for-each-ref: refactor subject and body placeholder parsing

The find_subpos function was a little hard to use, as well
as to read. It would sometimes write into the subject and
body pointers, and sometimes not. The body pointer sometimes
could be compared to subject, and sometimes not. When
actually duplicating the subject, the caller was forced to
figure out again how long the subject is (which is not too
big a deal when the subject is a single line, but hard to
extend).

The refactoring makes the function more straightforward, both
to read and to use. We will always put something into the
subject and body pointers, and we return explicit lengths
for them, too.

This lays the groundwork both for more complex subject
parsing (e.g., multiline), as well as splitting the body
into subparts (like the text versus the signature).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/for-each-ref.c

@@ -458,38 +458,42 @@ static void grab_person(const char *who, struct atom_value *val, int deref, stru
 	}
 }
 
-static void find_subpos(const char *buf, unsigned long sz, const char **sub, const char **body)
+static void find_subpos(const char *buf, unsigned long sz,
+			const char **sub, unsigned long *sublen,
+			const char **body, unsigned long *bodylen)
 {
-	while (*buf) {
-		const char *eol = strchr(buf, '\n');
-		if (!eol)
-			return;
-		if (eol[1] == '\n') {
-			buf = eol + 1;
-			break; /* found end of header */
-		}
-		buf = eol + 1;
+	const char *eol;
+	/* skip past header until we hit empty line */
+	while (*buf && *buf != '\n') {
+		eol = strchrnul(buf, '\n');
+		if (*eol)
+			eol++;
+		buf = eol;
 	}
+	/* skip any empty lines */
 	while (*buf == '\n')
 		buf++;
-	if (!*buf)
-		return;
-	*sub = buf; /* first non-empty line */
-	buf = strchr(buf, '\n');
-	if (!buf) {
-		*body = "";
-		return; /* no body */
-	}
+
+	/* subject is first non-empty line */
+	*sub = buf;
+	/* subject goes to end of line */
+	eol = strchrnul(buf, '\n');
+	*sublen = eol - buf;
+	buf = eol;
+
+	/* skip any empty lines */
 	while (*buf == '\n')
-		buf++; /* skip blank between subject and body */
+		buf++;
 	*body = buf;
+	*bodylen = strlen(buf);
 }
 
 /* See grab_values */
 static void grab_sub_body_contents(struct atom_value *val, int deref, struct object *obj, void *buf, unsigned long sz)
 {
 	int i;
-	const char *subpos = NULL, *bodypos = NULL;
+	const char *subpos = NULL, *bodypos;
+	unsigned long sublen, bodylen;
 
 	for (i = 0; i < used_atom_cnt; i++) {
 		const char *name = used_atom[i];
@@ -503,14 +507,14 @@ static void grab_sub_body_contents(struct atom_value *val, int deref, struct obj
 		    strcmp(name, "contents"))
 			continue;
 		if (!subpos)
-			find_subpos(buf, sz, &subpos, &bodypos);
-		if (!subpos)
-			return;
+			find_subpos(buf, sz,
+				    &subpos, &sublen,
+				    &bodypos, &bodylen);
 
 		if (!strcmp(name, "subject"))
-			v->s = copy_line(subpos);
+			v->s = xmemdupz(subpos, sublen);
 		else if (!strcmp(name, "body"))
-			v->s = xstrdup(bodypos);
+			v->s = xmemdupz(bodypos, bodylen);
 		else if (!strcmp(name, "contents"))
 			v->s = xstrdup(subpos);
 	}