receive-pack.c: consolidate find header logic

There are two functions that have very similar logic of finding a header
value. find_commit_header, and find_header. We can conslidate the logic
by introducing a new function find_header_mem, which is equivalent to
find_commit_header except it takes a len parameter that determines how
many bytes will be read. find_commit_header and find_header can then both
call find_header_mem.

This reduces duplicate logic, as the logic for finding header values
can now all live in one place.

Signed-off-by: John Cai <johncai86@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/receive-pack.c

@@ -581,32 +581,19 @@ static char *prepare_push_cert_nonce(const char *path, timestamp_t stamp)
 	return strbuf_detach(&buf, NULL);
 }
 
-/*
- * NEEDSWORK: reuse find_commit_header() from jk/commit-author-parsing
- * after dropping "_commit" from its name and possibly moving it out
- * of commit.c
- */
 static char *find_header(const char *msg, size_t len, const char *key,
 			 const char **next_line)
 {
-	int key_len = strlen(key);
-	const char *line = msg;
+	size_t out_len;
+	const char *val = find_header_mem(msg, len, key, &out_len);
 
-	while (line && line < msg + len) {
-		const char *eol = strchrnul(line, '\n');
-
-		if ((msg + len <= eol) || line == eol)
+	if (!val)
 		return NULL;
-		if (line + key_len < eol &&
-		    !memcmp(line, key, key_len) && line[key_len] == ' ') {
-			int offset = key_len + 1;
+
 	if (next_line)
-				*next_line = *eol ? eol + 1 : eol;
-			return xmemdupz(line + offset, (eol - line) - offset);
-		}
-		line = *eol ? eol + 1 : NULL;
-	}
-	return NULL;
+		*next_line = val + out_len + 1;
+
+	return xmemdupz(val, out_len);
 }
 
 /*

commit.c

@@ -1631,12 +1631,20 @@ struct commit_list **commit_list_append(struct commit *commit,
 	return &new_commit->next;
 }
 
-const char *find_commit_header(const char *msg, const char *key, size_t *out_len)
+const char *find_header_mem(const char *msg, size_t len,
+			const char *key, size_t *out_len)
 {
 	int key_len = strlen(key);
 	const char *line = msg;
 
-	while (line) {
+	/*
+	 * NEEDSWORK: It's possible for strchrnul() to scan beyond the range
+	 * given by len. However, current callers are safe because they compute
+	 * len by scanning a NUL-terminated block of memory starting at msg.
+	 * Nonetheless, it would be better to ensure the function does not look
+	 * at msg beyond the len provided by the caller.
+	 */
+	while (line && line < msg + len) {
 		const char *eol = strchrnul(line, '\n');
 
 		if (line == eol)
@@ -1653,6 +1661,10 @@ const char *find_commit_header(const char *msg, const char *key, size_t *out_len
 	return NULL;
 }
 
+const char *find_commit_header(const char *msg, const char *key, size_t *out_len)
+{
+	return find_header_mem(msg, strlen(msg), key, out_len);
+}
 /*
  * Inspect the given string and determine the true "end" of the log message, in
  * order to find where to put a new Signed-off-by trailer.  Ignored are

commit.h

@@ -290,12 +290,17 @@ void free_commit_extra_headers(struct commit_extra_header *extra);
 
 /*
  * Search the commit object contents given by "msg" for the header "key".
+ * Reads up to "len" bytes of "msg".
  * Returns a pointer to the start of the header contents, or NULL. The length
  * of the header, up to the first newline, is returned via out_len.
  *
  * Note that some headers (like mergetag) may be multi-line. It is the caller's
  * responsibility to parse further in this case!
  */
+const char *find_header_mem(const char *msg, size_t len,
+			const char *key,
+			size_t *out_len);
+
 const char *find_commit_header(const char *msg, const char *key,
 			       size_t *out_len);