ua: enforce magic cookie in Via branch

include/re_fmt.h

@@ -46,6 +46,7 @@ int      pl_strcpy(const struct pl *pl, char *str, size_t size);
 int      pl_strdup(char **dst, const struct pl *src);
 int      pl_dup(struct pl *dst, const struct pl *src);
 int      pl_strcmp(const struct pl *pl, const char *str);
+int      pl_strncmp(const struct pl *pl, const char *str, size_t n);
 int      pl_strcasecmp(const struct pl *pl, const char *str);
 int      pl_cmp(const struct pl *pl1, const struct pl *pl2);
 int      pl_casecmp(const struct pl *pl1, const struct pl *pl2);

include/re_sip.h

@@ -150,6 +150,7 @@ enum {
 
 
 /** SIP Via header */
+#define RE_RFC3261_BRANCH_ID "z9hG4bK"
 struct sip_via {
 	struct pl sentby;
 	struct sa addr;

src/fmt/pl.c

@@ -536,6 +536,28 @@ int pl_strcmp(const struct pl *pl, const char *str)
 }
 
 
+/**
+ * Compare n characters of a pointer-length object with a NULL-terminated
+ * string (case-sensitive)
+ *
+ * @param pl  Pointer-length object
+ * @param str NULL-terminated string
+ * @param n   number of characters that should be compared
+ *
+ * @return 0 if match, otherwise errorcode
+ */
+int pl_strncmp(const struct pl *pl, const char *str, size_t n)
+{
+	if (!pl_isset(pl) || !str || !n)
+		return EINVAL;
+
+	if (pl->l < n)
+		return EINVAL;
+
+	return strncmp(pl->p, str, n) == 0 ? 0 : EINVAL;
+}
+
+
 /**
  * Compare a pointer-length object with a NULL-terminated string
  * (case-insensitive)