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. 257 258 shallow <oid> 259 A client must notify the server of all commits for which it only 260 has shallow copies (meaning that it doesn't have the parents of 261 a commit) by supplying a 'shallow <oid>' line for each such 262 object so that the server is aware of the limitations of the 263 client's history. This is so that the server is aware that the 264 client may not have all objects reachable from such commits. 265 266 deepen <depth> 267 Requests that the fetch/clone should be shallow having a commit 268 depth of <depth> relative to the remote side. 269 270 deepen-relative 271 Requests that the semantics of the "deepen" command be changed 272 to indicate that the depth requested is relative to the client's 273 current shallow boundary, instead of relative to the requested 274 commits. 275 276 deepen-since <timestamp> 277 Requests that the shallow clone/fetch should be cut at a 278 specific time, instead of depth. Internally it's equivalent to 279 doing "git rev-list --max-age=<timestamp>". Cannot be used with 280 "deepen". 281 282 deepen-not <rev> 283 Requests that the shallow clone/fetch should be cut at a 284 specific revision specified by '<rev>', instead of a depth. 285 Internally it's equivalent of doing "git rev-list --not <rev>". 286 Cannot be used with "deepen", but can be used with 287 "deepen-since". 288 289The response of `fetch` is broken into a number of sections separated by 290delimiter packets (0001), with each section beginning with its section 291header. 292 293 output = *section 294 section = (acknowledgments | shallow-info | packfile) 295 (flush-pkt | delim-pkt) 296 297 acknowledgments = PKT-LINE("acknowledgments" LF) 298 (nak | *ack) 299 (ready) 300 ready = PKT-LINE("ready" LF) 301 nak = PKT-LINE("NAK" LF) 302 ack = PKT-LINE("ACK" SP obj-id LF) 303 304 shallow-info = PKT-LINE("shallow-info" LF) 305 *PKT-LINE((shallow | unshallow) LF) 306 shallow = "shallow" SP obj-id 307 unshallow = "unshallow" SP obj-id 308 309 packfile = PKT-LINE("packfile" LF) 310 *PKT-LINE(%x01-03 *%x00-ff) 311 312 acknowledgments section 313 * If the client determines that it is finished with negotiations 314 by sending a "done" line, the acknowledgments sections MUST be 315 omitted from the server's response. 316 317 * Always begins with the section header "acknowledgments" 318 319 * The server will respond with "NAK" if none of the object ids sent 320 as have lines were common. 321 322 * The server will respond with "ACK obj-id" for all of the 323 object ids sent as have lines which are common. 324 325 * A response cannot have both "ACK" lines as well as a "NAK" 326 line. 327 328 * The server will respond with a "ready" line indicating that 329 the server has found an acceptable common base and is ready to 330 make and send a packfile (which will be found in the packfile 331 section of the same response) 332 333 * If the server has found a suitable cut point and has decided 334 to send a "ready" line, then the server can decide to (as an 335 optimization) omit any "ACK" lines it would have sent during 336 its response. This is because the server will have already 337 determined the objects it plans to send to the client and no 338 further negotiation is needed. 339 340 shallow-info section 341 If the client has requested a shallow fetch/clone, a shallow 342 client requests a fetch or the server is shallow then the 343 server's response may include a shallow-info section. The 344 shallow-info section will be included if (due to one of the 345 above conditions) the server needs to inform the client of any 346 shallow boundaries or adjustments to the clients already 347 existing shallow boundaries. 348 349 * Always begins with the section header "shallow-info" 350 351 * If a positive depth is requested, the server will compute the 352 set of commits which are no deeper than the desired depth. 353 354 * The server sends a "shallow obj-id" line for each commit whose 355 parents will not be sent in the following packfile. 356 357 * The server sends an "unshallow obj-id" line for each commit 358 which the client has indicated is shallow, but is no longer 359 shallow as a result of the fetch (due to its parents being 360 sent in the following packfile). 361 362 * The server MUST NOT send any "unshallow" lines for anything 363 which the client has not indicated was shallow as a part of 364 its request. 365 366 * This section is only included if a packfile section is also 367 included in the response. 368 369 packfile section 370 * This section is only included if the client has sent 'want' 371 lines in its request and either requested that no more 372 negotiation be done by sending 'done' or if the server has 373 decided it has found a sufficient cut point to produce a 374 packfile. 375 376 * Always begins with the section header "packfile" 377 378 * The transmission of the packfile begins immediately after the 379 section header 380 381 * The data transfer of the packfile is always multiplexed, using 382 the same semantics of the 'side-band-64k' capability from 383 protocol version 1. This means that each packet, during the 384 packfile data stream, is made up of a leading 4-byte pkt-line 385 length (typical of the pkt-line format), followed by a 1-byte 386 stream code, followed by the actual data. 387 388 The stream code can be one of: 389 1 - pack data 390 2 - progress messages 391 3 - fatal error message just before stream aborts