Move Linux client & common packages into a public repo.

derp/derphttp/derphttp_client.go

@@ -0,0 +1,203 @@
+// 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 derphttp implements DERP-over-HTTP.
+//
+// This makes DERP look exactly like WebSockets.
+// A server can implement DERP over HTTPS and even if the TLS connection
+// intercepted using a fake root CA, unless the interceptor knows how to
+// detect DERP packets, it will look like a web socket.
+package derphttp
+
+import (
+	"bufio"
+	"bytes"
+	"crypto/tls"
+	"errors"
+	"fmt"
+	"io/ioutil"
+	"net"
+	"net/http"
+	"net/url"
+	"sync"
+
+	"tailscale.com/derp"
+)
+
+// Client is a DERP-over-HTTP client.
+//
+// It automatically reconnects on error retry. That is, a failed Send or
+// Recv will report the error and not retry, but subsequent calls to
+// Send/Recv will completely re-establish the connection.
+type Client struct {
+	privateKey [32]byte
+	logf       func(format string, args ...interface{})
+	closed     chan struct{}
+	url        *url.URL
+	resp       *http.Response
+
+	netConnMu sync.Mutex
+	netConn   net.Conn
+
+	clientMu sync.Mutex
+	client   *derp.Client
+}
+
+func NewClient(privateKey [32]byte, serverURL string, logf func(format string, args ...interface{})) (c *Client, err error) {
+	u, err := url.Parse(serverURL)
+	if err != nil {
+		return nil, fmt.Errorf("derphttp.NewClient: %v", err)
+	}
+
+	c = &Client{
+		privateKey: privateKey,
+		logf:       logf,
+		url:        u,
+		closed:     make(chan struct{}),
+	}
+	if _, err := c.connect("derphttp.NewClient"); err != nil {
+		c.logf("%v", err)
+	}
+	return c, nil
+}
+
+func (c *Client) connect(caller string) (client *derp.Client, err error) {
+	select {
+	case <-c.closed:
+		return nil, ErrClientClosed
+	default:
+	}
+
+	c.clientMu.Lock()
+	defer c.clientMu.Unlock()
+
+	if c.client != nil {
+		return c.client, nil
+	}
+
+	c.logf("%s: connecting", caller)
+
+	var netConn net.Conn
+	defer func() {
+		if err != nil {
+			err = fmt.Errorf("%s connect: %v", caller, err)
+			if netConn := netConn; netConn != nil {
+				netConn.Close()
+			}
+		}
+	}()
+
+	if c.url.Scheme == "https" {
+		port := c.url.Port()
+		if port == "" {
+			port = "443"
+		}
+		config := &tls.Config{}
+		var tlsConn *tls.Conn
+		tlsConn, err = tls.Dial("tcp", net.JoinHostPort(c.url.Host, port), config)
+		if tlsConn != nil {
+			netConn = tlsConn
+		}
+	} else {
+		netConn, err = net.Dial("tcp", c.url.Host)
+	}
+	if err != nil {
+		return nil, err
+	}
+
+	c.netConnMu.Lock()
+	c.netConn = netConn
+	c.netConnMu.Unlock()
+
+	conn := bufio.NewReadWriter(bufio.NewReader(netConn), bufio.NewWriter(netConn))
+
+	req, err := http.NewRequest("GET", c.url.String(), nil)
+	if err != nil {
+		return nil, err
+	}
+	req.Header.Set("Upgrade", "WebSocket")
+	req.Header.Set("Connection", "Upgrade")
+	if err := req.Write(conn); err != nil {
+		return nil, err
+	}
+	if err := conn.Flush(); err != nil {
+		return nil, err
+	}
+
+	resp, err := http.ReadResponse(conn.Reader, req)
+	if err != nil {
+		return nil, err
+	}
+	if resp.StatusCode != http.StatusSwitchingProtocols {
+		b, _ := ioutil.ReadAll(resp.Body)
+		resp.Body.Close()
+		return nil, fmt.Errorf("GET failed: %v: %s", err, b)
+	}
+	resp.Body = ioutil.NopCloser(bytes.NewReader([]byte{}))
+
+	derpClient, err := derp.NewClient(c.privateKey, netConn, conn, c.logf)
+	if err != nil {
+		return nil, err
+	}
+	c.resp = resp
+	c.client = derpClient
+	return c.client, nil
+}
+
+func (c *Client) Send(dstKey [32]byte, b []byte) error {
+	client, err := c.connect("derphttp.Client.Send")
+	if err != nil {
+		return err
+	}
+	if err := client.Send(dstKey, b); err != nil {
+		c.close()
+	}
+	return err
+}
+
+func (c *Client) Recv(b []byte) (int, error) {
+	client, err := c.connect("derphttp.Client.Recv")
+	if err != nil {
+		return 0, err
+	}
+	n, err := client.Recv(b)
+	if err != nil {
+		c.close()
+	}
+	return n, err
+}
+
+func (c *Client) Close() error {
+	select {
+	case <-c.closed:
+		return ErrClientClosed
+	default:
+	}
+	close(c.closed)
+	c.close()
+	return nil
+}
+
+func (c *Client) close() {
+	c.netConnMu.Lock()
+	netConn := c.netConn
+	c.netConnMu.Unlock()
+
+	if netConn != nil {
+		netConn.Close()
+	}
+
+	c.clientMu.Lock()
+	defer c.clientMu.Unlock()
+	if c.client == nil {
+		return
+	}
+	c.resp = nil
+	c.client = nil
+	c.netConnMu.Lock()
+	c.netConn = nil
+	c.netConnMu.Unlock()
+}
+
+var ErrClientClosed = errors.New("derphttp.Client closed")