rpc: add ability to get WSClient connection closure error

Close #2421.

pkg/rpc/client/wsclient.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"encoding/json"
 	"errors"
+	"fmt"
 	"strconv"
 	"sync"
 	"time"
@@ -41,6 +42,9 @@ type WSClient struct {
 	shutdown    chan struct{}
 	closeCalled atomic.Bool
 
+	closeErrLock sync.RWMutex
+	closeErr     error
+
 	subscriptionsLock sync.RWMutex
 	subscriptions     map[string]bool
 
@@ -128,27 +132,38 @@ func (c *WSClient) Close() {
 
 func (c *WSClient) wsReader() {
 	c.ws.SetReadLimit(wsReadLimit)
-	c.ws.SetPongHandler(func(string) error { return c.ws.SetReadDeadline(time.Now().Add(wsPongLimit)) })
+	c.ws.SetPongHandler(func(string) error {
+		err := c.ws.SetReadDeadline(time.Now().Add(wsPongLimit))
+		if err != nil {
+			c.setCloseErr(fmt.Errorf("failed to set pong read deadline: %w", err))
+		}
+		return err
+	})
+	var connCloseErr error
 readloop:
 	for {
 		rr := new(requestResponse)
 		err := c.ws.SetReadDeadline(time.Now().Add(wsPongLimit))
 		if err != nil {
+			connCloseErr = fmt.Errorf("failed to set response read deadline: %w", err)
 			break
 		}
 		err = c.ws.ReadJSON(rr)
 		if err != nil {
 			// Timeout/connection loss/malformed response.
+			connCloseErr = fmt.Errorf("failed to read JSON response (timeout/connection loss/malformed response): %w", err)
 			break
 		}
 		if rr.RawID == nil && rr.Method != "" {
 			event, err := response.GetEventIDFromString(rr.Method)
 			if err != nil {
 				// Bad event received.
+				connCloseErr = fmt.Errorf("failed to perse event ID from string %s: %w", rr.Method, err)
 				break
 			}
 			if event != response.MissedEventID && len(rr.RawParams) != 1 {
 				// Bad event received.
+				connCloseErr = fmt.Errorf("bad event received: %s / %d", event, len(rr.RawParams))
 				break
 			}
 			var val interface{}
@@ -157,7 +172,8 @@ readloop:
 				sr, err := c.StateRootInHeader()
 				if err != nil {
 					// Client is not initialized.
-					break
+					connCloseErr = fmt.Errorf("failed to fetch StateRootInHeader: %w", err)
+					break readloop
 				}
 				val = block.New(sr)
 			case response.TransactionEventID:
@@ -172,12 +188,14 @@ readloop:
 				// No value.
 			default:
 				// Bad event received.
+				connCloseErr = fmt.Errorf("unknown event received: %d", event)
 				break readloop
 			}
 			if event != response.MissedEventID {
 				err = json.Unmarshal(rr.RawParams[0].RawMessage, val)
 				if err != nil {
 					// Bad event received.
+					connCloseErr = fmt.Errorf("failed to unmarshal event of type %s from JSON: %w", event, err)
 					break
 				}
 			}
@@ -190,18 +208,24 @@ readloop:
 			resp.Result = rr.Result
 			id, err := strconv.Atoi(string(resp.ID))
 			if err != nil {
+				connCloseErr = fmt.Errorf("failed to retrieve response ID from string %s: %w", string(resp.ID), err)
 				break // Malformed response (invalid response ID).
 			}
 			ch := c.getResponseChannel(uint64(id))
 			if ch == nil {
+				connCloseErr = fmt.Errorf("unknown response channel for response %d", id)
 				break // Unknown response (unexpected response ID).
 			}
 			ch <- resp
 		} else {
 			// Malformed response, neither valid request, nor valid response.
+			connCloseErr = fmt.Errorf("malformed response")
 			break
 		}
 	}
+	if connCloseErr != nil {
+		c.setCloseErr(connCloseErr)
+	}
 	close(c.done)
 	c.respLock.Lock()
 	for _, ch := range c.respChannels {
@@ -216,6 +240,8 @@ func (c *WSClient) wsWriter() {
 	pingTicker := time.NewTicker(wsPingPeriod)
 	defer c.ws.Close()
 	defer pingTicker.Stop()
+	var connCloseErr error
+writeloop:
 	for {
 		select {
 		case <-c.shutdown:
@@ -227,20 +253,27 @@ func (c *WSClient) wsWriter() {
 				return
 			}
 			if err := c.ws.SetWriteDeadline(time.Now().Add(c.opts.RequestTimeout)); err != nil {
-				return
+				connCloseErr = fmt.Errorf("failed to set request write deadline: %w", err)
+				break writeloop
 			}
 			if err := c.ws.WriteJSON(req); err != nil {
-				return
+				connCloseErr = fmt.Errorf("failed to write JSON request: %w", err)
+				break writeloop
 			}
 		case <-pingTicker.C:
 			if err := c.ws.SetWriteDeadline(time.Now().Add(wsWriteLimit)); err != nil {
-				return
+				connCloseErr = fmt.Errorf("failed to set ping write deadline: %w", err)
+				break writeloop
 			}
 			if err := c.ws.WriteMessage(websocket.PingMessage, []byte{}); err != nil {
-				return
+				connCloseErr = fmt.Errorf("failed to write ping message: %w", err)
+				break writeloop
 			}
 		}
 	}
+	if connCloseErr != nil {
+		c.setCloseErr(connCloseErr)
+	}
 }
 
 func (c *WSClient) unregisterRespChannel(id uint64) {
@@ -399,3 +432,21 @@ func (c *WSClient) UnsubscribeAll() error {
 	}
 	return nil
 }
+
+// setCloseErr is a thread-safe method setting closeErr in case if it's not yet set.
+func (c *WSClient) setCloseErr(err error) {
+	c.closeErrLock.Lock()
+	defer c.closeErrLock.Unlock()
+
+	if c.closeErr == nil {
+		c.closeErr = err
+	}
+}
+
+// GetError returns the reason of WS connection closing.
+func (c *WSClient) GetError() error {
+	c.closeErrLock.RLock()
+	defer c.closeErrLock.RUnlock()
+
+	return c.closeErr
+}

pkg/rpc/client/wsclient_test.go

@@ -15,6 +15,8 @@ import (
 
 	"github.com/gorilla/websocket"
 	"github.com/nspcc-dev/neo-go/pkg/config/netmode"
+	"github.com/nspcc-dev/neo-go/pkg/core/transaction"
+	"github.com/nspcc-dev/neo-go/pkg/network/payload"
 	"github.com/nspcc-dev/neo-go/pkg/rpc/request"
 	"github.com/nspcc-dev/neo-go/pkg/util"
 	"github.com/stretchr/testify/require"
@@ -468,3 +470,36 @@ func TestWS_RequestAfterClose(t *testing.T) {
 	require.Error(t, err)
 	require.True(t, strings.Contains(err.Error(), "connection lost before registering response channel"))
 }
+
+func TestWSClient_ConnClosedError(t *testing.T) {
+	srv := initTestServer(t, "")
+
+	t.Run("standard closing", func(t *testing.T) {
+		c, err := NewWS(context.TODO(), httpURLtoWS(srv.URL), Options{})
+		require.NoError(t, err)
+
+		c.Close()
+
+		err = c.GetError()
+		require.Error(t, err)
+		require.True(t, strings.Contains(err.Error(), "use of closed network connection"))
+	})
+
+	t.Run("malformed request", func(t *testing.T) {
+		c, err := NewWS(context.TODO(), httpURLtoWS(srv.URL), Options{})
+		require.NoError(t, err)
+
+		defaultMaxBlockSize := 262144
+		_, err = c.SubmitP2PNotaryRequest(&payload.P2PNotaryRequest{
+			MainTransaction: &transaction.Transaction{
+				Script: make([]byte, defaultMaxBlockSize*3),
+			},
+			FallbackTransaction: &transaction.Transaction{},
+		})
+		require.Error(t, err)
+
+		err = c.GetError()
+		require.Error(t, err)
+		require.True(t, strings.Contains(err.Error(), "failed to read JSON response (timeout/connection loss/malformed response)"), err.Error())
+	})
+}