1 // Copyright 2010 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
13 // An UnknownFormatErr indicates that decoding encountered an unknown format.
14 var UnknownFormatErr = errors.New("image: unknown format")
16 // A format holds an image format's name, magic header and how to decode it.
19 decode func(io.Reader) (Image, error)
20 decodeConfig func(io.Reader) (Config, error)
23 // Formats is the list of registered formats.
26 // RegisterFormat registers an image format for use by Decode.
27 // Name is the name of the format, like "jpeg" or "png".
28 // Magic is the magic prefix that identifies the format's encoding. The magic
29 // string can contain "?" wildcards that each match any one byte.
30 // Decode is the function that decodes the encoded image.
31 // DecodeConfig is the function that decodes just its configuration.
32 func RegisterFormat(name, magic string, decode func(io.Reader) (Image, error), decodeConfig func(io.Reader) (Config, error)) {
33 formats = append(formats, format{name, magic, decode, decodeConfig})
36 // A reader is an io.Reader that can also peek ahead.
37 type reader interface {
39 Peek(int) ([]byte, error)
42 // AsReader converts an io.Reader to a reader.
43 func asReader(r io.Reader) reader {
44 if rr, ok := r.(reader); ok {
47 return bufio.NewReader(r)
50 // Match returns whether magic matches b. Magic may contain "?" wildcards.
51 func match(magic string, b []byte) bool {
52 if len(magic) != len(b) {
56 if magic[i] != c && magic[i] != '?' {
63 // Sniff determines the format of r's data.
64 func sniff(r reader) format {
65 for _, f := range formats {
66 b, err := r.Peek(len(f.magic))
67 if err == nil && match(f.magic, b) {
74 // Decode decodes an image that has been encoded in a registered format.
75 // The string returned is the format name used during format registration.
76 // Format registration is typically done by the init method of the codec-
78 func Decode(r io.Reader) (Image, string, error) {
82 return nil, "", UnknownFormatErr
84 m, err := f.decode(rr)
88 // DecodeConfig decodes the color model and dimensions of an image that has
89 // been encoded in a registered format. The string returned is the format name
90 // used during format registration. Format registration is typically done by
91 // the init method of the codec-specific package.
92 func DecodeConfig(r io.Reader) (Config, string, error) {
95 if f.decodeConfig == nil {
96 return Config{}, "", UnknownFormatErr
98 c, err := f.decodeConfig(rr)