feat(open-telemetry#5408): add otlplogfile exporter

This commit adds a new experimental exporter `otlplogfile`, that outputs log records to a JSON line file.
It is based on the following specification: https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/protocol/file-exporter.md

Signed-off-by: thomasgouveia <gouveia.thomas@outlook.fr>

exporters/otlp/otlplog/otlplogfile/README.md

@@ -0,0 +1,3 @@
+# OTLP Log File Exporter
+
+[![PkgGoDev](https://pkg.go.dev/badge/go.opentelemetry.io/otel/exporters/otlp/otlplog/otlplogfile)](https://pkg.go.dev/go.opentelemetry.io/otel/exporters/otlp/otlplog/otlplogfile)

exporters/otlp/otlplog/otlplogfile/config.go

@@ -0,0 +1,54 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package otlplogfile // import "go.opentelemetry.io/otel/exporters/otlp/otlplog/otlplogfile"
+
+import "time"
+
+type fnOpt func(config) config
+
+func (f fnOpt) applyOption(c config) config { return f(c) }
+
+// Option sets the configuration value for an Exporter.
+type Option interface {
+	applyOption(config) config
+}
+
+// config contains options for the OTLP Log file exporter.
+type config struct {
+	// Path to a file on disk where records must be appended.
+	// This file is preferably a json line file as stated in the specification.
+	// See: https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/protocol/file-exporter.md#json-lines-file
+	// See: https://jsonlines.org
+	path string
+	// Duration represents the interval when the buffer should be flushed.
+	flushInterval time.Duration
+}
+
+func newConfig(options []Option) config {
+	c := config{
+		path:          "/var/log/opentelemetry/logs.jsonl",
+		flushInterval: 5 * time.Second,
+	}
+	for _, opt := range options {
+		c = opt.applyOption(c)
+	}
+	return c
+}
+
+// WithFlushInterval configures the duration after which the buffer is periodically flushed to the disk.
+func WithFlushInterval(flushInterval time.Duration) Option {
+	return fnOpt(func(c config) config {
+		c.flushInterval = flushInterval
+		return c
+	})
+}
+
+// WithPath defines a path to a file where the log records will be written.
+// If not set, will default to /var/log/opentelemetry/logs.jsonl.
+func WithPath(path string) Option {
+	return fnOpt(func(c config) config {
+		c.path = path
+		return c
+	})
+}

exporters/otlp/otlplog/otlplogfile/doc.go

@@ -0,0 +1,12 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+/*
+Package otlplogfile provides an OTLP log exporter that outputs log records to a JSON line file. The exporter uses a buffered
+file writer to write log records to file to reduce I/O and improve performance.
+
+All Exporters must be created with [New].
+
+See: https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/protocol/file-exporter.md
+*/
+package otlplogfile // import "go.opentelemetry.io/otel/exporters/otlp/otlplog/otlplogfile"

exporters/otlp/otlplog/otlplogfile/exporter.go

@@ -0,0 +1,95 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package otlplogfile // import "go.opentelemetry.io/otel/exporters/otlp/otlplog/otlplogfile"
+
+import (
+	"context"
+	"sync"
+
+	"google.golang.org/protobuf/encoding/protojson"
+
+	"go.opentelemetry.io/otel/exporters/otlp/otlplog/otlplogfile/internal/transform"
+	"go.opentelemetry.io/otel/exporters/otlp/otlplog/otlplogfile/internal/writer"
+	"go.opentelemetry.io/otel/sdk/log"
+	lpb "go.opentelemetry.io/proto/otlp/logs/v1"
+)
+
+// Exporter is an OpenTelemetry log exporter that outputs log records
+// into JSON files. The implementation is based on the specification
+// defined here: https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/protocol/file-exporter.md
+type Exporter struct {
+	mu      sync.Mutex
+	fw      *writer.FileWriter
+	stopped bool
+}
+
+// Compile-time check that the implementation satisfies the interface.
+var _ log.Exporter = &Exporter{}
+
+// New returns a new [Exporter].
+func New(options ...Option) (*Exporter, error) {
+	cfg := newConfig(options)
+
+	fw, err := writer.NewFileWriter(cfg.path, cfg.flushInterval)
+	if err != nil {
+		return nil, err
+	}
+
+	return &Exporter{
+		fw:      fw,
+		stopped: false,
+	}, nil
+}
+
+// Export exports logs records to the file.
+func (e *Exporter) Export(ctx context.Context, records []log.Record) error {
+	// Honor context cancellation
+	if err := ctx.Err(); err != nil {
+		return err
+	}
+
+	e.mu.Lock()
+	defer e.mu.Unlock()
+
+	if e.stopped {
+		return nil
+	}
+
+	data := &lpb.LogsData{
+		ResourceLogs: transform.ResourceLogs(records),
+	}
+
+	by, err := protojson.Marshal(data)
+	if err != nil {
+		return err
+	}
+
+	return e.fw.Export(by)
+}
+
+// ForceFlush flushes data to the file.
+func (e *Exporter) ForceFlush(_ context.Context) error {
+	e.mu.Lock()
+	defer e.mu.Unlock()
+
+	if e.stopped {
+		return nil
+	}
+
+	return e.fw.Flush()
+}
+
+// Shutdown shuts down the exporter. Buffered data is written to disk,
+// and opened resources such as file will be closed.
+func (e *Exporter) Shutdown(_ context.Context) error {
+	e.mu.Lock()
+	defer e.mu.Unlock()
+
+	if e.stopped {
+		return nil
+	}
+
+	e.stopped = true
+	return e.fw.Shutdown()
+}

exporters/otlp/otlplog/otlplogfile/exporter_test.go

@@ -0,0 +1,139 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package otlplogfile // import "go.opentelemetry.io/otel/exporters/otlp/otlplog/otlplogfile"
+import (
+	"context"
+	"fmt"
+	"os"
+	"path"
+	"runtime"
+	"sync"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"go.opentelemetry.io/otel/log"
+
+	sdklog "go.opentelemetry.io/otel/sdk/log"
+)
+
+// tempFile creates a temporary file for the given test case and returns its path on disk.
+// The file is automatically cleaned up when the test ends.
+func tempFile(tb testing.TB) string {
+	f, err := os.CreateTemp(tb.TempDir(), tb.Name())
+	assert.NoError(tb, err, "must not error when creating temporary file")
+	tb.Cleanup(func() {
+		assert.NoError(tb, os.RemoveAll(path.Dir(f.Name())), "must clean up files after being written")
+	})
+	return f.Name()
+}
+
+// makeRecords is a helper function to generate an array of log record with the desired size.
+func makeRecords(count int, message string) []sdklog.Record {
+	var records []sdklog.Record
+	for i := 0; i < count; i++ {
+		r := sdklog.Record{}
+		r.SetSeverityText("INFO")
+		r.SetSeverity(log.SeverityInfo)
+		r.SetBody(log.StringValue(message))
+		r.SetTimestamp(time.Now())
+		r.SetObservedTimestamp(time.Now())
+		records = append(records, r)
+	}
+	return records
+}
+
+func TestExporter(t *testing.T) {
+	filepath := tempFile(t)
+	records := makeRecords(1, "hello, world!")
+
+	exporter, err := New(WithPath(filepath))
+	assert.NoError(t, err)
+	t.Cleanup(func() {
+		assert.NoError(t, exporter.Shutdown(context.TODO()))
+	})
+
+	err = exporter.Export(context.TODO(), records)
+	assert.NoError(t, err)
+	err = exporter.ForceFlush(context.TODO())
+	assert.NoError(t, err)
+}
+
+func TestExporterConcurrentSafe(t *testing.T) {
+	filepath := tempFile(t)
+	exporter, err := New(WithPath(filepath))
+	require.NoError(t, err, "New()")
+
+	const goroutines = 10
+
+	var wg sync.WaitGroup
+	ctx, cancel := context.WithCancel(context.Background())
+	runs := new(uint64)
+	for i := 0; i < goroutines; i++ {
+		wg.Add(1)
+		i := i
+		go func() {
+			defer wg.Done()
+			for {
+				select {
+				case <-ctx.Done():
+					return
+				default:
+					_ = exporter.Export(ctx, makeRecords(1, fmt.Sprintf("log from goroutine %d", i)))
+					_ = exporter.ForceFlush(ctx)
+					atomic.AddUint64(runs, 1)
+				}
+			}
+		}()
+	}
+
+	for atomic.LoadUint64(runs) == 0 {
+		runtime.Gosched()
+	}
+
+	assert.NoError(t, exporter.Shutdown(ctx), "must not error when shutting down")
+	cancel()
+	wg.Wait()
+}
+
+func BenchmarkExporter(b *testing.B) {
+	for _, logCount := range []int{
+		10,
+		100,
+		500,
+		1000,
+	} {
+		records := makeRecords(logCount, "benchmark")
+
+		for name, interval := range map[string]time.Duration{
+			"no-flush":    0,
+			"flush-10ms":  10 * time.Millisecond,
+			"flush-100ms": 100 * time.Millisecond,
+			"flush-1s":    time.Second,
+			"flush-10s":   10 * time.Second,
+		} {
+			filepath := tempFile(b)
+			exporter, err := New(WithPath(filepath), WithFlushInterval(interval))
+			require.NoError(b, err, "must not error when calling New()")
+
+			b.Run(fmt.Sprintf("%s/%d-logs", name, logCount), func(b *testing.B) {
+				b.ReportAllocs()
+				b.ResetTimer()
+
+				for i := 0; i < b.N; i++ {
+					if err := exporter.Export(context.Background(), records); err != nil {
+						b.Fatalf("failed to export records: %v", err)
+					}
+				}
+			})
+
+			if err := exporter.Shutdown(context.Background()); err != nil {
+				b.Fatalf("failed to shutdown exporter: %v", err)
+			}
+		}
+	}
+}

exporters/otlp/otlplog/otlplogfile/go.mod

@@ -0,0 +1,37 @@
+module go.opentelemetry.io/otel/exporters/otlp/otlplog/otlplogfile
+
+go 1.21
+
+require (
+	github.com/stretchr/testify v1.9.0
+	go.opentelemetry.io/otel v1.28.0
+	go.opentelemetry.io/otel/log v0.4.0
+	go.opentelemetry.io/otel/sdk v1.28.0
+	go.opentelemetry.io/otel/sdk/log v0.4.0
+	go.opentelemetry.io/otel/trace v1.28.0
+	go.opentelemetry.io/proto/otlp v1.3.1
+	google.golang.org/protobuf v1.34.1
+)
+
+require (
+	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/go-logr/logr v1.4.2 // indirect
+	github.com/go-logr/stdr v1.2.2 // indirect
+	github.com/google/uuid v1.6.0 // indirect
+	github.com/pmezard/go-difflib v1.0.0 // indirect
+	go.opentelemetry.io/otel/metric v1.28.0 // indirect
+	golang.org/x/sys v0.22.0 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
+)
+
+replace go.opentelemetry.io/otel => ../../../..
+
+replace go.opentelemetry.io/otel/sdk/log => ../../../../sdk/log
+
+replace go.opentelemetry.io/otel/sdk => ../../../../sdk
+
+replace go.opentelemetry.io/otel/log => ../../../../log
+
+replace go.opentelemetry.io/otel/trace => ../../../../trace
+
+replace go.opentelemetry.io/otel/metric => ../../../../metric

exporters/otlp/otlplog/otlplogfile/go.sum

@@ -0,0 +1,25 @@
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/go-logr/logr v1.2.2/go.mod h1:jdQByPbusPIv2/zmleS9BjJVeZ6kBagPoEUsqbVz/1A=
+github.com/go-logr/logr v1.4.2 h1:6pFjapn8bFcIbiKo3XT4j/BhANplGihG6tvd+8rYgrY=
+github.com/go-logr/logr v1.4.2/go.mod h1:9T104GzyrTigFIr8wt5mBrctHMim0Nb2HLGrmQ40KvY=
+github.com/go-logr/stdr v1.2.2 h1:hSWxHoqTgW2S2qGc0LTAI563KZ5YKYRhT3MFKZMbjag=
+github.com/go-logr/stdr v1.2.2/go.mod h1:mMo/vtBO5dYbehREoey6XUKy/eSumjCCveDpRre4VKE=
+github.com/google/go-cmp v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
+github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
+github.com/google/uuid v1.6.0 h1:NIvaJDMOsjHA8n1jAhLSgzrAzy1Hgr+hNrb57e+94F0=
+github.com/google/uuid v1.6.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/testify v1.9.0 h1:HtqpIVDClZ4nwg75+f6Lvsy/wHu+3BoSGCbBAcpTsTg=
+github.com/stretchr/testify v1.9.0/go.mod h1:r2ic/lqez/lEtzL7wO/rwa5dbSLXVDPFyf8C91i36aY=
+go.opentelemetry.io/proto/otlp v1.3.1 h1:TrMUixzpM0yuc/znrFTP9MMRh8trP93mkCiDVeXrui0=
+go.opentelemetry.io/proto/otlp v1.3.1/go.mod h1:0X1WI4de4ZsLrrJNLAQbFeLCm3T7yBkR0XqQ7niQU+8=
+golang.org/x/sys v0.22.0 h1:RI27ohtqKCnwULzJLqkv897zojh5/DwS/ENaMzUOaWI=
+golang.org/x/sys v0.22.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
+google.golang.org/protobuf v1.34.1 h1:9ddQBjfCyZPOHPUiPxpYESBLc+T8P3E+Vo4IbKZgFWg=
+google.golang.org/protobuf v1.34.1/go.mod h1:c6P6GXX6sHbq/GpV6MGZEdwhWPcYBgnhAHhKbcUYpos=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

exporters/otlp/otlplog/otlplogfile/internal/gen.go

@@ -0,0 +1,9 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package internal // import "go.opentelemetry.io/otel/exporters/otlp/otlplog/otlplogfile/internal"
+
+//go:generate gotmpl --body=../../../../../internal/shared/otlp/otlplog/transform/attr_test.go.tmpl "--data={}" --out=transform/attr_test.go
+//go:generate gotmpl --body=../../../../../internal/shared/otlp/otlplog/transform/log.go.tmpl "--data={}" --out=transform/log.go
+//go:generate gotmpl --body=../../../../../internal/shared/otlp/otlplog/transform/log_attr_test.go.tmpl "--data={}" --out=transform/log_attr_test.go
+//go:generate gotmpl --body=../../../../../internal/shared/otlp/otlplog/transform/log_test.go.tmpl "--data={}" --out=transform/log_test.go