MINOR: http: Add function to detect default port

http_is_default_port() can be used to test if a port is a default HTTP/HTTPS
port. A scheme may be specified. In this case, it is used to detect defaults
ports, 80 for "http://" and 443 for "https://". Otherwise, with no scheme, both
are considered as default ports.

include/haproxy/http.h

@@ -37,6 +37,7 @@ 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_is_default_port(const struct ist schm, const struct ist port);
 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

@@ -496,6 +496,20 @@ struct ist http_get_host_port(const struct ist host)
 	return istnext(ist2(ptr, end - ptr));
 }
 
+
+/* Return non-zero if the port <port> is a default port. If the scheme <schm> is
+ * set, it is used to detect default ports (HTTP => 80 and HTTPS => 443)
+ * port. Otherwise, both are considered as default ports.
+ */
+int http_is_default_port(const struct ist schm, const struct ist port)
+{
+	if (!isttest(schm))
+		return (isteq(port, ist("443")) || isteq(port, ist("80")));
+	else
+		return (isteq(port, ist("443")) && isteqi(schm, ist("https://"))) ||
+			(isteq(port, ist("80")) && isteqi(schm, ist("http://")));
+}
+
 /* 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 "://").