surveil

API Documentation

Watches a directory for new files and deletions, attempting to delay events until initial file creation is complete. Watches files in the directory for changes. Separates events for child files and directories. Also watches single files and doesn't require an alternate API to do so. Behaves gracefully when the watched path does not exist yet, emitting add with no filename when it appears.

Shares stat calls gathered during early setup so you don't have to duplicate any of the work surveil is already doing. This sort of efficiency trick can pay big dividends when querying against spinning rust.

Why

I tried a bunch of existing libs and they all exhibited blocking issues when faced with directories containing lots of files. On source examination I found a lot of use of fs.statSync and other Sync calls. This quickly made me disatisfied with the state of the art in Node.js file watching at the time. Surveil is much more performant in adverse conditions. While most watcher libs are designed to support task runners and other applications that can take their time starting up, surveil never assumes the caller doesn't care how long something blocks. Finally, because surveil was designed on windows and later tested for *nix it boasts superior cross-platform reliability.

Installation

$ npm install surveil

Running Tests

$ npm test

Usage

If the target path does not exist yet, you will receive an add event with no filename argument each time it appears. surveil will then gracefully watch the path whenever it exists.

var path = require ('path');
var surveil = require ('surveil');

var subjectDir = surveil (
  "super/secret/files/",
  { // options argument is optional - defaults shown
    /*
      `change` events closer together than
      this are grouped into one. Implies a
      minimum latency to `change` events
      being fired. (in milliseconds)
    */
    changeTimeout:    150,
    /*
      Number of times to retry establishing
      a file watch when receiving the
      `EPERM` event from the filesystem.
    */
    epermRetries:     5,
    /*
      Proper support for missing path
      features hasn't landed yet. For now a
      simple poll timeout is used to test
      the surveil'd path. (in milliseconds)
    */
    hack_missingPoll: 1000,
    /*
      Only accept files with names ending
      in one of the provided extensions.
      If the period is required you must
      specify it. Directories are not
      affected by filename filters.
      Default: undefined
    */
    extensions:       [
      ".jpg",
      ".jpeg",
      ".png",
      ".gif"
    ],
    /*
      Only accept files with names
      matching at least one of the
      provided regular expressions. Does
      not apply when `extensions` is set.
      Directories are not affected by
      filename filters.
      Default: undefined
    */
    patterns:         [
      /report/,
      /sallary/,
      /\.xls$/
    ],
    /*
      EXPERIMENTAL FEATURE (NO TESTS)
      Watches a directory recursively
      and emits normal events with local
      paths.
    */
    recursive:        true
  }
);

subjectDir.on ('ready', function (err) {
  // if present, the `err` argument will also
  // trigger an `error` event
});

subjectDir.on ('child', function (filename, stats) {
  // shares the `stat` call used to discover files
  // filename must match any filters present
  // only emitted before the "ready" event has fired
});

subjectDir.on ('childDir', function (dirname, stats) {
  // shares the `stat` call used to discover directories
  // dirname may not match any filters present
  // only emitted before the "ready" event has fired
});

subjectDir.on ('add', function (filename, stats) {
  // a new file has been added and the initial
  // content write operation appears to have
  // concluded.
  // if no arguments are passed, the watched path
  // was missing and has appeared.
  // If filename filters are present, filename will
  // conform to them.
});

subjectDir.on ('addDir', function (dirname, stats) {
  // a new subdirectory has appeared
  // it may not conform to any filename filters present
});

subjectDir.on ('remove', function (filename) {
  // a file has been removed.
  // If no filename argument is passed, the watched
  // path has disappeared.
});

subjectDir.on ('change', function (filename) {
  // a file change event or rapid group of
  // such events has just occured.
  // no new stat call is made, therefor none is shared.
  // If the watched path is a file, no filename
  // argument is passed.
});

LICENSE

The MIT License (MIT)

Copyright (c) 2017 Kevin "Schmidty" Smith

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.