1Git Wire Protocol, Version 2 2============================ 3 4This document presents a specification for a version 2 of Git's wire 5protocol. Protocol v2 will improve upon v1 in the following ways: 6 7 * Instead of multiple service names, multiple commands will be 8 supported by a single service 9 * Easily extendable as capabilities are moved into their own section 10 of the protocol, no longer being hidden behind a NUL byte and 11 limited by the size of a pkt-line 12 * Separate out other information hidden behind NUL bytes (e.g. agent 13 string as a capability and symrefs can be requested using 'ls-refs') 14 * Reference advertisement will be omitted unless explicitly requested 15 * ls-refs command to explicitly request some refs 16 * Designed with http and stateless-rpc in mind. With clear flush 17 semantics the http remote helper can simply act as a proxy 18 19In protocol v2 communication is command oriented. When first contacting a 20server a list of capabilities will advertised. Some of these capabilities 21will be commands which a client can request be executed. Once a command 22has completed, a client can reuse the connection and request that other 23commands be executed. 24 25Packet-Line Framing 26------------------- 27 28All communication is done using packet-line framing, just as in v1. See 29`Documentation/technical/pack-protocol.txt` and 30`Documentation/technical/protocol-common.txt` for more information. 31 32In protocol v2 these special packets will have the following semantics: 33 34 * '0000' Flush Packet (flush-pkt) - indicates the end of a message 35 * '0001' Delimiter Packet (delim-pkt) - separates sections of a message 36 37Initial Client Request 38---------------------- 39 40In general a client can request to speak protocol v2 by sending 41`version=2` through the respective side-channel for the transport being 42used which inevitably sets `GIT_PROTOCOL`. More information can be 43found in `pack-protocol.txt` and `http-protocol.txt`. In all cases the 44response from the server is the capability advertisement. 45 46Git Transport 47~~~~~~~~~~~~~ 48 49When using the git:// transport, you can request to use protocol v2 by 50sending "version=2" as an extra parameter: 51 52 003egit-upload-pack /project.git\0host=myserver.com\0\0version=2\0 53 54SSH and File Transport 55~~~~~~~~~~~~~~~~~~~~~~ 56 57When using either the ssh:// or file:// transport, the GIT_PROTOCOL 58environment variable must be set explicitly to include "version=2". 59 60HTTP Transport 61~~~~~~~~~~~~~~ 62 63When using the http:// or https:// transport a client makes a "smart" 64info/refs request as described in `http-protocol.txt` and requests that 65v2 be used by supplying "version=2" in the `Git-Protocol` header. 66 67 C: GET $GIT_URL/info/refs?service=git-upload-pack HTTP/1.0 68 C: Git-Protocol: version=2 69 70A v2 server would reply: 71 72 S: 200 OK 73 S: <Some headers> 74 S: ... 75 S: 76 S: 000eversion 2\n 77 S: <capability-advertisement> 78 79Subsequent requests are then made directly to the service 80`$GIT_URL/git-upload-pack`. (This works the same for git-receive-pack). 81 82Capability Advertisement 83------------------------ 84 85A server which decides to communicate (based on a request from a client) 86using protocol version 2, notifies the client by sending a version string 87in its initial response followed by an advertisement of its capabilities. 88Each capability is a key with an optional value. Clients must ignore all 89unknown keys. Semantics of unknown values are left to the definition of 90each key. Some capabilities will describe commands which can be requested 91to be executed by the client. 92 93 capability-advertisement = protocol-version 94 capability-list 95 flush-pkt 96 97 protocol-version = PKT-LINE("version 2" LF) 98 capability-list = *capability 99 capability = PKT-LINE(key[=value] LF) 100 101 key = 1*(ALPHA | DIGIT | "-_") 102 value = 1*(ALPHA | DIGIT | " -_.,?\/{}[]()<>!@#$%^&*+=:;") 103 104Command Request 105--------------- 106 107After receiving the capability advertisement, a client can then issue a 108request to select the command it wants with any particular capabilities 109or arguments. There is then an optional section where the client can 110provide any command specific parameters or queries. Only a single 111command can be requested at a time. 112 113 request = empty-request | command-request 114 empty-request = flush-pkt 115 command-request = command 116 capability-list 117 [command-args] 118 flush-pkt 119 command = PKT-LINE("command=" key LF) 120 command-args = delim-pkt 121 *command-specific-arg 122 123 command-specific-args are packet line framed arguments defined by 124 each individual command. 125 126The server will then check to ensure that the client's request is 127comprised of a valid command as well as valid capabilities which were 128advertised. If the request is valid the server will then execute the 129command. A server MUST wait till it has received the client's entire 130request before issuing a response. The format of the response is 131determined by the command being executed, but in all cases a flush-pkt 132indicates the end of the response. 133 134When a command has finished, and the client has received the entire 135response from the server, a client can either request that another 136command be executed or can terminate the connection. A client may 137optionally send an empty request consisting of just a flush-pkt to 138indicate that no more requests will be made. 139 140Capabilities 141------------ 142 143There are two different types of capabilities: normal capabilities, 144which can be used to to convey information or alter the behavior of a 145request, and commands, which are the core actions that a client wants to 146perform (fetch, push, etc). 147 148Protocol version 2 is stateless by default. This means that all commands 149must only last a single round and be stateless from the perspective of the 150server side, unless the client has requested a capability indicating that 151state should be maintained by the server. Clients MUST NOT require state 152management on the server side in order to function correctly. This 153permits simple round-robin load-balancing on the server side, without 154needing to worry about state management. 155 156agent 157~~~~~ 158 159The server can advertise the `agent` capability with a value `X` (in the 160form `agent=X`) to notify the client that the server is running version 161`X`. The client may optionally send its own agent string by including 162the `agent` capability with a value `Y` (in the form `agent=Y`) in its 163request to the server (but it MUST NOT do so if the server did not 164advertise the agent capability). The `X` and `Y` strings may contain any 165printable ASCII characters except space (i.e., the byte range 32 < x < 166127), and are typically of the form "package/version" (e.g., 167"git/1.8.3.1"). The agent strings are purely informative for statistics 168and debugging purposes, and MUST NOT be used to programmatically assume 169the presence or absence of particular features. 170 171ls-refs 172~~~~~~~ 173 174`ls-refs` is the command used to request a reference advertisement in v2. 175Unlike the current reference advertisement, ls-refs takes in arguments 176which can be used to limit the refs sent from the server. 177 178Additional features not supported in the base command will be advertised 179as the value of the command in the capability advertisement in the form 180of a space separated list of features: "<command>=<feature 1> <feature 2>" 181 182ls-refs takes in the following arguments: 183 184 symrefs 185 In addition to the object pointed by it, show the underlying ref 186 pointed by it when showing a symbolic ref. 187 peel 188 Show peeled tags. 189 ref-prefix <prefix> 190 When specified, only references having a prefix matching one of 191 the provided prefixes are displayed. 192 193The output of ls-refs is as follows: 194 195 output = *ref 196 flush-pkt 197 ref = PKT-LINE(obj-id SP refname *(SP ref-attribute) LF) 198 ref-attribute = (symref | peeled) 199 symref = "symref-target:" symref-target 200 peeled = "peeled:" obj-id 201 202fetch 203~~~~~ 204 205`fetch` is the command used to fetch a packfile in v2. It can be looked 206at as a modified version of the v1 fetch where the ref-advertisement is 207stripped out (since the `ls-refs` command fills that role) and the 208message format is tweaked to eliminate redundancies and permit easy 209addition of future extensions. 210 211Additional features not supported in the base command will be advertised 212as the value of the command in the capability advertisement in the form 213of a space separated list of features: "<command>=<feature 1> <feature 2>" 214 215A `fetch` request can take the following arguments: 216 217 want <oid> 218 Indicates to the server an object which the client wants to 219 retrieve. Wants can be anything and are not limited to 220 advertised objects. 221 222 have <oid> 223 Indicates to the server an object which the client has locally. 224 This allows the server to make a packfile which only contains 225 the objects that the client needs. Multiple 'have' lines can be 226 supplied. 227 228 done 229 Indicates to the server that negotiation should terminate (or 230 not even begin if performing a clone) and that the server should 231 use the information supplied in the request to construct the 232 packfile. 233 234 thin-pack 235 Request that a thin pack be sent, which is a pack with deltas 236 which reference base objects not contained within the pack (but 237 are known to exist at the receiving end). This can reduce the 238 network traffic significantly, but it requires the receiving end 239 to know how to "thicken" these packs by adding the missing bases 240 to the pack. 241 242 no-progress 243 Request that progress information that would normally be sent on 244 side-band channel 2, during the packfile transfer, should not be 245 sent. However, the side-band channel 3 is still used for error 246 responses. 247 248 include-tag 249 Request that annotated tags should be sent if the objects they 250 point to are being sent. 251 252 ofs-delta 253 Indicate that the client understands PACKv2 with delta referring 254 to its base by position in pack rather than by an oid. That is, 255 they can read OBJ_OFS_DELTA (ake type 6) in a packfile. 256 257If the 'shallow' feature is advertised the following arguments can be 258included in the clients request as well as the potential addition of the 259'shallow-info' section in the server's response as explained below. 260 261 shallow <oid> 262 A client must notify the server of all commits for which it only 263 has shallow copies (meaning that it doesn't have the parents of 264 a commit) by supplying a 'shallow <oid>' line for each such 265 object so that the server is aware of the limitations of the 266 client's history. This is so that the server is aware that the 267 client may not have all objects reachable from such commits. 268 269 deepen <depth> 270 Requests that the fetch/clone should be shallow having a commit 271 depth of <depth> relative to the remote side. 272 273 deepen-relative 274 Requests that the semantics of the "deepen" command be changed 275 to indicate that the depth requested is relative to the client's 276 current shallow boundary, instead of relative to the requested 277 commits. 278 279 deepen-since <timestamp> 280 Requests that the shallow clone/fetch should be cut at a 281 specific time, instead of depth. Internally it's equivalent to 282 doing "git rev-list --max-age=<timestamp>". Cannot be used with 283 "deepen". 284 285 deepen-not <rev> 286 Requests that the shallow clone/fetch should be cut at a 287 specific revision specified by '<rev>', instead of a depth. 288 Internally it's equivalent of doing "git rev-list --not <rev>". 289 Cannot be used with "deepen", but can be used with 290 "deepen-since". 291 292If the 'filter' feature is advertised, the following argument can be 293included in the client's request: 294 295 filter <filter-spec> 296 Request that various objects from the packfile be omitted 297 using one of several filtering techniques. These are intended 298 for use with partial clone and partial fetch operations. See 299 `rev-list` for possible "filter-spec" values. When communicating 300 with other processes, senders SHOULD translate scaled integers 301 (e.g. "1k") into a fully-expanded form (e.g. "1024") to aid 302 interoperability with older receivers that may not understand 303 newly-invented scaling suffixes. However, receivers SHOULD 304 accept the following suffixes: 'k', 'm', and 'g' for 1024, 305 1048576, and 1073741824, respectively. 306 307If the 'ref-in-want' feature is advertised, the following argument can 308be included in the client's request as well as the potential addition of 309the 'wanted-refs' section in the server's response as explained below. 310 311 want-ref <ref> 312 Indicates to the server that the client wants to retrieve a 313 particular ref, where <ref> is the full name of a ref on the 314 server. 315 316If the 'sideband-all' feature is advertised, the following argument can be 317included in the client's request: 318 319 sideband-all 320 Instruct the server to send the whole response multiplexed, not just 321 the packfile section. All non-flush and non-delim PKT-LINE in the 322 response (not only in the packfile section) will then start with a byte 323 indicating its sideband (1, 2, or 3), and the server may send "0005\2" 324 (a PKT-LINE of sideband 2 with no payload) as a keepalive packet. 325 326The response of `fetch` is broken into a number of sections separated by 327delimiter packets (0001), with each section beginning with its section 328header. 329 330 output = *section 331 section = (acknowledgments | shallow-info | wanted-refs | packfile) 332 (flush-pkt | delim-pkt) 333 334 acknowledgments = PKT-LINE("acknowledgments" LF) 335 (nak | *ack) 336 (ready) 337 ready = PKT-LINE("ready" LF) 338 nak = PKT-LINE("NAK" LF) 339 ack = PKT-LINE("ACK" SP obj-id LF) 340 341 shallow-info = PKT-LINE("shallow-info" LF) 342 *PKT-LINE((shallow | unshallow) LF) 343 shallow = "shallow" SP obj-id 344 unshallow = "unshallow" SP obj-id 345 346 wanted-refs = PKT-LINE("wanted-refs" LF) 347 *PKT-LINE(wanted-ref LF) 348 wanted-ref = obj-id SP refname 349 350 packfile = PKT-LINE("packfile" LF) 351 *PKT-LINE(%x01-03 *%x00-ff) 352 353 acknowledgments section 354 * If the client determines that it is finished with negotiations 355 by sending a "done" line, the acknowledgments sections MUST be 356 omitted from the server's response. 357 358 * Always begins with the section header "acknowledgments" 359 360 * The server will respond with "NAK" if none of the object ids sent 361 as have lines were common. 362 363 * The server will respond with "ACK obj-id" for all of the 364 object ids sent as have lines which are common. 365 366 * A response cannot have both "ACK" lines as well as a "NAK" 367 line. 368 369 * The server will respond with a "ready" line indicating that 370 the server has found an acceptable common base and is ready to 371 make and send a packfile (which will be found in the packfile 372 section of the same response) 373 374 * If the server has found a suitable cut point and has decided 375 to send a "ready" line, then the server can decide to (as an 376 optimization) omit any "ACK" lines it would have sent during 377 its response. This is because the server will have already 378 determined the objects it plans to send to the client and no 379 further negotiation is needed. 380 381 shallow-info section 382 * If the client has requested a shallow fetch/clone, a shallow 383 client requests a fetch or the server is shallow then the 384 server's response may include a shallow-info section. The 385 shallow-info section will be included if (due to one of the 386 above conditions) the server needs to inform the client of any 387 shallow boundaries or adjustments to the clients already 388 existing shallow boundaries. 389 390 * Always begins with the section header "shallow-info" 391 392 * If a positive depth is requested, the server will compute the 393 set of commits which are no deeper than the desired depth. 394 395 * The server sends a "shallow obj-id" line for each commit whose 396 parents will not be sent in the following packfile. 397 398 * The server sends an "unshallow obj-id" line for each commit 399 which the client has indicated is shallow, but is no longer 400 shallow as a result of the fetch (due to its parents being 401 sent in the following packfile). 402 403 * The server MUST NOT send any "unshallow" lines for anything 404 which the client has not indicated was shallow as a part of 405 its request. 406 407 * This section is only included if a packfile section is also 408 included in the response. 409 410 wanted-refs section 411 * This section is only included if the client has requested a 412 ref using a 'want-ref' line and if a packfile section is also 413 included in the response. 414 415 * Always begins with the section header "wanted-refs". 416 417 * The server will send a ref listing ("<oid> <refname>") for 418 each reference requested using 'want-ref' lines. 419 420 * The server MUST NOT send any refs which were not requested 421 using 'want-ref' lines. 422 423 packfile section 424 * This section is only included if the client has sent 'want' 425 lines in its request and either requested that no more 426 negotiation be done by sending 'done' or if the server has 427 decided it has found a sufficient cut point to produce a 428 packfile. 429 430 * Always begins with the section header "packfile" 431 432 * The transmission of the packfile begins immediately after the 433 section header 434 435 * The data transfer of the packfile is always multiplexed, using 436 the same semantics of the 'side-band-64k' capability from 437 protocol version 1. This means that each packet, during the 438 packfile data stream, is made up of a leading 4-byte pkt-line 439 length (typical of the pkt-line format), followed by a 1-byte 440 stream code, followed by the actual data. 441 442 The stream code can be one of: 443 1 - pack data 444 2 - progress messages 445 3 - fatal error message just before stream aborts 446 447server-option 448~~~~~~~~~~~~~ 449 450If advertised, indicates that any number of server specific options can be 451included in a request. This is done by sending each option as a 452"server-option=<option>" capability line in the capability-list section of 453a request. 454 455The provided options must not contain a NUL or LF character.