docs/http-backend: mention v2 protocol

Historically there was a little bit of configuration needed at the
webserver level in order to get the client's v2 protocol probes to Git.
But when we introduced the v2 protocol, we never documented these.

As of the previous commit, this should mostly work out of the box
without any explicit configuration. But it's worth documenting this to
make it clear how we expect it to work, especially in the face of
webservers which don't provide all headers over the CGI interface. Or
anybody who runs across this documentation but has an older version of
Git (or _used_ to have an older version, and wonders why they still have
a SetEnvIf line in their Apache config and whether it's still

Signed-off-by: Jeff King <>
Signed-off-by: Junio C Hamano <>
This commit is contained in:
Jeff King 2021-09-10 10:09:13 -04:00 committed by Junio C Hamano
parent ff6a37c99e
commit 295d81b9e4
1 changed files with 25 additions and 1 deletions

View File

@ -16,7 +16,9 @@ A simple CGI program to serve the contents of a Git repository to Git
clients accessing the repository over http:// and https:// protocols.
The program supports clients fetching using both the smart HTTP protocol
and the backwards-compatible dumb HTTP protocol, as well as clients
pushing using the smart HTTP protocol.
pushing using the smart HTTP protocol. It also supports Git's
more-efficient "v2" protocol if properly configured; see the
discussion of `GIT_PROTOCOL` in the ENVIRONMENT section below.
It verifies that the directory has the magic file
"git-daemon-export-ok", and it will refuse to export any Git directory
@ -77,6 +79,18 @@ Apache 2.x::
SetEnv GIT_PROJECT_ROOT /var/www/git
ScriptAlias /git/ /usr/libexec/git-core/git-http-backend/
# This is not strictly necessary using Apache and a modern version of
# git-http-backend, as the webserver will pass along the header in the
# environment as HTTP_GIT_PROTOCOL, and http-backend will copy that into
# GIT_PROTOCOL. But you may need this line (or something similar if you
# are using a different webserver), or if you want to support older Git
# versions that did not do that copying.
# Having the webserver set up GIT_PROTOCOL is perfectly fine even with
# modern versions (and will take precedence over HTTP_GIT_PROTOCOL,
# which means it can be used to override the client's request).
SetEnvIf Git-Protocol ".*" GIT_PROTOCOL=$0
To enable anonymous read access but authenticated write access,
@ -264,6 +278,16 @@ a repository with an extremely large number of refs. The value can be
specified with a unit (e.g., `100M` for 100 megabytes). The default is
10 megabytes.
Clients may probe for optional protocol capabilities (like the v2
protocol) using the `Git-Protocol` HTTP header. In order to support
these, the contents of that header must appear in the `GIT_PROTOCOL`
environment variable. Most webservers will pass this header to the CGI
via the `HTTP_GIT_PROTOCOL` variable, and `git-http-backend` will
automatically copy that to `GIT_PROTOCOL`. However, some webservers may
be more selective about which headers they'll pass, in which case they
need to be configured explicitly (see the mention of `Git-Protocol` in
the Apache config from the earlier EXAMPLES section).
The backend process sets GIT_COMMITTER_NAME to '$REMOTE_USER' and
ensuring that any reflogs created by 'git-receive-pack' contain some