Bifrost

Pluggable Erlang FTP Server

Then spoke Gangleri: "Does fire burn over Bifrost?" High said: "The red you see in the rainbow is burning fire. The frost-giants and mountain-giants would go up into heaven if Bifrost was crossable by everyone that wanted to go."

Description

Bifrost is an implementation of the FTP protocol that enables you to create an FTP server without worrying about the protocol details. Many legacy business systems still use FTP heavily for data transmission, and Bifrost can help bridge the gap between them and modern distributed systems. For example, using Bifrost you can pretty easily write an FTP server that serves files from Amazon's S3 and a Postgres SQL server instead of a filesystem.

Bifrost also includes FTP/SSL support, if you supply a certificate.

TODO

• Document interface
• Add real sample application with included supervisor, not just a gen_server.

Usage

See memory_server.erl, a somewhat-feature-complete-but-completely-useless in-memory FTP server for an example implementation.

Create a module with the gen_bifrost_server behaviour and implement all of the callbacks. Documentation is on its way, but until then memory_server will unfortunately have to suffice.

gen_bifrost_server

bifrost retains state for each connection which is stored in a record type connection_state. This state is passed into every gen_bifrost_server callback, and many of the callbacks should return a state.

-record(connection_state,
        {
          authenticated_state = AuthState,
          user_name = String,
          data_port = DataPort,
          pasv_listen = PasvPort,
          ip_address = IpAddress, % FTP server IP
          rnfr = String, % used by RNFR, RNTO
          module = GenBifrostServerModule,
          module_state = ModuleInternalState, % can be anything
          ssl_allowed = Boolean,
          ssl_cert = Path,
          ssl_key = Path,
          ssl_ca_cert = Path,
          protection_mode = ProtectionMode,
          pb_size = 0,
          control_socket = Socket,
          ssl_socket = Socket
         }).

• AuthState = authenticated | unauthenticated
• DataPort = {active, IpAddress, Port}
• PasvPort = {passive, Socket, {IpAddress, Port}}
• ProtectionMode = clear | private

In your application supervisor add a bifrost child:

my_supervisor.erl

init([]) ->
  GenBifrostServerModule = some_module,
  ExternalIpAddress = {127,0,0,1},
  Port = 21,
  {ok, { {one_for_one, 5, 10},
         [{bifrost,
           {bifrost,
            start_link,
            [GenBifrostServerModule, [{ip_address, ExternalIpAddress}, {port, Port}]]},
           permanent,
           5000,
           worker,
           [bifrost]}]}}.

SSL

Bifrost includes implicit FTP/SSL support. To use this functionality, just add some additional startup options to the start_link call.

• ssl should be true.
• ssl_key should be the path to the PEM-encoded private key file.
• ssl_cert should be the path to the PEM-encoded certificate file.
• ssl_ca_cert should be the path to the CA's PEM-encoded certificate file.

Contributions

Bifrost is being used in production environments, and has proven itself reliable. That being said, there are undoubtedly bugs and things that can be improved. Please feel free to submit issues (and pull requests!).

License

Copyright (C) 2012-2013 Ryan Crum

Distributed under the MIT License.