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// Licensed to the Apache Software Foundation (ASF) under one or more
// contributor license agreements. See the NOTICE file distributed with
// this work for additional information regarding copyright ownership.
// The ASF licenses this file to You 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
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
package beam
import (
// External defines a Beam external transform. The interpretation of this primitive is runner
// specific. The runner is responsible for parsing the payload based on the
// spec provided to implement the behavior of the operation. Transform
// libraries should expose an API that captures the user's intent and serialize
// the payload as a byte slice that the runner will deserialize.
func External(s Scope, spec string, payload []byte, in []PCollection, out []FullType, bounded bool) []PCollection {
return MustN(TryExternal(s, spec, payload, in, out, bounded))
// TryExternal attempts to perform the work of External, returning an error indicating why the operation
// failed.
func TryExternal(s Scope, spec string, payload []byte, in []PCollection, out []FullType, bounded bool) ([]PCollection, error) {
if !s.IsValid() {
return nil, errors.New("invalid scope")
for i, col := range in {
if !col.IsValid() {
return nil, errors.Errorf("invalid pcollection to external: index %v", i)
var ins []*graph.Node
for _, col := range in {
ins = append(ins, col.n)
edge := graph.NewExternal(s.real, s.scope, &graph.Payload{URN: spec, Data: payload}, ins, out, bounded)
var ret []PCollection
for _, out := range edge.Output {
c := PCollection{out.To}
ret = append(ret, c)
return ret, nil
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