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// Copyright (c) Tailscale Inc & contributors
// SPDX-License-Identifier: BSD-3-Clause
package memnet
import (
"bytes"
"context"
"fmt"
"io"
"log"
"net"
"os"
"sync"
"time"
)
const debugPipe = false
// Pipe implements an in-memory FIFO with timeouts.
type Pipe struct {
name string
maxBuf int
mu sync.Mutex
cnd *sync.Cond
blocked bool
closed bool
buf bytes.Buffer
readTimeout time.Time
writeTimeout time.Time
cancelReadTimer func()
cancelWriteTimer func()
}
// NewPipe creates a Pipe with a buffer size fixed at maxBuf.
func NewPipe(name string, maxBuf int) *Pipe {
p := &Pipe{
name: name,
maxBuf: maxBuf,
}
p.cnd = sync.NewCond(&p.mu)
return p
}
// readOrBlock attempts to read from the buffer, if the buffer is empty and
// the connection hasn't been closed it will block until there is a change.
func (p *Pipe) readOrBlock(b []byte) (int, error) {
p.mu.Lock()
defer p.mu.Unlock()
if !p.readTimeout.IsZero() && !time.Now().Before(p.readTimeout) {
return 0, os.ErrDeadlineExceeded
}
if p.blocked {
p.cnd.Wait()
return 0, nil
}
n, err := p.buf.Read(b)
// err will either be nil or io.EOF.
if err == io.EOF {
if p.closed {
return n, err
}
// Wait for something to change.
p.cnd.Wait()
}
return n, nil
}
// Read implements io.Reader.
// Once the buffer is drained (i.e. after Close), subsequent calls will
// return io.EOF.
func (p *Pipe) Read(b []byte) (n int, err error) {
if debugPipe {
orig := b
defer func() {
log.Printf("Pipe(%q).Read(%q) n=%d, err=%v", p.name, string(orig[:n]), n, err)
}()
}
for n == 0 {
n2, err := p.readOrBlock(b)
if err != nil {
return n2, err
}
n += n2
}
p.cnd.Signal()
return n, nil
}
// writeOrBlock attempts to write to the buffer, if the buffer is full it will
// block until there is a change.
func (p *Pipe) writeOrBlock(b []byte) (int, error) {
p.mu.Lock()
defer p.mu.Unlock()
if p.closed {
return 0, net.ErrClosed
}
if !p.writeTimeout.IsZero() && !time.Now().Before(p.writeTimeout) {
return 0, os.ErrDeadlineExceeded
}
if p.blocked {
p.cnd.Wait()
return 0, nil
}
// Optimistically we want to write the entire slice.
n := len(b)
if limit := p.maxBuf - p.buf.Len(); limit < n {
// However, we don't have enough capacity to write everything.
n = limit
}
if n == 0 {
// Wait for something to change.
p.cnd.Wait()
return 0, nil
}
p.buf.Write(b[:n])
p.cnd.Signal()
return n, nil
}
// Write implements io.Writer.
func (p *Pipe) Write(b []byte) (n int, err error) {
if debugPipe {
orig := b
defer func() {
log.Printf("Pipe(%q).Write(%q) n=%d, err=%v", p.name, string(orig), n, err)
}()
}
for len(b) > 0 {
n2, err := p.writeOrBlock(b)
if err != nil {
return n + n2, err
}
n += n2
b = b[n2:]
}
return n, nil
}
// Close closes the pipe.
func (p *Pipe) Close() error {
p.mu.Lock()
defer p.mu.Unlock()
p.closed = true
p.blocked = false
if p.cancelWriteTimer != nil {
p.cancelWriteTimer()
p.cancelWriteTimer = nil
}
if p.cancelReadTimer != nil {
p.cancelReadTimer()
p.cancelReadTimer = nil
}
p.cnd.Broadcast()
return nil
}
func (p *Pipe) deadlineTimer(t time.Time) func() {
if t.IsZero() {
return nil
}
if t.Before(time.Now()) {
p.cnd.Broadcast()
return nil
}
ctx, cancel := context.WithDeadline(context.Background(), t)
go func() {
<-ctx.Done()
if ctx.Err() == context.DeadlineExceeded {
p.cnd.Broadcast()
}
}()
return cancel
}
// SetReadDeadline sets the deadline for future Read calls.
func (p *Pipe) SetReadDeadline(t time.Time) error {
p.mu.Lock()
defer p.mu.Unlock()
p.readTimeout = t
// If we already have a deadline, cancel it and create a new one.
if p.cancelReadTimer != nil {
p.cancelReadTimer()
p.cancelReadTimer = nil
}
p.cancelReadTimer = p.deadlineTimer(t)
return nil
}
// SetWriteDeadline sets the deadline for future Write calls.
func (p *Pipe) SetWriteDeadline(t time.Time) error {
p.mu.Lock()
defer p.mu.Unlock()
p.writeTimeout = t
// If we already have a deadline, cancel it and create a new one.
if p.cancelWriteTimer != nil {
p.cancelWriteTimer()
p.cancelWriteTimer = nil
}
p.cancelWriteTimer = p.deadlineTimer(t)
return nil
}
// Block will cause all calls to Read and Write to block until they either
// timeout, are unblocked or the pipe is closed.
func (p *Pipe) Block() error {
p.mu.Lock()
defer p.mu.Unlock()
closed := p.closed
blocked := p.blocked
p.blocked = true
if closed {
return fmt.Errorf("memnet.Pipe(%q).Block: closed", p.name)
}
if blocked {
return fmt.Errorf("memnet.Pipe(%q).Block: already blocked", p.name)
}
p.cnd.Broadcast()
return nil
}
// Unblock will cause all blocked Read/Write calls to continue execution.
func (p *Pipe) Unblock() error {
p.mu.Lock()
defer p.mu.Unlock()
closed := p.closed
blocked := p.blocked
p.blocked = false
if closed {
return fmt.Errorf("memnet.Pipe(%q).Block: closed", p.name)
}
if !blocked {
return fmt.Errorf("memnet.Pipe(%q).Block: already unblocked", p.name)
}
p.cnd.Broadcast()
return nil
}
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