Introduction

The FTP server consists of the following parts:

• Account management
  • Membership providers (e.g. for anonymous users, PAM, etc...)
  • Member information (e.g. home directories, etc...)
• Authentication
  • Authentication mechanisms (e.g. AUTH TLS)
• Authorization
  • Authorization mechanisms (e.g. password)
  • Authorization actions (e.g. for setting the home directory)
• Commands (e.g. LIST)
• File systems
  • .NET I/O
  • Google Drive
  • Unix
  • In-memory

Account management

The account management is centered around the following interfaces:

• IMembershipProvider for username/password authentication
• IAccountDirectoryQuery to get the users root and home directories

The IMembershipProvider is only useful for password-based authorization mechanisms.

Authentication

There is currently only one authentication mechanism implemented: TLS.

Authorization

Only one authorization mechanism is implemented: PasswordAuthorization.

Every authorization mechanism is centered around three commands:

• USER: Provides the user name
• PASS: Provides the password
• ACCT: Provides additional information

The full state machine for an authentication/authorization can be found in RFC 2228.

Commands

All commands are implemented as thread-safe singletons. This is a requirement due to the fact that commands can provide extensions that will show up during a FEAT request.

There are two kinds of extensions:

• FEAT-Extensions (provided by a FTP command handler)
• Extensions hosted by an FTP command, like OPTS or SITE

The FEAT extensions are only there to tell the client that some commands support special features.

Extensions can also be attached to a command that is also an extension host, like OPTS or SITE. Those extensions are reported to the FEAT command through the extension hosts.

File systems

File systems are discussed here