access logger support sharing the same file, tests added for concurrent logging

internal/net/http/accesslog/mock_file.go

@@ -0,0 +1,74 @@
+package accesslog
+
+import (
+	"bytes"
+	"io"
+	"sync"
+)
+
+type MockFile struct {
+	data     []byte
+	position int64
+	sync.Mutex
+}
+
+func (m *MockFile) Seek(offset int64, whence int) (int64, error) {
+	switch whence {
+	case io.SeekStart:
+		m.position = offset
+	case io.SeekCurrent:
+		m.position += offset
+	case io.SeekEnd:
+		m.position = int64(len(m.data)) + offset
+	}
+	return m.position, nil
+}
+
+func (m *MockFile) Write(p []byte) (n int, err error) {
+	m.data = append(m.data, p...)
+	n = len(p)
+	m.position += int64(n)
+	return
+}
+
+func (m *MockFile) Name() string {
+	return "mock"
+}
+
+func (m *MockFile) Read(p []byte) (n int, err error) {
+	if m.position >= int64(len(m.data)) {
+		return 0, io.EOF
+	}
+	n = copy(p, m.data[m.position:])
+	m.position += int64(n)
+	return n, nil
+}
+
+func (m *MockFile) ReadAt(p []byte, off int64) (n int, err error) {
+	if off >= int64(len(m.data)) {
+		return 0, io.EOF
+	}
+	n = copy(p, m.data[off:])
+	m.position += int64(n)
+	return n, nil
+}
+
+func (m *MockFile) Close() error {
+	return nil
+}
+
+func (m *MockFile) Truncate(size int64) error {
+	m.data = m.data[:size]
+	m.position = size
+	return nil
+}
+
+func (m *MockFile) Count() int {
+	m.Lock()
+	defer m.Unlock()
+	return bytes.Count(m.data[:m.position], []byte("\n"))
+}
+
+func (m *MockFile) Len() int64 {
+	return m.position
+}