gitprotocol-capabilities.html

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 735 <body class="manpage">
 736 <div id="header">
 737 <h1>
 738 gitprotocol-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
 766 protocol. For version 2, please refer to the <a href="gitprotocol-v2.html">gitprotocol-v2(5)</a>
 767 doc.</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
 772 receive-pack and upload-pack the first reference is followed by
 773 a NUL byte and then a list of space delimited server capabilities.
 774 These allow the server to declare what it can and cannot support
 775 to the client.</p></div>
 776 <div class="paragraph"><p>Client will then send a space separated list of capabilities it wants
 777 to be in effect. The client MUST NOT ask for capabilities the server
 778 did not say it supports.</p></div>
 779 <div class="paragraph"><p>Server MUST diagnose and abort if capabilities it does not understand
 780 were sent.  Server MUST NOT ignore capabilities that client requested
 781 and server advertised.  As a consequence of these rules, server MUST
 782 NOT 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>,
 784 and <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
 787 by both upload-pack and receive-pack protocols.  The <em>agent</em> and <em>session-id</em>
 788 capabilities 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
 790 from 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
 797 continue" as soon as it finds a commit that it can use as a common
 798 base, 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
 800 from walking any further down that particular branch of the client&#8217;s
 801 repository history.  The client may still need to walk down other
 802 branches, sending have lines for those, until the server has a
 803 complete 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
 805 the server has found a common base.  That means the client will send
 806 have lines that are already known by the server to be common, because
 807 they overlap in time with another branch on which the server hasn&#8217;t found
 808 a common base yet.</p></div>
 809 <div class="paragraph"><p>For example suppose the client has commits in caps that the server
 810 doesn&#8217;t and the server has commits in lower case that the client
 811 doesn&#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  /              /
 817 a -- 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
 822 doesn&#8217;t know what F,S is.  Eventually the client says "have d" and
 823 the server sends "ACK d continue" to let the client know to stop
 824 walking down that line (so don&#8217;t send c-b-a), but it&#8217;s not done yet,
 825 it needs a base for x. The client keeps going with S-R-Q, until a
 826 gets reached, at which point the server has a clear base and it all
 827 ends.</p></div>
 828 <div class="paragraph"><p>Without multi_ack the client would have sent that c-b-a chain anyway,
 829 interleaved 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 the client to better
 836 understand the server&#8217;s in-memory state. See <a href="gitprotocol-pack.html">gitprotocol-pack(5)</a>,
 837 section "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
 844 multi_ack_detailed and no-done are both present, then the sender is
 845 free to immediately send a pack following its first "ACK obj-id ready"
 846 message.</p></div>
 847 <div class="paragraph"><p>Without no-done in the smart HTTP protocol, the server session would
 848 end and the client has to make another trip to send "done" before
 849 the server can send the pack. no-done removes the last round and
 850 thus 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
 857 contained within the pack (but are known to exist at the receiving
 858 end). This can reduce the network traffic significantly, but it
 859 requires the receiving end to know how to "thicken" these packs by
 860 adding 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
 862 and send a thin pack. A client requests the <em>thin-pack</em> capability
 863 when it understands how to "thicken" it, notifying the server that
 864 it 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
 866 self-contained pack.</p></div>
 867 <div class="paragraph"><p>Receive-pack, on the other hand, is assumed by default to be able to
 868 handle thin packs, but can ask the client not to use the feature by
 869 advertising the <em>no-thin</em> capability. A client MUST NOT send a thin
 870 pack 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
 872 program did not exist until after the invention of thin packs, so
 873 historically the reference implementation of receive-pack always
 874 understood thin packs. Adding <em>no-thin</em> later allowed receive-pack
 875 to 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 the server can send, and the client can understand, multiplexed
 882 progress 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
 884 favors <em>side-band-64k</em>.</p></div>
 885 <div class="paragraph"><p>Either mode indicates that the packfile data will be streamed broken
 886 up into packets of up to either 1000 bytes in the case of <em>side_band</em>,
 887 or 65520 bytes in the case of <em>side_band_64k</em>. Each packet is made up
 888 of a leading 4-byte pkt-line length of how much data is in the packet,
 889 followed 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
 894 2 - progress messages
 895 3 - 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
 898 that can handle much larger packets to request packets that are
 899 actually crammed nearly full, while maintaining backward compatibility
 900 for 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
 902 999 bytes of payload and 1 byte for the stream code. With side-band-64k,
 903 same deal, you have up to 65519 bytes of data and 1 byte for the stream
 904 code.</p></div>
 905 <div class="paragraph"><p>The client MUST send only one of "side-band" and "side-
 906 band-64k".  The server MUST diagnose it as an error if client requests
 907 both.</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>The server can send, and the client can understand, PACKv2 with delta referring to
 914 its base by position in pack rather than by an obj-id.  That is, they can
 915 send/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
 922 notify the client that the server is running version <code>X</code>. The client may
 923 optionally return its own agent string by responding with an <code>agent=Y</code>
 924 capability (but it MUST NOT do so if the server did not mention the
 925 agent capability). The <code>X</code> and <code>Y</code> strings may contain any printable
 926 ASCII characters except space (i.e., the byte range 32 &lt; x &lt; 127), and
 927 are typically of the form "package/version" (e.g., "git/1.8.3.1"). The
 928 agent strings are purely informative for statistics and debugging
 929 purposes, and MUST NOT be used to programmatically assume the presence
 930 or 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
 937 that the server supports the given hash algorithms.  It may be sent
 938 multiple times; if so, the first one given is the one used in the ref
 939 advertisement.</p></div>
 940 <div class="paragraph"><p>When provided by the client, this indicates that it intends to use the
 941 given hash algorithm to communicate.  The algorithm provided must be one
 942 that the server supports.</p></div>
 943 <div class="paragraph"><p>If this capability is not provided, it is assumed that the only
 944 supported 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
 951 points to which ref; for example, "symref=HEAD:refs/heads/master" tells the
 952 receiver that HEAD points to master. This capability can be repeated to
 953 represent multiple symrefs.</p></div>
 954 <div class="paragraph"><p>Servers SHOULD include this capability for the HEAD symref if it is one of the
 955 refs being sent.</p></div>
 956 <div class="paragraph"><p>Clients MAY use the parameters from this capability to select the proper initial
 957 branch 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
 964 the  fetch-pack/upload-pack protocol so clients can request shallow
 965 clones.</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
 972 protocol so the client can request shallow clones that are cut at a
 973 specific 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"
 975 cannot 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
 982 protocol so the client can request shallow clones that are cut at a
 983 specific revision, instead of depth. Internally it&#8217;s equivalent of
 984 doing "rev-list --not &lt;rev&gt;" on the server side. "deepen-not"
 985 cannot 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
 993 the 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 similar, and doesn&#8217;t
1000 want that side band 2.  Basically the client just says "I do not
1001 wish to receive stream 2 on sideband, so do not send it to me, and if
1002 you did, I will drop it on the floor anyway".  However, the sideband
1003 channel 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
1010 sending objects they point to.  If we pack an object to the client, and
1011 a tag object points exactly at that object, we pack the tag object too.
1012 In general this allows a client to get all new annotated tags when it
1013 fetches 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
1015 the server advertises this capability. The decision for a client to
1016 request include-tag only has to do with the client&#8217;s desires for tag
1017 data, whether or not a server had advertised objects in the
1018 refs/tags/* namespace.</p></div>
1019 <div class="paragraph"><p>Servers MUST pack the tags if their referent is packed and the client
1020 has requested include-tags.</p></div>
1021 <div class="paragraph"><p>Clients MUST be prepared for the case where a server has ignored
1022 include-tag and has not actually sent tags in the pack.  In such
1023 cases the client SHOULD issue a subsequent fetch to acquire the tags
1024 that 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
1026 of 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,
1033 which tells it that the client wants a report of what happened after
1034 a packfile upload and reference update.  If the pushing client requests
1035 this capability, after unpacking and updating references the server
1036 will respond with whether the packfile unpacked successfully and if
1037 each reference was updated successfully.  If any of those were not
1038 successful, it will send back an error message.  See <a href="gitprotocol-pack.html">gitprotocol-pack(5)</a>
1039 for 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
1046 adding new "option" directives in order to support reference rewritten by
1047 the "proc-receive" hook.  The "proc-receive" hook may handle a command
1048 for a pseudo-reference which may create or update a reference with
1049 different 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>
1051 for 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
1058 it is capable of accepting a zero-id value as the target
1059 value of a reference update.  It is not sent back by the client, it
1060 simply informs the client that it can be sent zero-id values
1061 to 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
1068 capable of silencing human-readable progress output which otherwise may
1069 be shown when processing the received pack. A send-pack client should
1070 respond with the <em>quiet</em> capability to suppress server-side progress
1071 reporting 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
1079 atomic pushes. If the pushing client requests this capability, the server
1080 will update the refs in one atomic transaction. Either all refs are
1081 updated 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
1088 push options after the update commands have been sent, but before the
1089 packfile is streamed. If the pushing client requests this capability,
1090 the server will pass the options to the pre- and post- receive hooks
1091 that 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
1098 send "want" lines with object names that exist at the server but are not
1099 advertised by upload-pack. For historical reasons, the name of this
1100 capability contains "sha1". Object names are always given using the
1101 object 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
1108 send "want" lines with object names that exist at the server but are not
1109 advertised by upload-pack. For historical reasons, the name of this
1110 capability contains "sha1". Object names are always given using the
1111 object 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
1118 to accept a signed push certificate, and asks the &lt;nonce&gt; to be
1119 included in the push certificate.  A send-pack client MUST NOT
1120 send a push-cert packet unless the receive-pack server advertises
1121 this 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,
1128 fetch-pack may send "filter" commands to request a partial clone
1129 or partial fetch and request that the server omit various objects
1130 from 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
1137 across multiple requests. The client may advertise its own session ID back to
1138 the server as well.</p></div>
1139 <div class="paragraph"><p>Session IDs should be unique to a given process. They must fit within a
1140 packet-line, and must not contain non-printable or whitespace characters. The
1141 current implementation uses trace2 session IDs (see
1142 <a href="technical/api-trace2.html">api-trace2</a> for details), but this may change
1143 and users of the session ID should not rely on this fact.</p></div>
1144 </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">
1156 Last updated
1157  2024-02-08 15:45:59 PST
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1159 </div>
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