[PATCH] connect: read $GIT_SSH_COMMAND from config file

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

Similar to $GIT_ASKPASS or $GIT_PROXY_COMMAND, we also read from
config file first then fall back to $GIT_SSH_COMMAND.

This is useful for selecting different private keys targetting the
same host (e.g. github)

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 core.gitProxy can also be used for my purpose (I need pushing, not
 fetching though; the document says for fetching but I guess
 core.gitProxy always works for pushing), but then the key file
 is hidden behind the script. And writing a script for this seems a
 bit overkill.

 Documentation/config.txt |  7 +++++++
 connect.c                | 15 ++++++++++++++-
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/Documentation/config.txt b/Documentation/config.txt
index 58673cf..3bf070c 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -443,6 +443,13 @@ specify that no proxy be used for a given domain pattern.
 This is useful for excluding servers inside a firewall from
 proxy use, while defaulting to a common proxy for external domains.
 
+core.sshCommand::
+	If this variable is set then 'git fetch' and 'git push' will
+	use the specified command instead of 'ssh' when they need to
+	connect to a remote system. The command is in the same form as
+	'GIT_SSH_COMMAND' environment variable and is overriden when
+	the environment variable is set.
+
 core.ignoreStat::
 	If true, Git will avoid using lstat() calls to detect if files have
 	changed by setting the "assume-unchanged" bit for those tracked files
diff --git a/connect.c b/connect.c
index c53f3f1..722dc3f 100644
--- a/connect.c
+++ b/connect.c
@@ -658,6 +658,19 @@ static enum protocol parse_connect_url(const char *url_orig, char **ret_host,
 
 static struct child_process no_fork = CHILD_PROCESS_INIT;
 
+static const char *get_ssh_command(void)
+{
+	const char *ssh;
+
+	if ((ssh = getenv("GIT_SSH_COMMAND")))
+		return ssh;
+
+	if (!git_config_get_string_const("core.sshcommand", &ssh))
+		return ssh;
+
+	return NULL;
+}
+
 /*
  * This returns a dummy child_process if the transport protocol does not
  * need fork(2), or a struct child_process object if it does.  Once done,
@@ -758,7 +771,7 @@ struct child_process *git_connect(int fd[2], const char *url,
 				return NULL;
 			}
 
-			ssh = getenv("GIT_SSH_COMMAND");
+			ssh = get_ssh_command();
 			if (!ssh) {
 				const char *base;
 				char *ssh_dup;
-- 
2.8.2.530.g66e63ce