Merge branch 'jn/remote-helpers-doc'

* jn/remote-helpers-doc:
  (short) documentation for the testgit remote helper
  Documentation/git-remote-helpers: explain how import works with multiple refs
  Documentation/remote-helpers: explain capabilities first

3 files changed, 195 insertions, 31 deletions

diff --git a/Documentation/git-remote-helpers.txt b/Documentation/git-remote-helpers.txt
index 4f83dea5a3..674797cd83 100644
--- a/Documentation/git-remote-helpers.txt
+++ b/Documentation/git-remote-helpers.txt
@@ -24,22 +24,141 @@ output. Because a remote helper runs as an independent process from
 git, there is no need to re-link git to add a new helper, nor any
 need to link the helper with the implementation of git.
 
-Every helper must support the "capabilities" command, which git will
-use to determine what other commands the helper will accept.  Other
-commands generally concern facilities like discovering and updating
-remote refs, transporting objects between the object database and
-the remote repository, and updating the local object store.
-
-Helpers supporting the 'fetch' capability can discover refs from the
-remote repository and transfer objects reachable from those refs to
-the local object store. Helpers supporting the 'push' capability can
-transfer local objects to the remote repository and update remote refs.
+Every helper must support the "capabilities" command, which git
+uses to determine what other commands the helper will accept.  Those
+other commands can be used to discover and update remote refs,
+transport objects between the object database and the remote repository,
+and update the local object store.
 
 Git comes with a "curl" family of remote helpers, that handle various
 transport protocols, such as 'git-remote-http', 'git-remote-https',
 'git-remote-ftp' and 'git-remote-ftps'. They implement the capabilities
 'fetch', 'option', and 'push'.
 
+INPUT FORMAT
+------------
+
+Git sends the remote helper a list of commands on standard input, one
+per line.  The first command is always the 'capabilities' command, in
+response to which the remote helper must print a list of the
+capabilities it supports (see below) followed by a blank line.  The
+response to the capabilities command determines what commands Git uses
+in the remainder of the command stream.
+
+The command stream is terminated by a blank line.  In some cases
+(indicated in the documentation of the relevant commands), this blank
+line is followed by a payload in some other protocol (e.g., the pack
+protocol), while in others it indicates the end of input.
+
+Capabilities
+~~~~~~~~~~~~
+
+Each remote helper is expected to support only a subset of commands.
+The operations a helper supports are declared to git in the response
+to the `capabilities` command (see COMMANDS, below).
+
+'option'::
+	For specifying settings like `verbosity` (how much output to
+	write to stderr) and `depth` (how much history is wanted in the
+	case of a shallow clone) that affect how other commands are
+	carried out.
+
+'connect'::
+	For fetching and pushing using git's native packfile protocol
+	that requires a bidirectional, full-duplex connection.
+
+'push'::
+	For listing remote refs and pushing specified objects from the
+	local object store to remote refs.
+
+'fetch'::
+	For listing remote refs and fetching the associated history to
+	the local object store.
+
+'import'::
+	For listing remote refs and fetching the associated history as
+	a fast-import stream.
+
+'refspec' <refspec>::
+	This modifies the 'import' capability, allowing the produced
+	fast-import stream to modify refs in a private namespace
+	instead of writing to refs/heads or refs/remotes directly.
+	It is recommended that all importers providing the 'import'
+	capability use this.
++
+A helper advertising the capability
+`refspec refs/heads/{asterisk}:refs/svn/origin/branches/{asterisk}`
+is saying that, when it is asked to `import refs/heads/topic`, the
+stream it outputs will update the `refs/svn/origin/branches/topic`
+ref.
++
+This capability can be advertised multiple times.  The first
+applicable refspec takes precedence.  The left-hand of refspecs
+advertised with this capability must cover all refs reported by
+the list command.  If no 'refspec' capability is advertised,
+there is an implied `refspec {asterisk}:{asterisk}`.
+
+Capabilities for Pushing
+~~~~~~~~~~~~~~~~~~~~~~~~
+'connect'::
+	Can attempt to connect to 'git receive-pack' (for pushing),
+	'git upload-pack', etc for communication using the
+	packfile protocol.
++
+Supported commands: 'connect'.
+
+'push'::
+	Can discover remote refs and push local commits and the
+	history leading up to them to new or existing remote refs.
++
+Supported commands: 'list for-push', 'push'.
+
+If a helper advertises both 'connect' and 'push', git will use
+'connect' if possible and fall back to 'push' if the helper requests
+so when connecting (see the 'connect' command under COMMANDS).
+
+Capabilities for Fetching
+~~~~~~~~~~~~~~~~~~~~~~~~~
+'connect'::
+	Can try to connect to 'git upload-pack' (for fetching),
+	'git receive-pack', etc for communication using the
+	packfile protocol.
++
+Supported commands: 'connect'.
+
+'fetch'::
+	Can discover remote refs and transfer objects reachable from
+	them to the local object store.
++
+Supported commands: 'list', 'fetch'.
+
+'import'::
+	Can discover remote refs and output objects reachable from
+	them as a stream in fast-import format.
++
+Supported commands: 'list', 'import'.
+
+If a helper advertises 'connect', git will use it if possible and
+fall back to another capability if the helper requests so when
+connecting (see the 'connect' command under COMMANDS).
+When choosing between 'fetch' and 'import', git prefers 'fetch'.
+Other frontends may have some other order of preference.
+
+'refspec' <refspec>::
+	This modifies the 'import' capability.
++
+A helper advertising
+`refspec refs/heads/{asterisk}:refs/svn/origin/branches/{asterisk}`
+in its capabilities is saying that, when it handles
+`import refs/heads/topic`, the stream it outputs will update the
+`refs/svn/origin/branches/topic` ref.
++
+This capability can be advertised multiple times.  The first
+applicable refspec takes precedence.  The left-hand of refspecs
+advertised with this capability must cover all refs reported by
+the list command.  If no 'refspec' capability is advertised,
+there is an implied `refspec {asterisk}:{asterisk}`.
+
 INVOCATION
 ----------
 
@@ -122,7 +241,22 @@ Supported if the helper has the "fetch" capability.
 'push' +<src>:<dst>::
 	Pushes the given local <src> commit or branch to the
 	remote branch described by <dst>.  A batch sequence of
-	one or more push commands is terminated with a blank line.
+	one or more 'push' commands is terminated with a blank line
+	(if there is only one reference to push, a single 'push' command
+	is followed by a blank line). For example, the following would
+	be two batches of 'push', the first asking the remote-helper
+	to push the local ref 'master' to the remote ref 'master' and
+	the local 'HEAD' to the remote 'branch', and the second
+	asking to push ref 'foo' to ref 'bar' (forced update requested
+	by the '+').
++
+------------
+push refs/heads/master:refs/heads/master
+push HEAD:refs/heads/branch
+\n
+push +refs/heads/foo:refs/heads/bar
+\n
+------------
 +
 Zero or more protocol options may be entered after the last 'push'
 command, before the batch's terminating blank line.
@@ -147,6 +281,11 @@ Supported if the helper has the "push" capability.
 Especially useful for interoperability with a foreign versioning
 system.
 +
+Just like 'push', a batch sequence of one or more 'import' is
+terminated with a blank line. For each batch of 'import', the remote
+helper should produce a fast-import stream terminated by a 'done'
+command.
++
 Supported if the helper has the "import" capability.
 
 'connect' <service>::
@@ -171,26 +310,6 @@ completing a valid response for the current command.
 Additional commands may be supported, as may be determined from
 capabilities reported by the helper.
 
-CAPABILITIES
-------------
-
-'fetch'::
-'option'::
-'push'::
-'import'::
-'connect'::
-	This helper supports the corresponding command with the same name.
-
-'refspec' 'spec'::
-	When using the import command, expect the source ref to have
-	been written to the destination ref. The earliest applicable
-	refspec takes precedence. For example
-	"refs/heads/{asterisk}:refs/svn/origin/branches/{asterisk}" means
-	that, after an "import refs/heads/name", the script has written to
-	refs/svn/origin/branches/name. If this capability is used at
-	all, it must cover all refs reported by the list command; if
-	it is not used, it is effectively "{asterisk}:{asterisk}"
-
 REF LIST ATTRIBUTES
 -------------------
 
@@ -243,6 +362,8 @@ SEE ALSO
 --------
 linkgit:git-remote[1]
 
+linkgit:git-remote-testgit[1]
+
 GIT
 ---
 Part of the linkgit:git[1] suite
diff --git a/Documentation/git-remote-testgit.txt b/Documentation/git-remote-testgit.txt
new file mode 100644
index 0000000000..2a67d456a3
--- /dev/null
+++ b/Documentation/git-remote-testgit.txt
@@ -0,0 +1,30 @@
+git-remote-testgit(1)
+=====================
+
+NAME
+----
+git-remote-testgit - Example remote-helper
+
+
+SYNOPSIS
+--------
+[verse]
+git clone testgit::<source-repo> [<destination>]
+
+DESCRIPTION
+-----------
+
+This command is a simple remote-helper, that is used both as a
+testcase for the remote-helper functionality, and as an example to
+show remote-helper authors one possible implementation.
+
+The best way to learn more is to read the comments and source code in
+'git-remote-testgit.py'.
+
+SEE ALSO
+--------
+linkgit:git-remote-helpers[1]
+
+GIT
+---
+Part of the linkgit:git[1] suite
diff --git a/git-remote-testgit.py b/git-remote-testgit.py
index e9c832bfd3..3dc4851cfc 100644
--- a/git-remote-testgit.py
+++ b/git-remote-testgit.py
@@ -1,5 +1,18 @@
 #!/usr/bin/env python
 
+# This command is a simple remote-helper, that is used both as a
+# testcase for the remote-helper functionality, and as an example to
+# show remote-helper authors one possible implementation.
+#
+# This is a Git <-> Git importer/exporter, that simply uses git
+# fast-import and git fast-export to consume and produce fast-import
+# streams.
+#
+# To understand better the way things work, one can activate debug
+# traces by setting (to any value) the environment variables
+# GIT_TRANSPORT_HELPER_DEBUG and GIT_DEBUG_TESTGIT, to see messages
+# from the transport-helper side, or from this example remote-helper.
+
 # hashlib is only available in python >= 2.5
 try:
     import hashlib