avf: move url utility functions in a separate file

libavformat/url.h

@@ -246,4 +246,41 @@ URLProtocol *ffurl_protocol_next(URLProtocol *prev);
 int ff_udp_set_remote_url(URLContext *h, const char *uri);
 int ff_udp_get_local_port(URLContext *h);
 
+/**
+ * Assemble a URL string from components. This is the reverse operation
+ * of av_url_split.
+ *
+ * Note, this requires networking to be initialized, so the caller must
+ * ensure ff_network_init has been called.
+ *
+ * @see av_url_split
+ *
+ * @param str the buffer to fill with the url
+ * @param size the size of the str buffer
+ * @param proto the protocol identifier, if null, the separator
+ *              after the identifier is left out, too
+ * @param authorization an optional authorization string, may be null.
+ *                      An empty string is treated the same as a null string.
+ * @param hostname the host name string
+ * @param port the port number, left out from the string if negative
+ * @param fmt a generic format string for everything to add after the
+ *            host/port, may be null
+ * @return the number of characters written to the destination buffer
+ */
+int ff_url_join(char *str, int size, const char *proto,
+                const char *authorization, const char *hostname,
+                int port, const char *fmt, ...) av_printf_format(7, 8);
+
+/*
+ * Convert a relative url into an absolute url, given a base url.
+ *
+ * @param buf the buffer where output absolute url is written
+ * @param size the size of buf
+ * @param base the base url, may be equal to buf.
+ * @param rel the new url, which is interpreted relative to base
+ */
+void ff_make_absolute_url(char *buf, int size, const char *base,
+                          const char *rel);
+
+
 #endif /* AVFORMAT_URL_H */