Simple, Extensible FTP Server in Pure JavaScript

Introduction
Usage
- FtpServer options:
  - host (string) - IP Address
  - options (object) - Configuration
File System Abstraction

Introduction

This is a simple but very configurable FTP server. Notable features include:

Abstracts out the fs module, so you can use any implementation, even on a per-user basis. This makes it possible for each user to have his/her own virtual file system, isolated from that of the system or other users.
Provides hooks for handling authentication, content modification, etc.
Supports TLS with explicit AUTH.

Installation

npm install ftpd

Usage

See example code in test.js

FtpServer options:

host (string) - IP Address

host is a string representation of the IP address clients use to connect to the FTP server. It's imperative that this actually reflects the remote IP the clients use to access the server, as this IP will be used in the establishment of PASV data connections. If this IP is not the one clients use to connect, you will see some strange behavior from the client side (hangs).

options (object) - Configuration

See test.js for a simple example. FtpServer accepts the following options:

Path Configurations

Both these need to be set - there are no defaults.

getInitialCwd: Gets the initial working directory for the user. Called after user is authenticated. This path is relative to the root directory. The user may escape their initial cwd.

Pattern: function(username, [callback(err, path)])
Arguments:
- username (string): the username to get CWD for
- callback (function, optional):

Examples:

Simplest usage, no callback, just return:

    getInitialCwd: function(connection) {
      return "/" + connection.username;
    }

Usage with callback:

    getInitialCwd: function(connection, callback) {
      var userDir = '/' + connection.username;
      fs.exists(userDir, function(exists) {
        if (exists) {
          callback(null, userDir);
        } else {
          fs.mkDir(userDir, function(err) {
            callback(err, userDir);
          });
        }
      });
    }
    // If the directory exists, callback immediately with that directory
    // If not, create the directory and callback possible error + directory

Typical cases where you would want/need the callback involve retrieving configurations from external datasources and suchlike.

getRoot: Gets the root directory for the user. This directory has the path '/' from the point of view of the user. The user is not able to escape this directory.

Pattern: function(connection, [callback(err, rootPath)])
Arguments:
- connection (object): the connection for which to get root
- callback (function, optional):

Examples:

    getRoot: function() {
      return process.cwd();
    }
    // The users will now enter at the '/' level, which is the directory passed to getInitialCwd.

Usage with callback:

    getRoot: function(connection, callback) {
      var rootPath = process.cwd() + '/' + connection.username;
      fs.exists(rootPath, function(exists) {
        if (exists) {
          callback(null, rootPath);
        } else {
          fs.mkDir(userDir, function(err) {
            if (err) {
              callback(null, '/'); // default to root
            } else {
              callback(err, rootPath);
            }
          });
        }
      });
    }
    // If the subdir exists, callback immediately with relative path to that directory
    // If not, create the directory, and callback relative path to the directory
    // Stupidly, instead of failing, we apparently want 'worst case' scenario to allow relative root.

Typical cases where you would want/need the callback involve retrieving configurations from external datasources and suchlike.
Additionally, you may want to provide emulation of a path, for instance /users/(username)/ftproot.

File/handling Configurations

useWriteFile: (default: false)
- If set to true, then files which the client uploads are buffered in memory and then written to disk using writeFile.
- If false, files are written using writeStream.
useReadFile: (default: false)
- If set to true, then files which the client downloads are slurped using 'readFile'.
- If false, files are read using readStream.
uploadMaxSlurpSize: (default: unlimited)
- Determines the maximum file size (in bytes) for which uploads are buffered in memory before being written to disk.
- Has an effect only if useWriteFile is set to true.
- If uploadMaxSlurpSize is not set, then there is no limit on buffer size.
hideDotFiles: (default: false)
- Hides files beginning with a dot (UNIX hidden files) on LIST commands.
maxStatsAtOnce: (default: 5)
- The maximum number of concurrent calls to fs.stat which will be made when processing a LIST request.
filenameSortFunc: (default: localeCompare)
- A function which can be used as the argument of an array's sort method. Used to sort filenames for directory listings.
  See [https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/Array/sort] for more info.
filenameSortMap: (default: function (x) { return x.toUpperCase() })
- A function which is applied to each filename before sorting.
- If set to false, filenames are unaltered.
dontSortFilenames: (default: false)
- If this is set, then filenames are not sorted in responses to the LIST and NLST commands.
noWildcards: (default: false)
- If set to true, then LIST and NLST treat the characters ? and * as literals instead of as wildcards.

Command configuration

allowedCommands: (default: undefined)
- List of strings, the server will respond to only commands contained in this list, all other commands will result in a 502 unimplemented error.

Connectivity settings

tlsOptions: (default: undefined)
- If this is set, the server will allow explicit TLS authentication.
- Value should be a dictionary which is suitable as the options argument of tls.createServer.
tlsOnly: (default: false)
- If this is set to true, and tlsOptions is also set, then the server will not allow logins over non-secure connections.
allowUnauthorizedTls: ?? I obviously set this to true when tlsOnly is on -someone needs to update this.
pasvPortRangeStart: (default: random?)
- Integer, specifies the lower-bound port (min port) for creating PASV connections
pasvPortRangeEnd: (default: random?)
- Integer, specifies the upper-bound port (max port) for creating PASV connections

Filesystem Abstraction

Filesystem abstraction makes it possible to create an FTP server which interacts directly with a database rather than the actual filesystem.

The server raises a command:pass event which is given pass, success and failure arguments. On successful login, success should be called with a username argument. It may also optionally be given a second argument, which should be an object providing an implementation of the API for Node's fs module.

The following must be implemented:

unlink
readdir
mkdir
open
close
rmdir
rename
stat →
- specific object properties: { mode, isDirectory(), size, mtime }
if useWriteFile option is not set or is false
- createWriteStream: Returns a writable stream, requiring:
  - events: 'open', 'error', 'finish'
  - functions: 'write', 'end'
  - properties: 'bytesWritten'
if useWriteFile option is set to 'true'
- writeFile
if useReadFile option is not set or is false
- createReadStream: Returns a readable stream, requiring:
  - events: 'error', 'data', 'end'
  - functions: 'destroy'
if useReadFile option is set to 'true'
- readFile