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PATH: usr / share / doc / git-1.8.3.1 / technical

Git-send-pack internals
=======================

Overall operation
-----------------

. Connects to the remote side and invokes git-receive-pack.

. Learns what refs the remote has and what commit they point at.
  Matches them to the refspecs we are pushing.

. Checks if there are non-fast-forwards.  Unlike fetch-pack,
  the repository send-pack runs in is supposed to be a superset
  of the recipient in fast-forward cases, so there is no need
  for want/have exchanges, and fast-forward check can be done
  locally.  Tell the result to the other end.

. Calls pack_objects() which generates a packfile and sends it
  over to the other end.

. If the remote side is new enough (v1.1.0 or later), wait for
  the unpack and hook status from the other end.

. Exit with appropriate error codes.

Pack_objects pipeline
---------------------

This function gets one file descriptor (`fd`) which is either a
socket (over the network) or a pipe (local).  What's written to
this fd goes to git-receive-pack to be unpacked.

send-pack ---> fd ---> receive-pack

The function pack_objects creates a pipe and then forks.  The
forked child execs pack-objects with --revs to receive revision
parameters from its standard input. This process will write the
packfile to the other end.

send-pack
       |
       pack_objects() ---> fd ---> receive-pack
          | ^ (pipe)
	  v |
         (child)

The child dup2's to arrange its standard output to go back to
the other end, and read its standard input to come from the
pipe.  After that it exec's pack-objects.  On the other hand,
the parent process, before starting to feed the child pipeline,
closes the reading side of the pipe and fd to receive-pack.

send-pack
       |
       pack_objects(parent)
          |
	  v [0]
         pack-objects [0] ---> receive-pack

[jc: the pipeline was much more complex and needed documentation before
 I understood an earlier bug, but now it is trivial and straightforward.]

[-] api-strbuf.html [edit]
[-] api-credentials.txt [edit]
[-] shallow.txt [edit]
[-] api-sigchain.html [edit]
[-] racy-git.html [edit]
[-] api-allocation-growing.txt [edit]
[-] api-tree-walking.html [edit]
[-] index-format.txt [edit]
[-] pack-protocol.html [edit]
[-] api-setup.txt [edit]
[-] api-lockfile.html [edit]
[-] api-directory-listing.txt [edit]
[-] api-remote.txt [edit]
[-] pack-format.html [edit]
[-] api-quote.txt [edit]
[-] index-format.html [edit]
[-] api-in-core-index.txt [edit]
[-] api-hash.txt [edit]
[-] send-pack-pipeline.html [edit]
[-] api-strbuf.txt [edit]
[+] ..
[-] protocol-common.html [edit]
[-] pack-heuristics.html [edit]
[-] api-sha1-array.html [edit]
[-] api-xdiff-interface.html [edit]
[-] api-xdiff-interface.txt [edit]
[-] api-hashmap.html [edit]
[-] api-ref-iteration.txt [edit]
[-] trivial-merge.html [edit]
[-] api-gitattributes.txt [edit]
[-] pack-format.txt [edit]
[-] api-run-command.txt [edit]
[-] api-parse-options.html [edit]
[-] api-ref-iteration.html [edit]
[-] trivial-merge.txt [edit]
[-] api-decorate.txt [edit]
[-] api-builtin.txt [edit]
[-] api-directory-listing.html [edit]
[-] pack-protocol.txt [edit]
[-] api-hash.html [edit]
[-] api-quote.html [edit]
[-] api-setup.html [edit]
[-] api-argv-array.html [edit]
[-] api-remote.html [edit]
[-] api-grep.txt [edit]
[-] protocol-capabilities.txt [edit]
[-] api-revision-walking.html [edit]
[-] api-string-list.txt [edit]
[-] api-history-graph.txt [edit]
[-] api-diff.html [edit]
[-] protocol-common.txt [edit]
[-] api-sigchain.txt [edit]
[-] api-gitattributes.html [edit]
[-] api-grep.html [edit]
[-] api-history-graph.html [edit]
[-] api-lockfile.txt [edit]
[-] api-index.txt [edit]
[-] api-revision-walking.txt [edit]
[-] api-sha1-array.txt [edit]
[-] api-string-list.html [edit]
[-] api-object-access.txt [edit]
[-] api-hashmap.txt [edit]
[-] protocol-capabilities.html [edit]
[-] api-object-access.html [edit]
[-] pack-heuristics.txt [edit]
[-] shallow.html [edit]
[-] api-run-command.html [edit]
[-] racy-git.txt [edit]
[-] api-merge.html [edit]
[-] api-index-skel.txt [edit]
[-] api-tree-walking.txt [edit]
[-] send-pack-pipeline.txt [edit]
[-] api-in-core-index.html [edit]
[-] api-diff.txt [edit]
[-] api-index.html [edit]
[-] api-credentials.html [edit]
[-] api-builtin.html [edit]
[-] api-allocation-growing.html [edit]
[-] api-merge.txt [edit]
[-] api-parse-options.txt [edit]
[-] api-config.html [edit]
[-] api-decorate.html [edit]
[-] api-index.sh [edit]
[-] api-argv-array.txt [edit]
[-] api-config.txt [edit]