# gitprotocol-v2

## NAME



           gitprotocol-v2 - Git Wire Protocol, Version 2
    


## SYNOPSIS



           <over-the-wire-protocol>
    


## DESCRIPTION



           This document presents a specification for a version 2 of Git’s
           wire protocol. Protocol v2 will improve upon v1 in the following
           ways:
    
           •   Instead of multiple service names, multiple commands will be
               supported by a single service
    
           •   Easily extendable as capabilities are moved into their own
               section of the protocol, no longer being hidden behind a NUL
               byte and limited by the size of a pkt-line
    
           •   Separate out other information hidden behind NUL bytes (e.g.
               agent string as a capability and symrefs can be requested
               using _ls-refs_)
    
           •   Reference advertisement will be omitted unless explicitly
               requested
    
           •   ls-refs command to explicitly request some refs
    
           •   Designed with http and stateless-rpc in mind. With clear flush
               semantics the http remote helper can simply act as a proxy
    
           In protocol v2 communication is command oriented. When first
           contacting a server a list of capabilities will be advertised.
           Some of these capabilities will be commands which a client can
           request be executed. Once a command has completed, a client can
           reuse the connection and request that other commands be executed.
    


## PACKET-LINE FRAMING



           All communication is done using packet-line framing, just as in
           v1. See gitprotocol-pack(5) and gitprotocol-common(5) for more
           information.
    
           In protocol v2 these special packets will have the following
           semantics:
    
           •   _0000_ Flush Packet (flush-pkt) - indicates the end of a message
    
           •   _0001_ Delimiter Packet (delim-pkt) - separates sections of a
               message
    
           •   _0002_ Response End Packet (response-end-pkt) - indicates the
               end of a response for stateless connections
    


## INITIAL CLIENT REQUEST



           In general a client can request to speak protocol v2 by sending
           **version=2** through the respective side-channel for the transport
           being used which inevitably sets **GIT_PROTOCOL**. More information
           can be found in gitprotocol-pack(5) and gitprotocol-http(5), as
           well as the **GIT_PROTOCOL** definition in git(1). In all cases the
           response from the server is the capability advertisement.
    
       **Git Transport**
           When using the git:// transport, you can request to use protocol
           v2 by sending "version=2" as an extra parameter:
    
               003egit-upload-pack /project.git\0host=myserver.com\0\0version=2\0
    
       **SSH and File Transport**
           When using either the ssh:// or file:// transport, the
           GIT_PROTOCOL environment variable must be set explicitly to
           include "version=2". The server may need to be configured to allow
           this environment variable to pass.
    
       **HTTP Transport**
           When using the http:// or https:// transport a client makes a
           "smart" info/refs request as described in gitprotocol-http(5) and
           requests that v2 be used by supplying "version=2" in the
           **Git-Protocol** header.
    
               C: GET $GIT_URL/info/refs?service=git-upload-pack HTTP/1.0
               C: Git-Protocol: version=2
    
           A v2 server would reply:
    
               S: 200 OK
               S: <Some headers>
               S: ...
               S:
               S: 000eversion 2\n
               S: <capability-advertisement>
    
           Subsequent requests are then made directly to the service
           **$GIT_URL/git-upload-pack**. (This works the same for
           git-receive-pack).
    
           Uses the **--http-backend-info-refs** option to git-upload-pack(1).
    
           The server may need to be configured to pass this header’s
           contents via the **GIT_PROTOCOL** variable. See the discussion in
           git-http-backend(1).
    


## CAPABILITY ADVERTISEMENT



           A server which decides to communicate (based on a request from a
           client) using protocol version 2, notifies the client by sending a
           version string in its initial response followed by an
           advertisement of its capabilities. Each capability is a key with
           an optional value. Clients must ignore all unknown keys. Semantics
           of unknown values are left to the definition of each key. Some
           capabilities will describe commands which can be requested to be
           executed by the client.
    
               capability-advertisement = protocol-version
                                          capability-list
                                          flush-pkt
    
               protocol-version = PKT-LINE("version 2" LF)
               capability-list = *capability
               capability = PKT-LINE(key[=value] LF)
    
               key = 1*(ALPHA | DIGIT | "-_")
               value = 1*(ALPHA | DIGIT | " -_.,?\/{}[]()<>!@#$%^&*+=:;")
    


## COMMAND REQUEST



           After receiving the capability advertisement, a client can then
           issue a request to select the command it wants with any particular
           capabilities or arguments. There is then an optional section where
           the client can provide any command specific parameters or queries.
           Only a single command can be requested at a time.
    
               request = empty-request | command-request
               empty-request = flush-pkt
               command-request = command
                                 capability-list
                                 delim-pkt
                                 command-args
                                 flush-pkt
               command = PKT-LINE("command=" key LF)
               command-args = *command-specific-arg
    
               command-specific-args are packet line framed arguments defined by
               each individual command.
    
           The server will then check to ensure that the client’s request is
           comprised of a valid command as well as valid capabilities which
           were advertised. If the request is valid the server will then
           execute the command. A server MUST wait till it has received the
           client’s entire request before issuing a response. The format of
           the response is determined by the command being executed, but in
           all cases a flush-pkt indicates the end of the response.
    
           When a command has finished, and the client has received the
           entire response from the server, a client can either request that
           another command be executed or can terminate the connection. A
           client may optionally send an empty request consisting of just a
           flush-pkt to indicate that no more requests will be made.
    


## CAPABILITIES



           There are two different types of capabilities: normal
           capabilities, which can be used to convey information or alter the
           behavior of a request, and commands, which are the core actions
           that a client wants to perform (fetch, push, etc).
    
           Protocol version 2 is stateless by default. This means that all
           commands must only last a single round and be stateless from the
           perspective of the server side, unless the client has requested a
           capability indicating that state should be maintained by the
           server. Clients MUST NOT require state management on the server
           side in order to function correctly. This permits simple
           round-robin load-balancing on the server side, without needing to
           worry about state management.
    
       **agent**
           The server can advertise the **agent** capability with a value **X**(in
           the form **agent=X**) to notify the client that the server is running
           version **X**. The client may optionally send its own agent string by
           including the **agent** capability with a value **Y**(in the form
           **agent=Y**) in its request to the server (but it MUST NOT do so if
           the server did not advertise the agent capability). The **X** and **Y**
           strings may contain any printable ASCII characters except space
           (i.e., the byte range 33 ⟨ x ⟨ 126), and are typically of the form
           "package/version-os" (e.g., "git/1.8.3.1-Linux") where **os** is the
           operating system name (e.g., "Linux"). **X** and **Y** can be configured
           using the GIT_USER_AGENT environment variable and it takes
           priority. The **os** is retrieved using the _sysname_ field of the
           **uname**(**2**) system call or its equivalent. 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.
    
       **ls-refs**
           **ls-refs** is the command used to request a reference advertisement
           in v2. Unlike the current reference advertisement, ls-refs takes
           in arguments which can be used to limit the refs sent from the
           server.
    
           Additional features not supported in the base command will be
           advertised as the value of the command in the capability
           advertisement in the form of a space separated list of features:
           "<command>=<feature-1> <feature-2>"
    
           ls-refs takes in the following arguments:
    
               symrefs
                   In addition to the object pointed by it, show the underlying ref
                   pointed by it when showing a symbolic ref.
               peel
                   Show peeled tags.
               ref-prefix <prefix>
                   When specified, only references having a prefix matching one of
                   the provided prefixes are displayed. Multiple instances may be
                   given, in which case references matching any prefix will be
                   shown. Note that this is purely for optimization; a server MAY
                   show refs not matching the prefix if it chooses, and clients
                   should filter the result themselves.
    
           If the _unborn_ feature is advertised the following argument can be
           included in the client’s request.
    
               unborn
                   The server will send information about HEAD even if it is a symref
                   pointing to an unborn branch in the form "unborn HEAD
                   symref-target:<target>".
    
           The output of ls-refs is as follows:
    
               output = *ref
                        flush-pkt
               obj-id-or-unborn = (obj-id | "unborn")
               ref = PKT-LINE(obj-id-or-unborn SP refname *(SP ref-attribute) LF)
               ref-attribute = (symref | peeled)
               symref = "symref-target:" symref-target
               peeled = "peeled:" obj-id
    
       **fetch**
           **fetch** is the command used to fetch a packfile in v2. It can be
           looked at as a modified version of the v1 fetch where the
           ref-advertisement is stripped out (since the **ls-refs** command fills
           that role) and the message format is tweaked to eliminate
           redundancies and permit easy addition of future extensions.
    
           Additional features not supported in the base command will be
           advertised as the value of the command in the capability
           advertisement in the form of a space separated list of features:
           "<command>=<feature-1> <feature-2>"
    
           A **fetch** request can take the following arguments:
    
               want <oid>
                   Indicates to the server an object which the client wants to
                   retrieve.  Wants can be anything and are not limited to
                   advertised objects.
    
               have <oid>
                   Indicates to the server an object which the client has locally.
                   This allows the server to make a packfile which only contains
                   the objects that the client needs. Multiple 'have' lines can be
                   supplied.
    
               done
                   Indicates to the server that negotiation should terminate (or
                   not even begin if performing a clone) and that the server should
                   use the information supplied in the request to construct the
                   packfile.
    
               thin-pack
                   Request that a thin pack be sent, which is a pack 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.
    
               no-progress
                   Request that progress information that would normally be sent on
                   side-band channel 2, during the packfile transfer, should not be
                   sent.  However, the side-band channel 3 is still used for error
                   responses.
    
               include-tag
                   Request that annotated tags should be sent if the objects they
                   point to are being sent.
    
               ofs-delta
                   Indicate that the client understands PACKv2 with delta referring
                   to its base by position in pack rather than by an oid.  That is,
                   they can read OBJ_OFS_DELTA (aka type 6) in a packfile.
    
           If the _shallow_ feature is advertised the following arguments can
           be included in the clients request as well as the potential
           addition of the _shallow-info_ section in the server’s response as
           explained below.
    
               shallow <oid>
                   A client must notify the server of all commits for which it only
                   has shallow copies (meaning that it doesn't have the parents of
                   a commit) by supplying a 'shallow <oid>' line for each such
                   object so that the server is aware of the limitations of the
                   client's history.  This is so that the server is aware that the
                   client may not have all objects reachable from such commits.
    
               deepen <depth>
                   Requests that the fetch/clone should be shallow having a commit
                   depth of <depth> relative to the remote side.
    
               deepen-relative
                   Requests that the semantics of the "deepen" command be changed
                   to indicate that the depth requested is relative to the client's
                   current shallow boundary, instead of relative to the requested
                   commits.
    
               deepen-since <timestamp>
                   Requests that the shallow clone/fetch should be cut at a
                   specific time, instead of depth.  Internally it's equivalent to
                   doing "git rev-list --max-age=<timestamp>". Cannot be used with
                   "deepen".
    
               deepen-not <rev>
                   Requests that the shallow clone/fetch should be cut at a
                   specific revision specified by '<rev>', instead of a depth.
                   Internally it's equivalent of doing "git rev-list --not <rev>".
                   Cannot be used with "deepen", but can be used with
                   "deepen-since".
    
           If the _filter_ feature is advertised, the following argument can be
           included in the client’s request:
    
               filter <filter-spec>
                   Request that various objects from the packfile be omitted
                   using one of several filtering techniques. These are intended
                   for use with partial clone and partial fetch operations. See
                   `rev-list` for possible "filter-spec" values. When communicating
                   with other processes, senders SHOULD translate scaled integers
                   (e.g. "1k") into a fully-expanded form (e.g. "1024") to aid
                   interoperability with older receivers that may not understand
                   newly-invented scaling suffixes. However, receivers SHOULD
                   accept the following suffixes: 'k', 'm', and 'g' for 1024,
                   1048576, and 1073741824, respectively.
    
           If the _ref-in-want_ feature is advertised, the following argument
           can be included in the client’s request as well as the potential
           addition of the _wanted-refs_ section in the server’s response as
           explained below.
    
               want-ref <ref>
                   Indicates to the server that the client wants to retrieve a
                   particular ref, where <ref> is the full name of a ref on the
                   server.  It is a protocol error to send want-ref for the
                   same ref more than once.
    
           If the _sideband-all_ feature is advertised, the following argument
           can be included in the client’s request:
    
               sideband-all
                   Instruct the server to send the whole response multiplexed, not just
                   the packfile section. All non-flush and non-delim PKT-LINE in the
                   response (not only in the packfile section) will then start with a byte
                   indicating its sideband (1, 2, or 3), and the server may send "0005\2"
                   (a PKT-LINE of sideband 2 with no payload) as a keepalive packet.
    
           If the _packfile-uris_ feature is advertised, the following argument
           can be included in the client’s request as well as the potential
           addition of the _packfile-uris_ section in the server’s response as
           explained below. Note that at most one **packfile-uris** line can be
           sent to the server.
    
               packfile-uris <comma-separated-list-of-protocols>
                   Indicates to the server that the client is willing to receive
                   URIs of any of the given protocols in place of objects in the
                   sent packfile. Before performing the connectivity check, the
                   client should download from all given URIs. Currently, the
                   protocols supported are "http" and "https".
    
           If the _wait-for-done_ feature is advertised, the following argument
           can be included in the client’s request.
    
               wait-for-done
                   Indicates to the server that it should never send "ready", but
                   should wait for the client to say "done" before sending the
                   packfile.
    
           The response of **fetch** is broken into a number of sections
           separated by delimiter packets (0001), with each section beginning
           with its section header. Most sections are sent only when the
           packfile is sent.
    
               output = acknowledgements flush-pkt |
                        [acknowledgments delim-pkt] [shallow-info delim-pkt]
                        [wanted-refs delim-pkt] [packfile-uris delim-pkt]
                        packfile flush-pkt
    
               acknowledgments = PKT-LINE("acknowledgments" LF)
                                 (nak | *ack)
                                 (ready)
               ready = PKT-LINE("ready" LF)
               nak = PKT-LINE("NAK" LF)
               ack = PKT-LINE("ACK" SP obj-id LF)
    
               shallow-info = PKT-LINE("shallow-info" LF)
                              *PKT-LINE((shallow | unshallow) LF)
               shallow = "shallow" SP obj-id
               unshallow = "unshallow" SP obj-id
    
               wanted-refs = PKT-LINE("wanted-refs" LF)
                             *PKT-LINE(wanted-ref LF)
               wanted-ref = obj-id SP refname
    
               packfile-uris = PKT-LINE("packfile-uris" LF) *packfile-uri
               packfile-uri = PKT-LINE(40*(HEXDIGIT) SP *%x20-ff LF)
    
               packfile = PKT-LINE("packfile" LF)
                          *PKT-LINE(%x01-03 *%x00-ff)
    
               acknowledgments section
                   * If the client determines that it is finished with negotiations by
                     sending a "done" line (thus requiring the server to send a packfile),
                     the acknowledgments sections MUST be omitted from the server's
                     response.
    
           •   Always begins with the section header "acknowledgments"
    
           •   The server will respond with "NAK" if none of the object ids
               sent as have lines were common.
    
           •   The server will respond with "ACK obj-id" for all of the
               object ids sent as have lines which are common.
    
           •   A response cannot have both "ACK" lines as well as a "NAK"
               line.
    
           •   The server will respond with a "ready" line indicating that
               the server has found an acceptable common base and is ready to
               make and send a packfile (which will be found in the packfile
               section of the same response)
    
           •   If the server has found a suitable cut point and has decided
               to send a "ready" line, then the server can decide to (as an
               optimization) omit any "ACK" lines it would have sent during
               its response. This is because the server will have already
               determined the objects it plans to send to the client and no
               further negotiation is needed.
    
                   shallow-info section
                       * If the client has requested a shallow fetch/clone, a shallow
                         client requests a fetch or the server is shallow then the
                         server's response may include a shallow-info section.  The
                         shallow-info section will be included if (due to one of the
                         above conditions) the server needs to inform the client of any
                         shallow boundaries or adjustments to the clients already
                         existing shallow boundaries.
    
           •   Always begins with the section header "shallow-info"
    
           •   If a positive depth is requested, the server will compute the
               set of commits which are no deeper than the desired depth.
    
           •   The server sends a "shallow obj-id" line for each commit whose
               parents will not be sent in the following packfile.
    
           •   The server sends an "unshallow obj-id" line for each commit
               which the client has indicated is shallow, but is no longer
               shallow as a result of the fetch (due to its parents being
               sent in the following packfile).
    
           •   The server MUST NOT send any "unshallow" lines for anything
               which the client has not indicated was shallow as a part of
               its request.
    
                   wanted-refs section
                       * This section is only included if the client has requested a
                         ref using a 'want-ref' line and if a packfile section is also
                         included in the response.
    
           •   Always begins with the section header "wanted-refs".
    
           •   The server will send a ref listing ("<oid> <refname>") for
               each reference requested using _want-ref_ lines.
    
           •   The server MUST NOT send any refs which were not requested
               using _want-ref_ lines.
    
                   packfile-uris section
                       * This section is only included if the client sent
                         'packfile-uris' and the server has at least one such URI to
                         send.
    
           •   Always begins with the section header "packfile-uris".
    
           •   For each URI the server sends, it sends a hash of the pack’s
               contents (as output by git index-pack) followed by the URI.
    
           •   The hashes are 40 hex characters long. When Git upgrades to a
               new hash algorithm, this might need to be updated. (It should
               match whatever index-pack outputs after "pack\t" or "keep\t".
    
                   packfile section
                       * This section is only included if the client has sent 'want'
                         lines in its request and either requested that no more
                         negotiation be done by sending 'done' or if the server has
                         decided it has found a sufficient cut point to produce a
                         packfile.
    
           •   Always begins with the section header "packfile"
    
           •   The transmission of the packfile begins immediately after the
               section header
    
           •   The data transfer of the packfile is always multiplexed, using
               the same semantics of the _side-band-64k_ capability from
               protocol version 1. This means that each packet, during the
               packfile data stream, is made up of a leading 4-byte pkt-line
               length (typical of the pkt-line format), 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
    
       **server-option**
           If advertised, indicates that any number of server specific
           options can be included in a request. This is done by sending each
           option as a "server-option=<option>" capability line in the
           capability-list section of a request.
    
           The provided options must not contain a NUL or LF character.
    
       **object-format**
           The server can advertise the **object-format** capability with a value
           **X**(in the form **object-format=X**) to notify the client that the
           server is able to deal with objects using hash algorithm X. If not
           specified, the server is assumed to only handle SHA-1. If the
           client would like to use a hash algorithm other than SHA-1, it
           should specify its object-format string.
    
       **session-id= <session-id>**
           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.**object-info**
           **object-info** is the command to retrieve information about one or
           more objects. Its main purpose is to allow a client to make
           decisions based on this information without having to fully fetch
           objects. Object size is the only information that is currently
           supported.
    
           An **object-info** request takes the following arguments:
    
               size
               Requests size information to be returned for each listed object id.
    
               oid <oid>
               Indicates to the server an object which the client wants to obtain
               information for.
    
           The response of **object-info** is a list of the requested object ids
           and associated requested information, each separated by a single
           space.
    
               output = info flush-pkt
    
               info = PKT-LINE(attrs) LF)
                       *PKT-LINE(obj-info LF)
    
               attrs = attr | attrs SP attrs
    
               attr = "size"
    
               obj-info = obj-id SP obj-size
    
       **bundle-uri**
           If the _bundle-uri_ capability is advertised, the server supports
           the ‘bundle-uri’ command.
    
           The capability is currently advertised with no value (i.e. not
           "bundle-uri=somevalue"), a value may be added in the future for
           supporting command-wide extensions. Clients MUST ignore any
           unknown capability values and proceed with the 'bundle-uri` dialog
           they support.
    
           The _bundle-uri_ command is intended to be issued before **fetch** to
           get URIs to bundle files (see git-bundle(1)) to "seed" and inform
           the subsequent **fetch** command.
    
           The client CAN issue **bundle-uri** before or after any other valid
           command. To be useful to clients it’s expected that it’ll be
           issued after an **ls-refs** and before **fetch** , but CAN be issued at any
           time in the dialog.
    
           **DISCUSSION of bundle-uri**
    
               The intent of the feature is optimize for server resource
               consumption in the common case by changing the common case of
               fetching a very large PACK during git-clone(1) into a smaller
               incremental fetch.
    
               It also allows servers to achieve better caching in
               combination with an **uploadpack.packObjectsHook**(see
               git-config(1)).
    
               By having new clones or fetches be a more predictable and
               common negotiation against the tips of recently produces
               *.bundle file(s). Servers might even pre-generate the results
               of such negotiations for the **uploadpack.packObjectsHook** as new
               pushes come in.
    
               One way that servers could take advantage of these bundles is
               that the server would anticipate that fresh clones will
               download a known bundle, followed by catching up to the
               current state of the repository using ref tips found in that
               bundle (or bundles).
    
           **PROTOCOL for bundle-uri**
    
               A **bundle-uri** request takes no arguments, and as noted above
               does not currently advertise a capability value. Both may be
               added in the future.
    
               When the client issues a **command=bundle-uri** request, the
               response is a list of key-value pairs provided as packet lines
               with value _< key>_**=**_< value>_. Each _< key>_ should be interpreted as
               a config key from the **bundle.*** namespace to construct a list
               of bundles. These keys are grouped by a **bundle.**_< id>_.
               subsection, where each key corresponding to a given _< id>_
               contributes attributes to the bundle defined by that _< id>_. See
               git-config(1) for the specific details of these keys and how
               the Git client will interpret their values.
    
               Clients MUST parse the line according to the above format,
               lines that do not conform to the format SHOULD be discarded.
               The user MAY be warned in such a case.
    
           **bundle-uri CLIENT AND SERVER EXPECTATIONS**
    
               URI CONTENTS
                   The content at the advertised URIs MUST be one of two
                   types.
    
                   The advertised URI may contain a bundle file that **git**
                   **bundle verify** would accept. I.e. they MUST contain one or
                   more reference tips for use by the client, MUST indicate
                   prerequisites (in any) with standard "-" prefixes, and
                   MUST indicate their "object-format", if applicable.
    
                   The advertised URI may alternatively contain a plaintext
                   file that **git config --list** would accept (with the **--file**
                   option). The key-value pairs in this list are in the
                   **bundle.*** namespace (see git-config(1)).
    
               bundle-uri CLIENT ERROR RECOVERY
                   A client MUST above all gracefully degrade on errors,
                   whether that error is because of bad missing/data in the
                   bundle URI(s), because that client is too dumb to e.g.
                   understand and fully parse out bundle headers and their
                   prerequisite relationships, or something else.
    
                   Server operators should feel confident in turning on
                   "bundle-uri" and not worry if e.g. their CDN goes down
                   that clones or fetches will run into hard failures. Even
                   if the server bundle(s) are incomplete, or bad in some way
                   the client should still end up with a functioning
                   repository, just as if it had chosen not to use this
                   protocol extension.
    
                   All subsequent discussion on client and server interaction
                   MUST keep this in mind.
    
               bundle-uri SERVER TO CLIENT
                   The ordering of the returned bundle uris is not
                   significant. Clients MUST parse their headers to discover
                   their contained OIDS and prerequisites. A client MUST
                   consider the content of the bundle(s) themselves and their
                   header as the ultimate source of truth.
    
                   A server MAY even return bundle(s) that don’t have any
                   direct relationship to the repository being cloned (either
                   through accident, or intentional "clever" configuration),
                   and expect a client to sort out what data they’d like from
                   the bundle(s), if any.
    
               bundle-uri CLIENT TO SERVER
                   The client SHOULD provide reference tips found in the
                   bundle header(s) as _have_ lines in any subsequent **fetch**
                   request. A client MAY also ignore the bundle(s) entirely
                   if doing so is deemed worse for some reason, e.g. if the
                   bundles can’t be downloaded, it doesn’t like the tips it
                   finds etc.
    
               WHEN ADVERTISED BUNDLE(S) REQUIRE NO FURTHER NEGOTIATION
                   If after issuing **bundle-uri** and **ls-refs** , and getting the
                   header(s) of the bundle(s) the client finds that the ref
                   tips it wants can be retrieved entirely from advertised
                   bundle(s), the client MAY disconnect from the Git server.
                   The results of such a _clone_ or _fetch_ should be
                   indistinguishable from the state attained without using
                   bundle-uri.
    
               EARLY CLIENT DISCONNECTIONS AND ERROR RECOVERY
                   A client MAY perform an early disconnect while still
                   downloading the bundle(s) (having streamed and parsed
                   their headers). In such a case the client MUST gracefully
                   recover from any errors related to finishing the download
                   and validation of the bundle(s).
    
                   I.e. a client might need to re-connect and issue a _fetch_
                   command, and possibly fall back to not making use of
                   _bundle-uri_ at all.
    
                   This "MAY" behavior is specified as such (and not a
                   "SHOULD") on the assumption that a server advertising
                   bundle uris is more likely than not to be serving up a
                   relatively large repository, and to be pointing to URIs
                   that have a good chance of being in working order. A
                   client MAY e.g. look at the payload size of the bundles as
                   a heuristic to see if an early disconnect is worth it,
                   should falling back on a full "fetch" dialog be necessary.
    
               WHEN ADVERTISED BUNDLE(S) REQUIRE FURTHER NEGOTIATION
                   A client SHOULD commence a negotiation of a PACK from the
                   server via the "fetch" command using the OID tips found in
                   advertised bundles, even if’s still in the process of
                   downloading those bundle(s).
    
                   This allows for aggressive early disconnects from any
                   interactive server dialog. The client blindly trusts that
                   the advertised OID tips are relevant, and issues them as
                   _have_ lines, it then requests any tips it would like
                   (usually from the "ls-refs" advertisement) via _want_ lines.
                   The server will then compute a (hopefully small) PACK with
                   the expected difference between the tips from the
                   bundle(s) and the data requested.
    
                   The only connection the client then needs to keep active
                   is to the concurrently downloading static bundle(s), when
                   those and the incremental PACK are retrieved they should
                   be inflated and validated. Any errors at this point should
                   be gracefully recovered from, see above.
    
           **bundle-uri PROTOCOL FEATURES**
    
               The client constructs a bundle list from the _< key>_**=**_< value>_
               pairs provided by the server. These pairs are part of the
               **bundle.*** namespace as documented in git-config(1). In this
               section, we discuss some of these keys and describe the
               actions the client will do in response to this information.
    
               In particular, the **bundle.version** key specifies an integer
               value. The only accepted value at the moment is **1** , but if the
               client sees an unexpected value here then the client MUST
               ignore the bundle list.
    
               As long as **bundle.version** is understood, all other unknown
               keys MAY be ignored by the client. The server will guarantee
               compatibility with older clients, though newer clients may be
               better able to use the extra keys to minimize downloads.
    
               Any backwards-incompatible addition of pre-URI key-value will
               be guarded by a new **bundle.version** value or values in
               _bundle-uri_ capability advertisement itself, and/or by new
               future **bundle-uri** request arguments.
    
               Some example key-value pairs that are not currently
               implemented but could be implemented in the future include:
    
               •   Add a "hash=<val>" or "size=<bytes>" advertise the
                   expected hash or size of the bundle file.
    
               •   Advertise that one or more bundle files are the same (to
                   e.g. have clients round-robin or otherwise choose one of N
                   possible files).
    
               •   A "oid=<OID>" shortcut and "prerequisite=<OID>" shortcut.
                   For expressing the common case of a bundle with one tip
                   and no prerequisites, or one tip and one prerequisite.
    
                   This would allow for optimizing the common case of servers
                   who’d like to provide one "big bundle" containing only
                   their "main" branch, and/or incremental updates thereof.
    
                   A client receiving such a response MAY assume that they
                   can skip retrieving the header from a bundle at the
                   indicated URI, and thus save themselves and the server(s)
                   the request(s) needed to inspect the headers of that
                   bundle or bundles.
    
       **promisor-remote= <pr-infos>**
           The server may advertise some promisor remotes it is using or
           knows about to a client which may want to use them as its promisor
           remotes, instead of this repository. In this case <pr-infos>
           should be of the form:
    
               pr-infos = pr-info | pr-infos ";" pr-info
    
               pr-info = "name=" pr-name | "name=" pr-name "," "url=" pr-url
    
           where **pr-name** is the urlencoded name of a promisor remote, and
           **pr-url** the urlencoded URL of that promisor remote.
    
           In this case, if the client decides to use one or more promisor
           remotes the server advertised, it can reply with
           "promisor-remote=<pr-names>" where <pr-names> should be of the
           form:
    
               pr-names = pr-name | pr-names ";" pr-name
    
           where **pr-name** is the urlencoded name of a promisor remote the
           server advertised and the client accepts.
    
           Note that, everywhere in this document, **pr-name** MUST be a valid
           remote name, and the _;_ and _,_ characters MUST be encoded if they
           appear in **pr-name** or **pr-url**.
    
           If the server doesn’t know any promisor remote that could be good
           for a client to use, or prefers a client not to use any promisor
           remote it uses or knows about, it shouldn’t advertise the
           "promisor-remote" capability at all.
    
           In this case, or if the client doesn’t want to use any promisor
           remote the server advertised, the client shouldn’t advertise the
           "promisor-remote" capability at all in its reply.
    
           The "promisor.advertise" and "promisor.acceptFromServer"
           configuration options can be used on the server and client side to
           control what they advertise or accept respectively. See the
           documentation of these configuration options for more information.
    
           Note that in the future it would be nice if the "promisor-remote"
           protocol capability could be used by the server, when responding
           to **git fetch** or **git clone** , to advertise better-connected remotes
           that the client can use as promisor remotes, instead of this
           repository, so that the client can lazily fetch objects from these
           other better-connected remotes. This would require the server to
           omit in its response the objects available on the better-connected
           remotes that the client has accepted. This hasn’t been implemented
           yet though. So for now this "promisor-remote" capability is useful
           only when the server advertises some promisor remotes it already
           uses to borrow objects from.
    


## GIT



           Part of the git(1) suite
    


## NOTES



            1. api-trace2
               file:///home/mtk/share/doc/git-doc/technical/api-trace2.html
    


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