long-running-process-protocol

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.