refs.c: add a function to append a reflog entry to a fd

Break out the code to create the string and writing it to the file
descriptor from log_ref_write and add it into a dedicated function
log_ref_write_fd. It is a nice unit of work.

For now this is only used from log_ref_write, but in the future it
might have other callers.

Signed-off-by: Ronnie Sahlberg <sahlberg@google.com>
Signed-off-by: Stefan Beller <sbeller@google.com>
Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

refs.c

@@ -2990,15 +2990,37 @@ int log_ref_setup(const char *refname, char *logfile, int bufsize)
 	return 0;
 }
 
+static int log_ref_write_fd(int fd, const unsigned char *old_sha1,
+			    const unsigned char *new_sha1,
+			    const char *committer, const char *msg)
+{
+	int msglen, written;
+	unsigned maxlen, len;
+	char *logrec;
+
+	msglen = msg ? strlen(msg) : 0;
+	maxlen = strlen(committer) + msglen + 100;
+	logrec = xmalloc(maxlen);
+	len = sprintf(logrec, "%s %s %s\n",
+		      sha1_to_hex(old_sha1),
+		      sha1_to_hex(new_sha1),
+		      committer);
+	if (msglen)
+		len += copy_msg(logrec + len - 1, msg) - 1;
+
+	written = len <= maxlen ? write_in_full(fd, logrec, len) : -1;
+	free(logrec);
+	if (written != len)
+		return -1;
+
+	return 0;
+}
+
 static int log_ref_write(const char *refname, const unsigned char *old_sha1,
 			 const unsigned char *new_sha1, const char *msg)
 {
-	int logfd, result, written, oflags = O_APPEND | O_WRONLY;
-	unsigned maxlen, len;
-	int msglen;
+	int logfd, result, oflags = O_APPEND | O_WRONLY;
 	char log_file[PATH_MAX];
-	char *logrec;
-	const char *committer;
 
 	if (log_all_ref_updates < 0)
 		log_all_ref_updates = !is_bare_repository();
@@ -3010,19 +3032,9 @@ static int log_ref_write(const char *refname, const unsigned char *old_sha1,
 	logfd = open(log_file, oflags);
 	if (logfd < 0)
 		return 0;
-	msglen = msg ? strlen(msg) : 0;
-	committer = git_committer_info(0);
-	maxlen = strlen(committer) + msglen + 100;
-	logrec = xmalloc(maxlen);
-	len = sprintf(logrec, "%s %s %s\n",
-		      sha1_to_hex(old_sha1),
-		      sha1_to_hex(new_sha1),
-		      committer);
-	if (msglen)
-		len += copy_msg(logrec + len - 1, msg) - 1;
-	written = len <= maxlen ? write_in_full(logfd, logrec, len) : -1;
-	free(logrec);
-	if (written != len) {
+	result = log_ref_write_fd(logfd, old_sha1, new_sha1,
+				  git_committer_info(0), msg);
+	if (result) {
 		int save_errno = errno;
 		close(logfd);
 		error("Unable to append to %s", log_file);