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, shadow } from "../shared/util.js";
import { EOF } from "./primitives.js";
import { isWhiteSpace } from "./core_utils.js";

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,
};

class PostScriptToken {
  static get opCache() {
    return shadow(this, "opCache", Object.create(null));
  }

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

  static getOperator(op) {
    return (PostScriptToken.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")
    );
  }
}

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 (!isWhiteSpace(ch)) {
        break;
      }
      ch = this.nextChar();
    }
    switch (ch | 0) {
      case 0x30: // '0'
      case 0x31: // '1'
      case 0x32: // '2'
      case 0x33: // '3'
      case 0x34: // '4'
      case 0x35: // '5'
      case 0x36: // '6'
      case 0x37: // '7'
      case 0x38: // '8'
      case 0x39: // '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 &&
      ((ch >= /* 'A' = */ 0x41 && ch <= /* 'Z' = */ 0x5a) ||
        (ch >= /* 'a' = */ 0x61 && ch <= /* 'z' = */ 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 >= /* '0' = */ 0x30 && ch <= /* '9' = */ 0x39) ||
        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 };