REP-5894 Fall back to isMaster if hello fails. (#103)

Some migrations are from source clusters old enough to lack the `hello` command.

This changeset teaches migration-verifier to fall back to `isMaster` if the `hello` command fails.

Author: FGasper

.github/workflows/all.yml

@@ -5,12 +5,23 @@ on:
     tags-ignore:
       - '*'
   pull_request:
+  workflow_dispatch:
 
 jobs:
   basics:
     strategy:
       fail-fast: false
       matrix:
+        include:
+
+          # Testing fallback when `hello` isn’t implemented
+          # (but appendOplogNote is).
+          - mongodb_versions: [ '4.2.5', '6.0' ]
+            topology:
+              name: replset
+              srcConnStr: mongodb://localhost:27020,localhost:27021,localhost:27022
+              dstConnStr: mongodb://localhost:27030,localhost:27031,localhost:27032
+
 
         # versions are: source, destination
         mongodb_versions:

internal/util/clusterinfo.go

@@ -3,6 +3,7 @@ package util
 import (
 	"context"
 
+	"github.com/10gen/migration-verifier/internal/logger"
 	"github.com/10gen/migration-verifier/mbson"
 	"github.com/pkg/errors"
 	"github.com/samber/lo"
@@ -22,15 +23,22 @@ const (
 	TopologyReplset ClusterTopology = "replset"
 )
 
-func GetClusterInfo(ctx context.Context, client *mongo.Client) (ClusterInfo, error) {
+func GetClusterInfo(ctx context.Context, logger *logger.Logger, client *mongo.Client) (ClusterInfo, error) {
 	va, err := getVersionArray(ctx, client)
 	if err != nil {
 		return ClusterInfo{}, errors.Wrap(err, "failed to fetch version array")
 	}
 
-	topology, err := getTopology(ctx, client)
+	topology, err := getTopology(ctx, "hello", client)
 	if err != nil {
-		return ClusterInfo{}, errors.Wrap(err, "failed to determine topology")
+		logger.Info().
+			Err(err).
+			Msgf("Failed to learn topology via %#q; falling back to %#q.", "hello", "isMaster")
+
+		topology, err = getTopology(ctx, "isMaster", client)
+		if err != nil {
+			return ClusterInfo{}, errors.Wrapf(err, "failed to learn topology via %#q", "isMaster")
+		}
 	}
 
 	return ClusterInfo{
@@ -56,23 +64,22 @@ func getVersionArray(ctx context.Context, client *mongo.Client) ([]int, error) {
 	return va, nil
 }
 
-func getTopology(ctx context.Context, client *mongo.Client) (ClusterTopology, error) {
+func getTopology(ctx context.Context, cmdName string, client *mongo.Client) (ClusterTopology, error) {
+
 	resp := client.Database("admin").RunCommand(
 		ctx,
-		bson.D{{"hello", 1}},
+		bson.D{{cmdName, 1}},
 	)
 
-	hello := struct {
-		Msg string
-	}{}
+	raw, err := resp.Raw()
+	if err != nil {
+		return "", errors.Wrapf(err, "failed learn topology via %#q", cmdName)
+	}
 
-	if err := resp.Decode(&hello); err != nil {
-		return "", errors.Wrapf(
-			err,
-			"failed to decode %#q response",
-			"hello",
-		)
+	hasMsg, err := mbson.RawContains(raw, "msg")
+	if err != nil {
+		return "", errors.Wrapf(err, "failed to check for %#q in %#q response (%v)", "msg", cmdName, raw)
 	}
 
-	return lo.Ternary(hello.Msg == "isdbgrid", TopologySharded, TopologyReplset), nil
+	return lo.Ternary(hasMsg, TopologySharded, TopologyReplset), nil
 }

internal/verifier/change_stream_test.go

@@ -687,7 +687,11 @@ func (suite *IntegrationTestSuite) testInsertsBeforeWritesOff(docsCount int) {
 
 func (suite *IntegrationTestSuite) TestCreateForbidden() {
 	ctx := suite.Context()
-	buildInfo, err := util.GetClusterInfo(ctx, suite.srcMongoClient)
+	buildInfo, err := util.GetClusterInfo(
+		ctx,
+		logger.NewDefaultLogger(),
+		suite.srcMongoClient,
+	)
 	suite.Require().NoError(err)
 
 	if buildInfo.VersionArray[0] < 6 {
@@ -724,7 +728,11 @@ func (suite *IntegrationTestSuite) TestCreateForbidden() {
 
 func (suite *IntegrationTestSuite) TestTolerateDestinationCollMod() {
 	ctx := suite.Context()
-	buildInfo, err := util.GetClusterInfo(ctx, suite.dstMongoClient)
+	buildInfo, err := util.GetClusterInfo(
+		ctx,
+		logger.NewDefaultLogger(),
+		suite.dstMongoClient,
+	)
 	suite.Require().NoError(err)
 
 	if buildInfo.VersionArray[0] < 6 {

internal/verifier/integration_test_suite.go

@@ -6,6 +6,7 @@ import (
 	"time"
 
 	"github.com/10gen/migration-verifier/contextplus"
+	"github.com/10gen/migration-verifier/internal/logger"
 	"github.com/10gen/migration-verifier/internal/util"
 	mapset "github.com/deckarep/golang-set/v2"
 	"github.com/pkg/errors"
@@ -142,6 +143,7 @@ func (suite *IntegrationTestSuite) TearDownTest() {
 func (suite *IntegrationTestSuite) GetTopology(client *mongo.Client) util.ClusterTopology {
 	clusterInfo, err := util.GetClusterInfo(
 		suite.Context(),
+		logger.NewDefaultLogger(),
 		client,
 	)
 	suite.Require().NoError(err, "should fetch src cluster info")

internal/verifier/metadata_test.go

@@ -3,6 +3,7 @@ package verifier
 import (
 	"fmt"
 
+	"github.com/10gen/migration-verifier/internal/logger"
 	"github.com/10gen/migration-verifier/internal/util"
 	"github.com/10gen/migration-verifier/mslices"
 	"github.com/samber/lo"
@@ -13,10 +14,10 @@ import (
 
 func (suite *IntegrationTestSuite) TestShardingMismatch() {
 	ctx := suite.Context()
-	srcInfo, err := util.GetClusterInfo(ctx, suite.srcMongoClient)
+	srcInfo, err := util.GetClusterInfo(ctx, logger.NewDefaultLogger(), suite.srcMongoClient)
 	suite.Require().NoError(err, "should fetch src cluster info")
 
-	dstInfo, err := util.GetClusterInfo(ctx, suite.dstMongoClient)
+	dstInfo, err := util.GetClusterInfo(ctx, logger.NewDefaultLogger(), suite.dstMongoClient)
 	suite.Require().NoError(err, "should fetch dst cluster info")
 
 	dbname := suite.DBNameForTest()

internal/verifier/uri.go

@@ -17,7 +17,7 @@ func (verifier *Verifier) SetSrcURI(ctx context.Context, uri string) error {
 		return errors.Wrapf(err, "failed to connect to source %#q", uri)
 	}
 
-	clusterInfo, err := util.GetClusterInfo(ctx, verifier.srcClient)
+	clusterInfo, err := util.GetClusterInfo(ctx, verifier.logger, verifier.srcClient)
 	if err != nil {
 		return errors.Wrap(err, "failed to read source cluster info")
 	}
@@ -50,7 +50,7 @@ func (verifier *Verifier) SetDstURI(ctx context.Context, uri string) error {
 		return errors.Wrapf(err, "failed to connect to destination %#q", uri)
 	}
 
-	clusterInfo, err := util.GetClusterInfo(ctx, verifier.dstClient)
+	clusterInfo, err := util.GetClusterInfo(ctx, verifier.logger, verifier.dstClient)
 	if err != nil {
 		return errors.Wrap(err, "failed to read destination build info")
 	}