GODRIVER-1620 Correctly unwrap network errors for SDAM error handling (#410)

Author: Divjot Arora

mongo/integration/primary_stepdown_test.go

@@ -124,24 +124,4 @@ func TestConnectionsSurvivePrimaryStepDown(t *testing.T) {
 			})
 		}
 	})
-	mt.RunOpts("network errors", mtest.NewOptions().ClientOptions(clientOpts).MinServerVersion("4.0"), func(mt *mtest.T) {
-		// expect that a server's connection pool will be cleared if a non-timeout network error occurs during an
-		// operation
-
-		clearPoolChan()
-		mt.SetFailPoint(mtest.FailPoint{
-			ConfigureFailPoint: "failCommand",
-			Mode: mtest.FailPointMode{
-				Times: 1,
-			},
-			Data: mtest.FailPointData{
-				FailCommands:    []string{"insert"},
-				CloseConnection: true,
-			},
-		})
-
-		_, err := mt.Coll.InsertOne(mtest.Background, bson.D{{"test", 1}})
-		assert.NotNil(mt, err, "expected InsertOne error, got nil")
-		assert.True(mt, isPoolCleared(), "expected pool to be cleared but was not")
-	})
 }

mongo/integration/sdam_error_handling_test.go

@@ -0,0 +1,67 @@
+// Copyright (C) MongoDB, Inc. 2017-present.
+//
+// Licensed under the Apache License, Version 2.0 (the "License"); you may
+// not use this file except in compliance with the License. You may obtain
+// a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
+
+package integration
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"go.mongodb.org/mongo-driver/bson"
+	"go.mongodb.org/mongo-driver/internal/testutil/assert"
+	"go.mongodb.org/mongo-driver/mongo/integration/mtest"
+	"go.mongodb.org/mongo-driver/mongo/options"
+)
+
+func TestSDAMErrorHandling(t *testing.T) {
+	mt := mtest.New(t, noClientOpts)
+	clientOpts := options.Client().
+		ApplyURI(mt.ConnString()).
+		SetRetryWrites(false).
+		SetPoolMonitor(poolMonitor).
+		SetWriteConcern(mtest.MajorityWc)
+	mtOpts := mtest.NewOptions().
+		Topologies(mtest.ReplicaSet). // Don't run on sharded clusters to avoid complexity of sharded failpoints.
+		MinServerVersion("4.0").      // 4.0+ is required to use failpoints on replica sets.
+		ClientOptions(clientOpts)
+
+	mt.RunOpts("network errors", mtOpts, func(mt *mtest.T) {
+		mt.Run("pool cleared on non-timeout network error", func(mt *mtest.T) {
+			clearPoolChan()
+			mt.SetFailPoint(mtest.FailPoint{
+				ConfigureFailPoint: "failCommand",
+				Mode: mtest.FailPointMode{
+					Times: 1,
+				},
+				Data: mtest.FailPointData{
+					FailCommands:    []string{"insert"},
+					CloseConnection: true,
+				},
+			})
+
+			_, err := mt.Coll.InsertOne(mtest.Background, bson.D{{"test", 1}})
+			assert.NotNil(mt, err, "expected InsertOne error, got nil")
+			assert.True(mt, isPoolCleared(), "expected pool to be cleared but was not")
+		})
+		mt.Run("pool not cleared on timeout network error", func(mt *mtest.T) {
+			clearPoolChan()
+
+			_, err := mt.Coll.InsertOne(mtest.Background, bson.D{{"x", 1}})
+			assert.Nil(mt, err, "InsertOne error: %v", err)
+
+			filter := bson.M{
+				"$where": "function() { sleep(1000); return false; }",
+			}
+			timeoutCtx, cancel := context.WithTimeout(mtest.Background, 100*time.Millisecond)
+			defer cancel()
+			_, err = mt.Coll.Find(timeoutCtx, filter)
+			assert.NotNil(mt, err, "expected Find error, got %v", err)
+
+			assert.False(mt, isPoolCleared(), "expected pool to not be cleared but was")
+		})
+	})
+}

x/mongo/driver/topology/server.go

@@ -634,14 +634,22 @@ func (ss *ServerSubscription) Unsubscribe() error {
 
 // unwrapConnectionError returns the connection error wrapped by err, or nil if err does not wrap a connection error.
 func unwrapConnectionError(err error) error {
+	// This is essentially an implementation of errors.As to unwrap this error until we get a ConnectionError and then
+	// return ConnectionError.Wrapped.
+
 	connErr, ok := err.(ConnectionError)
 	if ok {
 		return connErr.Wrapped
 	}
 
 	driverErr, ok := err.(driver.Error)
-	if ok && driverErr.NetworkError() {
-		return driverErr.Wrapped
+	if !ok || !driverErr.NetworkError() {
+		return nil
+	}
+
+	connErr, ok = driverErr.Wrapped.(ConnectionError)
+	if ok {
+		return connErr.Wrapped
 	}
 
 	return nil