MINOR: http: Add function to get port part of a host

http_get_host_port() function can be used to get the port part of a host. It
will be used to get the port of an uri authority or a host header
value. This function only look for a port starting from the end of the
host. It is the caller responsibility to call it with a valid host value. An
indirect string is returned.

include/haproxy/http.h

@@ -36,6 +36,7 @@ extern const uint8_t http_char_classes[256];
 enum http_meth_t find_http_meth(const char *str, const int len);
 int http_get_status_idx(unsigned int status);
 const char *http_get_reason(unsigned int status);
+struct ist http_get_host_port(const struct ist host);
 int http_validate_scheme(const struct ist schm);
 struct ist http_parse_scheme(struct http_uri_parser *parser);
 struct ist http_parse_authority(struct http_uri_parser *parser, int no_userinfo);

src/http.c

@@ -478,6 +478,24 @@ const char *http_get_reason(unsigned int status)
 	}
 }
 
+/* Returns the ist string corresponding to port part (without ':') in the host
+ * <host> or IST_NULL if not found.
+*/
+struct ist http_get_host_port(const struct ist host)
+{
+	char *start, *end, *ptr;
+
+	start = istptr(host);
+	end = istend(host);
+	for (ptr = end; ptr > start && isdigit((unsigned char)*--ptr););
+
+	/* no port found */
+	if (likely(*ptr != ':' || ptr+1 == end || ptr == start))
+		return IST_NULL;
+
+	return istnext(ist2(ptr, end - ptr));
+}
+
 /* Returns non-zero if the scheme <schm> is syntactically correct according to
  * RFC3986#3.1, otherwise zero. It expects only the scheme and nothing else
  * (particularly not the following "://").