strbuf: introduce starts_with() and ends_with()

prefixcmp() and suffixcmp() share the common "cmp" suffix that
typically are used to name functions that can be used for ordering,
but they can't, because they are not antisymmetric:

        prefixcmp("foo", "foobar") < 0
        prefixcmp("foobar", "foo") == 0

We in fact do not use these functions for ordering.  Replace them
with functions that just check for equality.

Add starts_with() and end_with() that will be used to replace
prefixcmp() and suffixcmp(), respectively, as the first step.  These
are named after corresponding functions/methods in programming
languages, like Java, Python and Ruby.

In vcs-svn/fast_export.c, there was already an ends_with() function
that did the same thing. Let's use the new one instead while at it.

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-compat-util.h

@@ -350,7 +350,9 @@ extern void set_die_routine(NORETURN_PTR void (*routine)(const char *err, va_lis
 extern void set_error_routine(void (*routine)(const char *err, va_list params));
 extern void set_die_is_recursing_routine(int (*routine)(void));
 
+extern int starts_with(const char *str, const char *prefix);
 extern int prefixcmp(const char *str, const char *prefix);
+extern int ends_with(const char *str, const char *suffix);
 extern int suffixcmp(const char *str, const char *suffix);
 
 static inline const char *skip_prefix(const char *str, const char *prefix)

strbuf.c

@@ -1,6 +1,15 @@
 #include "cache.h"
 #include "refs.h"
 
+int starts_with(const char *str, const char *prefix)
+{
+	for (; ; str++, prefix++)
+		if (!*prefix)
+			return 1;
+		else if (*str != *prefix)
+			return 0;
+}
+
 int prefixcmp(const char *str, const char *prefix)
 {
 	for (; ; str++, prefix++)
@@ -10,6 +19,15 @@ int prefixcmp(const char *str, const char *prefix)
 			return (unsigned char)*prefix - (unsigned char)*str;
 }
 
+int ends_with(const char *str, const char *suffix)
+{
+	int len = strlen(str), suflen = strlen(suffix);
+	if (len < suflen)
+		return 0;
+	else
+		return !strcmp(str + len - suflen, suffix);
+}
+
 int suffixcmp(const char *str, const char *suffix)
 {
 	int len = strlen(str), suflen = strlen(suffix);

vcs-svn/fast_export.c

@@ -162,22 +162,13 @@ static void die_short_read(struct line_buffer *input)
 	die("invalid dump: unexpected end of file");
 }
 
-static int ends_with(const char *s, size_t len, const char *suffix)
-{
-	const size_t suffixlen = strlen(suffix);
-	if (len < suffixlen)
-		return 0;
-	return !memcmp(s + len - suffixlen, suffix, suffixlen);
-}
-
 static int parse_cat_response_line(const char *header, off_t *len)
 {
-	size_t headerlen = strlen(header);
 	uintmax_t n;
 	const char *type;
 	const char *end;
 
-	if (ends_with(header, headerlen, " missing"))
+	if (ends_with(header, " missing"))
 		return error("cat-blob reports missing blob: %s", header);
 	type = strstr(header, " blob ");
 	if (!type)