Merge pull request #2145 from mitchellh/f-interpolate

Much more automated interpolation

builder/amazon/chroot/builder.go

@@ -6,7 +6,6 @@ package chroot
 
 import (
 	"errors"
-	"fmt"
 	"log"
 	"runtime"
 
@@ -14,7 +13,9 @@ import (
 	"github.com/mitchellh/multistep"
 	awscommon "github.com/mitchellh/packer/builder/amazon/common"
 	"github.com/mitchellh/packer/common"
+	"github.com/mitchellh/packer/helper/config"
 	"github.com/mitchellh/packer/packer"
+	"github.com/mitchellh/packer/template/interpolate"
 )
 
 // The unique ID for this builder
@@ -34,7 +35,7 @@ type Config struct {
 	MountPath      string     `mapstructure:"mount_path"`
 	SourceAmi      string     `mapstructure:"source_ami"`
 
-	tpl *packer.ConfigTemplate
+	ctx *interpolate.Context
 }
 
 type wrappedCommandTemplate struct {
@@ -47,17 +48,20 @@ type Builder struct {
 }
 
 func (b *Builder) Prepare(raws ...interface{}) ([]string, error) {
-	md, err := common.DecodeConfig(&b.config, raws...)
-	if err != nil {
-		return nil, err
-	}
-
-	b.config.tpl, err = packer.NewConfigTemplate()
+	b.config.ctx = &interpolate.Context{Funcs: awscommon.TemplateFuncs}
+	err := config.Decode(&b.config, &config.DecodeOpts{
+		Interpolate:        true,
+		InterpolateContext: b.config.ctx,
+		InterpolateFilter: &interpolate.RenderFilter{
+			Exclude: []string{
+				"command_wrapper",
+				"mount_path",
+			},
+		},
+	}, raws...)
 	if err != nil {
 		return nil, err
 	}
-	b.config.tpl.UserVars = b.config.PackerUserVars
-	b.config.tpl.Funcs(awscommon.TemplateFuncs)
 
 	// Defaults
 	if b.config.ChrootMounts == nil {
@@ -91,55 +95,22 @@ func (b *Builder) Prepare(raws ...interface{}) ([]string, error) {
 	}
 
 	// Accumulate any errors
-	errs := common.CheckUnusedConfig(md)
-	errs = packer.MultiErrorAppend(errs, b.config.AccessConfig.Prepare(b.config.tpl)...)
-	errs = packer.MultiErrorAppend(errs, b.config.AMIConfig.Prepare(b.config.tpl)...)
+	var errs *packer.MultiError
+	errs = packer.MultiErrorAppend(errs, b.config.AccessConfig.Prepare(b.config.ctx)...)
+	errs = packer.MultiErrorAppend(errs, b.config.AMIConfig.Prepare(b.config.ctx)...)
 
-	for i, mounts := range b.config.ChrootMounts {
+	for _, mounts := range b.config.ChrootMounts {
 		if len(mounts) != 3 {
 			errs = packer.MultiErrorAppend(
 				errs, errors.New("Each chroot_mounts entry should be three elements."))
 			break
 		}
-
-		for j, entry := range mounts {
-			b.config.ChrootMounts[i][j], err = b.config.tpl.Process(entry, nil)
-			if err != nil {
-				errs = packer.MultiErrorAppend(errs,
-					fmt.Errorf("Error processing chroot_mounts[%d][%d]: %s",
-						i, j, err))
-			}
-		}
-	}
-
-	for i, file := range b.config.CopyFiles {
-		var err error
-		b.config.CopyFiles[i], err = b.config.tpl.Process(file, nil)
-		if err != nil {
-			errs = packer.MultiErrorAppend(errs,
-				fmt.Errorf("Error processing copy_files[%d]: %s",
-					i, err))
-		}
 	}
 
 	if b.config.SourceAmi == "" {
 		errs = packer.MultiErrorAppend(errs, errors.New("source_ami is required."))
 	}
 
-	templates := map[string]*string{
-		"device_path": &b.config.DevicePath,
-		"source_ami":  &b.config.SourceAmi,
-	}
-
-	for n, ptr := range templates {
-		var err error
-		*ptr, err = b.config.tpl.Process(*ptr, nil)
-		if err != nil {
-			errs = packer.MultiErrorAppend(
-				errs, fmt.Errorf("Error processing %s: %s", n, err))
-		}
-	}
-
 	if errs != nil && len(errs.Errors) > 0 {
 		return nil, errs
 	}
@@ -166,10 +137,9 @@ func (b *Builder) Run(ui packer.Ui, hook packer.Hook, cache packer.Cache) (packe
 	ec2conn := ec2.New(auth, region)
 
 	wrappedCommand := func(command string) (string, error) {
-		return b.config.tpl.Process(
-			b.config.CommandWrapper, &wrappedCommandTemplate{
-				Command: command,
-			})
+		ctx := *b.config.ctx
+		ctx.Data = &wrappedCommandTemplate{Command: command}
+		return interpolate.Render(b.config.CommandWrapper, &ctx)
 	}
 
 	// Setup the state bag and initial state for the steps

builder/amazon/chroot/step_mount_device.go

@@ -3,12 +3,14 @@ package chroot
 import (
 	"bytes"
 	"fmt"
-	"github.com/mitchellh/goamz/ec2"
-	"github.com/mitchellh/multistep"
-	"github.com/mitchellh/packer/packer"
 	"log"
 	"os"
 	"path/filepath"
+
+	"github.com/mitchellh/goamz/ec2"
+	"github.com/mitchellh/multistep"
+	"github.com/mitchellh/packer/packer"
+	"github.com/mitchellh/packer/template/interpolate"
 )
 
 type mountPathData struct {
@@ -31,9 +33,9 @@ func (s *StepMountDevice) Run(state multistep.StateBag) multistep.StepAction {
 	device := state.Get("device").(string)
 	wrappedCommand := state.Get("wrappedCommand").(CommandWrapper)
 
-	mountPath, err := config.tpl.Process(config.MountPath, &mountPathData{
-		Device: filepath.Base(device),
-	})
+	ctx := *config.ctx
+	ctx.Data = &mountPathData{Device: filepath.Base(device)}
+	mountPath, err := interpolate.Render(config.MountPath, &ctx)
 
 	if err != nil {
 		err := fmt.Errorf("Error preparing mount directory: %s", err)

builder/amazon/common/access_config.go

@@ -2,10 +2,11 @@ package common
 
 import (
 	"fmt"
-	"github.com/mitchellh/goamz/aws"
-	"github.com/mitchellh/packer/packer"
 	"strings"
 	"unicode"
+
+	"github.com/mitchellh/goamz/aws"
+	"github.com/mitchellh/packer/template/interpolate"
 )
 
 // AccessConfig is for common configuration related to AWS access
@@ -49,31 +50,8 @@ func (c *AccessConfig) Region() (aws.Region, error) {
 	return aws.Regions[region], nil
 }
 
-func (c *AccessConfig) Prepare(t *packer.ConfigTemplate) []error {
-	if t == nil {
-		var err error
-		t, err = packer.NewConfigTemplate()
-		if err != nil {
-			return []error{err}
-		}
-	}
-
-	templates := map[string]*string{
-		"access_key": &c.AccessKey,
-		"secret_key": &c.SecretKey,
-		"region":     &c.RawRegion,
-	}
-
-	errs := make([]error, 0)
-	for n, ptr := range templates {
-		var err error
-		*ptr, err = t.Process(*ptr, nil)
-		if err != nil {
-			errs = append(
-				errs, fmt.Errorf("Error processing %s: %s", n, err))
-		}
-	}
-
+func (c *AccessConfig) Prepare(ctx *interpolate.Context) []error {
+	var errs []error
 	if c.RawRegion != "" {
 		if _, ok := aws.Regions[c.RawRegion]; !ok {
 			errs = append(errs, fmt.Errorf("Unknown region: %s", c.RawRegion))

builder/amazon/common/ami_config.go

@@ -4,7 +4,7 @@ import (
 	"fmt"
 
 	"github.com/mitchellh/goamz/aws"
-	"github.com/mitchellh/packer/packer"
+	"github.com/mitchellh/packer/template/interpolate"
 )
 
 // AMIConfig is for common configuration related to creating AMIs.
@@ -20,49 +20,8 @@ type AMIConfig struct {
 	AMIEnhancedNetworking bool              `mapstructure:"enhanced_networking"`
 }
 
-func (c *AMIConfig) Prepare(t *packer.ConfigTemplate) []error {
-	if t == nil {
-		var err error
-		t, err = packer.NewConfigTemplate()
-		if err != nil {
-			return []error{err}
-		}
-	}
-
-	templates := map[string]*string{
-		"ami_name":                &c.AMIName,
-		"ami_description":         &c.AMIDescription,
-		"ami_virtualization_type": &c.AMIVirtType,
-	}
-
-	errs := make([]error, 0)
-	for n, ptr := range templates {
-		var err error
-		*ptr, err = t.Process(*ptr, nil)
-		if err != nil {
-			errs = append(
-				errs, fmt.Errorf("Error processing %s: %s", n, err))
-		}
-	}
-
-	sliceTemplates := map[string][]string{
-		"ami_users":         c.AMIUsers,
-		"ami_groups":        c.AMIGroups,
-		"ami_product_codes": c.AMIProductCodes,
-		"ami_regions":       c.AMIRegions,
-	}
-
-	for n, slice := range sliceTemplates {
-		for i, elem := range slice {
-			var err error
-			slice[i], err = t.Process(elem, nil)
-			if err != nil {
-				errs = append(
-					errs, fmt.Errorf("Error processing %s[%d]: %s", n, i, err))
-			}
-		}
-	}
-
+func (c *AMIConfig) Prepare(ctx *interpolate.Context) []error {
+	var errs []error
 	if c.AMIName == "" {
 		errs = append(errs, fmt.Errorf("ami_name must be specified"))
 	}
@@ -92,27 +51,6 @@ func (c *AMIConfig) Prepare(t *packer.ConfigTemplate) []error {
 		c.AMIRegions = regions
 	}
 
-	newTags := make(map[string]string)
-	for k, v := range c.AMITags {
-		k, err := t.Process(k, nil)
-		if err != nil {
-			errs = append(errs,
-				fmt.Errorf("Error processing tag key %s: %s", k, err))
-			continue
-		}
-
-		v, err := t.Process(v, nil)
-		if err != nil {
-			errs = append(errs,
-				fmt.Errorf("Error processing tag value '%s': %s", v, err))
-			continue
-		}
-
-		newTags[k] = v
-	}
-
-	c.AMITags = newTags
-
 	if len(errs) > 0 {
 		return errs
 	}

builder/amazon/common/block_device.go

 package common
 
 import (
-	"fmt"
-
 	"github.com/mitchellh/goamz/ec2"
-	"github.com/mitchellh/packer/packer"
+	"github.com/mitchellh/packer/template/interpolate"
 )
 
 // BlockDevice
@@ -44,48 +42,7 @@ func buildBlockDevices(b []BlockDevice) []ec2.BlockDeviceMapping {
 	return blockDevices
 }
 
-func (b *BlockDevices) Prepare(t *packer.ConfigTemplate) []error {
-	if t == nil {
-		var err error
-		t, err = packer.NewConfigTemplate()
-		if err != nil {
-			return []error{err}
-		}
-	}
-
-	lists := map[string][]BlockDevice{
-		"ami_block_device_mappings":    b.AMIMappings,
-		"launch_block_device_mappings": b.LaunchMappings,
-	}
-
-	var errs []error
-	for outer, bds := range lists {
-		for i := 0; i < len(bds); i++ {
-			templates := map[string]*string{
-				"device_name":  &bds[i].DeviceName,
-				"snapshot_id":  &bds[i].SnapshotId,
-				"virtual_name": &bds[i].VirtualName,
-				"volume_type":  &bds[i].VolumeType,
-			}
-
-			errs := make([]error, 0)
-			for n, ptr := range templates {
-				var err error
-				*ptr, err = t.Process(*ptr, nil)
-				if err != nil {
-					errs = append(
-						errs, fmt.Errorf(
-							"Error processing %s[%d].%s: %s",
-							outer, i, n, err))
-				}
-			}
-		}
-	}
-
-	if len(errs) > 0 {
-		return errs
-	}
-
+func (b *BlockDevices) Prepare(ctx *interpolate.Context) []error {
 	return nil
 }
 

builder/amazon/common/run_config.go

@@ -7,7 +7,7 @@ import (
 	"time"
 
 	"github.com/mitchellh/packer/common/uuid"
-	"github.com/mitchellh/packer/packer"
+	"github.com/mitchellh/packer/template/interpolate"
 )
 
 // RunConfig contains configuration for running an instance from a source
@@ -38,43 +38,7 @@ type RunConfig struct {
 	sshTimeout time.Duration
 }
 
-func (c *RunConfig) Prepare(t *packer.ConfigTemplate) []error {
-	if t == nil {
-		var err error
-		t, err = packer.NewConfigTemplate()
-		if err != nil {
-			return []error{err}
-		}
-	}
-
-	templates := map[string]*string{
-		"iam_instance_profile":    &c.IamInstanceProfile,
-		"instance_type":           &c.InstanceType,
-		"spot_price":              &c.SpotPrice,
-		"spot_price_auto_product": &c.SpotPriceAutoProduct,
-		"ssh_timeout":             &c.RawSSHTimeout,
-		"ssh_username":            &c.SSHUsername,
-		"ssh_private_key_file":    &c.SSHPrivateKeyFile,
-		"source_ami":              &c.SourceAmi,
-		"subnet_id":               &c.SubnetId,
-		"temporary_key_pair_name": &c.TemporaryKeyPairName,
-		"vpc_id":                  &c.VpcId,
-		"availability_zone":       &c.AvailabilityZone,
-		"user_data":               &c.UserData,
-		"user_data_file":          &c.UserDataFile,
-		"security_group_id":       &c.SecurityGroupId,
-	}
-
-	errs := make([]error, 0)
-	for n, ptr := range templates {
-		var err error
-		*ptr, err = t.Process(*ptr, nil)
-		if err != nil {
-			errs = append(
-				errs, fmt.Errorf("Error processing %s: %s", n, err))
-		}
-	}
-
+func (c *RunConfig) Prepare(ctx *interpolate.Context) []error {
 	// Defaults
 	if c.SSHPort == 0 {
 		c.SSHPort = 22
@@ -90,7 +54,7 @@ func (c *RunConfig) Prepare(t *packer.ConfigTemplate) []error {
 	}
 
 	// Validation
-	var err error
+	var errs []error
 	if c.SourceAmi == "" {
 		errs = append(errs, errors.New("A source_ami must be specified"))
 	}
@@ -127,42 +91,7 @@ func (c *RunConfig) Prepare(t *packer.ConfigTemplate) []error {
 		}
 	}
 
-	sliceTemplates := map[string][]string{
-		"security_group_ids": c.SecurityGroupIds,
-	}
-
-	for n, slice := range sliceTemplates {
-		for i, elem := range slice {
-			var err error
-			slice[i], err = t.Process(elem, nil)
-			if err != nil {
-				errs = append(
-					errs, fmt.Errorf("Error processing %s[%d]: %s", n, i, err))
-			}
-		}
-	}
-
-	newTags := make(map[string]string)
-	for k, v := range c.RunTags {
-		k, err := t.Process(k, nil)
-		if err != nil {
-			errs = append(errs,
-				fmt.Errorf("Error processing tag key %s: %s", k, err))
-			continue
-		}
-
-		v, err := t.Process(v, nil)
-		if err != nil {
-			errs = append(errs,
-				fmt.Errorf("Error processing tag value '%s': %s", v, err))
-			continue
-		}
-
-		newTags[k] = v
-	}
-
-	c.RunTags = newTags
-
+	var err error
 	c.sshTimeout, err = time.ParseDuration(c.RawSSHTimeout)
 	if err != nil {
 		errs = append(errs, fmt.Errorf("Failed parsing ssh_timeout: %s", err))

builder/amazon/ebs/builder.go

@@ -13,46 +13,45 @@ import (
 	"github.com/mitchellh/multistep"
 	awscommon "github.com/mitchellh/packer/builder/amazon/common"
 	"github.com/mitchellh/packer/common"
+	"github.com/mitchellh/packer/helper/config"
 	"github.com/mitchellh/packer/packer"
+	"github.com/mitchellh/packer/template/interpolate"
 )
 
 // The unique ID for this builder
 const BuilderId = "mitchellh.amazonebs"
 
-type config struct {
+type Config struct {
 	common.PackerConfig    `mapstructure:",squash"`
 	awscommon.AccessConfig `mapstructure:",squash"`
 	awscommon.AMIConfig    `mapstructure:",squash"`
 	awscommon.BlockDevices `mapstructure:",squash"`
 	awscommon.RunConfig    `mapstructure:",squash"`
 
-	tpl *packer.ConfigTemplate
+	ctx *interpolate.Context
 }
 
 type Builder struct {
-	config config
+	config Config
 	runner multistep.Runner
 }
 
 func (b *Builder) Prepare(raws ...interface{}) ([]string, error) {
-	md, err := common.DecodeConfig(&b.config, raws...)
+	b.config.ctx = &interpolate.Context{Funcs: awscommon.TemplateFuncs}
+	err := config.Decode(&b.config, &config.DecodeOpts{
+		Interpolate:        true,
+		InterpolateContext: b.config.ctx,
+	}, raws...)
 	if err != nil {
 		return nil, err
 	}
 
-	b.config.tpl, err = packer.NewConfigTemplate()
-	if err != nil {
-		return nil, err
-	}
-	b.config.tpl.UserVars = b.config.PackerUserVars
-	b.config.tpl.Funcs(awscommon.TemplateFuncs)
-
 	// Accumulate any errors
-	errs := common.CheckUnusedConfig(md)
-	errs = packer.MultiErrorAppend(errs, b.config.AccessConfig.Prepare(b.config.tpl)...)
-	errs = packer.MultiErrorAppend(errs, b.config.BlockDevices.Prepare(b.config.tpl)...)
-	errs = packer.MultiErrorAppend(errs, b.config.AMIConfig.Prepare(b.config.tpl)...)
-	errs = packer.MultiErrorAppend(errs, b.config.RunConfig.Prepare(b.config.tpl)...)
+	var errs *packer.MultiError
+	errs = packer.MultiErrorAppend(errs, b.config.AccessConfig.Prepare(b.config.ctx)...)
+	errs = packer.MultiErrorAppend(errs, b.config.BlockDevices.Prepare(b.config.ctx)...)
+	errs = packer.MultiErrorAppend(errs, b.config.AMIConfig.Prepare(b.config.ctx)...)
+	errs = packer.MultiErrorAppend(errs, b.config.RunConfig.Prepare(b.config.ctx)...)
 
 	if errs != nil && len(errs.Errors) > 0 {
 		return nil, errs

builder/amazon/ebs/step_create_ami.go

@@ -13,7 +13,7 @@ type stepCreateAMI struct {
 }
 
 func (s *stepCreateAMI) Run(state multistep.StateBag) multistep.StepAction {
-	config := state.Get("config").(config)
+	config := state.Get("config").(Config)
 	ec2conn := state.Get("ec2").(*ec2.EC2)
 	instance := state.Get("instance").(*ec2.Instance)
 	ui := state.Get("ui").(packer.Ui)

builder/amazon/ebs/step_modify_instance.go

@@ -11,7 +11,7 @@ import (
 type stepModifyInstance struct{}
 
 func (s *stepModifyInstance) Run(state multistep.StateBag) multistep.StepAction {
-	config := state.Get("config").(config)
+	config := state.Get("config").(Config)
 	ec2conn := state.Get("ec2").(*ec2.EC2)
 	instance := state.Get("instance").(*ec2.Instance)
 	ui := state.Get("ui").(packer.Ui)

builder/amazon/instance/builder.go

@@ -13,7 +13,9 @@ import (
 	"github.com/mitchellh/multistep"
 	awscommon "github.com/mitchellh/packer/builder/amazon/common"
 	"github.com/mitchellh/packer/common"
+	"github.com/mitchellh/packer/helper/config"
 	"github.com/mitchellh/packer/packer"
+	"github.com/mitchellh/packer/template/interpolate"
 )
 
 // The unique ID for this builder
@@ -38,7 +40,7 @@ type Config struct {
 	X509KeyPath         string `mapstructure:"x509_key_path"`
 	X509UploadPath      string `mapstructure:"x509_upload_path"`
 
-	tpl *packer.ConfigTemplate
+	ctx *interpolate.Context
 }
 
 type Builder struct {
@@ -47,17 +49,20 @@ type Builder struct {
 }
 
 func (b *Builder) Prepare(raws ...interface{}) ([]string, error) {
-	md, err := common.DecodeConfig(&b.config, raws...)
-	if err != nil {
-		return nil, err
-	}
-
-	b.config.tpl, err = packer.NewConfigTemplate()
+	b.config.ctx = &interpolate.Context{Funcs: awscommon.TemplateFuncs}
+	err := config.Decode(&b.config, &config.DecodeOpts{
+		Interpolate:        true,
+		InterpolateContext: b.config.ctx,
+		InterpolateFilter: &interpolate.RenderFilter{
+			Exclude: []string{
+				"bundle_upload_command",
+				"bundle_vol_command",
+			},
+		},
+	}, raws...)
 	if err != nil {
 		return nil, err
 	}
-	b.config.tpl.UserVars = b.config.PackerUserVars
-	b.config.tpl.Funcs(awscommon.TemplateFuncs)
 
 	if b.config.BundleDestination == "" {
 		b.config.BundleDestination = "/tmp"
@@ -97,43 +102,11 @@ func (b *Builder) Prepare(raws ...interface{}) ([]string, error) {
 	}
 
 	// Accumulate any errors
-	errs := common.CheckUnusedConfig(md)
-	errs = packer.MultiErrorAppend(errs, b.config.AccessConfig.Prepare(b.config.tpl)...)
-	errs = packer.MultiErrorAppend(errs, b.config.BlockDevices.Prepare(b.config.tpl)...)
-	errs = packer.MultiErrorAppend(errs, b.config.AMIConfig.Prepare(b.config.tpl)...)
-	errs = packer.MultiErrorAppend(errs, b.config.RunConfig.Prepare(b.config.tpl)...)
-
-	validates := map[string]*string{
-		"bundle_upload_command": &b.config.BundleUploadCommand,
-		"bundle_vol_command":    &b.config.BundleVolCommand,
-	}
-
-	for n, ptr := range validates {
-		if err := b.config.tpl.Validate(*ptr); err != nil {
-			errs = packer.MultiErrorAppend(
-				errs, fmt.Errorf("Error parsing %s: %s", n, err))
-		}
-	}
-
-	templates := map[string]*string{
-		"account_id":         &b.config.AccountId,
-		"ami_name":           &b.config.AMIName,
-		"bundle_destination": &b.config.BundleDestination,
-		"bundle_prefix":      &b.config.BundlePrefix,
-		"s3_bucket":          &b.config.S3Bucket,
-		"x509_cert_path":     &b.config.X509CertPath,
-		"x509_key_path":      &b.config.X509KeyPath,
-		"x509_upload_path":   &b.config.X509UploadPath,
-	}
-
-	for n, ptr := range templates {
-		var err error
-		*ptr, err = b.config.tpl.Process(*ptr, nil)
-		if err != nil {
-			errs = packer.MultiErrorAppend(
-				errs, fmt.Errorf("Error processing %s: %s", n, err))
-		}
-	}
+	var errs *packer.MultiError
+	errs = packer.MultiErrorAppend(errs, b.config.AccessConfig.Prepare(b.config.ctx)...)
+	errs = packer.MultiErrorAppend(errs, b.config.BlockDevices.Prepare(b.config.ctx)...)
+	errs = packer.MultiErrorAppend(errs, b.config.AMIConfig.Prepare(b.config.ctx)...)
+	errs = packer.MultiErrorAppend(errs, b.config.RunConfig.Prepare(b.config.ctx)...)
 
 	if b.config.AccountId == "" {
 		errs = packer.MultiErrorAppend(errs, errors.New("account_id is required"))

builder/amazon/instance/step_bundle_volume.go

@@ -6,6 +6,7 @@ import (
 	"github.com/mitchellh/goamz/ec2"
 	"github.com/mitchellh/multistep"
 	"github.com/mitchellh/packer/packer"
+	"github.com/mitchellh/packer/template/interpolate"
 )
 
 type bundleCmdData struct {
@@ -32,7 +33,7 @@ func (s *StepBundleVolume) Run(state multistep.StateBag) multistep.StepAction {
 
 	// Bundle the volume
 	var err error
-	config.BundleVolCommand, err = config.tpl.Process(config.BundleVolCommand, bundleCmdData{
+	config.ctx.Data = bundleCmdData{
 		AccountId:    config.AccountId,
 		Architecture: instance.Architecture,
 		CertPath:     x509RemoteCertPath,
@@ -40,7 +41,8 @@ func (s *StepBundleVolume) Run(state multistep.StateBag) multistep.StepAction {
 		KeyPath:      x509RemoteKeyPath,
 		Prefix:       config.BundlePrefix,
 		PrivatePath:  config.X509UploadPath,
-	})
+	}
+	config.BundleVolCommand, err = interpolate.Render(config.BundleVolCommand, config.ctx)
 	if err != nil {
 		err := fmt.Errorf("Error processing bundle volume command: %s", err)
 		state.Put("error", err)

builder/amazon/instance/step_upload_bundle.go

@@ -5,6 +5,7 @@ import (
 
 	"github.com/mitchellh/multistep"
 	"github.com/mitchellh/packer/packer"
+	"github.com/mitchellh/packer/template/interpolate"
 )
 
 type uploadCmdData struct {
@@ -35,14 +36,15 @@ func (s *StepUploadBundle) Run(state multistep.StateBag) multistep.StepAction {
 		return multistep.ActionHalt
 	}
 
-	config.BundleUploadCommand, err = config.tpl.Process(config.BundleUploadCommand, uploadCmdData{
+	config.ctx.Data = uploadCmdData{
 		AccessKey:       config.AccessKey,
 		BucketName:      config.S3Bucket,
 		BundleDirectory: config.BundleDestination,
 		ManifestPath:    manifestPath,
 		Region:          region.Name,
 		SecretKey:       config.SecretKey,
-	})
+	}
+	config.BundleUploadCommand, err = interpolate.Render(config.BundleUploadCommand, config.ctx)
 	if err != nil {
 		err := fmt.Errorf("Error processing bundle upload command: %s", err)
 		state.Put("error", err)

helper/config/decode.go

+package config
+
+import (
+	"fmt"
+	"reflect"
+	"sort"
+	"strings"
+
+	"github.com/hashicorp/go-multierror"
+	"github.com/mitchellh/mapstructure"
+	"github.com/mitchellh/packer/template/interpolate"
+)
+
+// DecodeOpts are the options for decoding configuration.
+type DecodeOpts struct {
+	// Interpolate, if true, will automatically interpolate the
+	// configuration with the given InterpolateContext. User variables
+	// will be automatically detected and added in-place to the given
+	// context.
+	Interpolate        bool
+	InterpolateContext *interpolate.Context
+	InterpolateFilter  *interpolate.RenderFilter
+}
+
+// Decode decodes the configuration into the target and optionally
+// automatically interpolates all the configuration as it goes.
+func Decode(target interface{}, config *DecodeOpts, raws ...interface{}) error {
+	if config == nil {
+		config = &DecodeOpts{Interpolate: true}
+	}
+
+	// Interpolate first
+	if config.Interpolate {
+		// Detect user variables from the raws and merge them into our context
+		ctx, err := DetectContext(raws...)
+		if err != nil {
+			return err
+		}
+		if config.InterpolateContext == nil {
+			config.InterpolateContext = ctx
+		} else {
+			config.InterpolateContext.UserVariables = ctx.UserVariables
+		}
+		ctx = config.InterpolateContext
+
+		// Render everything
+		for i, raw := range raws {
+			m, err := interpolate.RenderMap(raw, ctx, config.InterpolateFilter)
+			if err != nil {
+				return err
+			}
+
+			raws[i] = m
+		}
+	}
+
+	// Build our decoder
+	var md mapstructure.Metadata
+	decoder, err := mapstructure.NewDecoder(&mapstructure.DecoderConfig{
+		Result:           target,
+		Metadata:         &md,
+		WeaklyTypedInput: true,
+		DecodeHook: mapstructure.ComposeDecodeHookFunc(
+			uint8ToStringHook,
+			mapstructure.StringToSliceHookFunc(","),
+		),
+	})
+	if err != nil {
+		return err
+	}
+	for _, raw := range raws {
+		if err := decoder.Decode(raw); err != nil {
+			return err
+		}
+	}
+
+	// If we have unused keys, it is an error
+	if len(md.Unused) > 0 {
+		var err error
+		sort.Strings(md.Unused)
+		for _, unused := range md.Unused {
+			if unused != "type" && !strings.HasPrefix(unused, "packer_") {
+				err = multierror.Append(err, fmt.Errorf(
+					"unknown configuration key: %q", unused))
+			}
+		}
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+// DetectContext builds a base interpolate.Context, automatically
+// detecting things like user variables from the raw configuration params.
+func DetectContext(raws ...interface{}) (*interpolate.Context, error) {
+	var s struct {
+		Vars map[string]string `mapstructure:"packer_user_variables"`
+	}
+
+	for _, r := range raws {
+		if err := mapstructure.Decode(r, &s); err != nil {
+			return nil, err
+		}
+	}
+
+	return &interpolate.Context{
+		UserVariables: s.Vars,
+	}, nil
+}
+
+func uint8ToStringHook(f reflect.Kind, t reflect.Kind, v interface{}) (interface{}, error) {
+	// We need to convert []uint8 to string. We have to do this
+	// because internally Packer uses MsgPack for RPC and the MsgPack
+	// codec turns strings into []uint8
+	if f == reflect.Slice && t == reflect.String {
+		dataVal := reflect.ValueOf(v)
+		dataType := dataVal.Type()
+		elemKind := dataType.Elem().Kind()
+		if elemKind == reflect.Uint8 {
+			v = string(dataVal.Interface().([]uint8))
+		}
+	}
+
+	return v, nil
+}

helper/config/decode_test.go

+package config
+
+import (
+	"reflect"
+	"testing"
+
+	"github.com/mitchellh/packer/template/interpolate"
+)
+
+func TestDecode(t *testing.T) {
+	type Target struct {
+		Name    string
+		Address string
+	}
+
+	cases := map[string]struct {
+		Input  []interface{}
+		Output *Target
+		Opts   *DecodeOpts
+	}{
+		"basic": {
+			[]interface{}{
+				map[string]interface{}{
+					"name": "bar",
+				},
+			},
+			&Target{
+				Name: "bar",
+			},
+			nil,
+		},
+
+		"variables": {
+			[]interface{}{
+				map[string]interface{}{
+					"name": "{{user `name`}}",
+				},
+				map[string]interface{}{
+					"packer_user_variables": map[string]string{
+						"name": "bar",
+					},
+				},
+			},
+			&Target{
+				Name: "bar",
+			},
+			nil,
+		},
+
+		"filter": {
+			[]interface{}{
+				map[string]interface{}{
+					"name":    "{{user `name`}}",
+					"address": "{{user `name`}}",
+				},
+				map[string]interface{}{
+					"packer_user_variables": map[string]string{
+						"name": "bar",
+					},
+				},
+			},
+			&Target{
+				Name:    "bar",
+				Address: "{{user `name`}}",
+			},
+			&DecodeOpts{
+				Interpolate: true,
+				InterpolateFilter: &interpolate.RenderFilter{
+					Include: []string{"name"},
+				},
+			},
+		},
+	}
+
+	for k, tc := range cases {
+		var result Target
+		err := Decode(&result, tc.Opts, tc.Input...)
+		if err != nil {
+			t.Fatalf("err: %s\n\n%s", k, err)
+		}
+
+		if !reflect.DeepEqual(&result, tc.Output) {
+			t.Fatalf("bad:\n\n%#v\n\n%#v", &result, tc.Output)
+		}
+	}
+}

template/interpolate/funcs.go

@@ -45,6 +45,11 @@ func Funcs(ctx *Context) template.FuncMap {
 	for k, v := range FuncGens {
 		result[k] = v(ctx)
 	}
+	if ctx != nil {
+		for k, v := range ctx.Funcs {
+			result[k] = v
+		}
+	}
 
 	return template.FuncMap(result)
 }

template/interpolate/i.go

@@ -11,6 +11,9 @@ type Context struct {
 	// Data is the data for the template that is available
 	Data interface{}
 
+	// Funcs are extra functions available in the template
+	Funcs map[string]interface{}
+
 	// UserVariables is the mapping of user variables that the
 	// "user" function reads from.
 	UserVariables map[string]string

template/interpolate/render.go

+package interpolate
+
+import (
+	"fmt"
+	"reflect"
+	"strings"
+	"sync"
+
+	"github.com/mitchellh/mapstructure"
+	"github.com/mitchellh/reflectwalk"
+)
+
+// RenderFilter is an option for filtering what gets rendered and
+// doesn't within an interface.
+type RenderFilter struct {
+	Include []string
+	Exclude []string
+
+	once       sync.Once
+	excludeSet map[string]struct{}
+	includeSet map[string]struct{}
+}
+
+// RenderMap renders all the strings in the given interface. The
+// interface must decode into a map[string]interface{}, but is left
+// as an interface{} type to ease backwards compatibility with the way
+// arguments are passed around in Packer.
+func RenderMap(v interface{}, ctx *Context, f *RenderFilter) (map[string]interface{}, error) {
+	// First decode it into the map
+	var m map[string]interface{}
+	if err := mapstructure.Decode(v, &m); err != nil {
+		return nil, err
+	}
+
+	// Now go through each value and render it
+	for k, raw := range m {
+		if !f.include(k) {
+			continue
+		}
+
+		raw, err := RenderInterface(raw, ctx)
+		if err != nil {
+			return nil, fmt.Errorf("render '%s': %s", k, err)
+		}
+
+		m[k] = raw
+	}
+
+	return m, nil
+}
+
+// RenderInterface renders any value and returns the resulting value.
+func RenderInterface(v interface{}, ctx *Context) (interface{}, error) {
+	f := func(v string) (string, error) {
+		return Render(v, ctx)
+	}
+
+	walker := &renderWalker{
+		F:       f,
+		Replace: true,
+	}
+	err := reflectwalk.Walk(v, walker)
+	if err != nil {
+		return nil, err
+	}
+
+	if walker.Top != nil {
+		v = walker.Top
+	}
+	return v, nil
+}
+
+// Include checks whether a key should be included.
+func (f *RenderFilter) include(k string) bool {
+	if f == nil {
+		return true
+	}
+
+	k = strings.ToLower(k)
+
+	f.once.Do(f.init)
+	if len(f.includeSet) > 0 {
+		_, ok := f.includeSet[k]
+		return ok
+	}
+	if len(f.excludeSet) > 0 {
+		_, ok := f.excludeSet[k]
+		return !ok
+	}
+
+	return true
+}
+
+func (f *RenderFilter) init() {
+	f.includeSet = make(map[string]struct{})
+	for _, v := range f.Include {
+		f.includeSet[strings.ToLower(v)] = struct{}{}
+	}
+
+	f.excludeSet = make(map[string]struct{})
+	for _, v := range f.Exclude {
+		f.excludeSet[strings.ToLower(v)] = struct{}{}
+	}
+}
+
+// renderWalker implements interfaces for the reflectwalk package
+// (github.com/mitchellh/reflectwalk) that can be used to automatically
+// execute a callback for an interpolation.
+type renderWalker struct {
+	// F is the function to call for every interpolation. It can be nil.
+	//
+	// If Replace is true, then the return value of F will be used to
+	// replace the interpolation.
+	F       renderWalkerFunc
+	Replace bool
+
+	// ContextF is an advanced version of F that also receives the
+	// location of where it is in the structure. This lets you do
+	// context-aware validation.
+	ContextF renderWalkerContextFunc
+
+	// Top is the top value of the walk. This might get replaced if the
+	// top value needs to be modified. It is valid to read after any walk.
+	// If it is nil, it means the top wasn't replaced.
+	Top interface{}
+
+	key         []string
+	lastValue   reflect.Value
+	loc         reflectwalk.Location
+	cs          []reflect.Value
+	csKey       []reflect.Value
+	csData      interface{}
+	sliceIndex  int
+	unknownKeys []string
+}
+
+// renderWalkerFunc is the callback called by interpolationWalk.
+// It is called with any interpolation found. It should return a value
+// to replace the interpolation with, along with any errors.
+//
+// If Replace is set to false in renderWalker, then the replace
+// value can be anything as it will have no effect.
+type renderWalkerFunc func(string) (string, error)
+
+// renderWalkerContextFunc is called by interpolationWalk if
+// ContextF is set. This receives both the interpolation and the location
+// where the interpolation is.
+//
+// This callback can be used to validate the location of the interpolation
+// within the configuration.
+type renderWalkerContextFunc func(reflectwalk.Location, string)
+
+func (w *renderWalker) Enter(loc reflectwalk.Location) error {
+	w.loc = loc
+	return nil
+}
+
+func (w *renderWalker) Exit(loc reflectwalk.Location) error {
+	w.loc = reflectwalk.None
+
+	switch loc {
+	case reflectwalk.Map:
+		w.cs = w.cs[:len(w.cs)-1]
+	case reflectwalk.MapValue:
+		w.key = w.key[:len(w.key)-1]
+		w.csKey = w.csKey[:len(w.csKey)-1]
+	case reflectwalk.Slice:
+		// Split any values that need to be split
+		w.cs = w.cs[:len(w.cs)-1]
+	case reflectwalk.SliceElem:
+		w.csKey = w.csKey[:len(w.csKey)-1]
+	}
+
+	return nil
+}
+
+func (w *renderWalker) Map(m reflect.Value) error {
+	w.cs = append(w.cs, m)
+	return nil
+}
+
+func (w *renderWalker) MapElem(m, k, v reflect.Value) error {
+	w.csData = k
+	w.csKey = append(w.csKey, k)
+	w.key = append(w.key, k.String())
+	w.lastValue = v
+	return nil
+}
+
+func (w *renderWalker) Slice(s reflect.Value) error {
+	w.cs = append(w.cs, s)
+	return nil
+}
+
+func (w *renderWalker) SliceElem(i int, elem reflect.Value) error {
+	w.csKey = append(w.csKey, reflect.ValueOf(i))
+	w.sliceIndex = i
+	return nil
+}
+
+func (w *renderWalker) Primitive(v reflect.Value) error {
+	setV := v
+
+	// We only care about strings
+	if v.Kind() == reflect.Interface {
+		setV = v
+		v = v.Elem()
+	}
+	if v.Kind() != reflect.String {
+		return nil
+	}
+
+	strV := v.String()
+	if w.ContextF != nil {
+		w.ContextF(w.loc, strV)
+	}
+
+	if w.F == nil {
+		return nil
+	}
+
+	replaceVal, err := w.F(strV)
+	if err != nil {
+		return fmt.Errorf(
+			"%s in:\n\n%s",
+			err, v.String())
+	}
+
+	if w.Replace {
+		resultVal := reflect.ValueOf(replaceVal)
+		switch w.loc {
+		case reflectwalk.MapKey:
+			m := w.cs[len(w.cs)-1]
+
+			// Delete the old value
+			var zero reflect.Value
+			m.SetMapIndex(w.csData.(reflect.Value), zero)
+
+			// Set the new key with the existing value
+			m.SetMapIndex(resultVal, w.lastValue)
+
+			// Set the key to be the new key
+			w.csData = resultVal
+		case reflectwalk.MapValue:
+			// If we're in a map, then the only way to set a map value is
+			// to set it directly.
+			m := w.cs[len(w.cs)-1]
+			mk := w.csData.(reflect.Value)
+			m.SetMapIndex(mk, resultVal)
+		case reflectwalk.WalkLoc:
+			// At the root element, we can't write that, so we just save it
+			w.Top = resultVal.Interface()
+		default:
+			// Otherwise, we should be addressable
+			setV.Set(resultVal)
+		}
+	}
+
+	return nil
+}
+
+func (w *renderWalker) removeCurrent() {
+	// Append the key to the unknown keys
+	w.unknownKeys = append(w.unknownKeys, strings.Join(w.key, "."))
+
+	for i := 1; i <= len(w.cs); i++ {
+		c := w.cs[len(w.cs)-i]
+		switch c.Kind() {
+		case reflect.Map:
+			// Zero value so that we delete the map key
+			var val reflect.Value
+
+			// Get the key and delete it
+			k := w.csData.(reflect.Value)
+			c.SetMapIndex(k, val)
+			return
+		}
+	}
+
+	panic("No container found for removeCurrent")
+}
+
+func (w *renderWalker) replaceCurrent(v reflect.Value) {
+	c := w.cs[len(w.cs)-2]
+	switch c.Kind() {
+	case reflect.Map:
+		// Get the key and delete it
+		k := w.csKey[len(w.csKey)-1]
+		c.SetMapIndex(k, v)
+	}
+}

template/interpolate/render_test.go

+package interpolate
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestRenderMap(t *testing.T) {
+	cases := map[string]struct {
+		Input  interface{}
+		Output interface{}
+		Filter *RenderFilter
+	}{
+		"basic": {
+			map[string]interface{}{
+				"foo": "{{upper `bar`}}",
+			},
+			map[string]interface{}{
+				"foo": "BAR",
+			},
+			nil,
+		},
+
+		"map keys shouldn't be interpolated": {
+			map[string]interface{}{
+				"{{foo}}": "{{upper `bar`}}",
+			},
+			map[string]interface{}{
+				"{{foo}}": "BAR",
+			},
+			nil,
+		},
+
+		"nested values": {
+			map[string]interface{}{
+				"foo": map[string]string{
+					"bar": "{{upper `baz`}}",
+				},
+			},
+			map[string]interface{}{
+				"foo": map[string]string{
+					"bar": "BAZ",
+				},
+			},
+			nil,
+		},
+
+		"nested value keys": {
+			map[string]interface{}{
+				"foo": map[string]string{
+					"{{upper `bar`}}": "{{upper `baz`}}",
+				},
+			},
+			map[string]interface{}{
+				"foo": map[string]string{
+					"BAR": "BAZ",
+				},
+			},
+			nil,
+		},
+
+		"filter": {
+			map[string]interface{}{
+				"bar": "{{upper `baz`}}",
+				"foo": map[string]string{
+					"{{upper `bar`}}": "{{upper `baz`}}",
+				},
+			},
+			map[string]interface{}{
+				"bar": "BAZ",
+				"foo": map[string]string{
+					"{{upper `bar`}}": "{{upper `baz`}}",
+				},
+			},
+			&RenderFilter{
+				Include: []string{"bar"},
+			},
+		},
+
+		"filter case-insensitive": {
+			map[string]interface{}{
+				"bar": "{{upper `baz`}}",
+				"foo": map[string]string{
+					"{{upper `bar`}}": "{{upper `baz`}}",
+				},
+			},
+			map[string]interface{}{
+				"bar": "BAZ",
+				"foo": map[string]string{
+					"{{upper `bar`}}": "{{upper `baz`}}",
+				},
+			},
+			&RenderFilter{
+				Include: []string{"baR"},
+			},
+		},
+	}
+
+	ctx := &Context{}
+	for k, tc := range cases {
+		actual, err := RenderMap(tc.Input, ctx, tc.Filter)
+		if err != nil {
+			t.Fatalf("err: %s\n\n%s", k, err)
+		}
+
+		if !reflect.DeepEqual(actual, tc.Output) {
+			t.Fatalf("err: %s\n\n%#v\n\n%#v", k, actual, tc.Output)
+		}
+	}
+}