[PATCH/RFC 1/4] Allow creation of arbitrary git-shell commands

[Greg Brockman <gdb@MIT.EDU>]

This provides a mechanism for the server to expose custom
functionality to clients.  My particular use case is that I would like
a way of discovering all repositories available for cloning.  A
client that clones via
  git clone user@example.com
can invoke a command by
  ssh user@example.com $command

Signed-off-by: Greg Brockman <gdb@mit.edu>
---
 shell.c |   16 ++++++++++++++++
 1 files changed, 16 insertions(+), 0 deletions(-)

diff --git a/shell.c b/shell.c
index e4864e0..3fee0ed 100644
--- a/shell.c
+++ b/shell.c
@@ -3,6 +3,8 @@
 #include "exec_cmd.h"
 #include "strbuf.h"
 
+#define COMMAND_DIR "git-shell-commands"
+
 static int do_generic_cmd(const char *me, char *arg)
 {
 	const char *my_argv[4];
@@ -33,6 +35,12 @@ static int do_cvs_cmd(const char *me, char *arg)
 	return execv_git_cmd(cvsserver_argv);
 }
 
+static int is_valid_cmd_name(const char *cmd)
+{
+	/* Test command contains no . or / characters */
+	return cmd[strcspn(cmd, "./")] == '\0';
+}
+
 
 static struct commands {
 	const char *name;
@@ -99,5 +107,13 @@ int main(int argc, char **argv)
 		}
 		exit(cmd->exec(cmd->name, arg));
 	}
+
+	/* Shell should be spawned with cwd in the git user's home directory */
+	if (chdir(COMMAND_DIR))
+		die("unrecognized command '%s'", prog);
+
+	if (is_valid_cmd_name(prog))
+		execl(prog, prog, (char *) NULL);
+
 	die("unrecognized command '%s'", prog);
 }
-- 
1.7.0.4