wrapper: add function to compare strings with different NUL termination

When parsing capabilities for the pack protocol, there are times we'll
want to compare the value of a capability to a NUL-terminated string.
Since the data we're reading will be space-terminated, not
NUL-terminated, we need a function that compares the two strings, but
also checks that they're the same length.  Otherwise, if we used strncmp
to compare these strings, we might accidentally accept a parameter that
was a prefix of the expected value.

Add a function, xstrncmpz, that takes a NUL-terminated string and a
non-NUL-terminated string, plus a length, and compares them, ensuring
that they are the same length.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/git-compat-util.h b/git-compat-util.h
index 8ba576e..a3dcfc8 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -869,6 +869,12 @@ FILE *fopen_for_writing(const char *path);
 FILE *fopen_or_warn(const char *path, const char *mode);
 
 /*
+ * Like strncmp, but only return zero if s is NUL-terminated and exactly len
+ * characters long.  If it is not, consider it greater than t.
+ */
+int xstrncmpz(const char *s, const char *t, size_t len);
+
+/*
  * FREE_AND_NULL(ptr) is like free(ptr) followed by ptr = NULL. Note
  * that ptr is used twice, so don't pass e.g. ptr++.
  */