rtsp: send responses as single packets

Under some circumstances, RTSP responses would be split into multiple
packets. This causes Airfoil to barf, as it interprets the end of the
packet as the end of the response. Since TCP_CORK is not portable, this
fix buffers the packet on the stack before using a single write.
This fixes issue #213.

rtsp.c

@@ -331,22 +331,32 @@ static rtsp_message * rtsp_read_request(int fd) {
 }
 
 static void msg_write_response(int fd, rtsp_message *resp) {
-    char rbuf[30];
-    int nrbuf;
-    nrbuf = snprintf(rbuf, sizeof(rbuf),
-                     "RTSP/1.0 %d %s\r\n", resp->respcode,
-                     resp->respcode==200 ? "OK" : "Error");
-    write(fd, rbuf, nrbuf);
-    debug(1, "sending response: %s", rbuf);
-    int i;
+    char pkt[1024];
+    int pktfree = sizeof(pkt);
+    char *p = pkt;
+    int i, n;
+
+    n = snprintf(p, pktfree,
+                 "RTSP/1.0 %d %s\r\n", resp->respcode,
+                 resp->respcode==200 ? "OK" : "Error");
+    debug(1, "sending response: %s", pkt);
+    pktfree -= n;
+    p += n;
+
     for (i=0; i<resp->nheaders; i++) {
         debug(2, "    %s: %s\n", resp->name[i], resp->value[i]);
-        write(fd, resp->name[i], strlen(resp->name[i]));
-        write(fd, ": ", 2);
-        write(fd, resp->value[i], strlen(resp->value[i]));
-        write(fd, "\r\n", 2);
+        n = snprintf(p, pktfree, "%s: %s\r\n", resp->name[i], resp->value[i]);
+        pktfree -= n;
+        p += n;
+        if (pktfree <= 0)
+            die("Attempted to write overlong RTSP packet");
     }
-    write(fd, "\r\n", 2);
+
+    if (pktfree < 3)
+        die("Attempted to write overlong RTSP packet");
+
+    strcpy(p, "\r\n");
+    write(fd, pkt, p-pkt+2);
 }
 
 static void handle_options(rtsp_conn_info *conn,