Documentation/git-remote-helpers: explain how import works with multiple refs
[git/git.git] / Documentation / git-remote-helpers.txt
1 git-remote-helpers(1)
2 =====================
3
4 NAME
5 ----
6 git-remote-helpers - Helper programs to interact with remote repositories
7
8 SYNOPSIS
9 --------
10 [verse]
11 'git remote-<transport>' <repository> [<URL>]
12
13 DESCRIPTION
14 -----------
15
16 Remote helper programs are normally not used directly by end users,
17 but they are invoked by git when it needs to interact with remote
18 repositories git does not support natively. A given helper will
19 implement a subset of the capabilities documented here. When git
20 needs to interact with a repository using a remote helper, it spawns
21 the helper as an independent process, sends commands to the helper's
22 standard input, and expects results from the helper's standard
23 output. Because a remote helper runs as an independent process from
24 git, there is no need to re-link git to add a new helper, nor any
25 need to link the helper with the implementation of git.
26
27 Every helper must support the "capabilities" command, which git
28 uses to determine what other commands the helper will accept. Those
29 other commands can be used to discover and update remote refs,
30 transport objects between the object database and the remote repository,
31 and update the local object store.
32
33 Git comes with a "curl" family of remote helpers, that handle various
34 transport 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'.
37
38 INPUT FORMAT
39 ------------
40
41 Git sends the remote helper a list of commands on standard input, one
42 per line. The first command is always the 'capabilities' command, in
43 response to which the remote helper must print a list of the
44 capabilities it supports (see below) followed by a blank line. The
45 response to the capabilities command determines what commands Git uses
46 in the remainder of the command stream.
47
48 The command stream is terminated by a blank line. In some cases
49 (indicated in the documentation of the relevant commands), this blank
50 line is followed by a payload in some other protocol (e.g., the pack
51 protocol), while in others it indicates the end of input.
52
53 Capabilities
54 ~~~~~~~~~~~~
55
56 Each remote helper is expected to support only a subset of commands.
57 The operations a helper supports are declared to git in the response
58 to 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 +
89 A helper advertising the capability
90 `refspec refs/heads/{asterisk}:refs/svn/origin/branches/{asterisk}`
91 is saying that, when it is asked to `import refs/heads/topic`, the
92 stream it outputs will update the `refs/svn/origin/branches/topic`
93 ref.
94 +
95 This capability can be advertised multiple times. The first
96 applicable refspec takes precedence. The left-hand of refspecs
97 advertised with this capability must cover all refs reported by
98 the list command. If no 'refspec' capability is advertised,
99 there is an implied `refspec {asterisk}:{asterisk}`.
100
101 Capabilities 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 +
108 Supported 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 +
114 Supported commands: 'list for-push', 'push'.
115
116 If a helper advertises both 'connect' and 'push', git will use
117 'connect' if possible and fall back to 'push' if the helper requests
118 so when connecting (see the 'connect' command under COMMANDS).
119
120 Capabilities 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 +
127 Supported commands: 'connect'.
128
129 'fetch'::
130 Can discover remote refs and transfer objects reachable from
131 them to the local object store.
132 +
133 Supported 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 +
139 Supported commands: 'list', 'import'.
140
141 If a helper advertises 'connect', git will use it if possible and
142 fall back to another capability if the helper requests so when
143 connecting (see the 'connect' command under COMMANDS).
144 When choosing between 'fetch' and 'import', git prefers 'fetch'.
145 Other frontends may have some other order of preference.
146
147 'refspec' <refspec>::
148 This modifies the 'import' capability.
149 +
150 A helper advertising
151 `refspec refs/heads/{asterisk}:refs/svn/origin/branches/{asterisk}`
152 in 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 +
156 This capability can be advertised multiple times. The first
157 applicable refspec takes precedence. The left-hand of refspecs
158 advertised with this capability must cover all refs reported by
159 the list command. If no 'refspec' capability is advertised,
160 there is an implied `refspec {asterisk}:{asterisk}`.
161
162 INVOCATION
163 ----------
164
165 Remote helper programs are invoked with one or (optionally) two
166 arguments. The first argument specifies a remote repository as in git;
167 it is either the name of a configured remote or a URL. The second
168 argument specifies a URL; it is usually of the form
169 '<transport>://<address>', but any arbitrary string is possible.
170 The 'GIT_DIR' environment variable is set up for the remote helper
171 and can be used to determine where to store additional data or from
172 which directory to invoke auxiliary git commands.
173
174 When git encounters a URL of the form '<transport>://<address>', where
175 '<transport>' is a protocol that it cannot handle natively, it
176 automatically invokes 'git remote-<transport>' with the full URL as
177 the second argument. If such a URL is encountered directly on the
178 command line, the first argument is the same as the second, and if it
179 is encountered in a configured remote, the first argument is the name
180 of that remote.
181
182 A URL of the form '<transport>::<address>' explicitly instructs git to
183 invoke 'git remote-<transport>' with '<address>' as the second
184 argument. If such a URL is encountered directly on the command line,
185 the first argument is '<address>', and if it is encountered in a
186 configured remote, the first argument is the name of that remote.
187
188 Additionally, 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
193 COMMANDS
194 --------
195
196 Commands 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
200 with a blank line. Each capability may be preceded with '*',
201 which marks them mandatory for git version using the remote
202 helper to understand (unknown mandatory capability is fatal
203 error).
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
210 the name; unrecognized attributes are ignored. The list ends
211 with a blank line.
212 +
213 If 'push' is supported this may be called as 'list for-push'
214 to obtain the current refs prior to sending one or more 'push'
215 commands to the helper.
216
217 'option' <name> <value>::
218 Sets the transport helper option <name> to <value>. Outputs a
219 single line containing one of 'ok' (option successfully set),
220 'unsupported' (option not recognized) or 'error <msg>'
221 (option <name> is supported but <value> is not valid
222 for it). Options should be set before other commands,
223 and may influence the behavior of those commands.
224 +
225 Supported if the helper has the "option" capability.
226
227 'fetch' <sha1> <name>::
228 Fetches the given object, writing the necessary objects
229 to the database. Fetch commands are sent in a batch, one
230 per line, terminated with a blank line.
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 +
235 Optionally may output a 'lock <file>' line indicating a file under
236 GIT_DIR/objects/pack which is keeping a pack until refs can be
237 suitably updated.
238 +
239 Supported if the helper has the "fetch" capability.
240
241 'push' +<src>:<dst>::
242 Pushes the given local <src> commit or branch to the
243 remote branch described by <dst>. A batch sequence of
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 ------------
254 push refs/heads/master:refs/heads/master
255 push HEAD:refs/heads/branch
256 \n
257 push +refs/heads/foo:refs/heads/bar
258 \n
259 ------------
260 +
261 Zero or more protocol options may be entered after the last 'push'
262 command, before the batch's terminating blank line.
263 +
264 When the push is complete, outputs one or more 'ok <dst>' or
265 'error <dst> <why>?' lines to indicate success or failure of
266 each pushed ref. The status report output is terminated by
267 a blank line. The option field <why> may be quoted in a C
268 style string if it contains an LF.
269 +
270 Supported if the helper has the "push" capability.
271
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
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.
280 +
281 Especially useful for interoperability with a foreign versioning
282 system.
283 +
284 Just like 'push', a batch sequence of one or more 'import' is
285 terminated with a blank line. For each batch of 'import', the remote
286 helper should produce a fast-import stream terminated by a 'done'
287 command.
288 +
289 Supported if the helper has the "import" capability.
290
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 +
303 Supported if the helper has the "connect" capability.
304
305 If a fatal error occurs, the program writes the error message to
306 stderr and exits. The caller should expect that a suitable error
307 message has been printed if the child closes the connection without
308 completing a valid response for the current command.
309
310 Additional commands may be supported, as may be determined from
311 capabilities reported by the helper.
312
313 REF LIST ATTRIBUTES
314 -------------------
315
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.
320
321 'unchanged'::
322 This ref is unchanged since the last import or fetch, although
323 the helper cannot necessarily determine what value that produced.
324
325 OPTIONS
326 -------
327 'option verbosity' <n>::
328 Changes the verbosity of messages displayed by the helper.
329 A value of 0 for <n> means that processes operate
330 quietly, and the helper produces only error output.
331 1 is the default level of verbosity, and higher values
332 of <n> correspond to the number of -v flags passed on the
333 command line.
334
335 'option progress' \{'true'|'false'\}::
336 Enables (or disables) progress messages displayed by the
337 transport helper during a command.
338
339 'option depth' <depth>::
340 Deepens the history of a shallow repository.
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
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
355 'option servpath <c-style-quoted-path>'::
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
359 connect request occurs.
360
361 SEE ALSO
362 --------
363 linkgit:git-remote[1]
364
365 GIT
366 ---
367 Part of the linkgit:git[1] suite