1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
use std::cmp;
use std::mem;
use std::default::Default;

use std::io;
use std::io::prelude::*;

use std::fmt;
use std::error;

use lzw;

use traits::Parameter;
use common::{Frame, Block, Extension, DisposalMethod};

/// GIF palettes are RGB
pub const PLTE_CHANNELS: usize = 3;

#[derive(Debug)]
/// Decoding error.
pub enum DecodingError {
    /// Returned if the image is found to be malformed.
    Format(&'static str),
    /// Internal (logic) error.
    Internal(&'static str),
    /// Wraps `std::io::Error`.
    Io(io::Error),
}

impl fmt::Display for DecodingError {
    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
        match *self {
            DecodingError::Format(ref d) => d.fmt(fmt),
            DecodingError::Internal(ref d) => d.fmt(fmt),
            DecodingError::Io(ref err) => err.fmt(fmt),
        }
    }
}

impl error::Error for DecodingError {
    fn description(&self) -> &str {
        match *self {
            DecodingError::Format(ref d) => d,
            DecodingError::Internal(ref d) => d,
            DecodingError::Io(ref err) => err.description(),
        }
    }

    fn cause(&self) -> Option<&error::Error> {
        match *self {
            DecodingError::Io(ref err) => Some(err),
            _ => None,
        }
    }
}

impl From<io::Error> for DecodingError {
    fn from(err: io::Error) -> Self {
        DecodingError::Io(err)
    }
}

/// Configures how extensions should be handled
#[derive(PartialEq, Debug)]
pub enum Extensions {
    /// Saves all extention data
    Save,
    /// Skips the data of unknown extensions
    /// and extracts the data from known ones
    Skip
}

impl Parameter<StreamingDecoder> for Extensions {
    type Result = ();
    fn set_param(self, this: &mut StreamingDecoder) {
        this.skip_extensions = match self {
            Extensions::Skip => true,
            Extensions::Save => false,

        }
    }
}

/// Indicates whether a certain object has been decoded
#[derive(Debug)]
pub enum Decoded<'a> {
    /// Decoded nothing.
    Nothing,
    /// Global palette.
    GlobalPalette(Vec<u8>),
    /// Index of the background color in the global palette.
    BackgroundColor(u8),
    /// Decoded the image trailer.
    Trailer,
    /// The start of a block.
    BlockStart(Block),
    /// Decoded a sub-block. More sub-block are available.
    SubBlockFinished(u8, &'a [u8]),
    /// Decoded the last (or only) sub-block of a block.
    BlockFinished(u8, &'a [u8]),
    /// Decoded all information of the next frame.
    /// The returned frame does **not** any image data.
    Frame(&'a Frame<'static>),
    /// Decoded some data of the current frame.
    Data(&'a [u8]),
    /// No more data available the current frame.
    DataEnd,

}

/// Internal state of the GIF decoder
#[derive(Debug)]
enum State {
    Magic(usize, [u8; 6]),
    U16Byte1(U16Value, u8),
    U16(U16Value),
    Byte(ByteValue),
    GlobalPalette(usize),
    BlockStart(Option<Block>),
    BlockEnd(u8),
    ExtensionBlock(u8),
    SkipBlock(usize),
    LocalPalette(usize),
    LzwInit(u8),
    DecodeSubBlock(usize),
    FrameDecoded,
    Trailer
}
use self::State::*;

/// U16 values that may occur in a GIF image
#[derive(Debug)]
enum U16Value {
    /// Logical screen descriptor width
    ScreenWidth,
    /// Logical screen descriptor height
    ScreenHeight,
    /// Delay time
    Delay,
    /// Left frame offset
    ImageLeft,
    /// Top frame offset
    ImageTop,
    /// Frame width
    ImageWidth,
    /// Frame height
    ImageHeight,
}

/// Single byte screen descriptor values
#[derive(Debug)]
enum ByteValue {
    GlobalFlags,
    Background { table_size: usize },
    AspectRatio { table_size: usize },
    ControlFlags,
    ImageFlags,
    TransparentIdx,
    CodeSize,
}

/// GIF decoder which supports streaming
#[derive(Debug)]
pub struct StreamingDecoder {
    state: Option<State>,
    lzw_reader: Option<lzw::Decoder<lzw::LsbReader>>,
    skip_extensions: bool,
    version: &'static str,
    width: u16,
    height: u16,
    global_color_table: Vec<u8>,
    background_color: [u8; 4],
    /// ext buffer
    ext: (u8, Vec<u8>, bool),
    /// Frame data
    current: Option<Frame<'static>>,
}

impl StreamingDecoder {
    /// Creates a new streaming decoder
    pub fn new() -> StreamingDecoder {
        StreamingDecoder {
            state: Some(Magic(0, [0; 6])),
            lzw_reader: None,
            skip_extensions: true,
            version: "",
            width: 0,
            height: 0,
            global_color_table: Vec::new(),
            background_color: [0, 0, 0, 0xFF],
            ext: (0, Vec::with_capacity(256), true), // 0xFF + 1 byte length
            current: None
        }
    }
    
    /// Updates the internal state of the decoder. 
    ///
    /// Returns the number of bytes consumed from the input buffer 
    /// and the last decoding result.
    pub fn update<'a>(&'a mut self, mut buf: &[u8])
    -> Result<(usize, Decoded<'a>), DecodingError> {
        // NOTE: Do not change the function signature without double-checking the
        //       unsafe block!
        let len = buf.len();
        while buf.len() > 0 && self.state.is_some() {
            match self.next_state(buf) {
                Ok((bytes, Decoded::Nothing)) => {
                    buf = &buf[bytes..]
                }
                Ok((bytes, Decoded::Trailer)) => {
                    buf = &buf[bytes..];
                    break
                }
                Ok((bytes, result)) => {
                    buf = &buf[bytes..];
                    return Ok(
                        (len-buf.len(), 
                        // This transmute just casts the lifetime away. Since Rust only 
                        // has SESE regions, this early return cannot be worked out and
                        // such that the borrow region of self includes the whole block.
                        // The explixit lifetimes in the function signature ensure that
                        // this is safe.
                        // ### NOTE
                        // To check that everything is sound, return the result without
                        // the match (e.g. `return Ok(try!(self.next_state(buf)))`). If
                        // it compiles the returned lifetime is correct.
                        unsafe { 
                            mem::transmute::<Decoded, Decoded>(result)
                        }
                    ))
                }
                Err(err) => return Err(err)
            }
        }
        Ok((len-buf.len(), Decoded::Nothing))
        
    }
    
    /// Returns the data of the last extension that has been decoded.
    pub fn last_ext(&self) -> (u8, &[u8], bool) {
        (self.ext.0, &*self.ext.1, self.ext.2)
    }
    
    #[inline(always)]
    /// Current frame info as a mutable ref.
    pub fn current_frame_mut<'a>(&'a mut self) -> &'a mut Frame<'static> {
        self.current.as_mut().unwrap()
    }
    
    #[inline(always)]
    /// Current frame info as a ref.
    pub fn current_frame<'a>(&'a self) -> &'a Frame<'static> {
        self.current.as_ref().unwrap()
    }

    /// Width of the image
    pub fn width(&self) -> u16 {
        self.width
    }

    /// Height of the image
    pub fn height(&self) -> u16 {
        self.height
    }

    fn next_state<'a>(&'a mut self, buf: &[u8]) -> Result<(usize, Decoded<'a>), DecodingError> {
        macro_rules! goto (
            ($n:expr, $state:expr) => ({
                self.state = Some($state); 
                Ok(($n, Decoded::Nothing))
            });
            ($state:expr) => ({
                self.state = Some($state); 
                Ok((1, Decoded::Nothing))
            });
            ($n:expr, $state:expr, emit $res:expr) => ({
                self.state = Some($state); 
                Ok(($n, $res))
            });
            ($state:expr, emit $res:expr) => ({
                self.state = Some($state); 
                Ok((1, $res))
            })
        );
        
        let b = buf[0];
        
        // Driver should ensure that state is never None
        let state = self.state.take().unwrap();
        //println!("{:?}", state);
        
        match state {
            Magic(i, mut version) => if i < 6 {
                version[i] = b;
                goto!(Magic(i+1, version))
            } else if &version[..3] == b"GIF" {
                self.version = match &version[3..] {
                    b"87a" => "87a",
                    b"89a" => "89a",
                    _ => return Err(DecodingError::Format("unsupported GIF version"))
                };
                goto!(U16Byte1(U16Value::ScreenWidth, b))
            } else {
                Err(DecodingError::Format("malformed GIF header"))
            },
            U16(next) => goto!(U16Byte1(next, b)),
            U16Byte1(next, value) => {
                use self::U16Value::*;
                let value = ((b as u16) << 8) | value as u16;
                match (next, value) {
                    (ScreenWidth, width) => {
                        self.width = width;
                        goto!(U16(U16Value::ScreenHeight))
                    },
                    (ScreenHeight, height) => {
                        self.height = height;
                        goto!(Byte(ByteValue::GlobalFlags))
                    },
                    (Delay, delay) => {
                        self.ext.1.push(value as u8);
                        self.ext.1.push(b);
                        self.current_frame_mut().delay = delay;
                        goto!(Byte(ByteValue::TransparentIdx))
                    },
                    (ImageLeft, left) => {
                        self.current_frame_mut().left = left;
                        goto!(U16(U16Value::ImageTop))
                    },
                    (ImageTop, top) => {
                        self.current_frame_mut().top = top;
                        goto!(U16(U16Value::ImageWidth))
                    },
                    (ImageWidth, width) => {
                        self.current_frame_mut().width = width;
                        goto!(U16(U16Value::ImageHeight))
                    },
                    (ImageHeight, height) => {
                        self.current_frame_mut().height = height;
                        goto!(Byte(ByteValue::ImageFlags))
                    }
                }
            }
            Byte(value) => {
                use self::ByteValue::*;
                match value {
                    GlobalFlags => {
                        let global_table = b & 0x80 != 0;
                        let entries = if global_table {
                            let entries = PLTE_CHANNELS*(1 << ((b & 0b111) + 1) as usize);
                            self.global_color_table.reserve_exact(entries);
                            entries
                        } else {
                            0usize
                        };
                        goto!(Byte(Background { table_size: entries }))
                    },
                    Background { table_size } => {
                        goto!(
                            Byte(AspectRatio { table_size: table_size }),
                            emit Decoded::BackgroundColor(b)
                        )
                    },
                    AspectRatio { table_size } => {
                        goto!(GlobalPalette(table_size))
                    },
                    ControlFlags => {
                        self.ext.1.push(b);
                        let control_flags = b;
                        if control_flags & 1 != 0 {
                            // Set to Some(...), gets overwritten later
                            self.current_frame_mut().transparent = Some(0)
                        }
                        self.current_frame_mut().needs_user_input =
                            control_flags & 0b10 != 0;
                        self.current_frame_mut().dispose = match DisposalMethod::from_u8(
                            (control_flags & 0b11100) >> 2
                        ) {
                            Some(method) => method,
                            None => return Err(DecodingError::Format(
                                "unknown disposal method"
                            ))
                        };
                        goto!(U16(U16Value::Delay))
                    }
                    TransparentIdx => {
                        self.ext.1.push(b);
                        if let Some(ref mut idx) = self.current_frame_mut().transparent {
                             *idx = b
                        }
                        goto!(SkipBlock(0))
                        //goto!(AwaitBlockEnd)
                    }
                    ImageFlags => {
                        let local_table = (b & 0b1000_0000) != 0;
                        let interlaced   = (b & 0b0100_0000) != 0;
                        let table_size  =  b & 0b0000_0111;
                        
                        self.current_frame_mut().interlaced = interlaced;
                        if local_table {
                            let entries = PLTE_CHANNELS * (1 << (table_size + 1));
                            
                            self.current_frame_mut().palette =
                                Some(Vec::with_capacity(entries));
                            goto!(LocalPalette(entries))
                        } else {
                            goto!(Byte(CodeSize))
                        }
                    },
                    CodeSize => goto!(LzwInit(b))
                }
            }
            GlobalPalette(left) => {
                let n = cmp::min(left, buf.len());
                if left > 0 {
                    self.global_color_table.extend(buf[..n].iter().cloned());
                    goto!(n, GlobalPalette(left - n))
                } else {
                    let idx = self.background_color[0];
                    match self.global_color_table.chunks(PLTE_CHANNELS).nth(idx as usize) {
                        Some(chunk) => for i in 0..PLTE_CHANNELS {
                            self.background_color[i] = chunk[i]
                        },
                        None => self.background_color[0] = 0
                    }
                    goto!(BlockStart(Block::from_u8(b)), emit Decoded::GlobalPalette(
                        mem::replace(&mut self.global_color_table, Vec::new())
                    ))
                }
            }
            BlockStart(type_) => {
                use common::Block::*;
                match type_ {
                    Some(Image) => {
                        self.add_frame();
                        goto!(U16Byte1(U16Value::ImageLeft, b), emit Decoded::BlockStart(Image))
                    }
                    Some(Extension) => goto!(ExtensionBlock(b), emit Decoded::BlockStart(Extension)),
                    Some(Trailer) => goto!(0, State::Trailer, emit Decoded::BlockStart(Trailer)),
                    None => {
                        return Err(DecodingError::Format(
                        "unknown block type encountered"
                    ))}
                }
            }
            BlockEnd(terminator) => {
                if terminator == 0 {
                    if b == Block::Trailer as u8 {
                        goto!(0, BlockStart(Some(Block::Trailer)))
                    } else {
                        goto!(BlockStart(Block::from_u8(b)))
                    }
                } else {
                    return Err(DecodingError::Format(
                        "expected block terminator not found"
                    ))
                }
            }
            ExtensionBlock(type_) => {
                use common::Extension::*;
                self.ext.0 = type_;
                self.ext.1.clear();
                self.ext.1.push(b);
                if let Some(ext) = Extension::from_u8(type_) {
                    match ext {
                        Control => {
                            goto!(try!(self.read_control_extension(b)))
                        }
                        Text | Comment | Application => {
                            goto!(SkipBlock(b as usize))
                        }
                    }
                } else {
                    return Err(DecodingError::Format(
                        "unknown extention block encountered"
                    ))
                }
            }
            SkipBlock(left) => {
                let n = cmp::min(left, buf.len());
                if left > 0 {
                    self.ext.1.push(b);
                    goto!(n, SkipBlock(left - n))
                } else {
                    if b == 0 {
                        self.ext.2 = true;
                        goto!(BlockEnd(b), emit Decoded::BlockFinished(self.ext.0, &self.ext.1))
                    } else {
                        self.ext.2 = false;
                        goto!(SkipBlock(b as usize), emit Decoded::SubBlockFinished(self.ext.0,&self.ext.1))
                    }
                    
                }
            }
            LocalPalette(left) => {
                let n = cmp::min(left, buf.len());
                if left > 0 {
                    
                    self.current_frame_mut().palette
                        .as_mut().unwrap().extend(buf[..n].iter().cloned());
                    goto!(n, LocalPalette(left - n))
                } else {
                    goto!(LzwInit(b))
                }
            }
            LzwInit(code_size) => {
                // LZW spec: max 12 bits per code
                if code_size > 11 {
                    return Err(DecodingError::Format(
                        "invalid minimal code size"
                    ))
                }
                self.lzw_reader = Some(lzw::Decoder::new(lzw::LsbReader::new(), code_size));
                goto!(DecodeSubBlock(b as usize), emit Decoded::Frame(self.current_frame_mut()))
            }
            DecodeSubBlock(left) => {
                if left > 0 {
                    let n = cmp::min(left, buf.len());
                    let decoder = self.lzw_reader.as_mut().unwrap();
                    let (consumed, bytes) = try!(decoder.decode_bytes(&buf[..n]));
                    goto!(consumed, DecodeSubBlock(left - consumed), emit Decoded::Data(bytes))
                }  else if b != 0 { // decode next sub-block
                    goto!(DecodeSubBlock(b as usize))
                } else {
                    // The end of the lzw stream is only reached if left == 0 and an additional call
                    // to `decode_bytes` results in an empty slice.
                    let decoder = self.lzw_reader.as_mut().unwrap();
                    let (_, bytes) = try!(decoder.decode_bytes(&[]));
                    if bytes.len() > 0 {
                        goto!(0, DecodeSubBlock(0), emit Decoded::Data(bytes))
                    } else {
                        // end of image data reached
                        self.current = None;
                        goto!(0, FrameDecoded, emit Decoded::DataEnd)
                    }
                }
            }
            FrameDecoded => {
                goto!(BlockEnd(b))
            }
            Trailer => {
                self.state = None;
                Ok((1, Decoded::Trailer))
                //panic!("EOF {:?}", self)
            }
        }
    }
    
    fn read_control_extension(&mut self, b: u8) -> Result<State, DecodingError> {
        self.add_frame();
        self.ext.1.push(b);
        if b != 4 {
            return Err(DecodingError::Format(
                "control extension has wrong length"
            ))
        }
        Ok(Byte(ByteValue::ControlFlags))
    }
    
    fn add_frame(&mut self) {
        if self.current.is_none() {
            self.current = Some(Frame::default())
        }
    }
}