[GitHub] [pulsar-client-go] cornelk commented on issue #328: HasNext returns false when reading last message inclusive

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

cornelk commented on issue #328:
URL: https://github.com/apache/pulsar-client-go/issues/328#issuecomment-674397141


   @quintans I had similar problems with this functionality in the past, I recreated this test in my alternative Pulsar-Go Client ( https://github.com/cornelk/pulsar-go ) to analyze the problem:
   
   ``` go
   package main
   
   import (
   	"context"
   	"fmt"
   	"log"
   	"os"
   	"testing"
   
   	"github.com/cornelk/pulsar-go"
   	"github.com/stretchr/testify/assert"
   	"github.com/stretchr/testify/require"
   )
   
   const (
   	lookupURL = "pulsar://localhost:6650"
   	topic     = "persistent://public/default/test"
   )
   
   func TestReaderLatestInclusiveHasNext(t *testing.T) {
   	l := log.New(os.Stderr, "", log.LstdFlags)
   	client, err := pulsar.NewClient(lookupURL, pulsar.WithLogger(l))
   	require.Nil(t, err)
   	defer client.Close()
   
   	ctx := context.Background()
   	err = client.Dial(ctx)
   	require.Nil(t, err)
   
   	// create producer
   	producer, err := client.NewProducer(ctx, pulsar.ProducerConfig{
   		Topic:     topic,
   		BatchSize: 1,
   	})
   	assert.Nil(t, err)
   	defer producer.Close()
   
   	// send 10 messages
   	var lastMsgID *pulsar.MessageID
   	for i := 0; i < 10; i++ {
   		lastMsgID, err = producer.WriteMessage(ctx, []byte(fmt.Sprintf("hello-%d", i)))
   		assert.NoError(t, err)
   		assert.NotNil(t, lastMsgID)
   	}
   
   	// create reader on the last message (inclusive)
   	reader, err := client.NewConsumer(ctx, pulsar.ConsumerConfig{
   		Topic:                   topic,
   		InitialPosition:         pulsar.LatestPosition,
   		StartMessageIDInclusive: true,
   	})
   
   	require.Nil(t, err)
   	defer reader.Close()
   
   	msg, err := reader.ReadMessage(context.Background())
   	require.NoError(t, err)
   
   	assert.Equal(t, []byte("hello-9"), msg.Body) // updated after original post
   	msgID := msg.ID
   
   	require.NotNil(t, msgID)
   	id1, err := lastMsgID.Marshal()
   	id2, err := msgID.Marshal()
   	assert.Equal(t, id1, id2) // updated after original post
   }
   ```
   
   The problem with your test code and my client was that after starting/subscribing the consumer, Pulsar was not done sending back the last message yet, which makes the `HasNext()` call fail. The solution for my client was to directly call `ReadMessage()`, which blocks until Pulsar sends the message back.


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