mongo: mongo version check during validation (#3166)

- Check mongo version for validation.
- Small refactors to use bson struct tags for deserialization.
- Extract shared logic to shared/mongo/validation.go
- Default read preference mode to SecondaryPreferred, which read from
primary only if secondary does not exists -- we should still support
read from primary via uri if user prefers, will work on this as a
subsequent PR as we separate out username/password from rest of uri.

Test: locally tested deserialization.

Author: jgao54

.github/workflows/flow.yml

@@ -328,10 +328,18 @@ jobs:
             </keeper_server>
           </clickhouse>
           EOF
-          mkdir ch1 ch2 chkeep
+          mkdir chkeep ch1 ch2
+          (cd chkeep && ../clickhouse keeper -C ../config-keeper.xml) &
+          while true; do
+            if echo "ruok" | nc -w 3 127.0.0.1 2181 2>/dev/null | grep -q "imok"; then
+                break
+            fi
+            echo "Waiting for keeper..."
+            sleep 1
+          done
+          sleep 5
           (cd ch1 && ../clickhouse server -C ../config1.xml) &
           (cd ch2 && ../clickhouse server -C ../config2.xml) &
-          (cd chkeep && ../clickhouse keeper -C ../config-keeper.xml) &
 
       - name: Install Temporal CLI
         uses: temporalio/setup-temporal@1059a504f87e7fa2f385e3fa40d1aa7e62f1c6ca # v0

flow/connectors/mongo/mongo.go

@@ -21,6 +21,7 @@ import (
 	"github.com/PeerDB-io/peerdb/flow/model"
 	"github.com/PeerDB-io/peerdb/flow/otel_metrics"
 	"github.com/PeerDB-io/peerdb/flow/shared"
+	peerdb_mongo "github.com/PeerDB-io/peerdb/flow/shared/mongo"
 	"github.com/PeerDB-io/peerdb/flow/shared/types"
 )
 
@@ -45,7 +46,7 @@ func NewMongoConnector(ctx context.Context, config *protos.MongoConfig) (*MongoC
 
 	client, err := mongo.Connect(options.Client().
 		SetAppName("PeerDB Mongo Connector").
-		SetReadPreference(readpref.Primary()).
+		SetReadPreference(readpref.SecondaryPreferred()).
 		SetCompressors([]string{"zstd", "snappy"}).
 		ApplyURI(config.Uri))
 	if err != nil {
@@ -80,47 +81,11 @@ func (c *MongoConnector) ConnectionActive(ctx context.Context) error {
 }
 
 func (c *MongoConnector) GetVersion(ctx context.Context) (string, error) {
-	db := c.client.Database("admin")
-
-	var buildInfoDoc bson.M
-	if err := db.RunCommand(ctx, bson.D{bson.E{Key: "buildInfo", Value: 1}}).Decode(&buildInfoDoc); err != nil {
-		return "", fmt.Errorf("failed to run buildInfo command: %w", err)
-	}
-
-	version, ok := buildInfoDoc["version"].(string)
-	if !ok {
-		return "", fmt.Errorf("buildInfo.version is not a string, but %T", buildInfoDoc["version"])
-	}
-	return version, nil
-}
-
-func (c *MongoConnector) ValidateMirrorSource(ctx context.Context, cfg *protos.FlowConnectionConfigs) error {
-	if cfg.DoInitialSnapshot && cfg.InitialSnapshotOnly {
-		return nil
-	}
-
-	// Check if MongoDB is configured as a replica set
-	var result bson.M
-	if err := c.client.Database("admin").RunCommand(ctx, bson.D{
-		{Key: "replSetGetStatus", Value: 1},
-	}).Decode(&result); err != nil {
-		return fmt.Errorf("failed to get replica set status: %w", err)
-	}
-
-	// Check if this is a replica set
-	if _, ok := result["set"]; !ok {
-		return errors.New("MongoDB is not configured as a replica set, which is required for CDC")
-	}
-
-	if myState, ok := result["myState"]; !ok {
-		return errors.New("myState not found in response")
-	} else if myStateInt, ok := myState.(int32); !ok {
-		return fmt.Errorf("failed to convert myState %v to int32", myState)
-	} else if myStateInt != 1 {
-		return fmt.Errorf("MongoDB is not the primary node in the replica set, current state: %d", myState)
+	buildInfo, err := peerdb_mongo.GetBuildInfo(ctx, c.client)
+	if err != nil {
+		return "", err
 	}
-
-	return nil
+	return buildInfo.Version, nil
 }
 
 func (c *MongoConnector) GetTableSchema(

flow/connectors/mongo/validate.go

@@ -0,0 +1,36 @@
+package connmongo
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/PeerDB-io/peerdb/flow/generated/protos"
+	shared_mongo "github.com/PeerDB-io/peerdb/flow/shared/mongo"
+)
+
+func (c *MongoConnector) ValidateCheck(ctx context.Context) error {
+	version, err := c.GetVersion(ctx)
+	if err != nil {
+		return err
+	}
+	cmp, err := shared_mongo.CompareServerVersions(version, shared_mongo.MinSupportedVersion)
+	if err != nil {
+		return err
+	}
+	if cmp == -1 {
+		return fmt.Errorf("require minimum mongo version %s", shared_mongo.MinSupportedVersion)
+	}
+	return nil
+}
+
+func (c *MongoConnector) ValidateMirrorSource(ctx context.Context, cfg *protos.FlowConnectionConfigs) error {
+	if cfg.DoInitialSnapshot && cfg.InitialSnapshotOnly {
+		return nil
+	}
+
+	_, err := shared_mongo.GetReplSetGetStatus(ctx, c.client)
+	if err != nil {
+		return fmt.Errorf("failed to get replica set status: %w", err)
+	}
+	return nil
+}

flow/shared/mongo/util.go

@@ -0,0 +1,44 @@
+package mongo
+
+import (
+	"cmp"
+	"fmt"
+	"strconv"
+	"strings"
+)
+
+func CompareServerVersions(a, b string) (int, error) {
+	aMajor, aRest, _ := strings.Cut(a, ".")
+	bMajor, bRest, _ := strings.Cut(b, ".")
+
+	if majorCompare, err := compareSubVersion("major", aMajor, bMajor, a, b); err != nil || majorCompare != 0 {
+		return majorCompare, err
+	}
+
+	aMinor, aPatch, _ := strings.Cut(aRest, ".")
+	bMinor, bPatch, _ := strings.Cut(bRest, ".")
+
+	if minorCompare, err := compareSubVersion("minor", aMinor, bMinor, a, b); err != nil || minorCompare != 0 {
+		return minorCompare, err
+	}
+
+	return compareSubVersion("patch", aPatch, bPatch, a, b)
+}
+
+func compareSubVersion(typ, a, b, aFull, bFull string) (int, error) {
+	if a == "" || b == "" {
+		return 0, nil
+	}
+
+	var aNum, bNum int
+	var err error
+
+	if aNum, err = strconv.Atoi(a); err != nil {
+		return 0, fmt.Errorf("cannot parse %s version %s of %s", typ, a, aFull)
+	}
+	if bNum, err = strconv.Atoi(b); err != nil {
+		return 0, fmt.Errorf("cannot parse %s version %s of %s", typ, b, bFull)
+	}
+
+	return cmp.Compare(aNum, bNum), nil
+}

flow/shared/mongo/validation.go

@@ -0,0 +1,46 @@
+package mongo
+
+import (
+	"context"
+	"fmt"
+
+	"go.mongodb.org/mongo-driver/v2/bson"
+	"go.mongodb.org/mongo-driver/v2/mongo"
+)
+
+const MinSupportedVersion = "5.1.0"
+
+type BuildInfo struct {
+	Version string `bson:"version"`
+}
+
+type ReplSetGetStatus struct {
+	Set     string `bson:"set"`
+	MyState int    `bson:"myState"`
+}
+
+func GetBuildInfo(ctx context.Context, client *mongo.Client) (*BuildInfo, error) {
+	singleResult := client.Database("admin").RunCommand(ctx, bson.D{bson.E{Key: "buildInfo", Value: 1}})
+	if singleResult.Err() != nil {
+		return nil, fmt.Errorf("failed to run 'buildInfo' command: %w", singleResult.Err())
+	}
+	var info BuildInfo
+	if err := singleResult.Decode(&info); err != nil {
+		return nil, fmt.Errorf("failed to decode BuildInfo: %w", err)
+	}
+	return &info, nil
+}
+
+func GetReplSetGetStatus(ctx context.Context, client *mongo.Client) (*ReplSetGetStatus, error) {
+	singleResult := client.Database("admin").RunCommand(ctx, bson.D{
+		bson.E{Key: "replSetGetStatus", Value: 1},
+	})
+	if singleResult.Err() != nil {
+		return nil, fmt.Errorf("failed to run 'replSetGetStatus' command: %w", singleResult.Err())
+	}
+	var status ReplSetGetStatus
+	if err := singleResult.Decode(&status); err != nil {
+		return nil, fmt.Errorf("failed to decode ReplSetGetStatus: %w", err)
+	}
+	return &status, nil
+}