git/Documentation/technical/long-running-process-protocol.txt
Ævar Arnfjörð Bjarmason 5db921054e docs: move protocol-related docs to man section 5
Continue the move of existing Documentation/technical/* protocol and
file-format documentation into our main documentation space. By moving
the things that discuss the protocol we can properly link from
e.g. lsrefs.unborn and protocol.version documentation to a manpage we
build by default.

So far we have been using the "gitformat-" prefix for the
documentation we've been moving over from Documentation/technical/*,
but for protocol documentation let's use "gitprotocol-*".

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2022-08-04 14:12:23 -07:00

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Long-running process protocol
=============================
This protocol is used when Git needs to communicate with an external
process throughout the entire life of a single Git command. All
communication is in pkt-line format (see linkgit:gitprotocol-common[5])
over standard input and standard output.
Handshake
---------
Git starts by sending a welcome message (for example,
"git-filter-client"), a list of supported protocol version numbers, and
a flush packet. Git expects to read the welcome message with "server"
instead of "client" (for example, "git-filter-server"), exactly one
protocol version number from the previously sent list, and a flush
packet. All further communication will be based on the selected version.
The remaining protocol description below documents "version=2". Please
note that "version=42" in the example below does not exist and is only
there to illustrate how the protocol would look like with more than one
version.
After the version negotiation Git sends a list of all capabilities that
it supports and a flush packet. Git expects to read a list of desired
capabilities, which must be a subset of the supported capabilities list,
and a flush packet as response:
------------------------
packet: git> git-filter-client
packet: git> version=2
packet: git> version=42
packet: git> 0000
packet: git< git-filter-server
packet: git< version=2
packet: git< 0000
packet: git> capability=clean
packet: git> capability=smudge
packet: git> capability=not-yet-invented
packet: git> 0000
packet: git< capability=clean
packet: git< capability=smudge
packet: git< 0000
------------------------
Shutdown
--------
Git will close
the command pipe on exit. The filter is expected to detect EOF
and exit gracefully on its own. Git will wait until the filter
process has stopped.