strbuf_split: add a max parameter

Sometimes when splitting, you only want a limited number of
fields, and for the final field to contain "everything
else", even if it includes the delimiter.

This patch introduces strbuf_split_max, which provides a
"max number of fields" parameter; it behaves similarly to
perl's "split" with a 3rd field.

The existing 2-argument form of strbuf_split is retained for
compatibility and ease-of-use.
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

strbuf.c

@@ -101,7 +101,7 @@ void strbuf_ltrim(struct strbuf *sb)
 	sb->buf[sb->len] = '\0';
 }
 
-struct strbuf **strbuf_split(const struct strbuf *sb, int delim)
+struct strbuf **strbuf_split_max(const struct strbuf *sb, int delim, int max)
 {
 	int alloc = 2, pos = 0;
 	char *n, *p;
@@ -112,7 +112,10 @@ struct strbuf **strbuf_split(const struct strbuf *sb, int delim)
 	p = n = sb->buf;
 	while (n < sb->buf + sb->len) {
 		int len;
-		n = memchr(n, delim, sb->len - (n - sb->buf));
+		if (max <= 0 || pos + 1 < max)
+			n = memchr(n, delim, sb->len - (n - sb->buf));
+		else
+			n = NULL;
 		if (pos + 1 >= alloc) {
 			alloc = alloc * 2;
 			ret = xrealloc(ret, sizeof(struct strbuf *) * alloc);

strbuf.h

@@ -47,7 +47,12 @@ extern void strbuf_rtrim(struct strbuf *);
 extern void strbuf_ltrim(struct strbuf *);
 extern int strbuf_cmp(const struct strbuf *, const struct strbuf *);
 
-extern struct strbuf **strbuf_split(const struct strbuf *, int delim);
+extern struct strbuf **strbuf_split_max(const struct strbuf *,
+					int delim, int max);
+static inline struct strbuf **strbuf_split(const struct strbuf *sb, int delim)
+{
+	return strbuf_split_max(sb, delim, 0);
+}
 extern void strbuf_list_free(struct strbuf **);
 
 /*----- add data in your buffer -----*/