Gracefully return error when no callback defined for response (#494)

Fixes #492 

Co-authored-by: Rouven Bauer <rouven.bauer@neo4j.com>

neo4j/internal/bolt/message_queue.go

@@ -23,6 +23,7 @@ import (
 	"container/list"
 	"context"
 	"errors"
+	"fmt"
 	"github.com/neo4j/neo4j-go-driver/v5/neo4j/db"
 	"github.com/neo4j/neo4j-go-driver/v5/neo4j/log"
 	"net"
@@ -153,19 +154,39 @@ func (q *messageQueue) receive(ctx context.Context) error {
 	if q.handlers.Len() == 0 {
 		return errors.New("no more response callback to apply")
 	}
-	callback := q.pop()
+	handler := q.pop()
 	switch message := res.(type) {
 	case *db.Record:
-		callback.onRecord(message)
+		onRecord := handler.onRecord
+		if onRecord == nil {
+			return errors.New("protocol violation: the server sent an unexpected RECORD response")
+		}
+		onRecord(message)
 	case *success:
-		callback.onSuccess(message)
+		onSuccess := handler.onSuccess
+		if onSuccess == nil {
+			return errors.New("protocol violation: the server sent an unexpected SUCCESS response")
+		}
+		onSuccess(message)
 	case *db.Neo4jError:
-		callback.onFailure(ctx, message)
+		onFailure := handler.onFailure
+		if onFailure == nil {
+			return errors.New("protocol violation: the server sent an unexpected FAILURE response")
+		}
+		onFailure(ctx, message)
 		return message
 	case *ignored:
-		callback.onIgnored(message)
+		onIgnored := handler.onIgnored
+		if onIgnored == nil {
+			return errors.New("protocol violation: the server sent an unexpected IGNORED response")
+		}
+		onIgnored(message)
 	default:
-		callback.onUnknown(message)
+		onUnknown := handler.onUnknown
+		if onUnknown == nil {
+			return fmt.Errorf("protocol violation: the server sent an unknown %v response", message)
+		}
+		onUnknown(message)
 	}
 	return nil
 }
@@ -195,8 +216,8 @@ func (q *messageQueue) receiveMsg(ctx context.Context) any {
 	return msg
 }
 
-func (q *messageQueue) enqueueCallback(callbacks responseHandler) {
-	q.handlers.PushBack(callbacks)
+func (q *messageQueue) enqueueCallback(handler responseHandler) {
+	q.handlers.PushBack(handler)
 }
 
 func (q *messageQueue) setLogId(logId string) {

neo4j/internal/bolt/message_queue_test.go

@@ -22,6 +22,7 @@ package bolt
 import (
 	"bytes"
 	"context"
+	"fmt"
 	"github.com/neo4j/neo4j-go-driver/v5/neo4j/db"
 	. "github.com/neo4j/neo4j-go-driver/v5/neo4j/internal/testutil"
 	"net"
@@ -227,7 +228,70 @@ func TestMessageQueue(outer *testing.T) {
 			writer.send(ctx, server)
 			<-done
 		})
+
+		inner.Run("returns error when nil callback called for", func(inner *testing.T) {
+			inner.Parallel()
+
+			type testCase struct {
+				description      string
+				writerWork       func(*outgoing)
+				expectedErrorMsg string
+			}
+
+			testCases := []testCase{
+				{
+					description: "RECORD",
+					writerWork: func(o *outgoing) {
+						writer.appendX(msgRecord, []any{})
+						writer.send(ctx, server)
+					},
+					expectedErrorMsg: "protocol violation: the server sent an unexpected RECORD response",
+				},
+				{
+					description: "SUCCESS",
+					writerWork: func(o *outgoing) {
+						writer.appendX(msgSuccess, map[string]any{})
+						writer.send(ctx, server)
+					},
+					expectedErrorMsg: "protocol violation: the server sent an unexpected SUCCESS response",
+				},
+				{
+					description: "FAILURE",
+					writerWork: func(o *outgoing) {
+						writer.appendX(msgFailure, map[string]any{})
+						writer.send(ctx, server)
+					},
+					expectedErrorMsg: "protocol violation: the server sent an unexpected FAILURE response",
+				},
+				{
+					description: "IGNORED",
+					writerWork: func(o *outgoing) {
+						writer.appendX(msgIgnored)
+						writer.send(ctx, server)
+					},
+					expectedErrorMsg: "protocol violation: the server sent an unexpected IGNORED response",
+				},
+			}
+
+			for _, test := range testCases {
+				inner.Run(fmt.Sprintf("%s response", test.description), func(t *testing.T) {
+					done := make(chan any)
+					queue.enqueueCallback(responseHandler{})
+
+					go func() {
+						err := queue.receive(ctx)
+
+						AssertErrorMessageContains(t, err, test.expectedErrorMsg)
+						done <- struct{}{}
+					}()
+
+					test.writerWork(writer)
+					<-done
+				})
+			}
+		})
 	})
+
 }
 
 func assertEqualResponseHandlers(t *testing.T, handler1, handler2 responseHandler) {