apache/beam · error

mongodbio.newReadFn: %v

Error message

mongodbio.newReadFn: %v

What it means

newReadFn encodes the ReadOption's filter into BSON before building the read DoFn. If encodeBSON fails (e.g. the filter contains values not marshalable to BSON), it panics because the transform cannot be constructed. This happens at pipeline-construction time, not at runtime.

Source

Thrown at sdks/go/pkg/beam/io/mongodbio/read.go:115

	mongoDBFn
	BucketAuto bool
	BundleSize int64
	Filter     []byte
	Type       beam.EncodedType
	filter     bson.M
	projection bson.D
}

func newReadFn(
	uri string,
	database string,
	collection string,
	t reflect.Type,
	option *ReadOption,
) *readFn {
	filter, err := encodeBSON[bson.M](option.Filter)
	if err != nil {
		panic(fmt.Sprintf("mongodbio.newReadFn: %v", err))
	}

	return &readFn{
		mongoDBFn: mongoDBFn{
			URI:        uri,
			Database:   database,
			Collection: collection,
		},
		BucketAuto: option.BucketAuto,
		BundleSize: option.BundleSize,
		Filter:     filter,
		Type:       beam.EncodedType{T: t},
	}
}

func (fn *readFn) Setup(ctx context.Context) error {
	var err error
	if err = fn.mongoDBFn.Setup(ctx); err != nil {

View on GitHub (pinned to 12126d8942)

Solutions

1. Ensure option.Filter is a bson.M / map[string]interface{} with BSON-supported value types
2. Test bson.Marshal(filter) standalone before building the pipeline to reproduce the marshal error
3. Replace unsupported field types (e.g. time in wrong format, non-UTF8 strings, funcs)
4. Upgrade the mongo-driver if the marshal error is a known type-support issue

Example fix

// before
opt.Filter = map[string]interface{}{"ts": someChannelOrFunc}
mongodbio.Read(s, scope, uri, db, col, typ, opt)
// after
opt.Filter = bson.M{"ts": bson.M{"$gte": time.Now().Add(-time.Hour)}}
mongodbio.Read(s, scope, uri, db, col, typ, opt)

if _, err := bson.Marshal(option.Filter); err != nil {
    return fmt.Errorf("filter not BSON-marshalable: %w", err)
}

func isBSONSafe(m bson.M) bool { b, err := bson.Marshal(m); return err == nil && b != nil }

defer func() { if r := recover(); r != nil { log.Fatalf("readFn construction: %v", r) } }()

When it happens

Trigger: Calling Read with a Filter option containing unsupported Go types (channels, funcs, cyclic structures) or an invalid shape that mongo's bson marshaler rejects.

Common situations: Building filters dynamically with unmarshaled JSON producing types bson cannot encode; embedding a struct with no BSON-marshalable fields; driver version incompatibilities with map types.

Understand the failure class

Background: json.Marshal / "failed to marshal" errors in Go: why "unsupported type" happens and how to fix it — this error's family across 22 libraries.

Related errors

• error encoding BSON: %w
• error decoding BSON: %w
• error decoding document ID: %w
• error decoding document: %w
• err

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/1829e66a1db702d2. Report an issue: GitHub.