lib/fetch: reuse http connection

With HTTP 1.1 persistent connection is default and Connection
header is not sent.
Before patch, for every file, including 512b signature, there was
done dns query, tls handshake etc.

Author: Chocimier

lib/fetch/http.c

@@ -424,7 +424,7 @@ http_cmd(conn_t *conn, const char *fmt, ...)
  * Get and parse status line
  */
 static int
-http_get_reply(conn_t *conn)
+http_get_reply(conn_t *conn, int *keep_alive)
 {
 	char *p;
 
@@ -445,6 +445,10 @@ http_get_reply(conn_t *conn)
 	if (*p == '/') {
 		if (p[1] != '1' || p[2] != '.' || (p[3] != '0' && p[3] != '1'))
 			return (HTTP_PROTOCOL_ERROR);
+		/* HTTP/1.1 defaults to the use of "persistent connections" */
+		if (keep_alive && p[3] == '1') {
+			*keep_alive = 1;
+		}
 		p += 4;
 	}
 	if (*p != ' ' ||
@@ -760,7 +764,7 @@ http_connect(struct url *URL, struct url *purl, const char *flags, int *cached)
 
 		http_cmd(conn, "\r\n");
 
-		if (http_get_reply(conn) != HTTP_OK) {
+		if (http_get_reply(conn, NULL) != HTTP_OK) {
 			http_seterr(conn->err);
 			fetch_close(conn);
 			return (NULL);
@@ -1011,7 +1015,7 @@ http_request(struct url *URL, const char *op, struct url_stat *us,
 			   sizeof(val));
 
 		/* get reply */
-		switch (http_get_reply(conn)) {
+		switch (http_get_reply(conn, &keep_alive)) {
 		case HTTP_OK:
 		case HTTP_PARTIAL:
 		case HTTP_NOT_MODIFIED: