tests: make buffer log writer thread safe (#11962)

When two goroutines attempt to access the content of the buffer log writer, they must be made thread safe with a write mutex.

The buffer log writer is only used in testing.

## Checklist

### Tests for Go changes

- I added test coverage for Go changes...
  - [x] in their respective `*_test.go` for unit tests.
  - [ ] in the `tests/integration` directory if it involves interactions with a live Forgejo server.
- I ran...
  - [ ] `make pr-go` before pushing

### Documentation

- [ ] I created a pull request [to the documentation](https://codeberg.org/forgejo/docs) to explain to Forgejo users how to use this change.
- [x] I did not document these changes and I do not expect someone else to do it.

### Release notes

- [ ] This change will be noticed by a Forgejo user or admin (feature, bug fix, performance, etc.). I suggest to include a release note for this change.
- [x] This change is not visible to a Forgejo user or admin (refactor, dependency upgrade, etc.). I think there is no need to add a release note for this change.

*The decision if the pull request will be shown in the release notes is up to the mergers / release team.*

The content of the `release-notes/<pull request number>.md` file will serve as the basis for the release notes. If the file does not exist, the title of the pull request will be used instead.

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/11962
Reviewed-by: Mathieu Fenniak <mfenniak@noreply.codeberg.org>
Co-authored-by: limiting-factor <limiting-factor@posteo.com>
Co-committed-by: limiting-factor <limiting-factor@posteo.com>

.deadcode-out

@@ -134,6 +134,9 @@ forgejo.org/modules/json
 	StdJSON.Indent
 
 forgejo.org/modules/log
+	eventWriterBuffer.Close
+	eventWriterBuffer.Write
+	eventWriterBuffer.GetString
 	NewEventWriterBuffer
 
 forgejo.org/modules/markup

modules/log/event_writer_buffer.go

@@ -5,18 +5,44 @@ package log
 
 import (
 	"bytes"
+	"sync"
 )
 
-type EventWriterBuffer struct {
-	*EventWriterBaseImpl
-	Buffer *bytes.Buffer
+type EventWriterBuffer interface {
+	EventWriter
+	GetString() string
 }
 
-var _ EventWriter = (*EventWriterBuffer)(nil)
+type eventWriterBuffer struct {
+	*EventWriterBaseImpl
+	buffer *bytes.Buffer
+	mu     sync.RWMutex
+}
 
-func NewEventWriterBuffer(name string, mode WriterMode) *EventWriterBuffer {
-	w := &EventWriterBuffer{EventWriterBaseImpl: NewEventWriterBase(name, "buffer", mode)}
-	w.Buffer = new(bytes.Buffer)
-	w.OutputWriteCloser = nopCloser{w.Buffer}
+var _ EventWriterBuffer = (*eventWriterBuffer)(nil)
+
+func (*eventWriterBuffer) Close() error {
+	return nil
+}
+
+func (o *eventWriterBuffer) Write(p []byte) (n int, err error) {
+	o.mu.Lock()
+	defer o.mu.Unlock()
+	return o.buffer.Write(p)
+}
+
+func (o *eventWriterBuffer) GetString() string {
+	o.mu.Lock()
+	defer o.mu.Unlock()
+	b := o.buffer.Bytes()
+	s := make([]byte, len(b))
+	copy(s, b)
+	return string(s)
+}
+
+func NewEventWriterBuffer(name string, mode WriterMode) EventWriter {
+	w := &eventWriterBuffer{EventWriterBaseImpl: NewEventWriterBase(name, "buffer", mode)}
+	w.buffer = new(bytes.Buffer)
+	w.OutputWriteCloser = w
 	return w
 }

modules/log/event_writer_buffer_test.go

@@ -29,7 +29,7 @@ func TestBufferLogger(t *testing.T) {
 		MsgSimpleText: expected,
 	})
 	logger.Close()
-	assert.Contains(t, bufferWriter.Buffer.String(), expected)
+	assert.Contains(t, bufferWriter.(log.EventWriterBuffer).GetString(), expected)
 }
 
 func TestBufferLoggerWithExclusion(t *testing.T) {
@@ -41,7 +41,7 @@ func TestBufferLoggerWithExclusion(t *testing.T) {
 		Level:     level,
 		Prefix:    prefix,
 		Exclusion: message,
-	})
+	}).(log.EventWriterBuffer)
 
 	logger := log.NewLoggerWithWriters(t.Context(), "test", bufferWriter)
 
@@ -50,7 +50,7 @@ func TestBufferLoggerWithExclusion(t *testing.T) {
 		MsgSimpleText: message,
 	})
 	logger.Close()
-	assert.NotContains(t, bufferWriter.Buffer.String(), message)
+	assert.NotContains(t, bufferWriter.GetString(), message)
 }
 
 func TestBufferLoggerWithExpressionAndExclusion(t *testing.T) {
@@ -64,7 +64,7 @@ func TestBufferLoggerWithExpressionAndExclusion(t *testing.T) {
 		Prefix:     prefix,
 		Expression: expression,
 		Exclusion:  exclusion,
-	})
+	}).(log.EventWriterBuffer)
 
 	logger := log.NewLoggerWithWriters(t.Context(), "test", bufferWriter)
 
@@ -74,6 +74,6 @@ func TestBufferLoggerWithExpressionAndExclusion(t *testing.T) {
 	logger.SendLogEvent(&log.Event{Level: log.INFO, MsgSimpleText: "none"})
 	logger.Close()
 
-	assert.Contains(t, bufferWriter.Buffer.String(), "foo expression")
-	assert.NotContains(t, bufferWriter.Buffer.String(), "bar")
+	assert.Contains(t, bufferWriter.GetString(), "foo expression")
+	assert.NotContains(t, bufferWriter.GetString(), "bar")
 }

modules/log/logger_impl_test.go

@@ -23,5 +23,5 @@ func TestLog(t *testing.T) {
 	testGeneric(logger, "I'm the generic value!")
 	logger.Close()
 
-	assert.Contains(t, bufferWriter.Buffer.String(), ".../logger_impl_test.go:13:testGeneric() [I] Just testing the logging of a generic function I'm the generic value!")
+	assert.Contains(t, bufferWriter.(EventWriterBuffer).GetString(), ".../logger_impl_test.go:13:testGeneric() [I] Just testing the logging of a generic function I'm the generic value!")
 }