Fix possible segfaults when header allocation fails

This fixes some possible segfaults that could happen if the header
(re)allocation fails.

src/format.c

@@ -282,6 +282,14 @@ int format_advance_queue(source_t *source, client_t *client)
 }
 
 
+/* Prepare headers
+ * If any error occurs in this function, return -1
+ * Do not send a error to the client using client_send_error
+ * here but instead set client->respcode to 500.
+ * Else client_send_error will destroy and free the client and all
+ * calling functions will use a already freed client struct and
+ * cause a segfault!
+ */
 static int format_prepare_headers (source_t *source, client_t *client)
 {
     unsigned remaining;
@@ -297,7 +305,7 @@ static int format_prepare_headers (source_t *source, client_t *client)
     bytes = util_http_build_header(ptr, remaining, 0, 0, 200, NULL, source->format->contenttype, NULL, NULL, source, client);
     if (bytes == -1) {
         ICECAST_LOG_ERROR("Dropping client as we can not build response headers.");
-        client_send_error(client, 500, 0, "Header generation failed.");
+        client->respcode = 500;
         return -1;
     } else if ((bytes + 1024) >= remaining) { /* we don't know yet how much to follow but want at least 1kB free space */
         void *new_ptr = realloc(ptr, bytes + 1024);
@@ -308,12 +316,12 @@ static int format_prepare_headers (source_t *source, client_t *client)
             bytes = util_http_build_header(ptr, remaining, 0, 0, 200, NULL, source->format->contenttype, NULL, NULL, source, client);
             if (bytes == -1 ) {
                 ICECAST_LOG_ERROR("Dropping client as we can not build response headers.");
-                client_send_error(client, 500, 0, "Header generation failed.");
+                client->respcode = 500;
                 return -1;
             }
         } else {
             ICECAST_LOG_ERROR("Client buffer reallocation failed. Dropping client.");
-            client_send_error(client, 500, 0, "Buffer reallocation failed.");
+            client->respcode = 500;
             return -1;
         }
     }

src/source.c

@@ -952,12 +952,18 @@ static int _free_client(void *key)
 {
     client_t *client = (client_t *)key;
 
-    /* if no response has been sent then send a 404 */
-    if (client->respcode == 0)
-        client_send_error(client, 404, 0, "Mount unavailable");
-    else
-        client_destroy(client);
-
+    switch (client->respcode) {
+        case 0:
+            /* if no response has been sent then send a 404 */
+            client_send_error(client, 404, 0, "Mount unavailable");
+            break;
+        case 500:
+            client_send_error(client, 500, 0, "Stream preparation error");
+            break;
+        default:
+            client_destroy(client);
+            break;
+    }
     return 1;
 }