Previously, the app was not notified when the client disconnection.

This caused issues especially in cases of websocket connections and
SSE Events where the app continued to send data to the router, which
could not deliver it to the client due to the disconnection.

Changes made:

    Added functionality to send a port message to notify the app of
    client disconnection in form of port message(_NXT_PORT_MSG_CLIENT_ERROR).

    On the App side, handled this message and called the registered close_hanlder
    callback if registered.

Author: gourav-kandoria

Diff for: src/nxt_port.h

@@ -59,6 +59,8 @@ struct nxt_port_handlers_s {
     /* Status report. */
     nxt_port_handler_t  status;
 
+    nxt_port_handler_t  client_error;
+
     nxt_port_handler_t  oosm;
     nxt_port_handler_t  shm_ack;
     nxt_port_handler_t  read_queue;
@@ -115,6 +117,7 @@ typedef enum {
     _NXT_PORT_MSG_APP_RESTART     = nxt_port_handler_idx(app_restart),
     _NXT_PORT_MSG_STATUS          = nxt_port_handler_idx(status),
 
+    _NXT_PORT_MSG_CLIENT_ERROR    = nxt_port_handler_idx(client_error),
     _NXT_PORT_MSG_OOSM            = nxt_port_handler_idx(oosm),
     _NXT_PORT_MSG_SHM_ACK         = nxt_port_handler_idx(shm_ack),
     _NXT_PORT_MSG_READ_QUEUE      = nxt_port_handler_idx(read_queue),
@@ -159,6 +162,7 @@ typedef enum {
     NXT_PORT_MSG_DATA_LAST        = nxt_msg_last(_NXT_PORT_MSG_DATA),
     NXT_PORT_MSG_APP_RESTART      = nxt_msg_last(_NXT_PORT_MSG_APP_RESTART),
     NXT_PORT_MSG_STATUS           = nxt_msg_last(_NXT_PORT_MSG_STATUS),
+    NXT_PORT_MSG_CLIENT_ERROR     = nxt_msg_last(_NXT_PORT_MSG_CLIENT_ERROR),
 
     NXT_PORT_MSG_OOSM             = nxt_msg_last(_NXT_PORT_MSG_OOSM),
     NXT_PORT_MSG_SHM_ACK          = nxt_msg_last(_NXT_PORT_MSG_SHM_ACK),

Diff for: src/nxt_router.c

@@ -5300,7 +5300,16 @@ nxt_router_http_request_done(nxt_task_t *task, void *obj, void *data)
     nxt_debug(task, "router http request done (rpc_data %p)", r->req_rpc_data);
 
     if (r->req_rpc_data != NULL) {
-        nxt_request_rpc_data_unlink(task, r->req_rpc_data);
+        nxt_request_rpc_data_t  *req_rpc_data = r->req_rpc_data;
+
+        if (r->error) {
+            nxt_port_socket_write(task, req_rpc_data->app_port,
+                                  NXT_PORT_MSG_CLIENT_ERROR,
+                                  -1, req_rpc_data->stream,
+                                  task->thread->engine->port->id, NULL);
+        }
+
+        nxt_request_rpc_data_unlink(task, req_rpc_data);
     }
 
     nxt_http_request_close_handler(task, r, r->proto.any);

Diff for: src/nxt_unit.c

@@ -74,6 +74,8 @@ static int nxt_unit_request_check_response_port(nxt_unit_request_info_t *req,
 static int nxt_unit_send_req_headers_ack(nxt_unit_request_info_t *req);
 static int nxt_unit_process_websocket(nxt_unit_ctx_t *ctx,
     nxt_unit_recv_msg_t *recv_msg);
+static int nxt_unit_process_client_error(nxt_unit_ctx_t *ctx, 
+    nxt_unit_recv_msg_t *recv_msg);
 static int nxt_unit_process_shm_ack(nxt_unit_ctx_t *ctx);
 static nxt_unit_request_info_impl_t *nxt_unit_request_info_get(
     nxt_unit_ctx_t *ctx);
@@ -1121,6 +1123,9 @@ nxt_unit_process_msg(nxt_unit_ctx_t *ctx, nxt_unit_read_buf_t *rbuf,
         rc = nxt_unit_process_websocket(ctx, &recv_msg);
         break;
 
+    case _NXT_PORT_MSG_CLIENT_ERROR:
+        rc = nxt_unit_process_client_error(ctx, &recv_msg);
+        break;
     case _NXT_PORT_MSG_REMOVE_PID:
         if (nxt_slow_path(recv_msg.size != sizeof(pid))) {
             nxt_unit_alert(ctx, "#%"PRIu32": remove_pid: invalid message size "
@@ -1377,18 +1382,16 @@ nxt_unit_process_req_headers(nxt_unit_ctx_t *ctx, nxt_unit_recv_msg_t *recv_msg,
 
         lib = nxt_container_of(ctx->unit, nxt_unit_impl_t, unit);
 
+        res = nxt_unit_request_hash_add(ctx, req);
+        if (nxt_slow_path(res != NXT_UNIT_OK)) {
+            nxt_unit_req_warn(req, "failed to add request to hash");
+            nxt_unit_request_done(req, NXT_UNIT_ERROR);
+            return NXT_UNIT_ERROR;
+        }
+
         if (req->content_length
             > (uint64_t) (req->content_buf->end - req->content_buf->free))
         {
-            res = nxt_unit_request_hash_add(ctx, req);
-            if (nxt_slow_path(res != NXT_UNIT_OK)) {
-                nxt_unit_req_warn(req, "failed to add request to hash");
-
-                nxt_unit_request_done(req, NXT_UNIT_ERROR);
-
-                return NXT_UNIT_ERROR;
-            }
-
             /*
              * If application have separate data handler, we may start
              * request processing and process data when it is arrived.
@@ -1418,7 +1421,7 @@ nxt_unit_process_req_body(nxt_unit_ctx_t *ctx, nxt_unit_recv_msg_t *recv_msg)
     nxt_unit_mmap_buf_t      *b;
     nxt_unit_request_info_t  *req;
 
-    req = nxt_unit_request_hash_find(ctx, recv_msg->stream, recv_msg->last);
+    req = nxt_unit_request_hash_find(ctx, recv_msg->stream, 0);
     if (req == NULL) {
         return NXT_UNIT_OK;
     }
@@ -1722,6 +1725,26 @@ nxt_unit_process_websocket(nxt_unit_ctx_t *ctx, nxt_unit_recv_msg_t *recv_msg)
     return NXT_UNIT_OK;
 }
 
+static int
+nxt_unit_process_client_error(nxt_unit_ctx_t *ctx, nxt_unit_recv_msg_t *recv_msg)
+{
+    nxt_unit_request_info_t          *req;
+    nxt_unit_impl_t               *lib;
+
+    req = nxt_unit_request_hash_find(ctx, recv_msg->stream, 0);
+
+    if (req == NULL) {
+        return NXT_UNIT_OK;
+    }
+    
+    lib = nxt_container_of(ctx->unit, nxt_unit_impl_t, unit);
+
+    if (lib->callbacks.close_handler) {
+        lib->callbacks.close_handler(req);
+    }
+
+    return NXT_UNIT_OK;
+}
 
 static int
 nxt_unit_process_shm_ack(nxt_unit_ctx_t *ctx)