agneta-platform/services/server/boot/process/logs/tail.js

Agneta Platform - Integrate and customize business applications

/*   Copyright 2017 Agneta Network Applications, LLC.
 *
 *   Source file: services/server/boot/process/logs/tail.js
 *
 *   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.
 */
const chokidar = require('chokidar');
const fs = require('fs-extra');
const os = require('os');
const Promise = require('bluebird');
const EventEmitter = require('events').EventEmitter;

function Tail(filename, options) {

  options = Object.assign(options || {}, {
    alwaysStat: true,
    ignoreInitial: false,
    persistent: true,
  });

  var watcher;
  var fd;
  var emitter = new EventEmitter();

  function closeFile() {
    return fs.close(fd);
  }

  function readLast() {
    var chunk = 30000;
    return fs.stat(filename)
      .then(function(stats) {
        return onChange(filename, chunk, stats.size - chunk);
      });
  }

  function watch() {

    if (watcher) {
      console.warn('already watching');
      return;
    }

    var lastSize = fs.statSync(filename).size;
    var pending = false;
    watcher = chokidar.watch(filename, options)
      .on('change', function(path) {

        if (pending) {
          return;
        }

        pending = true;
        var stats;

        return Promise.resolve()
          .then(function() {
            return Promise.delay(400);
          })
          .then(function() {

            stats = fs.statSync(filename);
            var diff = stats.size - lastSize;
            if (diff > 0) {

              return onChange(path, diff, lastSize)
                .then(function(result) {
                  emitter.emit('change', result);
                });

            }

          })
          .then(function() {
            return Promise.delay(300);
          })
          .then(function() {
            lastSize = stats.size;
            pending = false;
          });


      })
      .on('unlink', () => {
        lastSize = 0;
        closeFile.bind(this);
      });
  }

  function onChange(path, diff, position) {

    const buffer = new Buffer(diff);
    fd = fs.openSync(path, 'r');

    return fs.read(fd, buffer, 0, diff, position)
      .then(function() {
        fs.closeSync(fd);
        var entries = buffer.toString('utf8');
        entries = entries.split('>> ');
        entries.shift(1);

        var entriesFinal = [];
        var lastEntry = {};

        return Promise.map(entries, function(entry) {
          entry = entry.split(' :: ');
          var date = entry[0];
          var message = entry[1];
          if(!message){
            return;
          }
          var lines = message.split(os.EOL);
          var linesFinal = [];
          return Promise.map(lines, function(line) {
            if (!line || !line.length) {
              return;
            }
            linesFinal.push(line);
          })
            .then(function() {

              if (lastEntry.date != date) {

                lastEntry = {
                  date: date,
                  lines: linesFinal
                };

                entriesFinal.push(lastEntry);

              } else {
                lastEntry.lines = lastEntry.lines.concat(linesFinal);
              }
            });

        })
          .then(function() {
            return entriesFinal;
          });
      });

  }

  function close() {
    if (watcher) {
      watcher.unwatch(filename);
      watcher.close();
      watcher = undefined;
    }
  }

  return {
    emitter: emitter,
    close: close,
    watch: watch,
    readLast: readLast
  };
}

module.exports = Tail;