connect.c: finish_connect(): allow null pid parameter

git_connect() can return 0 if we use git protocol for example.
Users of this function don't know and don't care if a process
had been created or not, and to avoid them to check it before
calling finish_connect() this patch allows finish_connect() to
take a null pid. And in that case return 0.

[jc: updated function signature of git_connect() with a comment on
 its return value. ]

Signed-off-by: Franck Bui-Huu <vagabon.xyz@gmail.com>
Signed-off-by: Junio C Hamano <junkio@cox.net>

cache.h

@@ -359,7 +359,7 @@ struct ref {
 #define REF_HEADS	(1u << 1)
 #define REF_TAGS	(1u << 2)
 
-extern int git_connect(int fd[2], char *url, const char *prog);
+extern pid_t git_connect(int fd[2], char *url, const char *prog);
 extern int finish_connect(pid_t pid);
 extern int path_match(const char *path, int nr, char **match);
 extern int match_refs(struct ref *src, struct ref *dst, struct ref ***dst_tail,

connect.c

@@ -602,9 +602,15 @@ static void git_proxy_connect(int fd[2], char *host)
 #define MAX_CMD_LEN 1024
 
 /*
- * Yeah, yeah, fixme. Need to pass in the heads etc.
+ * This returns 0 if the transport protocol does not need fork(2),
+ * or a process id if it does.  Once done, finish the connection
+ * with finish_connect() with the value returned from this function
+ * (it is safe to call finish_connect() with 0 to support the former
+ * case).
+ *
+ * Does not return a negative value on error; it just dies.
  */
-int git_connect(int fd[2], char *url, const char *prog)
+pid_t git_connect(int fd[2], char *url, const char *prog)
 {
 	char *host, *path = url;
 	char *end;
@@ -748,6 +754,9 @@ int git_connect(int fd[2], char *url, const char *prog)
 
 int finish_connect(pid_t pid)
 {
+	if (pid == 0)
+		return 0;
+
 	while (waitpid(pid, NULL, 0) < 0) {
 		if (errno != EINTR)
 			return -1;