defmodule ThousandIsland do
@moduledoc """
Thousand Island is a modern, pure Elixir socket server, inspired heavily by
[ranch](https://github.com/ninenines/ranch). It aims to be easy to understand
& reason about, while also being at least as stable and performant as alternatives.
Thousand Island is implemented as a supervision tree which is intended to be hosted
inside a host application, often as a dependency embedded within a higher-level
protocol library such as [Bandit](https://github.com/mtrudel/bandit). Aside from
supervising the Thousand Island process tree, applications interact with Thousand
Island primarily via the `ThousandIsland.Handler` behaviour.
## Handlers
The `ThousandIsland.Handler` behaviour defines the interface that Thousand Island
uses to pass `ThousandIsland.Socket`s up to the application level; together they
form the primary interface that most applications will have with Thousand Island.
Thousand Island comes with a few simple protocol handlers to serve as examples;
these can be found in the [examples](https://github.com/mtrudel/thousand_island/tree/main/examples)
folder of this project. A simple implementation would look like this:
```elixir
defmodule Echo do
use ThousandIsland.Handler
@impl ThousandIsland.Handler
def handle_data(data, socket, state) do
ThousandIsland.Socket.send(socket, data)
{:continue, state}
end
end
{:ok, pid} = ThousandIsland.start_link(port: 1234, handler_module: Echo)
```
For more information, please consult the `ThousandIsland.Handler` documentation.
## Starting a Thousand Island Server
A typical use of `ThousandIsland` might look like the following:
```elixir
defmodule MyApp.Supervisor do
# ... other Supervisor boilerplate
def init(config) do
children = [
# ... other children as dictated by your app
{ThousandIsland, port: 1234, handler_module: MyApp.ConnectionHandler}
]
Supervisor.init(children, strategy: :one_for_one)
end
end
```
You can also start servers directly via the `start_link/1` function:
```elixir
{:ok, pid} = ThousandIsland.start_link(port: 1234, handler_module: MyApp.ConnectionHandler)
```
## Configuration
A number of options are defined when starting a server. The complete list is
defined by the `t:ThousandIsland.options/0` type.
## Connection Draining & Shutdown
`ThousandIsland` instances are just a process tree consisting of standard
Supervisor, GenServer and Task modules, and so the usual rules regarding
shutdown and shutdown timeouts apply. Immediately upon beginning the shutdown
sequence the ThousandIsland.ShutdownListener process will cause the listening socket
to shut down, which in turn will cause all of the `Acceptor` processes to shut
down as well. At this point all that is left in the supervision tree are several
layers of Supervisors and whatever `Handler` processes were in progress when
shutdown was initiated. At this point, standard Supervisor shutdown timeout
semantics give existing connections a chance to finish things up. `Handler`
processes trap exit, so they continue running beyond shutdown until they either
complete or are `:brutal_kill`ed after their shutdown timeout expires.
## Logging & Telemetry
As a low-level library, Thousand Island purposely does not do any inline
logging of any kind. The `ThousandIsland.Logging` module defines a number of
functions to aid in tracing connections at various log levels, and such logging
can be dynamically enabled and disabled against an already running server. This
logging is backed by `:telemetry` events internally, and if desired these events
can also be hooked by your application for logging or metric purposes. The following is a complete list of events emitted by Thousand Island:
* `[:listener, :start]`: Emitted when the server successfully listens on the configured port.
* `[:listener, :error]`: Emitted when the server encounters an error listening on the configured port.
* `[:listener, :shutdown]`: Emitted when the server shuts down.
* `[:acceptor, :start]`: Emitted when an acceptor process starts up.
* `[:acceptor, :accept]`: Emitted when an acceptor process accepts a new client connection.
* `[:acceptor, :shutdown]`: Emitted when an acceptor process shuts down.
* `[:handler, :start]`: Emitted whenever a `ThousandIsland.Handler` process is made ready
* `[:handler, :async_recv]`: Emitted whenever a `ThousandIsland.Handler` process receives data asynchronously
* `[:handler, :shutdown]`: Emitted whenever a `ThousandIsland.Handler` process terminates
* `[:handler, :error]`: Emitted whenever a `ThousandIsland.Handler` process shuts down due to error
* `[:socket, :handshake]`: Emitted whenever a `ThousandIsland.Socket.handshake/1` call completes.
* `[:socket, :handshake_error]`: Emitted whenever a `ThousandIsland.Socket.handshake/1` call errors.
* `[:socket, :recv]`: Emitted whenever a `ThousandIsland.Socket.recv/3` call completes.
* `[:socket, :send]`: Emitted whenever a `ThousandIsland.Socket.send/2` call completes.
* `[:socket, :sendfile]`: Emitted whenever a `ThousandIsland.Socket.sendfile/4` call completes.
* `[:socket, :shutdown]`: Emitted whenever a `ThousandIsland.Socket.shutdown/2` call completes.
* `[:socket, :close]`: Emitted whenever a `ThousandIsland.Socket.close/1` call completes.
Where meaurements indicate a time duration they are are expressed in `System`
`:native` units for performance reasons. They can be conveted to any desired
time unit via `System.convert_time_unit/3`.
"""
@typedoc """
Possible options to configure a server. Valid option values are as follows:
* `handler_module`: The name of the module used to handle connections to this server.
The module is expected to implement the `ThousandIsland.Handler` behaviour. Required.
* `handler_options`: A term which is passed as the initial state value to
`c:ThousandIsland.Handler.handle_connection/2` calls. Optional, defaulting to nil.
* `genserver_options`: A term which is passed as the value to the handler module's
underlying `GenServer.start_link/3` call. Optional, defaulting to [].
* `port`: The TCP port number to listen on. If not specified this defaults to 4000.
If a port number of `0` is given, the server will dynamically assign a port number
which can then be obtained via `local_info/1`.
* `transport_module`: The name of the module which provides basic socket functions.
Thousand Island provides `ThousandIsland.Transports.TCP` and `ThousandIsland.Transports.SSL`,
which provide clear and TLS encrypted TCP sockets respectively. If not specified this
defaults to `ThousandIsland.Transports.TCP`.
* `transport_options`: A keyword list of options to be passed to the transport module's
`c:ThousandIsland.Transport.listen/2` function. Valid values depend on the transport
module specified in `transport_module` and can be found in the documentation for the
`ThousandIsland.Transports.TCP` and `ThousandIsland.Transports.SSL` modules. Any options
in terms of interfaces to listen to / certificates and keys to use for SSL connections
will be passed in via this option.
* `num_acceptors`: The numbner of acceptor processes to run. Defaults to 10.
"""
@type options :: [
handler_module: module(),
handler_options: term(),
genserver_options: GenServer.options(),
port: :inet.port_number(),
transport_module: module(),
transport_options: transport_options(),
num_acceptors: pos_integer(),
read_timeout: timeout()
]
@type transport_options() ::
ThousandIsland.Transports.TCP.options() | ThousandIsland.Transports.SSL.options()
alias ThousandIsland.{Listener, Server, ServerConfig, Transport}
@doc false
@spec child_spec(options()) :: Supervisor.child_spec()
def child_spec(opts) do
%{
id: __MODULE__,
start: {__MODULE__, :start_link, [opts]},
type: :supervisor,
restart: :permanent,
shutdown: 5000
}
end
@doc """
Starts a `ThousandIsland` instance with the given options. Returns a pid
that can be used to further manipulate the server via other functions defined on
this module in the case of success, or an error tuple describing the reason the
server was unable to start in the case of failure.
"""
@spec start_link(options()) :: Supervisor.on_start()
def start_link(opts \\ []) do
opts
|> ServerConfig.new()
|> Server.start_link()
end
@doc """
Returns information about the address and port that the server is listening on
"""
@spec listener_info(pid()) :: {:ok, Transport.socket_info()}
def listener_info(pid) do
pid |> Server.listener_pid() |> Listener.listener_info()
end
@doc """
Synchronously stops the given server, waiting up to the given number of milliseconds
for existing connections to finish up. Immediately upon calling this function,
the server stops listening for new connections, and then proceeds to wait until
either all existing connections have completed or the specified timeout has
elapsed.
"""
@spec stop(pid(), timeout()) :: :ok
def stop(pid, connection_wait \\ 15_000) do
Supervisor.stop(pid, :normal, connection_wait)
end
end
