out_websocket: Add ability to provide additional headers

This adds the ability to add additional headers to the websocket handshake, identical to how we specify headers in out_http. This allows users of the websocket output to handshake with an authenticated endpoint for example.

Signed-off-by: Markus Thömmes <markusthoemmes@me.com>

plugins/out_websocket/websocket.c

@@ -43,6 +43,10 @@ static int flb_ws_handshake(struct flb_connection *u_conn,
     int ret;
     size_t bytes_sent;
     struct flb_http_client *c;
+    struct mk_list *head;
+    struct flb_config_map_val *mv;
+    struct flb_slist_entry *key = NULL;
+    struct flb_slist_entry *val = NULL;
 
     if (!u_conn) {
         flb_error("[output_ws] upstream connection error");
@@ -63,6 +67,16 @@ static int flb_ws_handshake(struct flb_connection *u_conn,
     flb_http_add_header(c, "Sec-WebSocket-Key", 17, "dGhlIHNhbXBsZSBub25jZQ==", 24);
     flb_http_add_header(c, "Sec-WebSocket-Version", 21, "13", 2);
 
+    /* Append additional headers from configuration */
+    flb_config_map_foreach(head, mv, ctx->headers) {
+        key = mk_list_entry_first(mv->val.list, struct flb_slist_entry, _head);
+        val = mk_list_entry_last(mv->val.list, struct flb_slist_entry, _head);
+
+        flb_http_add_header(c,
+                            key->str, flb_sds_len(key->str),
+                            val->str, flb_sds_len(val->str));
+    }
+
     /* Perform request*/
     ret = flb_http_do(c, &bytes_sent);
 
@@ -315,6 +329,11 @@ static struct flb_config_map config_map[] = {
      0, FLB_TRUE, offsetof(struct flb_out_ws, json_date_key),
      "Specify the name of the date field in output"
     },
+    {
+     FLB_CONFIG_MAP_SLIST_1, "header", NULL,
+     FLB_CONFIG_MAP_MULT, FLB_TRUE, offsetof(struct flb_out_ws, headers),
+     "Add a HTTP header key/value pair. Multiple headers can be set"
+    },
     /* EOF */
     {0}
 };

plugins/out_websocket/websocket.h

@@ -47,6 +47,9 @@ struct flb_out_ws {
     time_t last_input_timestamp;
     int idle_interval;
 
+    /* Arbitrary HTTP headers */
+    struct mk_list *headers;
+
     /* Plugin instance */
     struct flb_output_instance *ins;
 };