pdf.js/src/core/flate_stream.js

/* Copyright 2012 Mozilla Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
/* Copyright 1996-2003 Glyph & Cog, LLC
 *
 * The flate stream implementation contained in this file is a JavaScript port
 * of XPDF's implementation, made available under the Apache 2.0 open source
 * license.
 */

import { DecodeStream } from "./decode_stream.js";
import { FormatError } from "../shared/util.js";

const codeLenCodeMap = new Int32Array([
  16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15,
]);

const lengthDecode = new Int32Array([
  0x00003, 0x00004, 0x00005, 0x00006, 0x00007, 0x00008, 0x00009, 0x0000a,
  0x1000b, 0x1000d, 0x1000f, 0x10011, 0x20013, 0x20017, 0x2001b, 0x2001f,
  0x30023, 0x3002b, 0x30033, 0x3003b, 0x40043, 0x40053, 0x40063, 0x40073,
  0x50083, 0x500a3, 0x500c3, 0x500e3, 0x00102, 0x00102, 0x00102,
]);

const distDecode = new Int32Array([
  0x00001, 0x00002, 0x00003, 0x00004, 0x10005, 0x10007, 0x20009, 0x2000d,
  0x30011, 0x30019, 0x40021, 0x40031, 0x50041, 0x50061, 0x60081, 0x600c1,
  0x70101, 0x70181, 0x80201, 0x80301, 0x90401, 0x90601, 0xa0801, 0xa0c01,
  0xb1001, 0xb1801, 0xc2001, 0xc3001, 0xd4001, 0xd6001,
]);

const fixedLitCodeTab = [
  new Int32Array([
    0x70100, 0x80050, 0x80010, 0x80118, 0x70110, 0x80070, 0x80030, 0x900c0,
    0x70108, 0x80060, 0x80020, 0x900a0, 0x80000, 0x80080, 0x80040, 0x900e0,
    0x70104, 0x80058, 0x80018, 0x90090, 0x70114, 0x80078, 0x80038, 0x900d0,
    0x7010c, 0x80068, 0x80028, 0x900b0, 0x80008, 0x80088, 0x80048, 0x900f0,
    0x70102, 0x80054, 0x80014, 0x8011c, 0x70112, 0x80074, 0x80034, 0x900c8,
    0x7010a, 0x80064, 0x80024, 0x900a8, 0x80004, 0x80084, 0x80044, 0x900e8,
    0x70106, 0x8005c, 0x8001c, 0x90098, 0x70116, 0x8007c, 0x8003c, 0x900d8,
    0x7010e, 0x8006c, 0x8002c, 0x900b8, 0x8000c, 0x8008c, 0x8004c, 0x900f8,
    0x70101, 0x80052, 0x80012, 0x8011a, 0x70111, 0x80072, 0x80032, 0x900c4,
    0x70109, 0x80062, 0x80022, 0x900a4, 0x80002, 0x80082, 0x80042, 0x900e4,
    0x70105, 0x8005a, 0x8001a, 0x90094, 0x70115, 0x8007a, 0x8003a, 0x900d4,
    0x7010d, 0x8006a, 0x8002a, 0x900b4, 0x8000a, 0x8008a, 0x8004a, 0x900f4,
    0x70103, 0x80056, 0x80016, 0x8011e, 0x70113, 0x80076, 0x80036, 0x900cc,
    0x7010b, 0x80066, 0x80026, 0x900ac, 0x80006, 0x80086, 0x80046, 0x900ec,
    0x70107, 0x8005e, 0x8001e, 0x9009c, 0x70117, 0x8007e, 0x8003e, 0x900dc,
    0x7010f, 0x8006e, 0x8002e, 0x900bc, 0x8000e, 0x8008e, 0x8004e, 0x900fc,
    0x70100, 0x80051, 0x80011, 0x80119, 0x70110, 0x80071, 0x80031, 0x900c2,
    0x70108, 0x80061, 0x80021, 0x900a2, 0x80001, 0x80081, 0x80041, 0x900e2,
    0x70104, 0x80059, 0x80019, 0x90092, 0x70114, 0x80079, 0x80039, 0x900d2,
    0x7010c, 0x80069, 0x80029, 0x900b2, 0x80009, 0x80089, 0x80049, 0x900f2,
    0x70102, 0x80055, 0x80015, 0x8011d, 0x70112, 0x80075, 0x80035, 0x900ca,
    0x7010a, 0x80065, 0x80025, 0x900aa, 0x80005, 0x80085, 0x80045, 0x900ea,
    0x70106, 0x8005d, 0x8001d, 0x9009a, 0x70116, 0x8007d, 0x8003d, 0x900da,
    0x7010e, 0x8006d, 0x8002d, 0x900ba, 0x8000d, 0x8008d, 0x8004d, 0x900fa,
    0x70101, 0x80053, 0x80013, 0x8011b, 0x70111, 0x80073, 0x80033, 0x900c6,
    0x70109, 0x80063, 0x80023, 0x900a6, 0x80003, 0x80083, 0x80043, 0x900e6,
    0x70105, 0x8005b, 0x8001b, 0x90096, 0x70115, 0x8007b, 0x8003b, 0x900d6,
    0x7010d, 0x8006b, 0x8002b, 0x900b6, 0x8000b, 0x8008b, 0x8004b, 0x900f6,
    0x70103, 0x80057, 0x80017, 0x8011f, 0x70113, 0x80077, 0x80037, 0x900ce,
    0x7010b, 0x80067, 0x80027, 0x900ae, 0x80007, 0x80087, 0x80047, 0x900ee,
    0x70107, 0x8005f, 0x8001f, 0x9009e, 0x70117, 0x8007f, 0x8003f, 0x900de,
    0x7010f, 0x8006f, 0x8002f, 0x900be, 0x8000f, 0x8008f, 0x8004f, 0x900fe,
    0x70100, 0x80050, 0x80010, 0x80118, 0x70110, 0x80070, 0x80030, 0x900c1,
    0x70108, 0x80060, 0x80020, 0x900a1, 0x80000, 0x80080, 0x80040, 0x900e1,
    0x70104, 0x80058, 0x80018, 0x90091, 0x70114, 0x80078, 0x80038, 0x900d1,
    0x7010c, 0x80068, 0x80028, 0x900b1, 0x80008, 0x80088, 0x80048, 0x900f1,
    0x70102, 0x80054, 0x80014, 0x8011c, 0x70112, 0x80074, 0x80034, 0x900c9,
    0x7010a, 0x80064, 0x80024, 0x900a9, 0x80004, 0x80084, 0x80044, 0x900e9,
    0x70106, 0x8005c, 0x8001c, 0x90099, 0x70116, 0x8007c, 0x8003c, 0x900d9,
    0x7010e, 0x8006c, 0x8002c, 0x900b9, 0x8000c, 0x8008c, 0x8004c, 0x900f9,
    0x70101, 0x80052, 0x80012, 0x8011a, 0x70111, 0x80072, 0x80032, 0x900c5,
    0x70109, 0x80062, 0x80022, 0x900a5, 0x80002, 0x80082, 0x80042, 0x900e5,
    0x70105, 0x8005a, 0x8001a, 0x90095, 0x70115, 0x8007a, 0x8003a, 0x900d5,
    0x7010d, 0x8006a, 0x8002a, 0x900b5, 0x8000a, 0x8008a, 0x8004a, 0x900f5,
    0x70103, 0x80056, 0x80016, 0x8011e, 0x70113, 0x80076, 0x80036, 0x900cd,
    0x7010b, 0x80066, 0x80026, 0x900ad, 0x80006, 0x80086, 0x80046, 0x900ed,
    0x70107, 0x8005e, 0x8001e, 0x9009d, 0x70117, 0x8007e, 0x8003e, 0x900dd,
    0x7010f, 0x8006e, 0x8002e, 0x900bd, 0x8000e, 0x8008e, 0x8004e, 0x900fd,
    0x70100, 0x80051, 0x80011, 0x80119, 0x70110, 0x80071, 0x80031, 0x900c3,
    0x70108, 0x80061, 0x80021, 0x900a3, 0x80001, 0x80081, 0x80041, 0x900e3,
    0x70104, 0x80059, 0x80019, 0x90093, 0x70114, 0x80079, 0x80039, 0x900d3,
    0x7010c, 0x80069, 0x80029, 0x900b3, 0x80009, 0x80089, 0x80049, 0x900f3,
    0x70102, 0x80055, 0x80015, 0x8011d, 0x70112, 0x80075, 0x80035, 0x900cb,
    0x7010a, 0x80065, 0x80025, 0x900ab, 0x80005, 0x80085, 0x80045, 0x900eb,
    0x70106, 0x8005d, 0x8001d, 0x9009b, 0x70116, 0x8007d, 0x8003d, 0x900db,
    0x7010e, 0x8006d, 0x8002d, 0x900bb, 0x8000d, 0x8008d, 0x8004d, 0x900fb,
    0x70101, 0x80053, 0x80013, 0x8011b, 0x70111, 0x80073, 0x80033, 0x900c7,
    0x70109, 0x80063, 0x80023, 0x900a7, 0x80003, 0x80083, 0x80043, 0x900e7,
    0x70105, 0x8005b, 0x8001b, 0x90097, 0x70115, 0x8007b, 0x8003b, 0x900d7,
    0x7010d, 0x8006b, 0x8002b, 0x900b7, 0x8000b, 0x8008b, 0x8004b, 0x900f7,
    0x70103, 0x80057, 0x80017, 0x8011f, 0x70113, 0x80077, 0x80037, 0x900cf,
    0x7010b, 0x80067, 0x80027, 0x900af, 0x80007, 0x80087, 0x80047, 0x900ef,
    0x70107, 0x8005f, 0x8001f, 0x9009f, 0x70117, 0x8007f, 0x8003f, 0x900df,
    0x7010f, 0x8006f, 0x8002f, 0x900bf, 0x8000f, 0x8008f, 0x8004f, 0x900ff,
  ]),
  9,
];

const fixedDistCodeTab = [
  new Int32Array([
    0x50000, 0x50010, 0x50008, 0x50018, 0x50004, 0x50014, 0x5000c, 0x5001c,
    0x50002, 0x50012, 0x5000a, 0x5001a, 0x50006, 0x50016, 0x5000e, 0x00000,
    0x50001, 0x50011, 0x50009, 0x50019, 0x50005, 0x50015, 0x5000d, 0x5001d,
    0x50003, 0x50013, 0x5000b, 0x5001b, 0x50007, 0x50017, 0x5000f, 0x00000,
  ]),
  5,
];

class FlateStream extends DecodeStream {
  constructor(str, maybeLength) {
    super(maybeLength);

    this.str = str;
    this.dict = str.dict;

    const cmf = str.getByte();
    const flg = str.getByte();
    if (cmf === -1 || flg === -1) {
      throw new FormatError(`Invalid header in flate stream: ${cmf}, ${flg}`);
    }
    if ((cmf & 0x0f) !== 0x08) {
      throw new FormatError(
        `Unknown compression method in flate stream: ${cmf}, ${flg}`
      );
    }
    if (((cmf << 8) + flg) % 31 !== 0) {
      throw new FormatError(`Bad FCHECK in flate stream: ${cmf}, ${flg}`);
    }
    if (flg & 0x20) {
      throw new FormatError(`FDICT bit set in flate stream: ${cmf}, ${flg}`);
    }

    this.codeSize = 0;
    this.codeBuf = 0;
  }

  getBits(bits) {
    const str = this.str;
    let codeSize = this.codeSize;
    let codeBuf = this.codeBuf;

    let b;
    while (codeSize < bits) {
      if ((b = str.getByte()) === -1) {
        throw new FormatError("Bad encoding in flate stream");
      }
      codeBuf |= b << codeSize;
      codeSize += 8;
    }
    b = codeBuf & ((1 << bits) - 1);
    this.codeBuf = codeBuf >> bits;
    this.codeSize = codeSize -= bits;

    return b;
  }

  getCode(table) {
    const str = this.str;
    const codes = table[0];
    const maxLen = table[1];
    let codeSize = this.codeSize;
    let codeBuf = this.codeBuf;

    let b;
    while (codeSize < maxLen) {
      if ((b = str.getByte()) === -1) {
        // premature end of stream. code might however still be valid.
        // codeSize < codeLen check below guards against incomplete codeVal.
        break;
      }
      codeBuf |= b << codeSize;
      codeSize += 8;
    }
    const code = codes[codeBuf & ((1 << maxLen) - 1)];
    const codeLen = code >> 16;
    const codeVal = code & 0xffff;
    if (codeLen < 1 || codeSize < codeLen) {
      throw new FormatError("Bad encoding in flate stream");
    }
    this.codeBuf = codeBuf >> codeLen;
    this.codeSize = codeSize - codeLen;
    return codeVal;
  }

  generateHuffmanTable(lengths) {
    const n = lengths.length;

    // find max code length
    let maxLen = 0;
    let i;
    for (i = 0; i < n; ++i) {
      if (lengths[i] > maxLen) {
        maxLen = lengths[i];
      }
    }

    // build the table
    const size = 1 << maxLen;
    const codes = new Int32Array(size);
    for (
      let len = 1, code = 0, skip = 2;
      len <= maxLen;
      ++len, code <<= 1, skip <<= 1
    ) {
      for (let val = 0; val < n; ++val) {
        if (lengths[val] === len) {
          // bit-reverse the code
          let code2 = 0;
          let t = code;
          for (i = 0; i < len; ++i) {
            code2 = (code2 << 1) | (t & 1);
            t >>= 1;
          }

          // fill the table entries
          for (i = code2; i < size; i += skip) {
            codes[i] = (len << 16) | val;
          }
          ++code;
        }
      }
    }

    return [codes, maxLen];
  }

  readBlock() {
    let buffer, len;
    const str = this.str;
    // read block header
    let hdr = this.getBits(3);
    if (hdr & 1) {
      this.eof = true;
    }
    hdr >>= 1;

    if (hdr === 0) {
      // uncompressed block
      let b;

      if ((b = str.getByte()) === -1) {
        throw new FormatError("Bad block header in flate stream");
      }
      let blockLen = b;
      if ((b = str.getByte()) === -1) {
        throw new FormatError("Bad block header in flate stream");
      }
      blockLen |= b << 8;
      if ((b = str.getByte()) === -1) {
        throw new FormatError("Bad block header in flate stream");
      }
      let check = b;
      if ((b = str.getByte()) === -1) {
        throw new FormatError("Bad block header in flate stream");
      }
      check |= b << 8;
      if (check !== (~blockLen & 0xffff) && (blockLen !== 0 || check !== 0)) {
        // Ignoring error for bad "empty" block (see issue 1277)
        throw new FormatError("Bad uncompressed block length in flate stream");
      }

      this.codeBuf = 0;
      this.codeSize = 0;

      const bufferLength = this.bufferLength,
        end = bufferLength + blockLen;
      buffer = this.ensureBuffer(end);
      this.bufferLength = end;

      if (blockLen === 0) {
        if (str.peekByte() === -1) {
          this.eof = true;
        }
      } else {
        const block = str.getBytes(blockLen);
        buffer.set(block, bufferLength);
        if (block.length < blockLen) {
          this.eof = true;
        }
      }
      return;
    }

    let litCodeTable;
    let distCodeTable;
    if (hdr === 1) {
      // compressed block, fixed codes
      litCodeTable = fixedLitCodeTab;
      distCodeTable = fixedDistCodeTab;
    } else if (hdr === 2) {
      // compressed block, dynamic codes
      const numLitCodes = this.getBits(5) + 257;
      const numDistCodes = this.getBits(5) + 1;
      const numCodeLenCodes = this.getBits(4) + 4;

      // build the code lengths code table
      const codeLenCodeLengths = new Uint8Array(codeLenCodeMap.length);

      let i;
      for (i = 0; i < numCodeLenCodes; ++i) {
        codeLenCodeLengths[codeLenCodeMap[i]] = this.getBits(3);
      }
      const codeLenCodeTab = this.generateHuffmanTable(codeLenCodeLengths);

      // build the literal and distance code tables
      len = 0;
      i = 0;
      const codes = numLitCodes + numDistCodes;
      const codeLengths = new Uint8Array(codes);
      let bitsLength, bitsOffset, what;
      while (i < codes) {
        const code = this.getCode(codeLenCodeTab);
        if (code === 16) {
          bitsLength = 2;
          bitsOffset = 3;
          what = len;
        } else if (code === 17) {
          bitsLength = 3;
          bitsOffset = 3;
          what = len = 0;
        } else if (code === 18) {
          bitsLength = 7;
          bitsOffset = 11;
          what = len = 0;
        } else {
          codeLengths[i++] = len = code;
          continue;
        }

        let repeatLength = this.getBits(bitsLength) + bitsOffset;
        while (repeatLength-- > 0) {
          codeLengths[i++] = what;
        }
      }

      litCodeTable = this.generateHuffmanTable(
        codeLengths.subarray(0, numLitCodes)
      );
      distCodeTable = this.generateHuffmanTable(
        codeLengths.subarray(numLitCodes, codes)
      );
    } else {
      throw new FormatError("Unknown block type in flate stream");
    }

    buffer = this.buffer;
    let limit = buffer ? buffer.length : 0;
    let pos = this.bufferLength;
    while (true) {
      let code1 = this.getCode(litCodeTable);
      if (code1 < 256) {
        if (pos + 1 >= limit) {
          buffer = this.ensureBuffer(pos + 1);
          limit = buffer.length;
        }
        buffer[pos++] = code1;
        continue;
      }
      if (code1 === 256) {
        this.bufferLength = pos;
        return;
      }
      code1 -= 257;
      code1 = lengthDecode[code1];
      let code2 = code1 >> 16;
      if (code2 > 0) {
        code2 = this.getBits(code2);
      }
      len = (code1 & 0xffff) + code2;
      code1 = this.getCode(distCodeTable);
      code1 = distDecode[code1];
      code2 = code1 >> 16;
      if (code2 > 0) {
        code2 = this.getBits(code2);
      }
      const dist = (code1 & 0xffff) + code2;
      if (pos + len >= limit) {
        buffer = this.ensureBuffer(pos + len);
        limit = buffer.length;
      }
      for (let k = 0; k < len; ++k, ++pos) {
        buffer[pos] = buffer[pos - dist];
      }
    }
  }
}

export { FlateStream };