      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

    use std::io::Write;
    use std::io;

    use deflate_state::DeflateState;
    use encoder_state::EncoderState;
    use lzvalue::LZValue;
    use lz77::{lz77_compress_block, LZ77Status};
    use huffman_lengths::{gen_huffman_lengths, write_huffman_lengths, BlockType};
    use bitstream::LsbWriter;
    use stored_block::{compress_block_stored, write_stored_header, MAX_STORED_BLOCK_LENGTH};

    const LARGEST_OUTPUT_BUF_SIZE: usize = 1024 * 32;

    /// Flush mode to use when compressing input received in multiple steps.
    ///
    /// (The more obscure ZLIB flush modes are not implemented.)
    #[derive(Eq, PartialEq, Debug, Copy, Clone)]
    pub enum Flush {
        // Simply wait for more input when we are out of input data to process.
        None,
        // Send a "sync block", corresponding to Z_SYNC_FLUSH in zlib. This finishes compressing and
        // outputting all pending data, and then outputs an empty stored block.
        // (That is, the block header indicating a stored block followed by `0000FFFF`).
        Sync,
        _Partial,
        _Block,
        _Full,
        // Finish compressing and output all remaining input.
        Finish,
    }

    /// Write all the lz77 encoded data in the buffer using the specified `EncoderState`, and finish
    /// with the end of block code.
    pub fn flush_to_bitstream(buffer: &[LZValue], state: &mut EncoderState) {
        for &b in buffer {
            state.write_lzvalue(b.value());
        }
        state.write_end_of_block()
    }

    /// Compress the input data using only fixed huffman codes.
    ///
    /// Currently only used in tests.
    #[cfg(test)]
    pub fn compress_data_fixed(input: &[u8]) -> Vec<u8> {
        use lz77::lz77_compress;

        let mut state = EncoderState::fixed(Vec::new());
        let compressed = lz77_compress(input).unwrap();

        // We currently don't split blocks here(this function is just used for tests anyhow)
        state.write_start_of_block(true, true);
        flush_to_bitstream(&compressed, &mut state);

        state.flush();
        state.reset(Vec::new())
    }

    fn write_stored_block(input: &[u8], mut writer: &mut LsbWriter, final_block: bool) {

        // If the input is not zero, we write stored blocks for the input data.
        if !input.is_empty() {
            let mut i = input.chunks(MAX_STORED_BLOCK_LENGTH).peekable();

            while let Some(chunk) = i.next() {
                let last_chunk = i.peek().is_none();
                // Write the block header
                write_stored_header(writer, final_block && last_chunk);

                // Write the actual data.
                compress_block_stored(chunk, &mut writer).expect("Write error");

            }
        } else {
            // If the input length is zero, we output an empty block. This is used for syncing.
            write_stored_header(writer, final_block);
            compress_block_stored(&[], &mut writer).expect("Write error");
        }
    }

    /// Inner compression function used by both the writers and the simple compression functions.
    pub fn compress_data_dynamic_n<W: Write>(
        input: &[u8],
        deflate_state: &mut DeflateState<W>,
        flush: Flush,
    ) -> io::Result<usize> {
        let mut bytes_written = 0;

        let mut slice = input;

        loop {
            let output_buf_len = deflate_state.output_buf().len();
            let output_buf_pos = deflate_state.output_buf_pos;
            // If the output buffer has too much data in it already, flush it before doing anything
            // else.
            if output_buf_len > LARGEST_OUTPUT_BUF_SIZE {
                let written = deflate_state
                    .inner
                    .as_mut()
                    .expect("Missing writer!")
                    .write(&deflate_state.encoder_state.inner_vec()[output_buf_pos..])?;

                if written < output_buf_len.checked_sub(output_buf_pos).unwrap() {
                    // Only some of the data was flushed, so keep track of where we were.
                    deflate_state.output_buf_pos += written;
                } else {
                    // If we flushed all of the output, reset the output buffer.
                    deflate_state.output_buf_pos = 0;
                    deflate_state.output_buf().clear();
                }

                if bytes_written == 0 {
                    // If the buffer was already full when the function was called, this has to be
                    // returned rather than Ok(0) to indicate that we didn't write anything, but are
                    // not done yet.
                    return Err(io::Error::new(
                        io::ErrorKind::Interrupted,
                        "Internal buffer full.",
                    ));
                } else {
                    return Ok(bytes_written);
                }
            }

            if deflate_state.lz77_state.is_last_block() {
                // The last block has already been written, so we don't ave anything to compress.
                break;
            }

            let (written, status, position) = lz77_compress_block(
                slice,
                &mut deflate_state.lz77_state,
                &mut deflate_state.input_buffer,
                &mut deflate_state.lz77_writer,
                flush,
            );

            // Bytes written in this call
            bytes_written += written;
            // Total bytes written since the compression process started
            // TODO: Should we realistically have to worry about overflowing here?
            deflate_state.bytes_written += written as u64;

            if status == LZ77Status::NeedInput {
                // If we've consumed all the data input so far, and we're not
                // finishing or syncing or ending the block here, simply return
                // the number of bytes consumed so far.
                return Ok(bytes_written);
            }

            // Increment start of input data
            slice = &slice[written..];

            // We need to check if this is the last block as the header will then be
            // slightly different to indicate this.
            let last_block = deflate_state.lz77_state.is_last_block();

            let current_block_input_bytes = deflate_state.lz77_state.current_block_input_bytes();

            if cfg!(debug_assertions) {
                deflate_state
                    .bytes_written_control
                    .add(current_block_input_bytes);
            }

            let partial_bits = deflate_state.encoder_state.writer.pending_bits();

            let res = {
                let (l_freqs, d_freqs) = deflate_state.lz77_writer.get_frequencies();
                let (l_lengths, d_lengths) =
                    deflate_state.encoder_state.huffman_table.get_lengths_mut();

                gen_huffman_lengths(
                    l_freqs,
                    d_freqs,
                    current_block_input_bytes,
                    partial_bits,
                    l_lengths,
                    d_lengths,
                    &mut deflate_state.length_buffers,
                )
            };

            // Check if we've actually managed to compress the input, and output stored blocks
            // if not.
            match res {
                BlockType::Dynamic(header) => {
                    // Write the block header.
                    deflate_state
                        .encoder_state
                        .write_start_of_block(false, last_block);

                    // Output the lengths of the huffman codes used in this block.
                    write_huffman_lengths(
                        &header,
                        &deflate_state.encoder_state.huffman_table,
                        &mut deflate_state.length_buffers.length_buf,
                        &mut deflate_state.encoder_state.writer,
                    );

                    // Uupdate the huffman codes that will be used to encode the
                    // lz77-compressed data.
                    deflate_state
                        .encoder_state
                        .huffman_table
                        .update_from_lengths();

                    // Write the huffman compressed data and the end of block marker.
                    flush_to_bitstream(
                        deflate_state.lz77_writer.get_buffer(),
                        &mut deflate_state.encoder_state,
                    );
                }
                BlockType::Fixed => {
                    // Write the block header for fixed code blocks.
                    deflate_state
                        .encoder_state
                        .write_start_of_block(true, last_block);

                    // Use the pre-defined static huffman codes.
                    deflate_state.encoder_state.set_huffman_to_fixed();

                    // Write the compressed data and the end of block marker.
                    flush_to_bitstream(
                        deflate_state.lz77_writer.get_buffer(),
                        &mut deflate_state.encoder_state,
                    );
                }
                BlockType::Stored => {
                    // If compression fails, output a stored block instead.

                    let start_pos = position.saturating_sub(current_block_input_bytes as usize);

                    assert!(
                        position >= current_block_input_bytes as usize,
                        "Error! Trying to output a stored block with forgotten data!\
                         if you encounter this error, please file an issue!"
                    );

                    write_stored_block(
                        &deflate_state.input_buffer.get_buffer()[start_pos..position],
                        &mut deflate_state.encoder_state.writer,
                        flush == Flush::Finish && last_block,
                    );
                }
            };

            // Clear the current lz77 data in the writer for the next call.
            deflate_state.lz77_writer.clear();
            // We are done with the block, so we reset the number of bytes taken
            // for the next one.
            deflate_state.lz77_state.reset_input_bytes();

            // We are done for now.
            if status == LZ77Status::Finished {
                // This flush mode means that there should be an empty stored block at the end.
                if flush == Flush::Sync {
                    write_stored_block(&[], &mut deflate_state.encoder_state.writer, false);
                } else if !deflate_state.lz77_state.is_last_block() {
                    // Make sure a block with the last block header has been output.
                    // Not sure this can actually happen, but we make sure to finish properly
                    // if it somehow does.
                    // An empty fixed block is the shortest.
                    let es = &mut deflate_state.encoder_state;
                    es.set_huffman_to_fixed();
                    es.write_start_of_block(true, true);
                    es.write_end_of_block();
                }
                break;
            }
        }

        // If we reach this point, the remaining data in the buffers is to be flushed.
        deflate_state.encoder_state.flush();
        // Make sure we've output everything, and return the number of bytes written if everything
        // went well.
        let output_buf_pos = deflate_state.output_buf_pos;
        let written_to_writer = deflate_state
            .inner
            .as_mut()
            .expect("Missing writer!")
            .write(&deflate_state.encoder_state.inner_vec()[output_buf_pos..])?;
        if written_to_writer <
            deflate_state
                .output_buf()
                .len()
                .checked_sub(output_buf_pos)
                .unwrap()
        {
            deflate_state.output_buf_pos += written_to_writer;
        } else {
            // If we sucessfully wrote all the data, we can clear the output buffer.
            deflate_state.output_buf_pos = 0;
            deflate_state.output_buf().clear();
        }
        Ok(bytes_written)
    }

    #[cfg(test)]
    mod test {
        use super::*;
        use test_utils::{get_test_data, decompress_to_end};

        #[test]
        /// Test compressing a short string using fixed encoding.
        fn fixed_string_mem() {
            let test_data = String::from("                    GNU GENERAL PUBLIC LICENSE").into_bytes();
            let compressed = compress_data_fixed(&test_data);

            let result = decompress_to_end(&compressed);

            assert_eq!(test_data, result);
        }

        #[test]
        fn fixed_data() {
            let data = vec![190u8; 400];
            let compressed = compress_data_fixed(&data);
            let result = decompress_to_end(&compressed);

            assert_eq!(data, result);
        }

        /// Test deflate example.
        ///
        /// Check if the encoder produces the same code as the example given by Mark Adler here:
        /// https://stackoverflow.com/questions/17398931/deflate-encoding-with-static-huffman-codes/17415203
        #[test]
        fn fixed_example() {
            let test_data = b"Deflate late";
            // let check =
            // [0x73, 0x49, 0x4d, 0xcb, 0x49, 0x2c, 0x49, 0x55, 0xc8, 0x49, 0x2c, 0x49, 0x5, 0x0];
            let check = [
                0x73,
                0x49,
                0x4d,
                0xcb,
                0x49,
                0x2c,
                0x49,
                0x55,
                0x00,
                0x11,
                0x00,
            ];
            let compressed = compress_data_fixed(test_data);
            assert_eq!(&compressed, &check);
            let decompressed = decompress_to_end(&compressed);
            assert_eq!(&decompressed, test_data)
        }

        #[test]
        /// Test compression from a file.
        fn fixed_string_file() {
            let input = get_test_data();

            let compressed = compress_data_fixed(&input);
            println!("Fixed codes compressed len: {}", compressed.len());
            let result = decompress_to_end(&compressed);

            assert_eq!(input.len(), result.len());
            // Not using assert_eq here deliberately to avoid massive amounts of output spam.
            assert!(input == result);
        }
    }

# Help

## Keyboard Shortcuts

`?`
  Show this help dialog
`S`
  Focus the search field
`↑`
  Move up in search results
`↓`
  Move down in search results
`↹`
  Switch tab
`⏎`
  Go to active search result
`+`
  Expand all sections
`-`
  Collapse all sections

## Search Tricks

Prefix searches with a type followed by a colon (e.g., `fn:`) to restrict the search to a given type.

Accepted types are: `fn`, `mod`, `struct`, `enum`, `trait`, `type`, `macro`, and `const`.

Search functions by type signature (e.g., `vec -> usize` or `* -> vec`)

Search multiple things at once by splitting your query with comma (e.g., `str,u8` or `String,struct:Vec,test`)