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decode.go
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decode.go
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package internal
import (
"encoding/base64"
"fmt"
"mime"
"net/url"
"strings"
)
const (
// EncodingBase64 is base64 encoding for the data url
EncodingBase64 = "base64"
// EncodingASCII is ascii encoding for the data url
EncodingASCII = "ascii"
)
// DataURI represents the Data URI scheme
//
// [Data URI]: https://en.wikipedia.org/wiki/Data_URI_scheme
type DataURI struct {
MediaType string
Parameters map[string]string
Data string
}
// DecodeDataURI decodes data URI scheme
// data:[<media type>][;<key>=<value>][;<extension>],<data>
func DecodeDataURI(input string) (*DataURI, error) {
rawDataURI, ok := strings.CutPrefix(input, "data:")
if !ok {
// without data URI, decode base64 by default
rawDecodedBytes, err := base64.StdEncoding.DecodeString(input)
if err != nil {
return nil, err
}
return &DataURI{
Data: string(rawDecodedBytes),
}, nil
}
uriParts := strings.Split(rawDataURI, ",")
if len(uriParts) < 2 || uriParts[1] == "" {
return nil, fmt.Errorf("invalid data uri: %s", rawDataURI)
}
mediaTypes := strings.Split(uriParts[0], ";")
dataURI := &DataURI{}
switch strings.TrimSpace(mediaTypes[len(mediaTypes)-1]) {
case EncodingBase64:
rawDecodedBytes, err := base64.StdEncoding.DecodeString(uriParts[1])
if err != nil {
return nil, err
}
dataURI.Data = string(rawDecodedBytes)
mediaTypes = mediaTypes[:len(mediaTypes)-1]
case EncodingASCII:
dataURI.Data = url.PathEscape(uriParts[1])
mediaTypes = mediaTypes[:len(mediaTypes)-1]
default:
dataURI.Data = url.PathEscape(uriParts[1])
}
rawMediaType := strings.Join(mediaTypes, ";")
mediaType, params, err := mime.ParseMediaType(rawMediaType)
if err != nil {
return nil, fmt.Errorf("%s %s", err, rawMediaType)
}
dataURI.MediaType = mediaType
dataURI.Parameters = params
return dataURI, nil
}