From b34cfc47c4e0240b728f28e62f829dc25408746b Mon Sep 17 00:00:00 2001
From: Tyler Yahn <MrAlias@users.noreply.github.com>
Date: Mon, 22 Apr 2024 07:21:49 -0700
Subject: [PATCH] Default implementation for empty BatchProcessor (#5239)

Ensure an empty BatchProcessor does not panic when any method is called.
Default an empty BatchProcessor as being shut down.
---
 sdk/log/batch.go      | 12 +++++++-----
 sdk/log/batch_test.go | 12 ++++++++++++
 2 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/sdk/log/batch.go b/sdk/log/batch.go
index 5cb9f5956..2e705c86a 100644
--- a/sdk/log/batch.go
+++ b/sdk/log/batch.go
@@ -29,7 +29,9 @@ const (
 var _ Processor = (*BatchProcessor)(nil)
 
 // BatchProcessor is a processor that exports batches of log records.
-// A BatchProcessor must be created with [NewBatchProcessor].
+//
+// Use [NewBatchProcessor] to create a BatchProcessor. An empty BatchProcessor
+// is shut down by default, no records will be batched or exported.
 type BatchProcessor struct {
 	// The BatchProcessor is designed to provide the highest throughput of
 	// log records possible while being compatible with OpenTelemetry. The
@@ -170,7 +172,7 @@ func (b *BatchProcessor) poll(interval time.Duration) (done chan struct{}) {
 
 // OnEmit batches provided log record.
 func (b *BatchProcessor) OnEmit(_ context.Context, r Record) error {
-	if b.stopped.Load() {
+	if b.stopped.Load() || b.q == nil {
 		return nil
 	}
 	if n := b.q.Enqueue(r); n >= b.batchSize {
@@ -187,12 +189,12 @@ func (b *BatchProcessor) OnEmit(_ context.Context, r Record) error {
 
 // Enabled returns if b is enabled.
 func (b *BatchProcessor) Enabled(context.Context, Record) bool {
-	return !b.stopped.Load()
+	return !b.stopped.Load() && b.q != nil
 }
 
 // Shutdown flushes queued log records and shuts down the decorated exporter.
 func (b *BatchProcessor) Shutdown(ctx context.Context) error {
-	if b.stopped.Swap(true) {
+	if b.stopped.Swap(true) || b.q == nil {
 		return nil
 	}
 
@@ -219,7 +221,7 @@ var ctxErr = func(ctx context.Context) error {
 
 // ForceFlush flushes queued log records and flushes the decorated exporter.
 func (b *BatchProcessor) ForceFlush(ctx context.Context) error {
-	if b.stopped.Load() {
+	if b.stopped.Load() || b.q == nil {
 		return nil
 	}
 
diff --git a/sdk/log/batch_test.go b/sdk/log/batch_test.go
index 539f04d60..90630ac6b 100644
--- a/sdk/log/batch_test.go
+++ b/sdk/log/batch_test.go
@@ -18,6 +18,18 @@ import (
 	"go.opentelemetry.io/otel/log"
 )
 
+func TestEmptyBatchConfig(t *testing.T) {
+	assert.NotPanics(t, func() {
+		var bp BatchProcessor
+		ctx := context.Background()
+		var record Record
+		assert.NoError(t, bp.OnEmit(ctx, record), "OnEmit")
+		assert.False(t, bp.Enabled(ctx, record), "Enabled")
+		assert.NoError(t, bp.ForceFlush(ctx), "ForceFlush")
+		assert.NoError(t, bp.Shutdown(ctx), "Shutdown")
+	})
+}
+
 func TestNewBatchConfig(t *testing.T) {
 	otel.SetErrorHandler(otel.ErrorHandlerFunc(func(err error) {
 		t.Log(err)