Improve encoding layer

internal/encoding/decoder.go

@@ -4,10 +4,10 @@ import (
 	"sync"
 )
 
-// Decoder decodes the contents of b into a v representation.
+// Decoder decodes the contents of b into v.
 // It's primarily used for decoding contents of a file into a map[string]interface{}.
 type Decoder interface {
-	Decode(b []byte, v interface{}) error
+	Decode(b []byte, v map[string]interface{}) error
 }
 
 const (
@@ -48,7 +48,7 @@ func (e *DecoderRegistry) RegisterDecoder(format string, enc Decoder) error {
 }
 
 // Decode calls the underlying Decoder based on the format.
-func (e *DecoderRegistry) Decode(format string, b []byte, v interface{}) error {
+func (e *DecoderRegistry) Decode(format string, b []byte, v map[string]interface{}) error {
 	e.mu.RLock()
 	decoder, ok := e.decoders[format]
 	e.mu.RUnlock()

internal/encoding/decoder_test.go

@@ -1,16 +1,18 @@
 package encoding
 
 import (
+	"reflect"
 	"testing"
 )
 
 type decoder struct {
-	v interface{}
+	v map[string]interface{}
 }
 
-func (d decoder) Decode(_ []byte, v interface{}) error {
-	rv := v.(*string)
-	*rv = d.v.(string)
+func (d decoder) Decode(_ []byte, v map[string]interface{}) error {
+	for key, value := range d.v {
+		v[key] = value
+	}
 
 	return nil
 }
@@ -44,32 +46,34 @@ func TestDecoderRegistry_Decode(t *testing.T) {
 	t.Run("OK", func(t *testing.T) {
 		registry := NewDecoderRegistry()
 		decoder := decoder{
-			v: "decoded value",
+			v: map[string]interface{}{
+				"key": "value",
+			},
 		}
 
 		err := registry.RegisterDecoder("myformat", decoder)
 		if err != nil {
 			t.Fatal(err)
 		}
 
-		var v string
+		v := map[string]interface{}{}
 
-		err = registry.Decode("myformat", []byte("some value"), &v)
+		err = registry.Decode("myformat", []byte("key: value"), v)
 		if err != nil {
 			t.Fatal(err)
 		}
 
-		if v != "decoded value" {
-			t.Fatalf("expected 'decoded value', got: %#v", v)
+		if !reflect.DeepEqual(decoder.v, v) {
+			t.Fatalf("decoded value does not match the expected one\nactual:   %+v\nexpected: %+v", v, decoder.v)
 		}
 	})
 
 	t.Run("DecoderNotFound", func(t *testing.T) {
 		registry := NewDecoderRegistry()
 
-		var v string
+		v := map[string]interface{}{}
 
-		err := registry.Decode("myformat", []byte("some value"), &v)
+		err := registry.Decode("myformat", nil, v)
 		if err != ErrDecoderNotFound {
 			t.Fatalf("expected ErrDecoderNotFound, got: %v", err)
 		}

internal/encoding/dotenv/codec.go

@@ -0,0 +1,61 @@
+package dotenv
+
+import (
+	"bytes"
+	"fmt"
+	"sort"
+	"strings"
+
+	"github.com/subosito/gotenv"
+)
+
+const keyDelimiter = "_"
+
+// Codec implements the encoding.Encoder and encoding.Decoder interfaces for encoding data containing environment variables
+// (commonly called as dotenv format).
+type Codec struct{}
+
+func (Codec) Encode(v map[string]interface{}) ([]byte, error) {
+	flattened := map[string]interface{}{}
+
+	flattened = flattenAndMergeMap(flattened, v, "", keyDelimiter)
+
+	keys := make([]string, 0, len(flattened))
+
+	for key := range flattened {
+		keys = append(keys, key)
+	}
+
+	sort.Strings(keys)
+
+	var buf bytes.Buffer
+
+	for _, key := range keys {
+		_, err := buf.WriteString(fmt.Sprintf("%v=%v\n", strings.ToUpper(key), flattened[key]))
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	return buf.Bytes(), nil
+}
+
+func (Codec) Decode(b []byte, v map[string]interface{}) error {
+	var buf bytes.Buffer
+
+	_, err := buf.Write(b)
+	if err != nil {
+		return err
+	}
+
+	env, err := gotenv.StrictParse(&buf)
+	if err != nil {
+		return err
+	}
+
+	for key, value := range env {
+		v[key] = value
+	}
+
+	return nil
+}

internal/encoding/dotenv/codec_test.go

@@ -0,0 +1,63 @@
+package dotenv
+
+import (
+	"reflect"
+	"testing"
+)
+
+// original form of the data
+const original = `# key-value pair
+KEY=value
+`
+
+// encoded form of the data
+const encoded = `KEY=value
+`
+
+// Viper's internal representation
+var data = map[string]interface{}{
+	"KEY": "value",
+}
+
+func TestCodec_Encode(t *testing.T) {
+	codec := Codec{}
+
+	b, err := codec.Encode(data)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if encoded != string(b) {
+		t.Fatalf("decoded value does not match the expected one\nactual:   %#v\nexpected: %#v", string(b), encoded)
+	}
+}
+
+func TestCodec_Decode(t *testing.T) {
+	t.Run("OK", func(t *testing.T) {
+		codec := Codec{}
+
+		v := map[string]interface{}{}
+
+		err := codec.Decode([]byte(original), v)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		if !reflect.DeepEqual(data, v) {
+			t.Fatalf("decoded value does not match the expected one\nactual:   %#v\nexpected: %#v", v, data)
+		}
+	})
+
+	t.Run("InvalidData", func(t *testing.T) {
+		codec := Codec{}
+
+		v := map[string]interface{}{}
+
+		err := codec.Decode([]byte(`invalid data`), v)
+		if err == nil {
+			t.Fatal("expected decoding to fail")
+		}
+
+		t.Logf("decoding failed as expected: %s", err)
+	})
+}

internal/encoding/dotenv/map_utils.go

@@ -0,0 +1,41 @@
+package dotenv
+
+import (
+	"strings"
+
+	"github.com/spf13/cast"
+)
+
+// flattenAndMergeMap recursively flattens the given map into a new map
+// Code is based on the function with the same name in tha main package.
+// TODO: move it to a common place
+func flattenAndMergeMap(shadow map[string]interface{}, m map[string]interface{}, prefix string, delimiter string) map[string]interface{} {
+	if shadow != nil && prefix != "" && shadow[prefix] != nil {
+		// prefix is shadowed => nothing more to flatten
+		return shadow
+	}
+	if shadow == nil {
+		shadow = make(map[string]interface{})
+	}
+
+	var m2 map[string]interface{}
+	if prefix != "" {
+		prefix += delimiter
+	}
+	for k, val := range m {
+		fullKey := prefix + k
+		switch val.(type) {
+		case map[string]interface{}:
+			m2 = val.(map[string]interface{})
+		case map[interface{}]interface{}:
+			m2 = cast.ToStringMap(val)
+		default:
+			// immediate value
+			shadow[strings.ToLower(fullKey)] = val
+			continue
+		}
+		// recursively merge to shadow map
+		shadow = flattenAndMergeMap(shadow, m2, fullKey, delimiter)
+	}
+	return shadow
+}

internal/encoding/encoder.go

@@ -7,7 +7,7 @@ import (
 // Encoder encodes the contents of v into a byte representation.
 // It's primarily used for encoding a map[string]interface{} into a file format.
 type Encoder interface {
-	Encode(v interface{}) ([]byte, error)
+	Encode(v map[string]interface{}) ([]byte, error)
 }
 
 const (
@@ -47,7 +47,7 @@ func (e *EncoderRegistry) RegisterEncoder(format string, enc Encoder) error {
 	return nil
 }
 
-func (e *EncoderRegistry) Encode(format string, v interface{}) ([]byte, error) {
+func (e *EncoderRegistry) Encode(format string, v map[string]interface{}) ([]byte, error) {
 	e.mu.RLock()
 	encoder, ok := e.encoders[format]
 	e.mu.RUnlock()

internal/encoding/encoder_test.go

@@ -8,7 +8,7 @@ type encoder struct {
 	b []byte
 }
 
-func (e encoder) Encode(_ interface{}) ([]byte, error) {
+func (e encoder) Encode(_ map[string]interface{}) ([]byte, error) {
 	return e.b, nil
 }
 
@@ -41,28 +41,28 @@ func TestEncoderRegistry_Decode(t *testing.T) {
 	t.Run("OK", func(t *testing.T) {
 		registry := NewEncoderRegistry()
 		encoder := encoder{
-			b: []byte("encoded value"),
+			b: []byte("key: value"),
 		}
 
 		err := registry.RegisterEncoder("myformat", encoder)
 		if err != nil {
 			t.Fatal(err)
 		}
 
-		b, err := registry.Encode("myformat", "some value")
+		b, err := registry.Encode("myformat", map[string]interface{}{"key": "value"})
 		if err != nil {
 			t.Fatal(err)
 		}
 
-		if string(b) != "encoded value" {
-			t.Fatalf("expected 'encoded value', got: %#v", string(b))
+		if string(b) != "key: value" {
+			t.Fatalf("expected 'key: value', got: %#v", string(b))
 		}
 	})
 
 	t.Run("EncoderNotFound", func(t *testing.T) {
 		registry := NewEncoderRegistry()
 
-		_, err := registry.Encode("myformat", "some value")
+		_, err := registry.Encode("myformat", map[string]interface{}{"key": "value"})
 		if err != ErrEncoderNotFound {
 			t.Fatalf("expected ErrEncoderNotFound, got: %v", err)
 		}

internal/encoding/hcl/codec.go

@@ -12,7 +12,7 @@ import (
 // TODO: add printer config to the codec?
 type Codec struct{}
 
-func (Codec) Encode(v interface{}) ([]byte, error) {
+func (Codec) Encode(v map[string]interface{}) ([]byte, error) {
 	b, err := json.Marshal(v)
 	if err != nil {
 		return nil, err
@@ -35,6 +35,6 @@ func (Codec) Encode(v interface{}) ([]byte, error) {
 	return buf.Bytes(), nil
 }
 
-func (Codec) Decode(b []byte, v interface{}) error {
-	return hcl.Unmarshal(b, v)
+func (Codec) Decode(b []byte, v map[string]interface{}) error {
+	return hcl.Unmarshal(b, &v)
 }