pdf.js/src/core/ps_parser.js

/* Copyright 2014 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.
 */

import { FormatError, isSpace, shadow } from '../shared/util';
import { EOF } from './primitives';

class PostScriptParser {
  constructor(lexer) {
    this.lexer = lexer;
    this.operators = [];
    this.token = null;
    this.prev = null;
  }

  nextToken() {
    this.prev = this.token;
    this.token = this.lexer.getToken();
  }

  accept(type) {
    if (this.token.type === type) {
      this.nextToken();
      return true;
    }
    return false;
  }

  expect(type) {
    if (this.accept(type)) {
      return true;
    }
    throw new FormatError(
      `Unexpected symbol: found ${this.token.type} expected ${type}.`);
  }

  parse() {
    this.nextToken();
    this.expect(PostScriptTokenTypes.LBRACE);
    this.parseBlock();
    this.expect(PostScriptTokenTypes.RBRACE);
    return this.operators;
  }

  parseBlock() {
    while (true) {
      if (this.accept(PostScriptTokenTypes.NUMBER)) {
        this.operators.push(this.prev.value);
      } else if (this.accept(PostScriptTokenTypes.OPERATOR)) {
        this.operators.push(this.prev.value);
      } else if (this.accept(PostScriptTokenTypes.LBRACE)) {
        this.parseCondition();
      } else {
        return;
      }
    }
  }

  parseCondition() {
    // Add two place holders that will be updated later
    const conditionLocation = this.operators.length;
    this.operators.push(null, null);

    this.parseBlock();
    this.expect(PostScriptTokenTypes.RBRACE);
    if (this.accept(PostScriptTokenTypes.IF)) {
      // The true block is right after the 'if' so it just falls through on true
      // else it jumps and skips the true block.
      this.operators[conditionLocation] = this.operators.length;
      this.operators[conditionLocation + 1] = 'jz';
    } else if (this.accept(PostScriptTokenTypes.LBRACE)) {
      const jumpLocation = this.operators.length;
      this.operators.push(null, null);
      const endOfTrue = this.operators.length;
      this.parseBlock();
      this.expect(PostScriptTokenTypes.RBRACE);
      this.expect(PostScriptTokenTypes.IFELSE);
      // The jump is added at the end of the true block to skip the false block.
      this.operators[jumpLocation] = this.operators.length;
      this.operators[jumpLocation + 1] = 'j';

      this.operators[conditionLocation] = endOfTrue;
      this.operators[conditionLocation + 1] = 'jz';
    } else {
      throw new FormatError('PS Function: error parsing conditional.');
    }
  }
}

const PostScriptTokenTypes = {
  LBRACE: 0,
  RBRACE: 1,
  NUMBER: 2,
  OPERATOR: 3,
  IF: 4,
  IFELSE: 5,
};

const PostScriptToken = (function PostScriptTokenClosure() {
  const opCache = Object.create(null);

  class PostScriptToken {
    constructor(type, value) {
      this.type = type;
      this.value = value;
    }

    static getOperator(op) {
      const opValue = opCache[op];
      if (opValue) {
        return opValue;
      }
      return opCache[op] = new PostScriptToken(PostScriptTokenTypes.OPERATOR,
                                               op);
    }

    static get LBRACE() {
      return shadow(this, 'LBRACE',
                    new PostScriptToken(PostScriptTokenTypes.LBRACE, '{'));
    }

    static get RBRACE() {
      return shadow(this, 'RBRACE',
                    new PostScriptToken(PostScriptTokenTypes.RBRACE, '}'));
    }

    static get IF() {
      return shadow(this, 'IF',
                    new PostScriptToken(PostScriptTokenTypes.IF, 'IF'));
    }

    static get IFELSE() {
      return shadow(this, 'IFELSE',
                    new PostScriptToken(PostScriptTokenTypes.IFELSE, 'IFELSE'));
    }
  }
  return PostScriptToken;
})();

class PostScriptLexer {
  constructor(stream) {
    this.stream = stream;
    this.nextChar();

    this.strBuf = [];
  }

  nextChar() {
    return (this.currentChar = this.stream.getByte());
  }

  getToken() {
    let comment = false;
    let ch = this.currentChar;

    // skip comments
    while (true) {
      if (ch < 0) {
        return EOF;
      }

      if (comment) {
        if (ch === 0x0A || ch === 0x0D) {
          comment = false;
        }
      } else if (ch === 0x25) { // '%'
        comment = true;
      } else if (!isSpace(ch)) {
        break;
      }
      ch = this.nextChar();
    }
    switch (ch | 0) {
      case 0x30: case 0x31: case 0x32: case 0x33: case 0x34: // '0'-'4'
      case 0x35: case 0x36: case 0x37: case 0x38: case 0x39: // '5'-'9'
      case 0x2B: case 0x2D: case 0x2E: // '+', '-', '.'
        return new PostScriptToken(PostScriptTokenTypes.NUMBER,
                                   this.getNumber());
      case 0x7B: // '{'
        this.nextChar();
        return PostScriptToken.LBRACE;
      case 0x7D: // '}'
        this.nextChar();
        return PostScriptToken.RBRACE;
    }
    // operator
    const strBuf = this.strBuf;
    strBuf.length = 0;
    strBuf[0] = String.fromCharCode(ch);

    while ((ch = this.nextChar()) >= 0 && // and 'A'-'Z', 'a'-'z'
           ((ch >= 0x41 && ch <= 0x5A) || (ch >= 0x61 && ch <= 0x7A))) {
      strBuf.push(String.fromCharCode(ch));
    }
    const str = strBuf.join('');
    switch (str.toLowerCase()) {
      case 'if':
        return PostScriptToken.IF;
      case 'ifelse':
        return PostScriptToken.IFELSE;
      default:
        return PostScriptToken.getOperator(str);
    }
  }

  getNumber() {
    let ch = this.currentChar;
    const strBuf = this.strBuf;
    strBuf.length = 0;
    strBuf[0] = String.fromCharCode(ch);

    while ((ch = this.nextChar()) >= 0) {
      if ((ch >= 0x30 && ch <= 0x39) || // '0'-'9'
          ch === 0x2D || ch === 0x2E) { // '-', '.'
        strBuf.push(String.fromCharCode(ch));
      } else {
        break;
      }
    }
    const value = parseFloat(strBuf.join(''));
    if (isNaN(value)) {
      throw new FormatError(`Invalid floating point number: ${value}`);
    }
    return value;
  }
}

export {
  PostScriptLexer,
  PostScriptParser,
};