Add unix domain socket support to HTTP transport

This changeset introduces an `http.unixSocket` option so that users can
proxy their git over HTTP remotes to a unix domain socket. In terms of
why, since UDS are local and git already has a local protocol: some
corporate environments use a UDS to proxy requests to internal resources
(ie. source control), so this change would support those use-cases. This
proxy can occasionally be necessary to attach MFA tokens or client
certificates for CLI tools.

The implementation leverages `--unix-socket` option [0] via the
`CURLOPT_UNIX_SOCKET_PATH` flag available with libcurl [1].

`GIT_CURL_HAVE_CURLOPT_UNIX_SOCKET_PATH` and `NO_UNIX_SOCKETS` were kept
separate so that we can spit out better error messages for users if git
was compiled with `NO_UNIX_SOCKETS`.

[0] https://curl.se/docs/manpage.html#--unix-socket
[1] https://curl.se/libcurl/c/CURLOPT_UNIX_SOCKET_PATH.html

Signed-off-by: Leslie Cheng <[email protected]>

Documentation/config/http.txt

@@ -277,6 +277,11 @@ http.followRedirects::
  the base for the follow-up requests, this is generally
  sufficient. The default is `initial`.
 
+http.unixSocket::
+ Connect through this Unix domain socket via HTTP, instead of using the
+ network. If set, this config takes precendence over `http.proxy` and
+ is incompatible with the proxy options (see `curl(1)`).
+
 http.<url>.*::
  Any of the http.* options above can be applied selectively to some URLs.
  For a config key to match a URL, each element of the config key is

git-curl-compat.h

@@ -74,6 +74,13 @@
 #define GIT_CURL_HAVE_CURLE_SSL_PINNEDPUBKEYNOTMATCH 1
 #endif
 
+/**
+ * CURLOPT_UNIX_SOCKET_PATH was added in 7.40.0, released in January 2015.
+ */
+#if LIBCURL_VERSION_NUM >= 0x074000
+#define GIT_CURL_HAVE_CURLOPT_UNIX_SOCKET_PATH 1
+#endif
+
 /**
  * CURL_HTTP_VERSION_2 was added in 7.43.0, released in June 2015.
  *

http.c

@@ -79,6 +79,9 @@ static const char *http_proxy_ssl_ca_info;
 static struct credential proxy_cert_auth = CREDENTIAL_INIT;
 static int proxy_ssl_cert_password_required;
 
+#if defined(GIT_CURL_HAVE_CURLOPT_UNIX_SOCKET_PATH) && !defined(NO_UNIX_SOCKETS)
+static const char *curl_unix_socket_path;
+#endif
 static struct {
  const char *name;
  long curlauth_param;
@@ -455,6 +458,20 @@ static int http_options(const char *var, const char *value,
  return 0;
  }
 
+ if (!strcmp("http.unixsocket", var)) {
+#ifdef GIT_CURL_HAVE_CURLOPT_UNIX_SOCKET_PATH
+#ifndef NO_UNIX_SOCKETS
+ return git_config_string(&curl_unix_socket_path, var, value);
+#else
+ warning(_("Unix socket support unavailable in this build of Git"));
+ return 0;
+#endif
+#else
+ warning(_("Unix socket support is not supported with cURL < 7.40.0"));
+ return 0;
+#endif
+ }
+
  if (!strcmp("http.cookiefile", var))
  return git_config_pathname(&curl_cookie_file, var, value);
  if (!strcmp("http.savecookies", var)) {
@@ -1203,6 +1220,12 @@ static CURL *get_curl_handle(void)
  }
  init_curl_proxy_auth(result);
 
+#if defined(GIT_CURL_HAVE_CURLOPT_UNIX_SOCKET_PATH) && !defined(NO_UNIX_SOCKETS)
+ if (curl_unix_socket_path) {
+ curl_easy_setopt(result, CURLOPT_UNIX_SOCKET_PATH, curl_unix_socket_path);
+ }
+#endif
+
  set_curl_keepalive(result);
 
  return result;

t/t5565-http-unix-domain-socket.sh

@@ -0,0 +1,109 @@
+#!/bin/sh
+
+test_description="test fetching through http via unix domain socket"
+
+. ./test-lib.sh
+. "$TEST_DIRECTORY"/lib-httpd.sh
+
+test -z "$NO_UNIX_SOCKETS" || {
+ skip_all='skipping http-unix-socket tests, unix sockets not available'
+ test_done
+}
+
+if ! test_have_prereq PERL
+then
+ skip_all='skipping http-unix-socket tests; perl not available'
+ test_done
+fi
+
+SOCKET_PROXY_PIDFILE="$(pwd)/proxy.pid"
+UDS_SOCKET="$(pwd)/uds.sock"
+UNRESOLVABLE_ENDPOINT=http://unresolved
+
+start_proxy_unix_to_tcp() {
+ test_atexit 'stop_proxy_unix_to_tcp'
+
+ perl -Mstrict -MIO::Select -MIO::Socket::INET -MIO::Socket::UNIX -e '
+ my $uds_path = $ARGV[0];
+ my $host = $ARGV[1];
+ my $port = $ARGV[2];
+ my $pidfile = $ARGV[3];
+
+ open(my $fh, ">", $pidfile) or die "failed to create pidfile";
+ print $fh "$$";
+ close($fh);
+
+ my $uds = IO::Socket::UNIX->new(
+ Local => $uds_path,
+ Type => SOCK_STREAM,
+ Listen => 5,
+ ) or die "failed to create unix domain socket";
+
+ while (my $conn = $uds->accept()) {
+ my $tcp_client = IO::Socket::INET->new(
+ PeerAddr => $host,
+ PeerPort => $port,
+ Proto => "tcp",
+ ) or die "failed to create TCP socket";
+
+ my $sel = IO::Select->new($conn, $tcp_client);
+
+ while (my @ready = $sel->can_read(10)) {
+ foreach my $socket (@ready) {
+ my $other = ($socket == $conn) ? $tcp_client : $conn;
+ my $data;
+ my $bytes = $socket->sysread($data, 4096);
+
+ if ($bytes) {
+ $other->syswrite($data, $bytes);
+ } else {
+ $socket->close();
+ }
+ }
+ }
+ }
+ ' "$UDS_SOCKET" "127.0.0.1" "$LIB_HTTPD_PORT" "$SOCKET_PROXY_PIDFILE" &
+ SOCKET_PROXY_PID=$!
+}
+
+stop_proxy_unix_to_tcp() {
+ kill -9 "$(cat "$SOCKET_PROXY_PIDFILE")"
+ rm -f "$SOCKET_PROXY_PIDFILE"
+ rm -f "$UDS_SOCKET"
+}
+
+start_httpd
+start_proxy_unix_to_tcp
+
+test_expect_success 'setup repository' '
+ test_commit foo &&
+ git init --bare "$HTTPD_DOCUMENT_ROOT_PATH/repo.git" &&
+ git push --mirror "$HTTPD_DOCUMENT_ROOT_PATH/repo.git"
+'
+
+# sanity check that we can't clone normally
+test_expect_success 'cloning without UDS fails' '
+ test_must_fail git clone "$UNRESOLVABLE_ENDPOINT/smart/repo.git" clone
+'
+
+test_expect_success 'cloning with UDS succeeds' '
+ test_when_finished "rm -rf clone" &&
+ test_config_global http.unixsocket "$UDS_SOCKET" &&
+ git clone "$UNRESOLVABLE_ENDPOINT/smart/repo.git" clone
+'
+
+test_expect_success 'cloning with a non-existent http proxy fails' '
+ git clone $HTTPD_URL/smart/repo.git clone &&
+ rm -rf clone &&
+ test_config_global http.proxy 127.0.0.1:0 &&
+ test_must_fail git clone $HTTPD_URL/smart/repo.git clone
+'
+
+test_expect_success 'UDS socket takes precedence over http proxy' '
+ test_when_finished "rm -rf clone" &&
+ test_config_global http.proxy 127.0.0.1:0 &&
+ test_config_global http.unixsocket "$UDS_SOCKET" &&
+ git clone $HTTPD_URL/smart/repo.git clone
+'
+
+test_done