1// Copyright 2014 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.
4
5// Package riff implements the Resource Interchange File Format, used by media
6// formats such as AVI, WAVE and WEBP.
7//
8// A RIFF stream contains a sequence of chunks. Each chunk consists of an 8-byte
9// header (containing a 4-byte chunk type and a 4-byte chunk length), the chunk
10// data (presented as an io.Reader), and some padding bytes.
11//
12// A detailed description of the format is at
13// http://www.tactilemedia.com/info/MCI_Control_Info.html
14package riff // import "golang.org/x/image/riff"
15
16import (
17 "errors"
18 "io"
19 "io/ioutil"
20 "math"
21)
22
23var (
24 errMissingPaddingByte = errors.New("riff: missing padding byte")
25 errMissingRIFFChunkHeader = errors.New("riff: missing RIFF chunk header")
26 errListSubchunkTooLong = errors.New("riff: list subchunk too long")
27 errShortChunkData = errors.New("riff: short chunk data")
28 errShortChunkHeader = errors.New("riff: short chunk header")
29 errStaleReader = errors.New("riff: stale reader")
30)
31
32// u32 decodes the first four bytes of b as a little-endian integer.
33func u32(b []byte) uint32 {
34 return uint32(b[0]) | uint32(b[1])<<8 | uint32(b[2])<<16 | uint32(b[3])<<24
35}
36
37const chunkHeaderSize = 8
38
39// FourCC is a four character code.
40type FourCC [4]byte
41
42// LIST is the "LIST" FourCC.
43var LIST = FourCC{'L', 'I', 'S', 'T'}
44
45// NewReader returns the RIFF stream's form type, such as "AVI " or "WAVE", and
46// its chunks as a *Reader.
47func NewReader(r io.Reader) (formType FourCC, data *Reader, err error) {
48 var buf [chunkHeaderSize]byte
49 if _, err := io.ReadFull(r, buf[:]); err != nil {
50 if err == io.EOF || err == io.ErrUnexpectedEOF {
51 err = errMissingRIFFChunkHeader
52 }
53 return FourCC{}, nil, err
54 }
55 if buf[0] != 'R' || buf[1] != 'I' || buf[2] != 'F' || buf[3] != 'F' {
56 return FourCC{}, nil, errMissingRIFFChunkHeader
57 }
58 return NewListReader(u32(buf[4:]), r)
59}
60
61// NewListReader returns a LIST chunk's list type, such as "movi" or "wavl",
62// and its chunks as a *Reader.
63func NewListReader(chunkLen uint32, chunkData io.Reader) (listType FourCC, data *Reader, err error) {
64 if chunkLen < 4 {
65 return FourCC{}, nil, errShortChunkData
66 }
67 z := &Reader{r: chunkData}
68 if _, err := io.ReadFull(chunkData, z.buf[:4]); err != nil {
69 if err == io.EOF || err == io.ErrUnexpectedEOF {
70 err = errShortChunkData
71 }
72 return FourCC{}, nil, err
73 }
74 z.totalLen = chunkLen - 4
75 return FourCC{z.buf[0], z.buf[1], z.buf[2], z.buf[3]}, z, nil
76}
77
78// Reader reads chunks from an underlying io.Reader.
79type Reader struct {
80 r io.Reader
81 err error
82
83 totalLen uint32
84 chunkLen uint32
85
86 chunkReader *chunkReader
87 buf [chunkHeaderSize]byte
88 padded bool
89}
90
91// Next returns the next chunk's ID, length and data. It returns io.EOF if there
92// are no more chunks. The io.Reader returned becomes stale after the next Next
93// call, and should no longer be used.
94//
95// It is valid to call Next even if all of the previous chunk's data has not
96// been read.
97func (z *Reader) Next() (chunkID FourCC, chunkLen uint32, chunkData io.Reader, err error) {
98 if z.err != nil {
99 return FourCC{}, 0, nil, z.err
100 }
101
102 // Drain the rest of the previous chunk.
103 if z.chunkLen != 0 {
104 want := z.chunkLen
105 var got int64
106 got, z.err = io.Copy(ioutil.Discard, z.chunkReader)
107 if z.err == nil && uint32(got) != want {
108 z.err = errShortChunkData
109 }
110 if z.err != nil {
111 return FourCC{}, 0, nil, z.err
112 }
113 }
114 z.chunkReader = nil
115 if z.padded {
116 if z.totalLen == 0 {
117 z.err = errListSubchunkTooLong
118 return FourCC{}, 0, nil, z.err
119 }
120 z.totalLen--
121 _, z.err = io.ReadFull(z.r, z.buf[:1])
122 if z.err != nil {
123 if z.err == io.EOF {
124 z.err = errMissingPaddingByte
125 }
126 return FourCC{}, 0, nil, z.err
127 }
128 }
129
130 // We are done if we have no more data.
131 if z.totalLen == 0 {
132 z.err = io.EOF
133 return FourCC{}, 0, nil, z.err
134 }
135
136 // Read the next chunk header.
137 if z.totalLen < chunkHeaderSize {
138 z.err = errShortChunkHeader
139 return FourCC{}, 0, nil, z.err
140 }
141 z.totalLen -= chunkHeaderSize
142 if _, z.err = io.ReadFull(z.r, z.buf[:chunkHeaderSize]); z.err != nil {
143 if z.err == io.EOF || z.err == io.ErrUnexpectedEOF {
144 z.err = errShortChunkHeader
145 }
146 return FourCC{}, 0, nil, z.err
147 }
148 chunkID = FourCC{z.buf[0], z.buf[1], z.buf[2], z.buf[3]}
149 z.chunkLen = u32(z.buf[4:])
150 if z.chunkLen > z.totalLen {
151 z.err = errListSubchunkTooLong
152 return FourCC{}, 0, nil, z.err
153 }
154 z.padded = z.chunkLen&1 == 1
155 z.chunkReader = &chunkReader{z}
156 return chunkID, z.chunkLen, z.chunkReader, nil
157}
158
159type chunkReader struct {
160 z *Reader
161}
162
163func (c *chunkReader) Read(p []byte) (int, error) {
164 if c != c.z.chunkReader {
165 return 0, errStaleReader
166 }
167 z := c.z
168 if z.err != nil {
169 if z.err == io.EOF {
170 return 0, errStaleReader
171 }
172 return 0, z.err
173 }
174
175 n := int(z.chunkLen)
176 if n == 0 {
177 return 0, io.EOF
178 }
179 if n < 0 {
180 // Converting uint32 to int overflowed.
181 n = math.MaxInt32
182 }
183 if n > len(p) {
184 n = len(p)
185 }
186 n, err := z.r.Read(p[:n])
187 z.totalLen -= uint32(n)
188 z.chunkLen -= uint32(n)
189 if err != io.EOF {
190 z.err = err
191 }
192 return n, err
193}