Support unix sockets.

cmd/cloudflared/config/configuration.go

@@ -63,7 +63,17 @@ func FindDefaultConfigPath() string {
 	return ""
 }
 
+// ValidateUnixSocket ensures --unix-socket param is used exclusively
+// i.e. it fails if a user specifies both --url and --unix-socket
+func ValidateUnixSocket(c *cli.Context) (string, error) {
+	if c.IsSet("unix-socket") && (c.IsSet("url") || c.NArg() > 0) {
+		return "", errors.New("--unix-socket must be used exclusivly.")
+	}
+	return c.String("unix-socket"), nil
+}
+
 // ValidateUrl will validate url flag correctness. It can be either from --url or argument
+// Notice ValidateUnixSocket, it will enforce --unix-socket is not used with --url or argument
 func ValidateUrl(c *cli.Context) (string, error) {
 	var url = c.String("url")
 	if c.NArg() > 0 {

cmd/cloudflared/tunnel/cmd.go

@@ -476,6 +476,12 @@ func tunnelFlags(shouldHide bool) []cli.Flag {
 			EnvVars: []string{"TUNNEL_URL"},
 			Hidden:  shouldHide,
 		}),
+		altsrc.NewStringFlag(&cli.StringFlag{
+			Name:    "unix-socket",
+			Usage:   "Path to unix socket to use instead of --url",
+			EnvVars: []string{"TUNNEL_UNIX_SOCKET"},
+			Hidden:  shouldHide,
+		}),
 		altsrc.NewStringFlag(&cli.StringFlag{
 			Name:    "hostname",
 			Usage:   "Set a hostname on a Cloudflare zone to route traffic through this tunnel.",

cmd/cloudflared/tunnel/configuration.go

@@ -1,6 +1,7 @@
 package tunnel
 
 import (
+	"context"
 	"crypto/tls"
 	"crypto/x509"
 	"encoding/hex"
@@ -160,7 +161,6 @@ func prepareTunnelConfig(c *cli.Context, buildInfo *origin.BuildInfo, version st
 		logger.WithError(err).Error("Error validating origin URL")
 		return nil, errors.Wrap(err, "Error validating origin URL")
 	}
-	logger.Infof("Proxying tunnel requests to %s", originURL)
 
 	originCert, err := getOriginCert(c)
 	if err != nil {
@@ -175,12 +175,7 @@ func prepareTunnelConfig(c *cli.Context, buildInfo *origin.BuildInfo, version st
 
 	tunnelMetrics := origin.NewTunnelMetrics()
 	httpTransport := &http.Transport{
-		Proxy: http.ProxyFromEnvironment,
+		Proxy:                 http.ProxyFromEnvironment,
-		DialContext: (&net.Dialer{
-			Timeout:   c.Duration("proxy-connect-timeout"),
-			KeepAlive: c.Duration("proxy-tcp-keepalive"),
-			DualStack: !c.Bool("proxy-no-happy-eyeballs"),
-		}).DialContext,
 		MaxIdleConns:          c.Int("proxy-keepalive-connections"),
 		IdleConnTimeout:       c.Duration("proxy-keepalive-timeout"),
 		TLSHandshakeTimeout:   c.Duration("proxy-tls-timeout"),
@@ -188,6 +183,29 @@ func prepareTunnelConfig(c *cli.Context, buildInfo *origin.BuildInfo, version st
 		TLSClientConfig:       &tls.Config{RootCAs: originCertPool, InsecureSkipVerify: c.IsSet("no-tls-verify")},
 	}
 
+	dialContext := (&net.Dialer{
+		Timeout:   c.Duration("proxy-connect-timeout"),
+		KeepAlive: c.Duration("proxy-tcp-keepalive"),
+		DualStack: !c.Bool("proxy-no-happy-eyeballs"),
+	}).DialContext
+
+	if c.IsSet("unix-socket") {
+		unixSocket, err := config.ValidateUnixSocket(c)
+		if err != nil {
+			logger.WithError(err).Error("Error validating --unix-socket")
+			return nil, errors.Wrap(err, "Error validating --unix-socket")
+		}
+
+		logger.Infof("Proxying tunnel requests to unix:%s", unixSocket)
+		httpTransport.DialContext = func(ctx context.Context, _, _ string) (net.Conn, error) {
+			// if --unix-socket specified, enforce network type "unix"
+			return dialContext(ctx, "unix", unixSocket)
+		}
+	} else {
+		logger.Infof("Proxying tunnel requests to %s", originURL)
+		httpTransport.DialContext = dialContext
+	}
+
 	if !c.IsSet("hello-world") && c.IsSet("origin-server-name") {
 		httpTransport.TLSClientConfig.ServerName = c.String("origin-server-name")
 	}

origin/tunnel.go

@@ -37,8 +37,10 @@ const (
 )
 
 type TunnelConfig struct {
+	// OriginUrl may not be used if a user specifies a unix socket.
+	OriginUrl string
+
 	EdgeAddrs          []string
-	OriginUrl          string
 	Hostname           string
 	OriginCert         []byte
 	TlsConfig          *tls.Config