gitprotocol-v2(5) Git Manual gitprotocol-v2(5)
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:
o Instead of multiple service names, multiple commands will be
supported by a single service
o 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
o Separate out other information hidden behind NUL bytes (e.g. agent
string as a capability and symrefs can be requested using ls-refs)
o Reference advertisement will be omitted unless explicitly requested
o ls-refs command to explicitly request some refs
o 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:
o 0000 Flush Packet (flush-pkt) - indicates the end of a message
o 0001 Delimiter Packet (delim-pkt) - separates sections of a message
o 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.
o Always begins with the section header "acknowledgments"
o The server will respond with "NAK" if none of the object ids sent as
have lines were common.
o The server will respond with "ACK obj-id" for all of the object ids
sent as have lines which are common.
o A response cannot have both "ACK" lines as well as a "NAK" line.
o 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)
o 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.
o Always begins with the section header "shallow-info"
o If a positive depth is requested, the server will compute the set of
commits which are no deeper than the desired depth.
o The server sends a "shallow obj-id" line for each commit whose
parents will not be sent in the following packfile.
o 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).
o 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.
o Always begins with the section header "wanted-refs".
o The server will send a ref listing ("<oid> <refname>") for each
reference requested using want-ref lines.
o 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.
o Always begins with the section header "packfile-uris".
o 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.
o 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.
o Always begins with the section header "packfile"
o The transmission of the packfile begins immediately after the section
header
o 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. Currently only
object size and type are supported.
An object-info request takes the following arguments:
size
Requests size information to be returned for each listed object id.
type
Requests type 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. They must be full OIDs.
The response of object-info consists of one pkt-line per requested
attribute, echoing the attributes the server will report, followed by one
pkt-line per requested object id with its information, each field
separated by a single space.
output = info flush-pkt
info = *PKT-LINE(attr LF)
*PKT-LINE(obj-info LF)
attr = "size" | "type"
obj-size = 1*DIGIT
obj-type = "blob" | "tree" | "commit" | "tag"
obj-val = obj-size | obj-type
obj-info = obj-id [SP [obj-val *(SP obj-val)]]
The values in obj-info appear in the same order as the corresponding attr
lines, with exactly one value per requested attribute.
If the server does not recognize the OID, the response will be <oid> SP
regardless of the number of attributes requested.
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:
o Add a "hash=<val>" or "size=<bytes>" advertise the expected hash
or size of the bundle file.
o 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).
o 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-info>
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-info> should be of the form:
pr-info = pr-fields | pr-info ";" pr-fields
pr-fields = pr-field | pr-fields "," pr-field
pr-field = field-name "=" field-value
where all the field-name and field-value in a given pr-fields are field
names and values related to a single promisor remote. A given field-name
MUST NOT appear more than once in given pr-fields.
The server MUST advertise at least the "name" and "url" field names along
with the associated field values, which are the name of a valid remote
and its URL, in each pr-fields. The "name" and "url" fields MUST appear
first in each pr-fields, in that order.
After these mandatory fields, the server MAY advertise the following
optional fields in any order:
partialCloneFilter
The filter specification for the remote. It corresponds to the
"remote.<name>.partialCloneFilter" config setting. Clients can use
this to determine if the remote's filtering strategy is compatible
with their needs (e.g., checking if both use "blob:none").
Additionally they can use this through the --filter=auto option in
git-clone(1). With that option, the filter specification of the clone
will be automatically computed by combining the filter specifications
of the promisor remotes the client accepts.
token
An authentication token that clients can use when connecting to the
remote. It corresponds to the "remote.<name>.token" config setting.
No other fields are defined by the protocol at this time. Field names are
case-sensitive and MUST be transmitted exactly as specified above.
Clients MUST ignore fields they don't recognize to allow for future
protocol extensions.
The client can use information transmitted through these fields to decide
if it accepts the advertised promisor remote. Also, the client can be
configured to store the values of these fields or use them to
automatically configure the repository (see "promisor.storeFields" in
git-config(1) and --filter=auto in git-clone(1)).
Field values MUST be urlencoded.
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.
The promisor remotes that the client accepted will be tried before the
other configured promisor remotes when the client attempts to fetch
missing objects.
Note that, everywhere in this document, the ; and , characters MUST be
encoded if they appear in pr-name or field-value.
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.
On the server side, the "promisor.advertise" and "promisor.sendFields"
configuration options can be used to control what it advertises. On the
client side, the "promisor.acceptFromServer" and
"promisor.acceptFromServerUrl" configuration options can be used to
control what it accepts, and the "promisor.storeFields" option, to
control what it stores. See the documentation of these configuration
options in git-config(1) 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
git-htmldocs/technical/api-trace2.html
Git 2.56.0 2026-09-27 gitprotocol-v2(5)
git 2.56.0 - Generated Thu Oct 1 18:54:15 CDT 2026