[chore] Simplify the OTEL setup (#4110)

# Description

This simplifies our OTEL setup by:

* Getting rid of some deprecated things.
* Using `autoexport` and letting things get configured by the `OTEL_` environment variables.
* Removing all the unnecessary config options.

## Checklist

Please put an x inside each checkbox to indicate that you've read and followed it: `[ ]` -> `[x]`

If this is a documentation change, only the first checkbox must be filled (you can delete the others if you want).

- [x] I/we have read the [GoToSocial contribution guidelines](https://codeberg.org/superseriousbusiness/gotosocial/src/branch/main/CONTRIBUTING.md).
- [x] I/we have discussed the proposed changes already, either in an issue on the repository, or in the Matrix chat.
- [x] I/we have not leveraged AI to create the proposed changes.
- [x] I/we have performed a self-review of added code.
- [x] I/we have written code that is legible and maintainable by others.
- [ ] I/we have commented the added code, particularly in hard-to-understand areas.
- [x] I/we have made any necessary changes to documentation.
- [ ] I/we have added tests that cover new code.
- [x] I/we have run tests and they pass locally with the changes.
- [x] I/we have run `go fmt ./...` and `golangci-lint run`.

Reviewed-on: https://codeberg.org/superseriousbusiness/gotosocial/pulls/4110
Reviewed-by: tobi <kipvandenbos@noreply.codeberg.org>
Co-authored-by: Daenney <daenney@noreply.codeberg.org>
Co-committed-by: Daenney <daenney@noreply.codeberg.org>

1 files changed, 477 insertions, 0 deletions

diff --git a/vendor/go.opentelemetry.io/otel/sdk/log/batch.go b/vendor/go.opentelemetry.io/otel/sdk/log/batch.go
new file mode 100644
index 000000000..28c969262
--- /dev/null
+++ b/vendor/go.opentelemetry.io/otel/sdk/log/batch.go
@@ -0,0 +1,477 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package log // import "go.opentelemetry.io/otel/sdk/log"
+
+import (
+	"context"
+	"errors"
+	"slices"
+	"sync"
+	"sync/atomic"
+	"time"
+
+	"go.opentelemetry.io/otel/internal/global"
+)
+
+const (
+	dfltMaxQSize        = 2048
+	dfltExpInterval     = time.Second
+	dfltExpTimeout      = 30 * time.Second
+	dfltExpMaxBatchSize = 512
+	dfltExpBufferSize   = 1
+
+	envarMaxQSize        = "OTEL_BLRP_MAX_QUEUE_SIZE"
+	envarExpInterval     = "OTEL_BLRP_SCHEDULE_DELAY"
+	envarExpTimeout      = "OTEL_BLRP_EXPORT_TIMEOUT"
+	envarExpMaxBatchSize = "OTEL_BLRP_MAX_EXPORT_BATCH_SIZE"
+)
+
+// Compile-time check BatchProcessor implements Processor.
+var _ Processor = (*BatchProcessor)(nil)
+
+// BatchProcessor is a processor that exports batches of log records.
+//
+// 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
+	// entry point of log records is the OnEmit method. This method is designed
+	// to receive records as fast as possible while still honoring shutdown
+	// commands. All records received are enqueued to queue.
+	//
+	// In order to block OnEmit as little as possible, a separate "poll"
+	// goroutine is spawned at the creation of a BatchProcessor. This
+	// goroutine is responsible for batching the queue at regular polled
+	// intervals, or when it is directly signaled to.
+	//
+	// To keep the polling goroutine from backing up, all batches it makes are
+	// exported with a bufferedExporter. This exporter allows the poll
+	// goroutine to enqueue an export payload that will be handled in a
+	// separate goroutine dedicated to the export. This asynchronous behavior
+	// allows the poll goroutine to maintain accurate interval polling.
+	//
+	//   ___BatchProcessor____     __Poll Goroutine__     __Export Goroutine__
+	// ||                     || ||                  || ||                    ||
+	// ||          ********** || ||                  || ||     **********     ||
+	// || Records=>* OnEmit * || ||   | - ticker     || ||     * export *     ||
+	// ||          ********** || ||   | - trigger    || ||     **********     ||
+	// ||             ||      || ||   |              || ||         ||         ||
+	// ||             ||      || ||   |              || ||         ||         ||
+	// ||   __________\/___   || ||   |***********   || ||   ______/\_______  ||
+	// ||  (____queue______)>=||=||===|*  batch  *===||=||=>[_export_buffer_] ||
+	// ||                     || ||   |***********   || ||                    ||
+	// ||_____________________|| ||__________________|| ||____________________||
+	//
+	//
+	// The "release valve" in this processing is the record queue. This queue
+	// is a ring buffer. It will overwrite the oldest records first when writes
+	// to OnEmit are made faster than the queue can be flushed. If batches
+	// cannot be flushed to the export buffer, the records will remain in the
+	// queue.
+
+	// exporter is the bufferedExporter all batches are exported with.
+	exporter *bufferExporter
+
+	// q is the active queue of records that have not yet been exported.
+	q *queue
+	// batchSize is the minimum number of records needed before an export is
+	// triggered (unless the interval expires).
+	batchSize int
+
+	// pollTrigger triggers the poll goroutine to flush a batch from the queue.
+	// This is sent to when it is known that the queue contains at least one
+	// complete batch.
+	//
+	// When a send is made to the channel, the poll loop will be reset after
+	// the flush. If there is still enough records in the queue for another
+	// batch the reset of the poll loop will automatically re-trigger itself.
+	// There is no need for the original sender to monitor and resend.
+	pollTrigger chan struct{}
+	// pollKill kills the poll goroutine. This is only expected to be closed
+	// once by the Shutdown method.
+	pollKill chan struct{}
+	// pollDone signals the poll goroutine has completed.
+	pollDone chan struct{}
+
+	// stopped holds the stopped state of the BatchProcessor.
+	stopped atomic.Bool
+
+	noCmp [0]func() //nolint: unused  // This is indeed used.
+}
+
+// NewBatchProcessor decorates the provided exporter
+// so that the log records are batched before exporting.
+//
+// All of the exporter's methods are called synchronously.
+func NewBatchProcessor(exporter Exporter, opts ...BatchProcessorOption) *BatchProcessor {
+	cfg := newBatchConfig(opts)
+	if exporter == nil {
+		// Do not panic on nil export.
+		exporter = defaultNoopExporter
+	}
+	// Order is important here. Wrap the timeoutExporter with the chunkExporter
+	// to ensure each export completes in timeout (instead of all chunked
+	// exports).
+	exporter = newTimeoutExporter(exporter, cfg.expTimeout.Value)
+	// Use a chunkExporter to ensure ForceFlush and Shutdown calls are batched
+	// appropriately on export.
+	exporter = newChunkExporter(exporter, cfg.expMaxBatchSize.Value)
+
+	b := &BatchProcessor{
+		exporter: newBufferExporter(exporter, cfg.expBufferSize.Value),
+
+		q:           newQueue(cfg.maxQSize.Value),
+		batchSize:   cfg.expMaxBatchSize.Value,
+		pollTrigger: make(chan struct{}, 1),
+		pollKill:    make(chan struct{}),
+	}
+	b.pollDone = b.poll(cfg.expInterval.Value)
+	return b
+}
+
+// poll spawns a goroutine to handle interval polling and batch exporting. The
+// returned done chan is closed when the spawned goroutine completes.
+func (b *BatchProcessor) poll(interval time.Duration) (done chan struct{}) {
+	done = make(chan struct{})
+
+	ticker := time.NewTicker(interval)
+	// TODO: investigate using a sync.Pool instead of cloning.
+	buf := make([]Record, b.batchSize)
+	go func() {
+		defer close(done)
+		defer ticker.Stop()
+
+		for {
+			select {
+			case <-ticker.C:
+			case <-b.pollTrigger:
+				ticker.Reset(interval)
+			case <-b.pollKill:
+				return
+			}
+
+			if d := b.q.Dropped(); d > 0 {
+				global.Warn("dropped log records", "dropped", d)
+			}
+
+			qLen := b.q.TryDequeue(buf, func(r []Record) bool {
+				ok := b.exporter.EnqueueExport(r)
+				if ok {
+					buf = slices.Clone(buf)
+				}
+				return ok
+			})
+			if qLen >= b.batchSize {
+				// There is another full batch ready. Immediately trigger
+				// another export attempt.
+				select {
+				case b.pollTrigger <- struct{}{}:
+				default:
+					// Another flush signal already received.
+				}
+			}
+		}
+	}()
+	return done
+}
+
+// OnEmit batches provided log record.
+func (b *BatchProcessor) OnEmit(_ context.Context, r *Record) error {
+	if b.stopped.Load() || b.q == nil {
+		return nil
+	}
+	// The record is cloned so that changes done by subsequent processors
+	// are not going to lead to a data race.
+	if n := b.q.Enqueue(r.Clone()); n >= b.batchSize {
+		select {
+		case b.pollTrigger <- struct{}{}:
+		default:
+			// Flush chan full. The poll goroutine will handle this by
+			// re-sending any trigger until the queue has less than batchSize
+			// records.
+		}
+	}
+	return 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) || b.q == nil {
+		return nil
+	}
+
+	// Stop the poll goroutine.
+	close(b.pollKill)
+	select {
+	case <-b.pollDone:
+	case <-ctx.Done():
+		// Out of time.
+		return errors.Join(ctx.Err(), b.exporter.Shutdown(ctx))
+	}
+
+	// Flush remaining queued before exporter shutdown.
+	err := b.exporter.Export(ctx, b.q.Flush())
+	return errors.Join(err, b.exporter.Shutdown(ctx))
+}
+
+var errPartialFlush = errors.New("partial flush: export buffer full")
+
+// Used for testing.
+var ctxErr = func(ctx context.Context) error {
+	return ctx.Err()
+}
+
+// ForceFlush flushes queued log records and flushes the decorated exporter.
+func (b *BatchProcessor) ForceFlush(ctx context.Context) error {
+	if b.stopped.Load() || b.q == nil {
+		return nil
+	}
+
+	buf := make([]Record, b.q.cap)
+	notFlushed := func() bool {
+		var flushed bool
+		_ = b.q.TryDequeue(buf, func(r []Record) bool {
+			flushed = b.exporter.EnqueueExport(r)
+			return flushed
+		})
+		return !flushed
+	}
+	var err error
+	// For as long as ctx allows, try to make a single flush of the queue.
+	for notFlushed() {
+		// Use ctxErr instead of calling ctx.Err directly so we can test
+		// the partial error return.
+		if e := ctxErr(ctx); e != nil {
+			err = errors.Join(e, errPartialFlush)
+			break
+		}
+	}
+	return errors.Join(err, b.exporter.ForceFlush(ctx))
+}
+
+// queue holds a queue of logging records.
+//
+// When the queue becomes full, the oldest records in the queue are
+// overwritten.
+type queue struct {
+	sync.Mutex
+
+	dropped     atomic.Uint64
+	cap, len    int
+	read, write *ring
+}
+
+func newQueue(size int) *queue {
+	r := newRing(size)
+	return &queue{
+		cap:   size,
+		read:  r,
+		write: r,
+	}
+}
+
+// Dropped returns the number of Records dropped during enqueueing since the
+// last time Dropped was called.
+func (q *queue) Dropped() uint64 {
+	return q.dropped.Swap(0)
+}
+
+// Enqueue adds r to the queue. The queue size, including the addition of r, is
+// returned.
+//
+// If enqueueing r will exceed the capacity of q, the oldest Record held in q
+// will be dropped and r retained.
+func (q *queue) Enqueue(r Record) int {
+	q.Lock()
+	defer q.Unlock()
+
+	q.write.Value = r
+	q.write = q.write.Next()
+
+	q.len++
+	if q.len > q.cap {
+		// Overflow. Advance read to be the new "oldest".
+		q.len = q.cap
+		q.read = q.read.Next()
+		q.dropped.Add(1)
+	}
+	return q.len
+}
+
+// TryDequeue attempts to dequeue up to len(buf) Records. The available Records
+// will be assigned into buf and passed to write. If write fails, returning
+// false, the Records will not be removed from the queue. If write succeeds,
+// returning true, the dequeued Records are removed from the queue. The number
+// of Records remaining in the queue are returned.
+//
+// When write is called the lock of q is held. The write function must not call
+// other methods of this q that acquire the lock.
+func (q *queue) TryDequeue(buf []Record, write func([]Record) bool) int {
+	q.Lock()
+	defer q.Unlock()
+
+	origRead := q.read
+
+	n := min(len(buf), q.len)
+	for i := 0; i < n; i++ {
+		buf[i] = q.read.Value
+		q.read = q.read.Next()
+	}
+
+	if write(buf[:n]) {
+		q.len -= n
+	} else {
+		q.read = origRead
+	}
+	return q.len
+}
+
+// Flush returns all the Records held in the queue and resets it to be
+// empty.
+func (q *queue) Flush() []Record {
+	q.Lock()
+	defer q.Unlock()
+
+	out := make([]Record, q.len)
+	for i := range out {
+		out[i] = q.read.Value
+		q.read = q.read.Next()
+	}
+	q.len = 0
+
+	return out
+}
+
+type batchConfig struct {
+	maxQSize        setting[int]
+	expInterval     setting[time.Duration]
+	expTimeout      setting[time.Duration]
+	expMaxBatchSize setting[int]
+	expBufferSize   setting[int]
+}
+
+func newBatchConfig(options []BatchProcessorOption) batchConfig {
+	var c batchConfig
+	for _, o := range options {
+		c = o.apply(c)
+	}
+
+	c.maxQSize = c.maxQSize.Resolve(
+		clearLessThanOne[int](),
+		getenv[int](envarMaxQSize),
+		clearLessThanOne[int](),
+		fallback[int](dfltMaxQSize),
+	)
+	c.expInterval = c.expInterval.Resolve(
+		clearLessThanOne[time.Duration](),
+		getenv[time.Duration](envarExpInterval),
+		clearLessThanOne[time.Duration](),
+		fallback[time.Duration](dfltExpInterval),
+	)
+	c.expTimeout = c.expTimeout.Resolve(
+		clearLessThanOne[time.Duration](),
+		getenv[time.Duration](envarExpTimeout),
+		clearLessThanOne[time.Duration](),
+		fallback[time.Duration](dfltExpTimeout),
+	)
+	c.expMaxBatchSize = c.expMaxBatchSize.Resolve(
+		clearLessThanOne[int](),
+		getenv[int](envarExpMaxBatchSize),
+		clearLessThanOne[int](),
+		clampMax[int](c.maxQSize.Value),
+		fallback[int](dfltExpMaxBatchSize),
+	)
+	c.expBufferSize = c.expBufferSize.Resolve(
+		clearLessThanOne[int](),
+		fallback[int](dfltExpBufferSize),
+	)
+
+	return c
+}
+
+// BatchProcessorOption applies a configuration to a [BatchProcessor].
+type BatchProcessorOption interface {
+	apply(batchConfig) batchConfig
+}
+
+type batchOptionFunc func(batchConfig) batchConfig
+
+func (fn batchOptionFunc) apply(c batchConfig) batchConfig {
+	return fn(c)
+}
+
+// WithMaxQueueSize sets the maximum queue size used by the Batcher.
+// After the size is reached log records are dropped.
+//
+// If the OTEL_BLRP_MAX_QUEUE_SIZE environment variable is set,
+// and this option is not passed, that variable value will be used.
+//
+// By default, if an environment variable is not set, and this option is not
+// passed, 2048 will be used.
+// The default value is also used when the provided value is less than one.
+func WithMaxQueueSize(size int) BatchProcessorOption {
+	return batchOptionFunc(func(cfg batchConfig) batchConfig {
+		cfg.maxQSize = newSetting(size)
+		return cfg
+	})
+}
+
+// WithExportInterval sets the maximum duration between batched exports.
+//
+// If the OTEL_BLRP_SCHEDULE_DELAY environment variable is set,
+// and this option is not passed, that variable value will be used.
+//
+// By default, if an environment variable is not set, and this option is not
+// passed, 1s will be used.
+// The default value is also used when the provided value is less than one.
+func WithExportInterval(d time.Duration) BatchProcessorOption {
+	return batchOptionFunc(func(cfg batchConfig) batchConfig {
+		cfg.expInterval = newSetting(d)
+		return cfg
+	})
+}
+
+// WithExportTimeout sets the duration after which a batched export is canceled.
+//
+// If the OTEL_BLRP_EXPORT_TIMEOUT environment variable is set,
+// and this option is not passed, that variable value will be used.
+//
+// By default, if an environment variable is not set, and this option is not
+// passed, 30s will be used.
+// The default value is also used when the provided value is less than one.
+func WithExportTimeout(d time.Duration) BatchProcessorOption {
+	return batchOptionFunc(func(cfg batchConfig) batchConfig {
+		cfg.expTimeout = newSetting(d)
+		return cfg
+	})
+}
+
+// WithExportMaxBatchSize sets the maximum batch size of every export.
+// A batch will be split into multiple exports to not exceed this size.
+//
+// If the OTEL_BLRP_MAX_EXPORT_BATCH_SIZE environment variable is set,
+// and this option is not passed, that variable value will be used.
+//
+// By default, if an environment variable is not set, and this option is not
+// passed, 512 will be used.
+// The default value is also used when the provided value is less than one.
+func WithExportMaxBatchSize(size int) BatchProcessorOption {
+	return batchOptionFunc(func(cfg batchConfig) batchConfig {
+		cfg.expMaxBatchSize = newSetting(size)
+		return cfg
+	})
+}
+
+// WithExportBufferSize sets the batch buffer size.
+// Batches will be temporarily kept in a memory buffer until they are exported.
+//
+// By default, a value of 1 will be used.
+// The default value is also used when the provided value is less than one.
+func WithExportBufferSize(size int) BatchProcessorOption {
+	return batchOptionFunc(func(cfg batchConfig) batchConfig {
+		cfg.expBufferSize = newSetting(size)
+		return cfg
+	})
+}