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1 '\" t
2 .\" Title: gitprotocol-pack
3 .\" Author: [FIXME: author] [see http://www.docbook.org/tdg5/en/html/author]
4 .\" Generator: DocBook XSL Stylesheets vsnapshot <http://docbook.sf.net/>
5 .\" Date: 04/25/2023
6 .\" Manual: Git Manual
7 .\" Source: Git 2.40.1.423.g2807bd2c10
8 .\" Language: English
9 .\"
10 .TH "GITPROTOCOL\-PACK" "5" "04/25/2023" "Git 2\&.40\&.1\&.423\&.g2807bd" "Git Manual"
11 .\" -----------------------------------------------------------------
12 .\" * Define some portability stuff
13 .\" -----------------------------------------------------------------
14 .\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
15 .\" http://bugs.debian.org/507673
16 .\" http://lists.gnu.org/archive/html/groff/2009-02/msg00013.html
17 .\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
18 .ie \n(.g .ds Aq \(aq
19 .el .ds Aq '
20 .\" -----------------------------------------------------------------
21 .\" * set default formatting
22 .\" -----------------------------------------------------------------
23 .\" disable hyphenation
24 .nh
25 .\" disable justification (adjust text to left margin only)
26 .ad l
27 .\" -----------------------------------------------------------------
28 .\" * MAIN CONTENT STARTS HERE *
29 .\" -----------------------------------------------------------------
30 .SH "NAME"
31 gitprotocol-pack \- How packs are transferred over\-the\-wire
32 .SH "SYNOPSIS"
33 .sp
34 .nf
35 <over\-the\-wire\-protocol>
36 .fi
37 .sp
38 .SH "DESCRIPTION"
39 .sp
40 Git supports transferring data in packfiles over the ssh://, git://, http:// and file:// transports\&. There exist two sets of protocols, one for pushing data from a client to a server and another for fetching data from a server to a client\&. The three transports (ssh, git, file) use the same protocol to transfer data\&. http is documented in \fBgitprotocol-http\fR(5)\&.
41 .sp
42 The processes invoked in the canonical Git implementation are \fIupload\-pack\fR on the server side and \fIfetch\-pack\fR on the client side for fetching data; then \fIreceive\-pack\fR on the server and \fIsend\-pack\fR on the client for pushing data\&. The protocol functions to have a server tell a client what is currently on the server, then for the two to negotiate the smallest amount of data to send in order to fully update one or the other\&.
43 .SH "PKT\-LINE FORMAT"
44 .sp
45 The descriptions below build on the pkt\-line format described in \fBgitprotocol-common\fR(5)\&. When the grammar indicate \fBPKT\-LINE(\&.\&.\&.)\fR, unless otherwise noted the usual pkt\-line LF rules apply: the sender SHOULD include a LF, but the receiver MUST NOT complain if it is not present\&.
46 .sp
47 An error packet is a special pkt\-line that contains an error string\&.
48 .sp
49 .if n \{\
50 .RS 4
51 .\}
52 .nf
53 error\-line = PKT\-LINE("ERR" SP explanation\-text)
54 .fi
55 .if n \{\
56 .RE
57 .\}
58 .sp
59 .sp
60 Throughout the protocol, where \fBPKT\-LINE(\&.\&.\&.)\fR is expected, an error packet MAY be sent\&. Once this packet is sent by a client or a server, the data transfer process defined in this protocol is terminated\&.
61 .SH "TRANSPORTS"
62 .sp
63 There are three transports over which the packfile protocol is initiated\&. The Git transport is a simple, unauthenticated server that takes the command (almost always \fIupload\-pack\fR, though Git servers can be configured to be globally writable, in which \fIreceive\- pack\fR initiation is also allowed) with which the client wishes to communicate and executes it and connects it to the requesting process\&.
64 .sp
65 In the SSH transport, the client just runs the \fIupload\-pack\fR or \fIreceive\-pack\fR process on the server over the SSH protocol and then communicates with that invoked process over the SSH connection\&.
66 .sp
67 The file:// transport runs the \fIupload\-pack\fR or \fIreceive\-pack\fR process locally and communicates with it over a pipe\&.
68 .SH "EXTRA PARAMETERS"
69 .sp
70 The protocol provides a mechanism in which clients can send additional information in its first message to the server\&. These are called "Extra Parameters", and are supported by the Git, SSH, and HTTP protocols\&.
71 .sp
72 Each Extra Parameter takes the form of \fB<key>=<value>\fR or \fB<key>\fR\&.
73 .sp
74 Servers that receive any such Extra Parameters MUST ignore all unrecognized keys\&. Currently, the only Extra Parameter recognized is "version" with a value of \fI1\fR or \fI2\fR\&. See \fBgitprotocol-v2\fR(5) for more information on protocol version 2\&.
75 .SH "GIT TRANSPORT"
76 .sp
77 The Git transport starts off by sending the command and repository on the wire using the pkt\-line format, followed by a NUL byte and a hostname parameter, terminated by a NUL byte\&.
78 .sp
79 .if n \{\
80 .RS 4
81 .\}
82 .nf
83 0033git\-upload\-pack /project\&.git\e0host=myserver\&.com\e0
84 .fi
85 .if n \{\
86 .RE
87 .\}
88 .sp
89 The transport may send Extra Parameters by adding an additional NUL byte, and then adding one or more NUL\-terminated strings:
90 .sp
91 .if n \{\
92 .RS 4
93 .\}
94 .nf
95 003egit\-upload\-pack /project\&.git\e0host=myserver\&.com\e0\e0version=1\e0
96 .fi
97 .if n \{\
98 .RE
99 .\}
100 .sp
101 .if n \{\
102 .RS 4
103 .\}
104 .nf
105 git\-proto\-request = request\-command SP pathname NUL
106 [ host\-parameter NUL ] [ NUL extra\-parameters ]
107 request\-command = "git\-upload\-pack" / "git\-receive\-pack" /
108 "git\-upload\-archive" ; case sensitive
109 pathname = *( %x01\-ff ) ; exclude NUL
110 host\-parameter = "host=" hostname [ ":" port ]
111 extra\-parameters = 1*extra\-parameter
112 extra\-parameter = 1*( %x01\-ff ) NUL
113 .fi
114 .if n \{\
115 .RE
116 .\}
117 .sp
118 host\-parameter is used for the git\-daemon name based virtual hosting\&. See \-\-interpolated\-path option to git daemon, with the %H/%CH format characters\&.
119 .sp
120 Basically what the Git client is doing to connect to an \fIupload\-pack\fR process on the server side over the Git protocol is this:
121 .sp
122 .if n \{\
123 .RS 4
124 .\}
125 .nf
126 $ echo \-e \-n \e
127 "003agit\-upload\-pack /schacon/gitbook\&.git\e0host=example\&.com\e0" |
128 nc \-v example\&.com 9418
129 .fi
130 .if n \{\
131 .RE
132 .\}
133 .SH "SSH TRANSPORT"
134 .sp
135 Initiating the upload\-pack or receive\-pack processes over SSH is executing the binary on the server via SSH remote execution\&. It is basically equivalent to running this:
136 .sp
137 .if n \{\
138 .RS 4
139 .\}
140 .nf
141 $ ssh git\&.example\&.com "git\-upload\-pack \*(Aq/project\&.git\*(Aq"
142 .fi
143 .if n \{\
144 .RE
145 .\}
146 .sp
147 For a server to support Git pushing and pulling for a given user over SSH, that user needs to be able to execute one or both of those commands via the SSH shell that they are provided on login\&. On some systems, that shell access is limited to only being able to run those two commands, or even just one of them\&.
148 .sp
149 In an ssh:// format URI, it\(cqs absolute in the URI, so the \fI/\fR after the host name (or port number) is sent as an argument, which is then read by the remote git\-upload\-pack exactly as is, so it\(cqs effectively an absolute path in the remote filesystem\&.
150 .sp
151 .if n \{\
152 .RS 4
153 .\}
154 .nf
155 git clone ssh://user@example\&.com/project\&.git
156 |
157 v
158 ssh user@example\&.com "git\-upload\-pack \*(Aq/project\&.git\*(Aq"
159 .fi
160 .if n \{\
161 .RE
162 .\}
163 .sp
164 In a "user@host:path" format URI, its relative to the user\(cqs home directory, because the Git client will run:
165 .sp
166 .if n \{\
167 .RS 4
168 .\}
169 .nf
170 git clone user@example\&.com:project\&.git
171 |
172 v
173 ssh user@example\&.com "git\-upload\-pack \*(Aqproject\&.git\*(Aq"
174 .fi
175 .if n \{\
176 .RE
177 .\}
178 .sp
179 The exception is if a \fI~\fR is used, in which case we execute it without the leading \fI/\fR\&.
180 .sp
181 .if n \{\
182 .RS 4
183 .\}
184 .nf
185 ssh://user@example\&.com/~alice/project\&.git,
186 |
187 v
188 ssh user@example\&.com "git\-upload\-pack \*(Aq~alice/project\&.git\*(Aq"
189 .fi
190 .if n \{\
191 .RE
192 .\}
193 .sp
194 Depending on the value of the \fBprotocol\&.version\fR configuration variable, Git may attempt to send Extra Parameters as a colon\-separated string in the GIT_PROTOCOL environment variable\&. This is done only if the \fBssh\&.variant\fR configuration variable indicates that the ssh command supports passing environment variables as an argument\&.
195 .sp
196 A few things to remember here:
197 .sp
198 .RS 4
199 .ie n \{\
200 \h'-04'\(bu\h'+03'\c
201 .\}
202 .el \{\
203 .sp -1
204 .IP \(bu 2.3
205 .\}
206 The "command name" is spelled with dash (e\&.g\&. git\-upload\-pack), but this can be overridden by the client;
207 .RE
208 .sp
209 .RS 4
210 .ie n \{\
211 \h'-04'\(bu\h'+03'\c
212 .\}
213 .el \{\
214 .sp -1
215 .IP \(bu 2.3
216 .\}
217 The repository path is always quoted with single quotes\&.
218 .RE
219 .SH "FETCHING DATA FROM A SERVER"
220 .sp
221 When one Git repository wants to get data that a second repository has, the first can \fIfetch\fR from the second\&. This operation determines what data the server has that the client does not then streams that data down to the client in packfile format\&.
222 .SH "REFERENCE DISCOVERY"
223 .sp
224 When the client initially connects the server will immediately respond with a version number (if "version=1" is sent as an Extra Parameter), and a listing of each reference it has (all branches and tags) along with the object name that each reference currently points to\&.
225 .sp
226 .if n \{\
227 .RS 4
228 .\}
229 .nf
230 $ echo \-e \-n "0045git\-upload\-pack /schacon/gitbook\&.git\e0host=example\&.com\e0\e0version=1\e0" |
231 nc \-v example\&.com 9418
232 000eversion 1
233 00887217a7c7e582c46cec22a130adf4b9d7d950fba0 HEAD\e0multi_ack thin\-pack
234 side\-band side\-band\-64k ofs\-delta shallow no\-progress include\-tag
235 00441d3fcd5ced445d1abc402225c0b8a1299641f497 refs/heads/integration
236 003f7217a7c7e582c46cec22a130adf4b9d7d950fba0 refs/heads/master
237 003cb88d2441cac0977faf98efc80305012112238d9d refs/tags/v0\&.9
238 003c525128480b96c89e6418b1e40909bf6c5b2d580f refs/tags/v1\&.0
239 003fe92df48743b7bc7d26bcaabfddde0a1e20cae47c refs/tags/v1\&.0^{}
240 0000
241 .fi
242 .if n \{\
243 .RE
244 .\}
245 .sp
246 The returned response is a pkt\-line stream describing each ref and its current value\&. The stream MUST be sorted by name according to the C locale ordering\&.
247 .sp
248 If HEAD is a valid ref, HEAD MUST appear as the first advertised ref\&. If HEAD is not a valid ref, HEAD MUST NOT appear in the advertisement list at all, but other refs may still appear\&.
249 .sp
250 The stream MUST include capability declarations behind a NUL on the first ref\&. The peeled value of a ref (that is "ref^{}") MUST be immediately after the ref itself, if presented\&. A conforming server MUST peel the ref if it\(cqs an annotated tag\&.
251 .sp
252 .if n \{\
253 .RS 4
254 .\}
255 .nf
256 advertised\-refs = *1("version 1")
257 (no\-refs / list\-of\-refs)
258 *shallow
259 flush\-pkt
261 no\-refs = PKT\-LINE(zero\-id SP "capabilities^{}"
262 NUL capability\-list)
264 list\-of\-refs = first\-ref *other\-ref
265 first\-ref = PKT\-LINE(obj\-id SP refname
266 NUL capability\-list)
268 other\-ref = PKT\-LINE(other\-tip / other\-peeled)
269 other\-tip = obj\-id SP refname
270 other\-peeled = obj\-id SP refname "^{}"
272 shallow = PKT\-LINE("shallow" SP obj\-id)
274 capability\-list = capability *(SP capability)
275 capability = 1*(LC_ALPHA / DIGIT / "\-" / "_")
276 LC_ALPHA = %x61\-7A
277 .fi
278 .if n \{\
279 .RE
280 .\}
281 .sp
282 .sp
283 Server and client MUST use lowercase for obj\-id, both MUST treat obj\-id as case\-insensitive\&.
284 .sp
285 See protocol\-capabilities\&.txt for a list of allowed server capabilities and descriptions\&.
286 .SH "PACKFILE NEGOTIATION"
287 .sp
288 After reference and capabilities discovery, the client can decide to terminate the connection by sending a flush\-pkt, telling the server it can now gracefully terminate, and disconnect, when it does not need any pack data\&. This can happen with the ls\-remote command, and also can happen when the client already is up to date\&.
289 .sp
290 Otherwise, it enters the negotiation phase, where the client and server determine what the minimal packfile necessary for transport is, by telling the server what objects it wants, its shallow objects (if any), and the maximum commit depth it wants (if any)\&. The client will also send a list of the capabilities it wants to be in effect, out of what the server said it could do with the first \fIwant\fR line\&.
291 .sp
292 .if n \{\
293 .RS 4
294 .\}
295 .nf
296 upload\-request = want\-list
297 *shallow\-line
298 *1depth\-request
299 [filter\-request]
300 flush\-pkt
302 want\-list = first\-want
303 *additional\-want
305 shallow\-line = PKT\-LINE("shallow" SP obj\-id)
307 depth\-request = PKT\-LINE("deepen" SP depth) /
308 PKT\-LINE("deepen\-since" SP timestamp) /
309 PKT\-LINE("deepen\-not" SP ref)
311 first\-want = PKT\-LINE("want" SP obj\-id SP capability\-list)
312 additional\-want = PKT\-LINE("want" SP obj\-id)
314 depth = 1*DIGIT
316 filter\-request = PKT\-LINE("filter" SP filter\-spec)
317 .fi
318 .if n \{\
319 .RE
320 .\}
321 .sp
322 .sp
323 Clients MUST send all the obj\-ids it wants from the reference discovery phase as \fIwant\fR lines\&. Clients MUST send at least one \fIwant\fR command in the request body\&. Clients MUST NOT mention an obj\-id in a \fIwant\fR command which did not appear in the response obtained through ref discovery\&.
324 .sp
325 The client MUST write all obj\-ids which it only has shallow copies of (meaning that it does not have the parents of a commit) as \fIshallow\fR lines so that the server is aware of the limitations of the client\(cqs history\&.
326 .sp
327 The client now sends the maximum commit history depth it wants for this transaction, which is the number of commits it wants from the tip of the history, if any, as a \fIdeepen\fR line\&. A depth of 0 is the same as not making a depth request\&. The client does not want to receive any commits beyond this depth, nor does it want objects needed only to complete those commits\&. Commits whose parents are not received as a result are defined as shallow and marked as such in the server\&. This information is sent back to the client in the next step\&.
328 .sp
329 The client can optionally request that pack\-objects omit various objects from the packfile using one of several filtering techniques\&. These are intended for use with partial clone and partial fetch operations\&. An object that does not meet a filter\-spec value is omitted unless explicitly requested in a \fIwant\fR line\&. See \fBrev\-list\fR for possible filter\-spec values\&.
330 .sp
331 Once all the \fIwant\(cqs and \*(Aqshallow\(cqs (and optional \*(Aqdeepen\fR) are transferred, clients MUST send a flush\-pkt, to tell the server side that it is done sending the list\&.
332 .sp
333 Otherwise, if the client sent a positive depth request, the server will determine which commits will and will not be shallow and send this information to the client\&. If the client did not request a positive depth, this step is skipped\&.
334 .sp
335 .if n \{\
336 .RS 4
337 .\}
338 .nf
339 shallow\-update = *shallow\-line
340 *unshallow\-line
341 flush\-pkt
343 shallow\-line = PKT\-LINE("shallow" SP obj\-id)
345 unshallow\-line = PKT\-LINE("unshallow" SP obj\-id)
346 .fi
347 .if n \{\
348 .RE
349 .\}
350 .sp
351 .sp
352 If the client has requested a positive depth, the server will compute the set of commits which are no deeper than the desired depth\&. The set of commits start at the client\(cqs wants\&.
353 .sp
354 The server writes \fIshallow\fR lines for each commit whose parents will not be sent as a result\&. The server writes an \fIunshallow\fR line for each commit which the client has indicated is shallow, but is no longer shallow at the currently requested depth (that is, its parents will now be sent)\&. The server MUST NOT mark as unshallow anything which the client has not indicated was shallow\&.
355 .sp
356 Now the client will send a list of the obj\-ids it has using \fIhave\fR lines, so the server can make a packfile that only contains the objects that the client needs\&. In multi_ack mode, the canonical implementation will send up to 32 of these at a time, then will send a flush\-pkt\&. The canonical implementation will skip ahead and send the next 32 immediately, so that there is always a block of 32 "in\-flight on the wire" at a time\&.
357 .sp
358 .if n \{\
359 .RS 4
360 .\}
361 .nf
362 upload\-haves = have\-list
363 compute\-end
365 have\-list = *have\-line
366 have\-line = PKT\-LINE("have" SP obj\-id)
367 compute\-end = flush\-pkt / PKT\-LINE("done")
368 .fi
369 .if n \{\
370 .RE
371 .\}
372 .sp
373 .sp
374 If the server reads \fIhave\fR lines, it then will respond by ACKing any of the obj\-ids the client said it had that the server also has\&. The server will ACK obj\-ids differently depending on which ack mode is chosen by the client\&.
375 .sp
376 In multi_ack mode:
377 .sp
378 .RS 4
379 .ie n \{\
380 \h'-04'\(bu\h'+03'\c
381 .\}
382 .el \{\
383 .sp -1
384 .IP \(bu 2.3
385 .\}
386 the server will respond with
387 \fIACK obj\-id continue\fR
388 for any common commits\&.
389 .RE
390 .sp
391 .RS 4
392 .ie n \{\
393 \h'-04'\(bu\h'+03'\c
394 .\}
395 .el \{\
396 .sp -1
397 .IP \(bu 2.3
398 .\}
399 once the server has found an acceptable common base commit and is ready to make a packfile, it will blindly ACK all
400 \fIhave\fR
401 obj\-ids back to the client\&.
402 .RE
403 .sp
404 .RS 4
405 .ie n \{\
406 \h'-04'\(bu\h'+03'\c
407 .\}
408 .el \{\
409 .sp -1
410 .IP \(bu 2.3
411 .\}
412 the server will then send a
413 \fINAK\fR
414 and then wait for another response from the client \- either a
415 \fIdone\fR
416 or another list of
417 \fIhave\fR
418 lines\&.
419 .RE
420 .sp
421 In multi_ack_detailed mode:
422 .sp
423 .RS 4
424 .ie n \{\
425 \h'-04'\(bu\h'+03'\c
426 .\}
427 .el \{\
428 .sp -1
429 .IP \(bu 2.3
430 .\}
431 the server will differentiate the ACKs where it is signaling that it is ready to send data with
432 \fIACK obj\-id ready\fR
433 lines, and signals the identified common commits with
434 \fIACK obj\-id common\fR
435 lines\&.
436 .RE
437 .sp
438 Without either multi_ack or multi_ack_detailed:
439 .sp
440 .RS 4
441 .ie n \{\
442 \h'-04'\(bu\h'+03'\c
443 .\}
444 .el \{\
445 .sp -1
446 .IP \(bu 2.3
447 .\}
448 upload\-pack sends "ACK obj\-id" on the first common object it finds\&. After that it says nothing until the client gives it a "done"\&.
449 .RE
450 .sp
451 .RS 4
452 .ie n \{\
453 \h'-04'\(bu\h'+03'\c
454 .\}
455 .el \{\
456 .sp -1
457 .IP \(bu 2.3
458 .\}
459 upload\-pack sends "NAK" on a flush\-pkt if no common object has been found yet\&. If one has been found, and thus an ACK was already sent, it\(cqs silent on the flush\-pkt\&.
460 .RE
461 .sp
462 After the client has gotten enough ACK responses that it can determine that the server has enough information to send an efficient packfile (in the canonical implementation, this is determined when it has received enough ACKs that it can color everything left in the \-\-date\-order queue as common with the server, or the \-\-date\-order queue is empty), or the client determines that it wants to give up (in the canonical implementation, this is determined when the client sends 256 \fIhave\fR lines without getting any of them ACKed by the server \- meaning there is nothing in common and the server should just send all of its objects), then the client will send a \fIdone\fR command\&. The \fIdone\fR command signals to the server that the client is ready to receive its packfile data\&.
463 .sp
464 However, the 256 limit \fBonly\fR turns on in the canonical client implementation if we have received at least one "ACK %s continue" during a prior round\&. This helps to ensure that at least one common ancestor is found before we give up entirely\&.
465 .sp
466 Once the \fIdone\fR line is read from the client, the server will either send a final \fIACK obj\-id\fR or it will send a \fINAK\fR\&. \fIobj\-id\fR is the object name of the last commit determined to be common\&. The server only sends ACK after \fIdone\fR if there is at least one common base and multi_ack or multi_ack_detailed is enabled\&. The server always sends NAK after \fIdone\fR if there is no common base found\&.
467 .sp
468 Instead of \fIACK\fR or \fINAK\fR, the server may send an error message (for example, if it does not recognize an object in a \fIwant\fR line received from the client)\&.
469 .sp
470 Then the server will start sending its packfile data\&.
471 .sp
472 .if n \{\
473 .RS 4
474 .\}
475 .nf
476 server\-response = *ack_multi ack / nak
477 ack_multi = PKT\-LINE("ACK" SP obj\-id ack_status)
478 ack_status = "continue" / "common" / "ready"
479 ack = PKT\-LINE("ACK" SP obj\-id)
480 nak = PKT\-LINE("NAK")
481 .fi
482 .if n \{\
483 .RE
484 .\}
485 .sp
486 .sp
487 A simple clone may look like this (with no \fIhave\fR lines):
488 .sp
489 .if n \{\
490 .RS 4
491 .\}
492 .nf
493 C: 0054want 74730d410fcb6603ace96f1dc55ea6196122532d multi_ack \e
494 side\-band\-64k ofs\-delta\en
495 C: 0032want 7d1665144a3a975c05f1f43902ddaf084e784dbe\en
496 C: 0032want 5a3f6be755bbb7deae50065988cbfa1ffa9ab68a\en
497 C: 0032want 7e47fe2bd8d01d481f44d7af0531bd93d3b21c01\en
498 C: 0032want 74730d410fcb6603ace96f1dc55ea6196122532d\en
499 C: 0000
500 C: 0009done\en
502 S: 0008NAK\en
503 S: [PACKFILE]
504 .fi
505 .if n \{\
506 .RE
507 .\}
508 .sp
509 .sp
510 An incremental update (fetch) response might look like this:
511 .sp
512 .if n \{\
513 .RS 4
514 .\}
515 .nf
516 C: 0054want 74730d410fcb6603ace96f1dc55ea6196122532d multi_ack \e
517 side\-band\-64k ofs\-delta\en
518 C: 0032want 7d1665144a3a975c05f1f43902ddaf084e784dbe\en
519 C: 0032want 5a3f6be755bbb7deae50065988cbfa1ffa9ab68a\en
520 C: 0000
521 C: 0032have 7e47fe2bd8d01d481f44d7af0531bd93d3b21c01\en
522 C: [30 more have lines]
523 C: 0032have 74730d410fcb6603ace96f1dc55ea6196122532d\en
524 C: 0000
526 S: 003aACK 7e47fe2bd8d01d481f44d7af0531bd93d3b21c01 continue\en
527 S: 003aACK 74730d410fcb6603ace96f1dc55ea6196122532d continue\en
528 S: 0008NAK\en
530 C: 0009done\en
532 S: 0031ACK 74730d410fcb6603ace96f1dc55ea6196122532d\en
533 S: [PACKFILE]
534 .fi
535 .if n \{\
536 .RE
537 .\}
538 .sp
539 .SH "PACKFILE DATA"
540 .sp
541 Now that the client and server have finished negotiation about what the minimal amount of data that needs to be sent to the client is, the server will construct and send the required data in packfile format\&.
542 .sp
543 See \fBgitformat-pack\fR(5) for what the packfile itself actually looks like\&.
544 .sp
545 If \fIside\-band\fR or \fIside\-band\-64k\fR capabilities have been specified by the client, the server will send the packfile data multiplexed\&.
546 .sp
547 Each packet starting with the packet\-line length of the amount of data that follows, followed by a single byte specifying the sideband the following data is coming in on\&.
548 .sp
549 In \fIside\-band\fR mode, it will send up to 999 data bytes plus 1 control code, for a total of up to 1000 bytes in a pkt\-line\&. In \fIside\-band\-64k\fR mode it will send up to 65519 data bytes plus 1 control code, for a total of up to 65520 bytes in a pkt\-line\&.
550 .sp
551 The sideband byte will be a \fI1\fR, \fI2\fR or a \fI3\fR\&. Sideband \fI1\fR will contain packfile data, sideband \fI2\fR will be used for progress information that the client will generally print to stderr and sideband \fI3\fR is used for error information\&.
552 .sp
553 If no \fIside\-band\fR capability was specified, the server will stream the entire packfile without multiplexing\&.
554 .SH "PUSHING DATA TO A SERVER"
555 .sp
556 Pushing data to a server will invoke the \fIreceive\-pack\fR process on the server, which will allow the client to tell it which references it should update and then send all the data the server will need for those new references to be complete\&. Once all the data is received and validated, the server will then update its references to what the client specified\&.
557 .SH "AUTHENTICATION"
558 .sp
559 The protocol itself contains no authentication mechanisms\&. That is to be handled by the transport, such as SSH, before the \fIreceive\-pack\fR process is invoked\&. If \fIreceive\-pack\fR is configured over the Git transport, those repositories will be writable by anyone who can access that port (9418) as that transport is unauthenticated\&.
560 .SH "REFERENCE DISCOVERY"
561 .sp
562 The reference discovery phase is done nearly the same way as it is in the fetching protocol\&. Each reference obj\-id and name on the server is sent in packet\-line format to the client, followed by a flush\-pkt\&. The only real difference is that the capability listing is different \- the only possible values are \fIreport\-status\fR, \fIreport\-status\-v2\fR, \fIdelete\-refs\fR, \fIofs\-delta\fR, \fIatomic\fR and \fIpush\-options\fR\&.
563 .SH "REFERENCE UPDATE REQUEST AND PACKFILE TRANSFER"
564 .sp
565 Once the client knows what references the server is at, it can send a list of reference update requests\&. For each reference on the server that it wants to update, it sends a line listing the obj\-id currently on the server, the obj\-id the client would like to update it to and the name of the reference\&.
566 .sp
567 This list is followed by a flush\-pkt\&.
568 .sp
569 .if n \{\
570 .RS 4
571 .\}
572 .nf
573 update\-requests = *shallow ( command\-list | push\-cert )
575 shallow = PKT\-LINE("shallow" SP obj\-id)
577 command\-list = PKT\-LINE(command NUL capability\-list)
578 *PKT\-LINE(command)
579 flush\-pkt
581 command = create / delete / update
582 create = zero\-id SP new\-id SP name
583 delete = old\-id SP zero\-id SP name
584 update = old\-id SP new\-id SP name
586 old\-id = obj\-id
587 new\-id = obj\-id
589 push\-cert = PKT\-LINE("push\-cert" NUL capability\-list LF)
590 PKT\-LINE("certificate version 0\&.1" LF)
591 PKT\-LINE("pusher" SP ident LF)
592 PKT\-LINE("pushee" SP url LF)
593 PKT\-LINE("nonce" SP nonce LF)
594 *PKT\-LINE("push\-option" SP push\-option LF)
595 PKT\-LINE(LF)
596 *PKT\-LINE(command LF)
597 *PKT\-LINE(gpg\-signature\-lines LF)
598 PKT\-LINE("push\-cert\-end" LF)
600 push\-option = 1*( VCHAR | SP )
601 .fi
602 .if n \{\
603 .RE
604 .\}
605 .sp
606 .sp
607 If the server has advertised the \fIpush\-options\fR capability and the client has specified \fIpush\-options\fR as part of the capability list above, the client then sends its push options followed by a flush\-pkt\&.
608 .sp
609 .if n \{\
610 .RS 4
611 .\}
612 .nf
613 push\-options = *PKT\-LINE(push\-option) flush\-pkt
614 .fi
615 .if n \{\
616 .RE
617 .\}
618 .sp
619 .sp
620 For backwards compatibility with older Git servers, if the client sends a push cert and push options, it MUST send its push options both embedded within the push cert and after the push cert\&. (Note that the push options within the cert are prefixed, but the push options after the cert are not\&.) Both these lists MUST be the same, modulo the prefix\&.
621 .sp
622 After that the packfile that should contain all the objects that the server will need to complete the new references will be sent\&.
623 .sp
624 .if n \{\
625 .RS 4
626 .\}
627 .nf
628 packfile = "PACK" 28*(OCTET)
629 .fi
630 .if n \{\
631 .RE
632 .\}
633 .sp
634 .sp
635 If the receiving end does not support delete\-refs, the sending end MUST NOT ask for delete command\&.
636 .sp
637 If the receiving end does not support push\-cert, the sending end MUST NOT send a push\-cert command\&. When a push\-cert command is sent, command\-list MUST NOT be sent; the commands recorded in the push certificate is used instead\&.
638 .sp
639 The packfile MUST NOT be sent if the only command used is \fIdelete\fR\&.
640 .sp
641 A packfile MUST be sent if either create or update command is used, even if the server already has all the necessary objects\&. In this case the client MUST send an empty packfile\&. The only time this is likely to happen is if the client is creating a new branch or a tag that points to an existing obj\-id\&.
642 .sp
643 The server will receive the packfile, unpack it, then validate each reference that is being updated that it hasn\(cqt changed while the request was being processed (the obj\-id is still the same as the old\-id), and it will run any update hooks to make sure that the update is acceptable\&. If all of that is fine, the server will then update the references\&.
644 .SH "PUSH CERTIFICATE"
645 .sp
646 A push certificate begins with a set of header lines\&. After the header and an empty line, the protocol commands follow, one per line\&. Note that the trailing LF in push\-cert PKT\-LINEs is \fInot\fR optional; it must be present\&.
647 .sp
648 Currently, the following header fields are defined:
649 .PP
650 \fBpusher\fR ident
651 .RS 4
652 Identify the GPG key in "Human Readable Name <\m[blue]\fBemail@address\fR\m[]\&\s-2\u[1]\d\s+2>" format\&.
653 .RE
654 .PP
655 \fBpushee\fR url
656 .RS 4
657 The repository URL (anonymized, if the URL contains authentication material) the user who ran
658 \fBgit push\fR
659 intended to push into\&.
660 .RE
661 .PP
662 \fBnonce\fR nonce
663 .RS 4
664 The
665 \fInonce\fR
666 string the receiving repository asked the pushing user to include in the certificate, to prevent replay attacks\&.
667 .RE
668 .sp
669 The GPG signature lines are a detached signature for the contents recorded in the push certificate before the signature block begins\&. The detached signature is used to certify that the commands were given by the pusher, who must be the signer\&.
670 .SH "REPORT STATUS"
671 .sp
672 After receiving the pack data from the sender, the receiver sends a report if \fIreport\-status\fR or \fIreport\-status\-v2\fR capability is in effect\&. It is a short listing of what happened in that update\&. It will first list the status of the packfile unpacking as either \fIunpack ok\fR or \fIunpack [error]\fR\&. Then it will list the status for each of the references that it tried to update\&. Each line is either \fIok [refname]\fR if the update was successful, or \fIng [refname] [error]\fR if the update was not\&.
673 .sp
674 .if n \{\
675 .RS 4
676 .\}
677 .nf
678 report\-status = unpack\-status
679 1*(command\-status)
680 flush\-pkt
682 unpack\-status = PKT\-LINE("unpack" SP unpack\-result)
683 unpack\-result = "ok" / error\-msg
685 command\-status = command\-ok / command\-fail
686 command\-ok = PKT\-LINE("ok" SP refname)
687 command\-fail = PKT\-LINE("ng" SP refname SP error\-msg)
689 error\-msg = 1*(OCTET) ; where not "ok"
690 .fi
691 .if n \{\
692 .RE
693 .\}
694 .sp
695 .sp
696 The \fIreport\-status\-v2\fR capability extends the protocol by adding new option lines in order to support reporting of reference rewritten by the \fIproc\-receive\fR hook\&. The \fIproc\-receive\fR hook may handle a command for a pseudo\-reference which may create or update one or more references, and each reference may have different name, different new\-oid, and different old\-oid\&.
697 .sp
698 .if n \{\
699 .RS 4
700 .\}
701 .nf
702 report\-status\-v2 = unpack\-status
703 1*(command\-status\-v2)
704 flush\-pkt
706 unpack\-status = PKT\-LINE("unpack" SP unpack\-result)
707 unpack\-result = "ok" / error\-msg
709 command\-status\-v2 = command\-ok\-v2 / command\-fail
710 command\-ok\-v2 = command\-ok
711 *option\-line
713 command\-ok = PKT\-LINE("ok" SP refname)
714 command\-fail = PKT\-LINE("ng" SP refname SP error\-msg)
716 error\-msg = 1*(OCTET) ; where not "ok"
718 option\-line = *1(option\-refname)
719 *1(option\-old\-oid)
720 *1(option\-new\-oid)
721 *1(option\-forced\-update)
723 option\-refname = PKT\-LINE("option" SP "refname" SP refname)
724 option\-old\-oid = PKT\-LINE("option" SP "old\-oid" SP obj\-id)
725 option\-new\-oid = PKT\-LINE("option" SP "new\-oid" SP obj\-id)
726 option\-force = PKT\-LINE("option" SP "forced\-update")
727 .fi
728 .if n \{\
729 .RE
730 .\}
731 .sp
732 .sp
733 Updates can be unsuccessful for a number of reasons\&. The reference can have changed since the reference discovery phase was originally sent, meaning someone pushed in the meantime\&. The reference being pushed could be a non\-fast\-forward reference and the update hooks or configuration could be set to not allow that, etc\&. Also, some references can be updated while others can be rejected\&.
734 .sp
735 An example client/server communication might look like this:
736 .sp
737 .if n \{\
738 .RS 4
739 .\}
740 .nf
741 S: 006274730d410fcb6603ace96f1dc55ea6196122532d refs/heads/local\e0report\-status delete\-refs ofs\-delta\en
742 S: 003e7d1665144a3a975c05f1f43902ddaf084e784dbe refs/heads/debug\en
743 S: 003f74730d410fcb6603ace96f1dc55ea6196122532d refs/heads/master\en
744 S: 003d74730d410fcb6603ace96f1dc55ea6196122532d refs/heads/team\en
745 S: 0000
747 C: 00677d1665144a3a975c05f1f43902ddaf084e784dbe 74730d410fcb6603ace96f1dc55ea6196122532d refs/heads/debug\en
748 C: 006874730d410fcb6603ace96f1dc55ea6196122532d 5a3f6be755bbb7deae50065988cbfa1ffa9ab68a refs/heads/master\en
749 C: 0000
750 C: [PACKDATA]
752 S: 000eunpack ok\en
753 S: 0018ok refs/heads/debug\en
754 S: 002ang refs/heads/master non\-fast\-forward\en
755 .fi
756 .if n \{\
757 .RE
758 .\}
759 .sp
760 .SH "GIT"
761 .sp
762 Part of the \fBgit\fR(1) suite
763 .SH "NOTES"
764 .IP " 1." 4
765 email@address
766 .RS 4
767 \%mailto:email@address
768 .RE