capability.</p></div>
1112</div>
1113</div>
1114<div class="sect1">
1115<h2 id="_push_cert_lt_nonce_gt">push-cert=&lt;nonce&gt;</h2>
1116<div class="sectionbody">
1117<div class="paragraph"><p>The receive-pack server that advertises this capability is willing
1118to accept a signed push certificate, and asks the &lt;nonce&gt; to be
1119included in the push certificate. A send-pack client MUST NOT
1120send a push-cert packet unless the receive-pack server advertises
1121this capability.</p></div>
1122</div>
1123</div>
1124<div class="sect1">
1125<h2 id="_filter">filter</h2>
1126<div class="sectionbody">
1127<div class="paragraph"><p>If the upload-pack server advertises the <em>filter</em> capability,
1128fetch-pack may send "filter" commands to request a partial clone
1129or partial fetch and request that the server omit various objects
1130from the packfile.</p></div>
1131</div>
1132</div>
1133<div class="sect1">
1134<h2 id="_session_id_lt_session_id_gt">session-id=&lt;session id&gt;</h2>
1135<div class="sectionbody">
1136<div class="paragraph"><p>The server may advertise a session ID that can be used to identify this process
1137across multiple requests. The client may advertise its own session ID back to
1138the server as well.</p></div>
1139<div class="paragraph"><p>Session IDs should be unique to a given process. They must fit within a
1140packet-line, and must not contain non-printable or whitespace characters. The
1141current implementation uses trace2 session IDs (see
Junio C Hamanoa1ee1292022-09-21 22:47:521142<a href="technical/api-trace2.html">api-trace2</a> for details), but this may change
1143and users of the session ID should not rely on this fact.</p></div>
Junio C Hamano04495a12022-08-18 21:13:081144</div>
1145</div>
1146<div class="sect1">
1147<h2 id="_git">GIT</h2>
1148<div class="sectionbody">
1149<div class="paragraph"><p>Part of the <a href="git.html">git(1)</a> suite</p></div>
1150</div>
1151</div>
1152</div>
1153<div id="footnotes"><hr /></div>
1154<div id="footer">
1155<div id="footer-text">
1156Last updated
Junio C Hamanod2309372023-01-16 21:19:041157 2022-09-21 15:44:34 PDT
Junio C Hamano04495a12022-08-18 21:13:081158</div>
1159</div>
1160</body>
1161</html>