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gitprotocol-capabilities(5)       Git Manual       gitprotocol-capabilities(5)


       gitprotocol-capabilities - Protocol v0 and v1 capabilities





           this document describes capabilities for versions 0 and 1 of the
           pack protocol. For version 2, please refer to the gitprotocol-v2(5)

       Servers SHOULD support all capabilities defined in this document.

       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 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.

       Server MUST diagnose and abort if capabilities it does not understand
       were 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.

       The atomic, report-status, report-status-v2, delete-refs, quiet, and
       push-cert capabilities are sent and recognized by the receive-pack
       (push to server) process.

       The ofs-delta and side-band-64k capabilities are sent and recognized by
       both upload-pack and receive-pack protocols. The agent and session-id
       capabilities may optionally be sent in both protocols.

       All other capabilities are only recognized by the upload-pack (fetch
       from server) process.


       The multi_ack 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.

       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".

       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 on which the server hasn't found a
       common base yet.

       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:

              +---- u ---------------------- x
             /              +----- y
            /              /
           a -- b -- c -- d -- E -- F
               +--- Q -- R -- S

       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.

       Without multi_ack the client would have sent that c-b-a chain anyway,
       interleaved with S-R-Q.


       This is an extension of multi_ack that permits the client to better
       understand the server's in-memory state. See gitprotocol-pack(5),
       section "Packfile Negotiation" for more information.


       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"

       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.


       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.

       The upload-pack server advertises thin-pack when it can generate and
       send a thin pack. A client requests the thin-pack capability when it
       understands how to "thicken" it, notifying the server that it can
       receive such a pack. A client MUST NOT request the thin-pack capability
       if it cannot turn a thin pack into a self-contained pack.

       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 no-thin capability. A client MUST NOT send a thin pack
       if the server advertises the no-thin capability.

       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 no-thin later allowed receive-pack to disable the feature
       in a backwards-compatible manner.


       This capability means that the server can send, and the client can
       understand, multiplexed progress reports and error info interleaved
       with the packfile itself.

       These two options are mutually exclusive. A modern client always favors

       Either mode indicates that the packfile data will be streamed broken up
       into packets of up to either 1000 bytes in the case of side_band, or
       65520 bytes in the case of side_band_64k. 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.

       The stream code can be one of:

           1 - pack data
           2 - progress messages
           3 - fatal error message just before stream aborts

       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.

       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.

       The client MUST send only one of "side-band" and "side- band-64k". The
       server MUST diagnose it as an error if client requests both.


       The server can send, and the client can 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.


       The server may optionally send a capability of the form agent=X to
       notify the client that the server is running version X. The client may
       optionally return its own agent string by responding with an agent=Y
       capability (but it MUST NOT do so if the server did not mention the
       agent capability). The X and Y strings may contain any printable ASCII
       characters except space (i.e., the byte range 32 < x < 127), and are
       typically of the form "package/version" (e.g., "git/"). 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.


       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

       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.

       If this capability is not provided, it is assumed that the only
       supported algorithm is SHA-1.


       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.

       Servers SHOULD include this capability for the HEAD symref if it is one
       of the refs being sent.

       Clients MAY use the parameters from this capability to select the
       proper initial branch when cloning a repository.


       This capability adds "deepen", "shallow" and "unshallow" commands to
       the fetch-pack/upload-pack protocol so clients can request shallow


       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".


       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".


       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.


       The client was started with "git clone -q" or something similar, 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.


       The include-tag 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.

       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/*

       Servers MUST pack the tags if their referent is packed and the client
       has requested include-tags.

       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.

       The server SHOULD send include-tag, if it supports it, regardless of
       whether or not there are tags available.


       The receive-pack process can receive a report-status 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 gitprotocol-pack(5)
       for example messages.


       Capability report-status-v2 extends capability report-status 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 report-status cannot
       report for such case. See gitprotocol-pack(5) for details.


       If the server sends back the delete-refs 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.


       If the receive-pack server advertises the quiet 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 quiet capability to suppress server-side progress
       reporting if the local progress reporting is also being suppressed
       (e.g., via push -q, or if stderr does not go to a tty).


       If the server sends the atomic 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.


       If the server sends the push-options 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.


       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 object-format capability.


       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 object-format capability.


       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.


       If the upload-pack server advertises the filter 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.


       The server may advertise a session ID that can be used to identify this
       process across multiple requests. The client may advertise its own
       session ID back to the server as well.

       Session IDs should be unique to a given process. They must fit within a
       packet-line, and must not contain non-printable or whitespace
       characters. The current implementation uses trace2 session IDs (see
       api-trace2[1] for details), but this may change and users of the
       session ID should not rely on this fact.


       Part of the git(1) suite


        1. api-trace2

Git 2.44.0                        2024-02-22       gitprotocol-capabilities(5)

git 2.44.0 - Generated Sat Feb 24 18:41:36 CST 2024
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