carrier.go

// Package carrier provides a WebSocket proxy to carry or proxy a connection
// from the local client to the edge. See it as a wrapper around any protocol
// that it packages up in a WebSocket connection to the edge.
package carrier

import (
	"crypto/tls"
	"fmt"
	"io"
	"net"
	"net/http"
	"net/url"
	"os"
	"strings"

	"github.com/pkg/errors"
	"github.com/rs/zerolog"

	"github.com/cloudflare/cloudflared/token"
)

const (
	LogFieldOriginURL       = "originURL"
	CFAccessTokenHeader     = "Cf-Access-Token"
	cfJumpDestinationHeader = "Cf-Access-Jump-Destination"
)

type StartOptions struct {
	AppInfo         *token.AppInfo
	OriginURL       string
	Headers         http.Header
	Host            string
	TLSClientConfig *tls.Config
}

// Connection wraps up all the needed functions to forward over the tunnel
type Connection interface {
	// ServeStream is used to forward data from the client to the edge
	ServeStream(*StartOptions, io.ReadWriter) error
}

// StdinoutStream is empty struct for wrapping stdin/stdout
// into a single ReadWriter
type StdinoutStream struct{}

// Read will read from Stdin
func (c *StdinoutStream) Read(p []byte) (int, error) {
	return os.Stdin.Read(p)

}

// Write will write to Stdout
func (c *StdinoutStream) Write(p []byte) (int, error) {
	return os.Stdout.Write(p)
}

// Helper to allow deferring the response close with a check that the resp is not nil
func closeRespBody(resp *http.Response) {
	if resp != nil {
		_ = resp.Body.Close()
	}
}

// StartForwarder will setup a listener on a specified address/port and then
// forward connections to the origin by calling `Serve()`.
func StartForwarder(conn Connection, address string, shutdownC <-chan struct{}, options *StartOptions) error {
	listener, err := net.Listen("tcp", address)
	if err != nil {
		return errors.Wrap(err, "failed to start forwarding server")
	}
	return Serve(conn, listener, shutdownC, options)
}

// StartClient will copy the data from stdin/stdout over a WebSocket connection
// to the edge (originURL)
func StartClient(conn Connection, stream io.ReadWriter, options *StartOptions) error {
	return conn.ServeStream(options, stream)
}

// Serve accepts incoming connections on the specified net.Listener.
// Each connection is handled in a new goroutine: its data is copied over a
// WebSocket connection to the edge (originURL).
// `Serve` always closes `listener`.
func Serve(remoteConn Connection, listener net.Listener, shutdownC <-chan struct{}, options *StartOptions) error {
	defer listener.Close()
	errChan := make(chan error)

	go func() {
		for {
			conn, err := listener.Accept()
			if err != nil {
				// don't block if parent goroutine quit early
				select {
				case errChan <- err:
				default:
				}
				return
			}
			go serveConnection(remoteConn, conn, options)
		}
	}()

	select {
	case <-shutdownC:
		return nil
	case err := <-errChan:
		return err
	}
}

// serveConnection handles connections for the Serve() call
func serveConnection(remoteConn Connection, c net.Conn, options *StartOptions) {
	defer c.Close()
	_ = remoteConn.ServeStream(options, c)
}

// IsAccessResponse checks the http Response to see if the url location
// contains the Access structure.
func IsAccessResponse(resp *http.Response) bool {
	if resp == nil || resp.StatusCode != http.StatusFound {
		return false
	}

	location, err := resp.Location()
	if err != nil || location == nil {
		return false
	}
	if strings.HasPrefix(location.Path, token.AccessLoginWorkerPath) {
		return true
	}

	return false
}

// BuildAccessRequest builds an HTTP request with the Access token set
func BuildAccessRequest(options *StartOptions, log *zerolog.Logger) (*http.Request, error) {
	req, err := http.NewRequest(http.MethodGet, options.OriginURL, nil)
	if err != nil {
		return nil, err
	}

	token, err := token.FetchTokenWithRedirect(req.URL, options.AppInfo, log)
	if err != nil {
		return nil, err
	}

	// We need to create a new request as FetchToken will modify req (boo mutable)
	// as it has to follow redirect on the API and such, so here we init a new one
	originRequest, err := http.NewRequest(http.MethodGet, options.OriginURL, nil)
	if err != nil {
		return nil, err
	}
	originRequest.Header.Set(CFAccessTokenHeader, token)

	for k, v := range options.Headers {
		if len(v) >= 1 {
			originRequest.Header.Set(k, v[0])
		}
	}

	return originRequest, nil
}

func SetBastionDest(header http.Header, destination string) {
	if destination != "" {
		header.Set(cfJumpDestinationHeader, destination)
	}
}

func ResolveBastionDest(r *http.Request) (string, error) {
	jumpDestination := r.Header.Get(cfJumpDestinationHeader)
	if jumpDestination == "" {
		return "", fmt.Errorf("Did not receive final destination from client. The --destination flag is likely not set on the client side")
	}
	// Strip scheme and path set by client. Without a scheme
	// Parsing a hostname and path without scheme might not return an error due to parsing ambiguities
	if jumpURL, err := url.Parse(jumpDestination); err == nil && jumpURL.Host != "" {
		return removePath(jumpURL.Host), nil
	}
	return removePath(jumpDestination), nil
}

func removePath(dest string) string {
	return strings.SplitN(dest, "/", 2)[0]
}