helper/config: decoder

helper/config/decode.go

@@ -0,0 +1,108 @@
+package config
+
+import (
+	"reflect"
+
+	"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
+		}
+	}
+
+	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

@@ -0,0 +1,86 @@
+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)
+		}
+	}
+}