Add persistent-https to contrib

Git over HTTPS has a high request startup latency, since the SSL
negotiation can take up to a second. In order to reduce this latency,
connections should be left open to the Git server across requests
(or invocations of the git commandline).

Reduce SSL startup latency by running a daemon job that keeps
connections open to a Git server. The daemon job
(git-remote-persistent-https--proxy) is started on the first request
through the client binary (git-remote-persistent-https) and remains
running for 24 hours after the last request, or until a new daemon
binary is placed in the PATH. The client determines the daemon's
HTTP address by communicating over a UNIX socket with the daemon.
From there, the rest of the Git protocol work is delegated to the
"git-remote-http" binary, with the environment's http_proxy set to
the daemon.

Accessing /pub/scm/linux/kernel/git/torvalds/linux repository hosted
at kernel.googlesource.com with "git ls-remote" over https:// and
persistent-https:// 5 times shows that the first request takes about
the same time (0.193s vs 0.208s---there is a slight set-up cost for
the local proxy); as expected, the other four requests are much
faster (~0.18s vs ~0.08s).

Incidentally, this also has the benefit of HTTP keep-alive working
across Git command invocations. Its common for servers to use a 5
minute keep-alive on an HTTP 1.1 connection. Git-over-HTTP commonly
uses Transfer-Encoding: chunked on replies, so keep-alive will
generally just work, even though a pack stream's length isn't known
in advance. Because the helper is an external process holding that
connection open, we also benefit from being able to reuse an
existing TCP connection to the server.  The same "git ls-remote"
test against http:// vs persistent-https:// URL shows that the
former takes ~0.09s while the first request for the latter is about
0.134s with set-up cost, and subsequent requests are ~0.065s,
shaving around one RTT to the server.

Signed-off-by: Colby Ranger <cranger@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 62 insertions, 0 deletions

diff --git a/contrib/persistent-https/README b/contrib/persistent-https/README
new file mode 100644
index 000000000..f784dd2e6
--- /dev/null
+++ b/contrib/persistent-https/README
@@ -0,0 +1,62 @@
+git-remote-persistent-https
+
+The git-remote-persistent-https binary speeds up SSL operations
+by running a daemon job (git-remote-persistent-https--proxy) that
+keeps a connection open to a server.
+
+
+PRE-BUILT BINARIES
+
+Darwin amd64:
+https://commondatastorage.googleapis.com/git-remote-persistent-https/darwin_amd64.tar.gz
+
+Linux amd64:
+https://commondatastorage.googleapis.com/git-remote-persistent-https/linux_amd64.tar.gz
+
+
+INSTALLING
+
+Move all of the git-remote-persistent-http* binaries to a directory
+in PATH.
+
+
+USAGE
+
+HTTPS requests can be delegated to the proxy by using the
+"persistent-https" scheme, e.g.
+
+git clone persistent-https://kernel.googlesource.com/pub/scm/git/git
+
+Likewise, .gitconfig can be updated as follows to rewrite https urls
+to use persistent-https:
+
+[url "persistent-https"]
+	insteadof = https
+[url "persistent-http"]
+	insteadof = http
+
+
+#####################################################################
+# BUILDING FROM SOURCE
+#####################################################################
+
+LOCATION
+
+The source is available in the contrib/persistent-https directory of
+the Git source repository. The Git source repository is available at
+git://git.kernel.org/pub/scm/git/git.git/
+https://kernel.googlesource.com/pub/scm/git/git
+
+
+PREREQUISITES
+
+The code is written in Go (http://golang.org/) and the Go compiler is
+required. Currently, the compiler must be built and installed from tip
+of source, in order to include a fix in the reverse http proxy:
+http://code.google.com/p/go/source/detail?r=a615b796570a2cd8591884767a7d67ede74f6648
+
+
+BUILDING
+
+Run "make" to build the binaries. See the section on
+INSTALLING above.