Added image & JSON encoding/decoding facilities.

io.go

@@ -0,0 +1,91 @@
+package zntg
+
+import (
+	"encoding/json"
+	"image"
+	_ "image/gif"  // decoding of GIF
+	_ "image/jpeg" // decoding of JPEG
+	"image/png"
+	"io"
+	"os"
+)
+
+// CreateJSONDecoder create a new a generic JSON decoder for the specified value.
+func CreateJSONDecoder(value interface{}) DecoderFn {
+	return func(r io.Reader) (interface{}, error) {
+		decoder := json.NewDecoder(r)
+		return value, decoder.Decode(value)
+	}
+}
+
+// DecoderFn describes a generic decoder.
+type DecoderFn func(io.Reader) (interface{}, error)
+
+// DecodeFile is a generic decode method to decode content from disk.
+func DecodeFile(path string, decoder func(io.Reader) (interface{}, error)) (interface{}, error) {
+	f, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+	return decoder(f)
+}
+
+// DecodeImage tries to decode a file to an image.
+func DecodeImage(path string) (image.Image, error) {
+	value, err := DecodeFile(path, ImageDecoder)
+	if err != nil {
+		return nil, err
+	}
+	return value.(image.Image), nil
+}
+
+// DecodeJSON tries to decode a file to specifed value.
+func DecodeJSON(path string, value interface{}) error {
+	_, err := DecodeFile(path, CreateJSONDecoder(value))
+	return err
+}
+
+// EncoderFn describes a generic encoder.
+type EncoderFn func(io.Writer, interface{}) error
+
+// EncodeFile is a generic encode method to encode content to disk.
+func EncodeFile(path string, value interface{}, encoder EncoderFn) error {
+	dst, err := os.Create(path)
+	if err != nil {
+		return err
+	}
+	defer dst.Close()
+	return encoder(dst, value)
+}
+
+// EncodeJSON encodes a JSON struct to a file.
+func EncodeJSON(path string, value interface{}) error {
+	return EncodeFile(path, value, JSONEncoder)
+}
+
+// EncodePNG encodes an image to a file.
+func EncodePNG(path string, im image.Image) error {
+	return EncodeFile(path, im, PNGEncoder)
+}
+
+var _ DecoderFn = ImageDecoder
+
+// ImageDecoder is a generic image decoder.
+func ImageDecoder(r io.Reader) (interface{}, error) {
+	im, _, err := image.Decode(r)
+	return im, err
+}
+
+var _ EncoderFn = JSONEncoder
+
+// JSONEncoder is a generic JSON encoder.
+func JSONEncoder(w io.Writer, value interface{}) error {
+	encoder := json.NewEncoder(w)
+	return encoder.Encode(value)
+}
+
+var _ EncoderFn = PNGEncoder
+
+// PNGEncoder is a generic PNG encoder.
+func PNGEncoder(w io.Writer, value interface{}) error { return png.Encode(w, value.(image.Image)) }