1 Git 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 25 Packet-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 37 Initial 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 46 Git 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 54 SSH 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 60 HTTP 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: Git-Protocol: version=2 68 C: 69 C: GET $GIT_URL/info/refs?service=git-upload-pack HTTP/1.0 70 71A v2 server would reply: 72 73 S: 200 OK 74 S: <Some headers> 75 S: ... 76 S: 77 S: 000eversion 2\n 78 S: <capability-advertisement> 79 80Subsequent requests are then made directly to the service 81`$GIT_URL/git-upload-pack`. (This works the same for git-receive-pack). 82 83 Capability Advertisement 84-------------------------- 85 86A server which decides to communicate (based on a request from a client) 87using protocol version 2, notifies the client by sending a version string 88in its initial response followed by an advertisement of its capabilities. 89Each capability is a key with an optional value. Clients must ignore all 90unknown keys. Semantics of unknown values are left to the definition of 91each key. Some capabilities will describe commands which can be requested 92to be executed by the client. 93 94 capability-advertisement = protocol-version 95 capability-list 96 flush-pkt 97 98 protocol-version = PKT-LINE("version 2" LF) 99 capability-list = *capability 100 capability = PKT-LINE(key[=value] LF) 101 102 key = 1*(ALPHA | DIGIT | "-_") 103 value = 1*(ALPHA | DIGIT | " -_.,?\/{}[]()<>!@#$%^&*+=:;") 104 105 Command Request 106----------------- 107 108After receiving the capability advertisement, a client can then issue a 109request to select the command it wants with any particular capabilities 110or arguments. There is then an optional section where the client can 111provide any command specific parameters or queries. Only a single 112command can be requested at a time. 113 114 request = empty-request | command-request 115 empty-request = flush-pkt 116 command-request = command 117 capability-list 118 [command-args] 119 flush-pkt 120 command = PKT-LINE("command=" key LF) 121 command-args = delim-pkt 122 *command-specific-arg 123 124 command-specific-args are packet line framed arguments defined by 125 each individual command. 126 127The server will then check to ensure that the client's request is 128comprised of a valid command as well as valid capabilities which were 129advertised. If the request is valid the server will then execute the 130command. A server MUST wait till it has received the client's entire 131request before issuing a response. The format of the response is 132determined by the command being executed, but in all cases a flush-pkt 133indicates the end of the response. 134 135When a command has finished, and the client has received the entire 136response from the server, a client can either request that another 137command be executed or can terminate the connection. A client may 138optionally send an empty request consisting of just a flush-pkt to 139indicate that no more requests will be made. 140 141 Capabilities 142-------------- 143 144There are two different types of capabilities: normal capabilities, 145which can be used to to convey information or alter the behavior of a 146request, and commands, which are the core actions that a client wants to 147perform (fetch, push, etc). 148 149Protocol version 2 is stateless by default. This means that all commands 150must only last a single round and be stateless from the perspective of the 151server side, unless the client has requested a capability indicating that 152state should be maintained by the server. Clients MUST NOT require state 153management on the server side in order to function correctly. This 154permits simple round-robin load-balancing on the server side, without 155needing to worry about state management. 156 157 agent 158~~~~~~~ 159 160The server can advertise the `agent` capability with a value `X` (in the 161form `agent=X`) to notify the client that the server is running version 162`X`. The client may optionally send its own agent string by including 163the `agent` capability with a value `Y` (in the form `agent=Y`) in its 164request to the server (but it MUST NOT do so if the server did not 165advertise the agent capability). The `X` and `Y` strings may contain any 166printable ASCII characters except space (i.e., the byte range 32 < x < 167127), and are typically of the form "package/version" (e.g., 168"git/1.8.3.1"). The agent strings are purely informative for statistics 169and debugging purposes, and MUST NOT be used to programmatically assume 170the presence or absence of particular features. 171 172 ls-refs 173~~~~~~~~~ 174 175`ls-refs` is the command used to request a reference advertisement in v2. 176Unlike the current reference advertisement, ls-refs takes in arguments 177which can be used to limit the refs sent from the server. 178 179Additional features not supported in the base command will be advertised 180as the value of the command in the capability advertisement in the form 181of a space separated list of features: "<command>=<feature 1> <feature 2>" 182 183ls-refs takes in the following arguments: 184 185 symrefs 186 In addition to the object pointed by it, show the underlying ref 187 pointed by it when showing a symbolic ref. 188 peel 189 Show peeled tags. 190 ref-prefix <prefix> 191 When specified, only references having a prefix matching one of 192 the provided prefixes are displayed. 193 194The output of ls-refs is as follows: 195 196 output = *ref 197 flush-pkt 198 ref = PKT-LINE(obj-id SP refname *(SP ref-attribute) LF) 199 ref-attribute = (symref | peeled) 200 symref = "symref-target:" symref-target 201 peeled = "peeled:" obj-id 202 203 fetch 204~~~~~~~ 205 206`fetch` is the command used to fetch a packfile in v2. It can be looked 207at as a modified version of the v1 fetch where the ref-advertisement is 208stripped out (since the `ls-refs` command fills that role) and the 209message format is tweaked to eliminate redundancies and permit easy 210addition of future extensions. 211 212Additional features not supported in the base command will be advertised 213as the value of the command in the capability advertisement in the form 214of a space separated list of features: "<command>=<feature 1> <feature 2>" 215 216A `fetch` request can take the following arguments: 217 218 want <oid> 219 Indicates to the server an object which the client wants to 220 retrieve. Wants can be anything and are not limited to 221 advertised objects. 222 223 have <oid> 224 Indicates to the server an object which the client has locally. 225 This allows the server to make a packfile which only contains 226 the objects that the client needs. Multiple 'have' lines can be 227 supplied. 228 229 done 230 Indicates to the server that negotiation should terminate (or 231 not even begin if performing a clone) and that the server should 232 use the information supplied in the request to construct the 233 packfile. 234 235 thin-pack 236 Request that a thin pack be sent, which is a pack with deltas 237 which reference base objects not contained within the pack (but 238 are known to exist at the receiving end). This can reduce the 239 network traffic significantly, but it requires the receiving end 240 to know how to "thicken" these packs by adding the missing bases 241 to the pack. 242 243 no-progress 244 Request that progress information that would normally be sent on 245 side-band channel 2, during the packfile transfer, should not be 246 sent. However, the side-band channel 3 is still used for error 247 responses. 248 249 include-tag 250 Request that annotated tags should be sent if the objects they 251 point to are being sent. 252 253 ofs-delta 254 Indicate that the client understands PACKv2 with delta referring 255 to its base by position in pack rather than by an oid. That is, 256 they can read OBJ_OFS_DELTA (ake type 6) in a packfile. 257 258If the 'shallow' feature is advertised the following arguments can be 259included in the clients request as well as the potential addition of the 260'shallow-info' section in the server's response as explained below. 261 262 shallow <oid> 263 A client must notify the server of all commits for which it only 264 has shallow copies (meaning that it doesn't have the parents of 265 a commit) by supplying a 'shallow <oid>' line for each such 266 object so that the server is aware of the limitations of the 267 client's history. This is so that the server is aware that the 268 client may not have all objects reachable from such commits. 269 270 deepen <depth> 271 Requests that the fetch/clone should be shallow having a commit 272 depth of <depth> relative to the remote side. 273 274 deepen-relative 275 Requests that the semantics of the "deepen" command be changed 276 to indicate that the depth requested is relative to the client's 277 current shallow boundary, instead of relative to the requested 278 commits. 279 280 deepen-since <timestamp> 281 Requests that the shallow clone/fetch should be cut at a 282 specific time, instead of depth. Internally it's equivalent to 283 doing "git rev-list --max-age=<timestamp>". Cannot be used with 284 "deepen". 285 286 deepen-not <rev> 287 Requests that the shallow clone/fetch should be cut at a 288 specific revision specified by '<rev>', instead of a depth. 289 Internally it's equivalent of doing "git rev-list --not <rev>". 290 Cannot be used with "deepen", but can be used with 291 "deepen-since". 292 293If the 'filter' feature is advertised, the following argument can be 294included in the client's request: 295 296 filter <filter-spec> 297 Request that various objects from the packfile be omitted 298 using one of several filtering techniques. These are intended 299 for use with partial clone and partial fetch operations. See 300 `rev-list` for possible "filter-spec" values. 301 302The response of `fetch` is broken into a number of sections separated by 303delimiter packets (0001), with each section beginning with its section 304header. 305 306 output = *section 307 section = (acknowledgments | shallow-info | packfile) 308 (flush-pkt | delim-pkt) 309 310 acknowledgments = PKT-LINE("acknowledgments" LF) 311 (nak | *ack) 312 (ready) 313 ready = PKT-LINE("ready" LF) 314 nak = PKT-LINE("NAK" LF) 315 ack = PKT-LINE("ACK" SP obj-id LF) 316 317 shallow-info = PKT-LINE("shallow-info" LF) 318 *PKT-LINE((shallow | unshallow) LF) 319 shallow = "shallow" SP obj-id 320 unshallow = "unshallow" SP obj-id 321 322 packfile = PKT-LINE("packfile" LF) 323 *PKT-LINE(%x01-03 *%x00-ff) 324 325 acknowledgments section 326 * If the client determines that it is finished with negotiations 327 by sending a "done" line, the acknowledgments sections MUST be 328 omitted from the server's response. 329 330 * Always begins with the section header "acknowledgments" 331 332 * The server will respond with "NAK" if none of the object ids sent 333 as have lines were common. 334 335 * The server will respond with "ACK obj-id" for all of the 336 object ids sent as have lines which are common. 337 338 * A response cannot have both "ACK" lines as well as a "NAK" 339 line. 340 341 * The server will respond with a "ready" line indicating that 342 the server has found an acceptable common base and is ready to 343 make and send a packfile (which will be found in the packfile 344 section of the same response) 345 346 * If the server has found a suitable cut point and has decided 347 to send a "ready" line, then the server can decide to (as an 348 optimization) omit any "ACK" lines it would have sent during 349 its response. This is because the server will have already 350 determined the objects it plans to send to the client and no 351 further negotiation is needed. 352 353 shallow-info section 354 * If the client has requested a shallow fetch/clone, a shallow 355 client requests a fetch or the server is shallow then the 356 server's response may include a shallow-info section. The 357 shallow-info section will be included if (due to one of the 358 above conditions) the server needs to inform the client of any 359 shallow boundaries or adjustments to the clients already 360 existing shallow boundaries. 361 362 * Always begins with the section header "shallow-info" 363 364 * If a positive depth is requested, the server will compute the 365 set of commits which are no deeper than the desired depth. 366 367 * The server sends a "shallow obj-id" line for each commit whose 368 parents will not be sent in the following packfile. 369 370 * The server sends an "unshallow obj-id" line for each commit 371 which the client has indicated is shallow, but is no longer 372 shallow as a result of the fetch (due to its parents being 373 sent in the following packfile). 374 375 * The server MUST NOT send any "unshallow" lines for anything 376 which the client has not indicated was shallow as a part of 377 its request. 378 379 * This section is only included if a packfile section is also 380 included in the response. 381 382 packfile section 383 * This section is only included if the client has sent 'want' 384 lines in its request and either requested that no more 385 negotiation be done by sending 'done' or if the server has 386 decided it has found a sufficient cut point to produce a 387 packfile. 388 389 * Always begins with the section header "packfile" 390 391 * The transmission of the packfile begins immediately after the 392 section header 393 394 * The data transfer of the packfile is always multiplexed, using 395 the same semantics of the 'side-band-64k' capability from 396 protocol version 1. This means that each packet, during the 397 packfile data stream, is made up of a leading 4-byte pkt-line 398 length (typical of the pkt-line format), followed by a 1-byte 399 stream code, followed by the actual data. 400 401 The stream code can be one of: 402 1 - pack data 403 2 - progress messages 404 3 - fatal error message just before stream aborts 405 406 server-option 407~~~~~~~~~~~~~~~ 408 409If advertised, indicates that any number of server specific options can be 410included in a request. This is done by sending each option as a 411"server-option=<option>" capability line in the capability-list section of 412a request. 413 414The provided options must not contain a NUL or LF character.