chainscript/src/utils/writeToPDF.js

Client for chainscript.io

import fs from 'fs';

/**
 * This could be improved by not putting the entire PDF in a buffer.
 */
export default function writeToPDF(input, output, script) {
  return new Promise((resolve, reject) => {
    const reader = typeof input === 'string' ?
                   fs.createReadStream(input) :
                   input;

    let buffer = new Buffer([]);

    reader.on('error', reject);

    reader.on('data', data => buffer = Buffer.concat([buffer, data]));

    reader.on('end', () => {
      let start = buffer.indexOf('\n% Chainscript: ');
      let end;

      if (start < 0) {
        let pos = 0;

        do {
          pos = buffer.indexOf('startxref', pos + 9);

          if (pos >= 0) {
            start = end = pos;
          }
        } while (pos >= 0)

        if (start < 0) {
          reject(new Error('Could not find startxref'));
          return;
        }
      } else {
        end = buffer.indexOf('\n', start + 16) + 1;
      }

      const writer = typeof output === 'string' ?
                     fs.createWriteStream(output, {
                       defaultEncoding: 'binary',
                       mode: 0o644
                     }) :
                     output;

      writer.on('error', reject);
      writer.write(buffer.slice(0, start));

      if (script) {
        writer.write('\n% Chainscript: ' + JSON.stringify(script) + '\n');
      }

      writer.end(buffer.slice(end), resolve);
    });
  });
}