libbeat: optimize asset data decoding (#42180)

While working on #41888 I was benchmarking the filebeatreceiver
CreateLogs factory and noticed that the asset decoding in libbeat
dominates the cpu and memory profile of the receiver creation.

This behavior is expected since asset decoding is intended to occur at
startup. However, it's still worthwhile to optimize it if possible.

Some time ago I worked on `iobuf.ReadAll` at
elastic/elastic-agent-libs#229, an optimized version of `io.ReadAll`
that has a better growth algorithm—based on bytes.Buffer—and
benefits from the `io.ReaderFrom` optimization. The choice of when to
use this is very picky, as using it with a reader that is not a
`io.ReaderFrom` can be slower than the standard `io.ReadAll`. For this
case we are certain of the reader implementation, so we can use it.
Benchmark results show that it is 5% faster and uses 17% less memory.

After these fixes the profiles are still dominated by the asset
decoding, but I guess that is expected, at least it is a bit faster now.

(cherry picked from commit 3d1bdcf)

libbeat/asset/registry.go

@@ -21,8 +21,9 @@ import (
 	"bytes"
 	"compress/zlib"
 	"encoding/base64"
-	"io/ioutil"
 	"sort"
+
+	"github.com/elastic/elastic-agent-libs/iobuf"
 )
 
 // FieldsRegistry contains a list of fields.yml files
@@ -106,7 +107,6 @@ func EncodeData(data string) (string, error) {
 
 // DecodeData base64 decodes the data and uncompresses it
 func DecodeData(data string) ([]byte, error) {
-
 	decoded, err := base64.StdEncoding.DecodeString(data)
 	if err != nil {
 		return nil, err
@@ -119,5 +119,5 @@ func DecodeData(data string) ([]byte, error) {
 	}
 	defer r.Close()
 
-	return ioutil.ReadAll(r)
+	return iobuf.ReadAll(r)
 }

x-pack/filebeat/fbreceiver/receiver_test.go

@@ -11,6 +11,7 @@ import (
 	"time"
 
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 	"go.opentelemetry.io/collector/consumer"
 	"go.opentelemetry.io/collector/pdata/plog"
 	"go.opentelemetry.io/collector/receiver"
@@ -89,3 +90,47 @@ found:
 	err = r.Shutdown(context.Background())
 	assert.NoError(t, err, "Error shutting down filebeatreceiver")
 }
+
+func BenchmarkFactory(b *testing.B) {
+	tmpDir := b.TempDir()
+
+	cfg := &Config{
+		Beatconfig: map[string]interface{}{
+			"filebeat": map[string]interface{}{
+				"inputs": []map[string]interface{}{
+					{
+						"type":    "benchmark",
+						"enabled": true,
+						"message": "test",
+						"count":   10,
+					},
+				},
+			},
+			"output": map[string]interface{}{
+				"otelconsumer": map[string]interface{}{},
+			},
+			"logging": map[string]interface{}{
+				"level": "debug",
+				"selectors": []string{
+					"*",
+				},
+			},
+			"path.home": tmpDir,
+		},
+	}
+
+	var zapLogs bytes.Buffer
+	core := zapcore.NewCore(
+		zapcore.NewJSONEncoder(zap.NewProductionEncoderConfig()),
+		zapcore.AddSync(&zapLogs),
+		zapcore.DebugLevel)
+
+	receiverSettings := receiver.Settings{}
+	receiverSettings.Logger = zap.New(core)
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_, err := NewFactory().CreateLogsReceiver(context.Background(), receiverSettings, cfg, nil)
+		require.NoError(b, err)
+	}
+}