net/memnet: rename from net/nettest

This is just #cleanup to resolve a TODO

Also add a package doc.

Signed-off-by: Maisem Ali <maisem@tailscale.com>

net/memnet/pipe.go

@@ -0,0 +1,244 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// 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
+}