bytestring: Add bytestring_slice function

Add a bytestring_slice() function to take a sub(byte)string of a
bytestring.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

diff --git a/ccan/bytestring/bytestring.h b/ccan/bytestring/bytestring.h
index bd525601eb3a71cb40c050838db1f76268b5530b..abc7dd7bb0424bb684bdd5000006cfce97cc8578 100644 (file)
--- a/ccan/bytestring/bytestring.h
+++ b/ccan/bytestring/bytestring.h
@@ -95,4 +95,31 @@ static inline char bytestring_byte(struct bytestring s, size_t n)
        return s.ptr[n];
 }
 
+/**
+ * bytestring_slice - extract a substring from a bytestring
+ * @s: bytestring
+ * @start, @end: indexes
+ *
+ * Return a sub-bytestring of @s, starting at byte index @start, and
+ * running to, but not including byte @end.  If @end is before start,
+ * returns a zero-length bytestring.  If @start is out of range,
+ * return a zero length bytestring at the end of @s.
+ *
+ * Note that this doesn't copy or allocate anything - the returned
+ * bytestring occupies (some of) the same memory as the given
+ * bytestring.
+ */
+static inline struct bytestring bytestring_slice(struct bytestring s,
+                                                size_t start, size_t end)
+{
+       if (start > s.len)
+               start = s.len;
+       if (end > s.len)
+               end = s.len;
+       if (end < start)
+               end = start;
+
+       return bytestring(s.ptr + start, end - start);
+}
+
 #endif /* CCAN_BYTESTRING_H_ */

diff --git a/ccan/bytestring/test/run.c b/ccan/bytestring/test/run.c
index 2d86926d06301b2c5ed8dd9d5242cd31aa3bb2b2..97fa8c5cc5d41e7d570cc1ac68c1b30a6057b068 100644 (file)
--- a/ccan/bytestring/test/run.c
+++ b/ccan/bytestring/test/run.c
@@ -12,7 +12,7 @@ int main(void)
        struct bytestring bs, bs1, bs2, bs3, bs4, bs5;
 
        /* This is how many tests you plan to run */
-       plan_tests(16);
+       plan_tests(22);
 
        bs = bytestring(str1, sizeof(str1) - 1);
        ok1(bs.ptr == str1);
@@ -42,7 +42,14 @@ int main(void)
        ok1(bytestring_byte(bs2, 4) == 'd');
        ok1(bytestring_byte(bs2, 5) == 'e');
        ok1(bytestring_byte(bs2, 6) == 'f');
-       
+
+       ok1(bytestring_eq(bytestring_slice(bs, 0, 4), BYTESTRING("test")));
+       ok1(bytestring_eq(bytestring_slice(bs, 5, 8), BYTESTRING("str")));
+       ok1(bytestring_eq(bytestring_slice(bs2, 2, 5), BYTESTRING("c\0d")));
+       ok1(bytestring_eq(bytestring_slice(bs2, 0, -1U), bs2));
+       ok1(bytestring_eq(bytestring_slice(bs2, 10, 20), bytestring_NULL));
+       ok1(bytestring_eq(bytestring_slice(bs2, 2, 1), bytestring_NULL));
+
        /* This exits depending on whether all tests passed */
        return exit_status();
 }