Documentation/git-remote-helpers: explain how import works with multiple refs
[git/git.git] / Documentation / git-remote-helpers.txt
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1git-remote-helpers(1)
2=====================
3
4NAME
5----
00b84e9d 6git-remote-helpers - Helper programs to interact with remote repositories
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7
8SYNOPSIS
9--------
7791a1d9 10[verse]
b6c8d2d6 11'git remote-<transport>' <repository> [<URL>]
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12
13DESCRIPTION
14-----------
15
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16Remote helper programs are normally not used directly by end users,
17but they are invoked by git when it needs to interact with remote
18repositories git does not support natively. A given helper will
19implement a subset of the capabilities documented here. When git
20needs to interact with a repository using a remote helper, it spawns
21the helper as an independent process, sends commands to the helper's
22standard input, and expects results from the helper's standard
23output. Because a remote helper runs as an independent process from
24git, there is no need to re-link git to add a new helper, nor any
25need to link the helper with the implementation of git.
26
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27Every helper must support the "capabilities" command, which git
28uses to determine what other commands the helper will accept. Those
29other commands can be used to discover and update remote refs,
30transport objects between the object database and the remote repository,
31and update the local object store.
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32
33Git comes with a "curl" family of remote helpers, that handle various
34transport protocols, such as 'git-remote-http', 'git-remote-https',
35'git-remote-ftp' and 'git-remote-ftps'. They implement the capabilities
36'fetch', 'option', and 'push'.
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38INPUT FORMAT
39------------
40
41Git sends the remote helper a list of commands on standard input, one
42per line. The first command is always the 'capabilities' command, in
43response to which the remote helper must print a list of the
44capabilities it supports (see below) followed by a blank line. The
45response to the capabilities command determines what commands Git uses
46in the remainder of the command stream.
47
48The command stream is terminated by a blank line. In some cases
49(indicated in the documentation of the relevant commands), this blank
50line is followed by a payload in some other protocol (e.g., the pack
51protocol), while in others it indicates the end of input.
52
53Capabilities
54~~~~~~~~~~~~
55
56Each remote helper is expected to support only a subset of commands.
57The operations a helper supports are declared to git in the response
58to the `capabilities` command (see COMMANDS, below).
59
60'option'::
61 For specifying settings like `verbosity` (how much output to
62 write to stderr) and `depth` (how much history is wanted in the
63 case of a shallow clone) that affect how other commands are
64 carried out.
65
66'connect'::
67 For fetching and pushing using git's native packfile protocol
68 that requires a bidirectional, full-duplex connection.
69
70'push'::
71 For listing remote refs and pushing specified objects from the
72 local object store to remote refs.
73
74'fetch'::
75 For listing remote refs and fetching the associated history to
76 the local object store.
77
78'import'::
79 For listing remote refs and fetching the associated history as
80 a fast-import stream.
81
82'refspec' <refspec>::
83 This modifies the 'import' capability, allowing the produced
84 fast-import stream to modify refs in a private namespace
85 instead of writing to refs/heads or refs/remotes directly.
86 It is recommended that all importers providing the 'import'
87 capability use this.
88+
89A helper advertising the capability
90`refspec refs/heads/{asterisk}:refs/svn/origin/branches/{asterisk}`
91is saying that, when it is asked to `import refs/heads/topic`, the
92stream it outputs will update the `refs/svn/origin/branches/topic`
93ref.
94+
95This capability can be advertised multiple times. The first
96applicable refspec takes precedence. The left-hand of refspecs
97advertised with this capability must cover all refs reported by
98the list command. If no 'refspec' capability is advertised,
99there is an implied `refspec {asterisk}:{asterisk}`.
100
101Capabilities for Pushing
102~~~~~~~~~~~~~~~~~~~~~~~~
103'connect'::
104 Can attempt to connect to 'git receive-pack' (for pushing),
105 'git upload-pack', etc for communication using the
106 packfile protocol.
107+
108Supported commands: 'connect'.
109
110'push'::
111 Can discover remote refs and push local commits and the
112 history leading up to them to new or existing remote refs.
113+
114Supported commands: 'list for-push', 'push'.
115
116If a helper advertises both 'connect' and 'push', git will use
117'connect' if possible and fall back to 'push' if the helper requests
118so when connecting (see the 'connect' command under COMMANDS).
119
120Capabilities for Fetching
121~~~~~~~~~~~~~~~~~~~~~~~~~
122'connect'::
123 Can try to connect to 'git upload-pack' (for fetching),
124 'git receive-pack', etc for communication using the
125 packfile protocol.
126+
127Supported commands: 'connect'.
128
129'fetch'::
130 Can discover remote refs and transfer objects reachable from
131 them to the local object store.
132+
133Supported commands: 'list', 'fetch'.
134
135'import'::
136 Can discover remote refs and output objects reachable from
137 them as a stream in fast-import format.
138+
139Supported commands: 'list', 'import'.
140
141If a helper advertises 'connect', git will use it if possible and
142fall back to another capability if the helper requests so when
143connecting (see the 'connect' command under COMMANDS).
144When choosing between 'fetch' and 'import', git prefers 'fetch'.
145Other frontends may have some other order of preference.
146
147'refspec' <refspec>::
148 This modifies the 'import' capability.
149+
150A helper advertising
151`refspec refs/heads/{asterisk}:refs/svn/origin/branches/{asterisk}`
152in its capabilities is saying that, when it handles
153`import refs/heads/topic`, the stream it outputs will update the
154`refs/svn/origin/branches/topic` ref.
155+
156This capability can be advertised multiple times. The first
157applicable refspec takes precedence. The left-hand of refspecs
158advertised with this capability must cover all refs reported by
159the list command. If no 'refspec' capability is advertised,
160there is an implied `refspec {asterisk}:{asterisk}`.
161
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162INVOCATION
163----------
164
165Remote helper programs are invoked with one or (optionally) two
166arguments. The first argument specifies a remote repository as in git;
167it is either the name of a configured remote or a URL. The second
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168argument specifies a URL; it is usually of the form
169'<transport>://<address>', but any arbitrary string is possible.
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170The 'GIT_DIR' environment variable is set up for the remote helper
171and can be used to determine where to store additional data or from
172which directory to invoke auxiliary git commands.
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173
174When git encounters a URL of the form '<transport>://<address>', where
175'<transport>' is a protocol that it cannot handle natively, it
176automatically invokes 'git remote-<transport>' with the full URL as
177the second argument. If such a URL is encountered directly on the
178command line, the first argument is the same as the second, and if it
179is encountered in a configured remote, the first argument is the name
180of that remote.
181
182A URL of the form '<transport>::<address>' explicitly instructs git to
183invoke 'git remote-<transport>' with '<address>' as the second
184argument. If such a URL is encountered directly on the command line,
185the first argument is '<address>', and if it is encountered in a
186configured remote, the first argument is the name of that remote.
187
188Additionally, when a configured remote has 'remote.<name>.vcs' set to
189'<transport>', git explicitly invokes 'git remote-<transport>' with
190'<name>' as the first argument. If set, the second argument is
191'remote.<name>.url'; otherwise, the second argument is omitted.
192
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193COMMANDS
194--------
195
196Commands are given by the caller on the helper's standard input, one per line.
197
198'capabilities'::
199 Lists the capabilities of the helper, one per line, ending
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200 with a blank line. Each capability may be preceded with '*',
201 which marks them mandatory for git version using the remote
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202 helper to understand (unknown mandatory capability is fatal
203 error).
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204
205'list'::
206 Lists the refs, one per line, in the format "<value> <name>
207 [<attr> ...]". The value may be a hex sha1 hash, "@<dest>" for
208 a symref, or "?" to indicate that the helper could not get the
209 value of the ref. A space-separated list of attributes follows
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210 the name; unrecognized attributes are ignored. The list ends
211 with a blank line.
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212+
213If 'push' is supported this may be called as 'list for-push'
214to obtain the current refs prior to sending one or more 'push'
215commands to the helper.
6eb996b5 216
ef08ef9e 217'option' <name> <value>::
d43427d3 218 Sets the transport helper option <name> to <value>. Outputs a
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219 single line containing one of 'ok' (option successfully set),
220 'unsupported' (option not recognized) or 'error <msg>'
d43427d3 221 (option <name> is supported but <value> is not valid
ef08ef9e 222 for it). Options should be set before other commands,
d43427d3 223 and may influence the behavior of those commands.
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224+
225Supported if the helper has the "option" capability.
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226
227'fetch' <sha1> <name>::
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228 Fetches the given object, writing the necessary objects
229 to the database. Fetch commands are sent in a batch, one
d43427d3 230 per line, terminated with a blank line.
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231 Outputs a single blank line when all fetch commands in the
232 same batch are complete. Only objects which were reported
233 in the ref list with a sha1 may be fetched this way.
234+
235Optionally may output a 'lock <file>' line indicating a file under
236GIT_DIR/objects/pack which is keeping a pack until refs can be
237suitably updated.
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238+
239Supported if the helper has the "fetch" capability.
240
ae4efe19 241'push' +<src>:<dst>::
d43427d3 242 Pushes the given local <src> commit or branch to the
ae4efe19 243 remote branch described by <dst>. A batch sequence of
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244 one or more 'push' commands is terminated with a blank line
245 (if there is only one reference to push, a single 'push' command
246 is followed by a blank line). For example, the following would
247 be two batches of 'push', the first asking the remote-helper
248 to push the local ref 'master' to the remote ref 'master' and
249 the local 'HEAD' to the remote 'branch', and the second
250 asking to push ref 'foo' to ref 'bar' (forced update requested
251 by the '+').
252+
253------------
254push refs/heads/master:refs/heads/master
255push HEAD:refs/heads/branch
256\n
257push +refs/heads/foo:refs/heads/bar
258\n
259------------
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260+
261Zero or more protocol options may be entered after the last 'push'
262command, before the batch's terminating blank line.
263+
264When the push is complete, outputs one or more 'ok <dst>' or
265'error <dst> <why>?' lines to indicate success or failure of
266each pushed ref. The status report output is terminated by
267a blank line. The option field <why> may be quoted in a C
268style string if it contains an LF.
269+
270Supported if the helper has the "push" capability.
271
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272'import' <name>::
273 Produces a fast-import stream which imports the current value
274 of the named ref. It may additionally import other refs as
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275 needed to construct the history efficiently. The script writes
276 to a helper-specific private namespace. The value of the named
277 ref should be written to a location in this namespace derived
278 by applying the refspecs from the "refspec" capability to the
279 name of the ref.
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281Especially useful for interoperability with a foreign versioning
282system.
283+
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284Just like 'push', a batch sequence of one or more 'import' is
285terminated with a blank line. For each batch of 'import', the remote
286helper should produce a fast-import stream terminated by a 'done'
287command.
288+
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289Supported if the helper has the "import" capability.
290
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291'connect' <service>::
292 Connects to given service. Standard input and standard output
293 of helper are connected to specified service (git prefix is
294 included in service name so e.g. fetching uses 'git-upload-pack'
295 as service) on remote side. Valid replies to this command are
296 empty line (connection established), 'fallback' (no smart
297 transport support, fall back to dumb transports) and just
298 exiting with error message printed (can't connect, don't
299 bother trying to fall back). After line feed terminating the
300 positive (empty) response, the output of service starts. After
301 the connection ends, the remote helper exits.
302+
303Supported if the helper has the "connect" capability.
304
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305If a fatal error occurs, the program writes the error message to
306stderr and exits. The caller should expect that a suitable error
307message has been printed if the child closes the connection without
308completing a valid response for the current command.
309
310Additional commands may be supported, as may be determined from
311capabilities reported by the helper.
312
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313REF LIST ATTRIBUTES
314-------------------
315
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316'for-push'::
317 The caller wants to use the ref list to prepare push
318 commands. A helper might chose to acquire the ref list by
319 opening a different type of connection to the destination.
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321'unchanged'::
322 This ref is unchanged since the last import or fetch, although
323 the helper cannot necessarily determine what value that produced.
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325OPTIONS
326-------
3b0d2405 327'option verbosity' <n>::
d43427d3 328 Changes the verbosity of messages displayed by the helper.
3b0d2405 329 A value of 0 for <n> means that processes operate
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330 quietly, and the helper produces only error output.
331 1 is the default level of verbosity, and higher values
3b0d2405 332 of <n> correspond to the number of -v flags passed on the
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333 command line.
334
335'option progress' \{'true'|'false'\}::
d43427d3 336 Enables (or disables) progress messages displayed by the
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337 transport helper during a command.
338
339'option depth' <depth>::
d43427d3 340 Deepens the history of a shallow repository.
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341
342'option followtags' \{'true'|'false'\}::
343 If enabled the helper should automatically fetch annotated
344 tag objects if the object the tag points at was transferred
345 during the fetch command. If the tag is not fetched by
346 the helper a second fetch command will usually be sent to
347 ask for the tag specifically. Some helpers may be able to
348 use this option to avoid a second network connection.
349
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350'option dry-run' \{'true'|'false'\}:
351 If true, pretend the operation completed successfully,
352 but don't actually change any repository data. For most
353 helpers this only applies to the 'push', if supported.
354
fa8c097c 355'option servpath <c-style-quoted-path>'::
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356 Sets service path (--upload-pack, --receive-pack etc.) for
357 next connect. Remote helper may support this option, but
358 must not rely on this option being set before
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359 connect request occurs.
360
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361SEE ALSO
362--------
363linkgit:git-remote[1]
364
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365GIT
366---
367Part of the linkgit:git[1] suite