Move Linux client & common packages into a public repo.

logtail/buffer.go

@@ -0,0 +1,82 @@
+// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package logtail
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"sync"
+)
+
+type Buffer interface {
+	// TryReadLine tries to read a log line from the ring buffer.
+	// If no line is available it returns a nil slice.
+	// If the ring buffer is closed it returns io.EOF.
+	TryReadLine() ([]byte, error)
+
+	// Write writes a log line into the ring buffer.
+	Write([]byte) (int, error)
+}
+
+func NewMemoryBuffer(numEntries int) Buffer {
+	return &memBuffer{
+		pending: make(chan qentry, numEntries),
+	}
+}
+
+type memBuffer struct {
+	next    []byte
+	pending chan qentry
+
+	dropMu    sync.Mutex
+	dropCount int
+}
+
+func (m *memBuffer) TryReadLine() ([]byte, error) {
+	if m.next != nil {
+		msg := m.next
+		m.next = nil
+		return msg, nil
+	}
+
+	select {
+	case ent := <-m.pending:
+		if ent.dropCount > 0 {
+			m.next = ent.msg
+			buf := new(bytes.Buffer)
+			fmt.Fprintf(buf, "----------- %d logs dropped ----------", ent.dropCount)
+			return buf.Bytes(), nil
+		}
+		return ent.msg, nil
+	default:
+		return nil, nil
+	}
+}
+
+func (m *memBuffer) Write(b []byte) (int, error) {
+	m.dropMu.Lock()
+	defer m.dropMu.Unlock()
+
+	ent := qentry{
+		msg:       b,
+		dropCount: m.dropCount,
+	}
+	select {
+	case m.pending <- ent:
+		m.dropCount = 0
+		return len(b), nil
+	default:
+		m.dropCount++
+		return 0, errBufferFull
+	}
+}
+
+type qentry struct {
+	msg       []byte
+	dropCount int
+}
+
+var errBufferFull = errors.New("logtail: buffer full")