Documentation/technical/long-running-process-protocol.adoc

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.