[GitHub] [beam] pabloem commented on a change in pull request #15996: [BEAM-13156][Playground] Implement streaming output for the run code logs

[GitBox <gi...@apache.org>]

pabloem commented on a change in pull request #15996:
URL: https://github.com/apache/beam/pull/15996#discussion_r754769661



##########
File path: playground/backend/internal/code_processing/code_processing.go
##########
@@ -93,14 +105,27 @@ func Process(ctx context.Context, cacheService cache.Cache, lc *fs_tool.LifeCycl
 	}
 
 	// build executor for run step
-	exec = runBuilder.Build()
+	executor = runBuilder.Build()
 
 	// run
 	logger.Infof("%s: Run() ...\n", pipelineId)
-	runCmd := exec.Run(ctxWithTimeout)
-	go processCmd(runCmd, successChannel, errorChannel, dataChannel)
+	runCmd := executor.Run(ctxWithTimeout)
+
+	var runError bytes.Buffer
+	runOutput := &streaming.RunOutputWriter{Ctx: ctxWithTimeout, CacheService: cacheService, PipelineId: pipelineId}

Review comment:
       I am a little confused. I think `RunOutputWriter` fails if there has not been any output, right? what happens at the very begining when there's no output at all? what adds the very first output?

##########
File path: playground/backend/internal/streaming/run_output_writer.go
##########
@@ -0,0 +1,60 @@
+// 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
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package streaming
+
+import (
+	"beam.apache.org/playground/backend/internal/cache"
+	"context"
+	"fmt"
+	"github.com/google/uuid"
+)
+
+// RunOutputWriter is used to write the run step's output to cache as a stream.
+type RunOutputWriter struct {
+	Ctx          context.Context
+	CacheService cache.Cache
+	PipelineId   uuid.UUID
+}
+
+// Write writes len(p) bytes from p to cache with cache.RunOutput subKey.
+// In case some error occurs - returns (0, error).
+// In case finished with no error - returns (len(p), nil).
+//
+// As a result new bytes will be added to cache with old run output value.
+// Example:
+// 	p = []byte(" with new run output")
+// 	before Write(p): {pipelineId}:cache.RunOutput = "old run output"
+// 	after Write(p): {pipelineId}:cache.RunOutput = "old run output with new run output"
+func (row *RunOutputWriter) Write(p []byte) (int, error) {
+	if len(p) == 0 {
+		return 0, nil
+	}
+
+	prevOutput, err := row.CacheService.GetValue(row.Ctx, row.PipelineId, cache.RunOutput)
+	if err != nil {
+		return 0, err
+	}
+
+	// concat prevValue and new value
+	str := fmt.Sprintf("%s%s", prevOutput.(string), string(p))

Review comment:
       it seems like redis supports an "append" operation that would save us having to get the last value (https://redis.io/commands/append). Maybe we should add this capability? (it's fine to leave for later)




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