forked from pierrre/imageserver
/
encoder.go
94 lines (82 loc) · 2.29 KB
/
encoder.go
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package image
import (
"bytes"
"fmt"
"image"
"io"
"github.com/Destinia/imageserver"
)
// Encoder encodes an Image.
//
// An Encoder must encode to only one specific format.
type Encoder interface {
Encode(io.Writer, image.Image, imageserver.Params) error
Changer
}
// EncoderFunc is an Encoder func.
type EncoderFunc func(io.Writer, image.Image, imageserver.Params) error
// Encode implements Encoder.
func (f EncoderFunc) Encode(w io.Writer, nim image.Image, params imageserver.Params) error {
return f(w, nim, params)
}
// Change implements Encoder.
func (f EncoderFunc) Change(params imageserver.Params) bool {
return true
}
var encoders = make(map[string]Encoder)
// RegisterEncoder registers an Encoder for a format.
func RegisterEncoder(format string, enc Encoder) {
encoders[format] = enc
}
func getEncoder(format string) (Encoder, error) {
enc, ok := encoders[format]
if !ok {
return nil, fmt.Errorf("no registered encoder for format \"%s\"", format)
}
return enc, nil
}
func getEncoderFormat(defaultFormat string, params imageserver.Params) (Encoder, string, error) {
fromParams := false
format := defaultFormat
if params.Has("format") || defaultFormat == "" {
fromParams = true
var err error
format, err = params.GetString("format")
if err != nil {
return nil, "", err
}
}
enc, err := getEncoder(format)
if err != nil {
if fromParams {
err = &imageserver.ParamError{Param: "format", Message: err.Error()}
}
return nil, "", err
}
return enc, format, nil
}
func encode(nim image.Image, format string, enc Encoder, params imageserver.Params) (*imageserver.Image, error) {
buf := new(bytes.Buffer)
err := enc.Encode(buf, nim, params)
if err != nil {
return nil, err
}
im := &imageserver.Image{
Format: format,
Data: buf.Bytes(),
}
return im, nil
}
// Decode decodes a raw Image to a Go Image.
//
// It returns an error if the decoded Image format does not match the raw Image format.
func Decode(im *imageserver.Image) (image.Image, error) {
nim, format, err := image.Decode(bytes.NewReader(im.Data))
if err != nil {
return nil, &imageserver.ImageError{Message: err.Error()}
}
if format != im.Format {
return nil, &imageserver.ImageError{Message: fmt.Sprintf("decoded format \"%s\" does not match image format \"%s\"", format, im.Format)}
}
return nim, nil
}