| Git Wire Protocol, Version 2 |
| ============================ |
| |
| 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 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 |
| `Documentation/technical/pack-protocol.txt` and |
| `Documentation/technical/protocol-common.txt` 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 `pack-protocol.txt` and `http-protocol.txt`. 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". |
| |
| HTTP Transport |
| ~~~~~~~~~~~~~~ |
| |
| When using the http:// or https:// transport a client makes a "smart" |
| info/refs request as described in `http-protocol.txt` 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). |
| |
| 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 |
| [command-args] |
| flush-pkt |
| command = PKT-LINE("command=" key LF) |
| command-args = delim-pkt |
| *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 32 < x < |
| 127), and are typically of the form "package/version" (e.g., |
| "git/1.8.3.1"). 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. |
| |
| 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. |
| |
| 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. |
| |
| 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". |
| |
| 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 |
| link:api-trace2.html[api-trace2] for details), but this may change and users of |
| the session ID should not rely on this fact. |