feat: enable predefined VNC passwords

This commit makes it possible to set a predefined password when
connecting to QEMU machines via VNC when `vnc_use_password` is `true`.

This way, having to set `PACKER_LOG=1` to retrieve the password is no
longer needed when troubleshooting builder VM bootstrap issues.

Signed-off-by: Carlos Nunez <13461447+carlosonunez@users.noreply.github.com>

.gitignore

@@ -3,3 +3,4 @@ dist/*
 packer-plugin-scaffolding
 example/output-ubuntu1804
 crash.log
+packer-plugin-qemu

builder/qemu/config.go

@@ -562,6 +562,8 @@ type Config struct {
 	// binded to for VNC. By default packer will use 127.0.0.1 for this. If you
 	// wish to bind to all interfaces use 0.0.0.0.
 	VNCBindAddress string `mapstructure:"vnc_bind_address" required:"false"`
+	// The password to set when VNCUsePassword == true.
+	VNCPassword string `mapstructure:"vnc_password" required:"false"`
 	// Whether or not to set a password on the VNC server. This option
 	// automatically enables the QMP socket. See `qmp_socket_path`. Defaults to
 	// `false`.

builder/qemu/config_test.go

@@ -15,6 +15,7 @@ import (
 	"github.com/hashicorp/packer-plugin-sdk/common"
 	packersdk "github.com/hashicorp/packer-plugin-sdk/packer"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 var testPem = `
@@ -642,6 +643,42 @@ func TestBuilderPrepare_VNCPassword(t *testing.T) {
 	}
 }
 
+func TestVNCPasswordEmptyWhenUsePasswordFalse(t *testing.T) {
+	var c Config
+	config := testConfig()
+	config["vnc_use_password"] = false
+	config["vnc_password"] = "supersecret"
+	warns, err := c.Prepare(config)
+	require.NoError(t, err)
+	assert.Len(t, warns, 0, "bad: %#v", warns)
+	p := vncpwd{}
+	assert.Empty(t, p.VNCPassword(&c))
+}
+
+func TestVNCPasswordRandomWhenVNCPasswordEmpty(t *testing.T) {
+	var c Config
+	config := testConfig()
+	config["vnc_use_password"] = true
+	config["vnc_password"] = ""
+	warns, err := c.Prepare(config)
+	require.NoError(t, err)
+	assert.Len(t, warns, 0, "bad: %#v", warns)
+	p := vncpwd{}
+	assert.Len(t, p.VNCPassword(&c), 8)
+}
+
+func TestVNCPasswordSetWhenVNCPasswordNotEmpty(t *testing.T) {
+	var c Config
+	config := testConfig()
+	config["vnc_use_password"] = true
+	config["vnc_password"] = "supersecret"
+	warns, err := c.Prepare(config)
+	require.NoError(t, err)
+	assert.Len(t, warns, 0, "bad: %#v", warns)
+	p := vncpwd{}
+	assert.Equal(t, p.VNCPassword(&c), config["vnc_password"])
+}
+
 func TestCommConfigPrepare_BackwardsCompatibility(t *testing.T) {
 	var c Config
 	config := testConfig()

builder/qemu/step_configure_vnc.go

@@ -28,7 +28,15 @@ type stepConfigureVNC struct {
 	l *net.Listener
 }
 
-func VNCPassword() string {
+type vncpwd struct{}
+
+func (p *vncpwd) VNCPassword(c *Config) string {
+	if !c.VNCUsePassword {
+		return ""
+	}
+	if len(c.VNCPassword) != 0 {
+		return c.VNCPassword
+	}
 	length := int(8)
 
 	charSet := []byte("012345689abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ")
@@ -39,7 +47,6 @@ func VNCPassword() string {
 	for i := 0; i < length; i++ {
 		password[i] = charSet[rand.Intn(charSetLength)]
 	}
-
 	return string(password)
 }
 
@@ -54,7 +61,6 @@ func (s *stepConfigureVNC) Run(ctx context.Context, state multistep.StateBag) mu
 	ui.Say(msg)
 	log.Print(msg)
 
-	var vncPassword string
 	var err error
 	s.l, err = net.ListenRangeConfig{
 		Addr:    config.VNCBindAddress,
@@ -70,16 +76,11 @@ func (s *stepConfigureVNC) Run(ctx context.Context, state multistep.StateBag) mu
 	}
 	s.l.Listener.Close() // free port, but don't unlock lock file
 	vncPort := s.l.Port
-
-	if config.VNCUsePassword {
-		vncPassword = VNCPassword()
-	} else {
-		vncPassword = ""
-	}
+	vncPassword := vncpwd{}
 
 	log.Printf("Found available VNC port: %d on IP: %s", vncPort, config.VNCBindAddress)
 	state.Put("vnc_port", vncPort)
-	state.Put("vnc_password", vncPassword)
+	state.Put("vnc_password", vncPassword.VNCPassword(config))
 
 	return multistep.ActionContinue
 }

docs-partials/builder/qemu/Config-not-required.mdx

@@ -331,6 +331,9 @@
   binded to for VNC. By default packer will use 127.0.0.1 for this. If you
   wish to bind to all interfaces use 0.0.0.0.
 
+- `vnc_password` (bool) - The password to set for the VNC password when
+  `vnc_use_password` is true; automatically generated otherwise.
+
 - `vnc_use_password` (bool) - Whether or not to set a password on the VNC server. This option
   automatically enables the QMP socket. See `qmp_socket_path`. Defaults to
   `false`.