# All files / lib/winston tail-file.js

61.29% Statements 38/62
37.5% Branches 12/32
66.67% Functions 4/6
61.29% Lines 38/62

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     /**
     * tail-file.js: TODO: add file header description.
     *
     * (C) 2010 Charlie Robbins
     * MIT LICENCE
     */

    'use strict';

    const fs = require('fs');
    const { StringDecoder } = require('string_decoder');
    const { Stream } = require('readable-stream');

    /**
     * Simple no-op function.
     * @returns {undefined}
     */
    function noop() {}

    /**
     * TODO: add function description.
     * @param {Object} options - Options for tail.
     * @param {function} iter - Iterator function to execute on every line.
    * `tail -f` a file. Options must include file.
     * @returns {mixed} - TODO: add return description.
     */
    module.exports = (options, iter) => {
      const buffer = Buffer.alloc(64 * 1024);
      const decode = new StringDecoder('utf8');
      const stream = new Stream();
      let buff = '';
      let pos = 0;
      let row = 0;

      Iif (options.start === -1) {
        delete options.start;
      }

      stream.readable = true;
      stream.destroy = () => {
        stream.destroyed = true;
        stream.emit('end');
        stream.emit('close');
      };

      fs.open(options.file, 'a+', '0644', (err, fd) => {
        Iif (err) {
          if (!iter) {
            stream.emit('error', err);
          } else {
            iter(err);
          }
          stream.destroy();
          return;
        }

        (function read() {
          Iif (stream.destroyed) {
            fs.close(fd, noop);
            return;
          }

          return fs.read(fd, buffer, 0, buffer.length, pos, (err, bytes) => {
            Iif (err) {
              if (!iter) {
                stream.emit('error', err);
              } else {
                iter(err);
              }
              stream.destroy();
              return;
            }

            if (!bytes) {
              Iif (buff) {
                // eslint-disable-next-line eqeqeq
                if (options.start == null || row > options.start) {
                  if (!iter) {
                    stream.emit('line', buff);
                  } else {
                    iter(null, buff);
                  }
                }
                row++;
                buff = '';
              }
              return setTimeout(read, 1000);
            }

            let data = decode.write(buffer.slice(0, bytes));
            Eif (!iter) {
              stream.emit('data', data);
            }

            data = (buff + data).split(/\n+/);

            const l = data.length - 1;
            let i = 0;

            for (; i < l; i++) {
              // eslint-disable-next-line eqeqeq
              Eif (options.start == null || row > options.start) {
                Eif (!iter) {
                  stream.emit('line', data[i]);
                } else {
                  iter(null, data[i]);
                }
              }
              row++;
            }

            buff = data[l];
            pos += bytes;
            return read();
          });
        }());
      });

      Eif (!iter) {
        return stream;
      }

      return stream.destroy;
    };