expect_disconnect option

provisioner/shell: Adds option to fail if the remote server disconnects
us.

communicator/ssh/communicator.go

@@ -118,15 +118,13 @@ func (c *comm) Start(cmd *packer.RemoteCmd) (err error) {
 				log.Printf("Remote command exited with '%d': %s", exitStatus, cmd.Command)
 			case *ssh.ExitMissingError:
 				log.Printf("Remote command exited without exit status or exit signal.")
-				exitStatus = -1
+				exitStatus = packer.CmdDisconnect
 			default:
 				log.Printf("Error occurred waiting for ssh session: %s", err.Error())
-				exitStatus = -1
 			}
 		}
 		cmd.SetExited(exitStatus)
 	}()
-
 	return
 }
 

packer/communicator.go

@@ -9,6 +9,10 @@ import (
 	"github.com/mitchellh/iochan"
 )
 
+// CmdDisconnect is a sentry value to indicate a RemoteCmd
+// exited because the remote side disconnected us.
+const CmdDisconnect int = 2300218
+
 // RemoteCmd represents a remote command being prepared or run.
 type RemoteCmd struct {
 	// Command is the command to run remotely. This is executed as if

provisioner/shell/provisioner.go

@@ -70,6 +70,8 @@ type Config struct {
 	// Whether to clean scripts up
 	SkipClean bool `mapstructure:"skip_clean"`
 
+	ExpectDisconnect *bool `mapstructure:"expect_disconnect"`
+
 	startRetryTimeout time.Duration
 	ctx               interpolate.Context
 }
@@ -101,6 +103,11 @@ func (p *Provisioner) Prepare(raws ...interface{}) error {
 		p.config.ExecuteCommand = "chmod +x {{.Path}}; {{.Vars}} {{.Path}}"
 	}
 
+	if p.config.ExpectDisconnect == nil {
+		t := true
+		p.config.ExpectDisconnect = &t
+	}
+
 	if p.config.Inline != nil && len(p.config.Inline) == 0 {
 		p.config.Inline = nil
 	}
@@ -283,11 +290,18 @@ func (p *Provisioner) Provision(ui packer.Ui, comm packer.Communicator) error {
 			cmd = &packer.RemoteCmd{Command: command}
 			return cmd.StartWithUi(comm, ui)
 		})
+
 		if err != nil {
 			return err
 		}
 
-		if cmd.ExitStatus != 0 {
+		// If the exit code indicates a remote disconnect, fail unless
+		// we were expecting it.
+		if cmd.ExitStatus == packer.CmdDisconnect {
+			if !*p.config.ExpectDisconnect {
+				return fmt.Errorf("Script disconnected unexpectedly.")
+			}
+		} else if cmd.ExitStatus != 0 {
 			return fmt.Errorf("Script exited with non-zero exit status: %d", cmd.ExitStatus)
 		}
 

provisioner/shell/provisioner_test.go

@@ -32,11 +32,42 @@ func TestProvisionerPrepare_Defaults(t *testing.T) {
 		t.Fatalf("err: %s", err)
 	}
 
+	if *p.config.ExpectDisconnect != true {
+		t.Errorf("expected ExpectDisconnect to be true")
+	}
+
 	if p.config.RemotePath == "" {
 		t.Errorf("unexpected remote path: %s", p.config.RemotePath)
 	}
 }
 
+func TestProvisionerPrepare_ExpectDisconnect(t *testing.T) {
+	config := testConfig()
+	p := new(Provisioner)
+	config["expect_disconnect"] = false
+
+	err := p.Prepare(config)
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	if *p.config.ExpectDisconnect != false {
+		t.Errorf("expected ExpectDisconnect to be false")
+	}
+
+	config["expect_disconnect"] = true
+	p = new(Provisioner)
+	err = p.Prepare(config)
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	if *p.config.ExpectDisconnect != true {
+		t.Errorf("expected ExpectDisconnect to be true")
+	}
+
+}
+
 func TestProvisionerPrepare_InlineShebang(t *testing.T) {
 	config := testConfig()
 

website/source/docs/provisioners/shell.html.md

@@ -71,6 +71,10 @@ Optional parameters:
     available variables: `Path`, which is the path to the script to run, and
     `Vars`, which is the list of `environment_vars`, if configured.
 
+-   `expect_disconnect` (bool) - Defaults to true. Whether to error if the
+    server disconnects us. A disconnect might happen if you restart the ssh
+    server or reboot the host. May default to false in the future.
+
 -   `inline_shebang` (string) - The
     [shebang](https://en.wikipedia.org/wiki/Shebang_%28Unix%29) value to use when
     running commands specified by `inline`. By default, this is `/bin/sh -e`. If