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
ThousandIsland.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.Logger` 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.
Thousand Island emits a rich set of telemetry events including spans for each
server, acceptor process, and individual client connection. These telemetry
events are documented in the `ThousandIsland.Telemetry` module.
"""
@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 `sockname/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 number of acceptor processes to run. Defaults to 100
* `num_connections`: The maximum number of concurrent connections which each acceptor will
accept before throttling connections. Connections will be throttled by having the acceptor
process wait `max_connections_retry_wait` milliseconds, up to `max_connections_retry_count`
times for existing connections to terminate & make room for this new connection. If there is
still no room for this new connection after this interval, the acceptor will close the client
connection and emit a `[:thousand_island, :acceptor, :spawn_error]` telemetry event. This number
is expressed per-acceptor, so the total number of maximum connections for a Thousand Island
server is `num_acceptors * num_connections`. Defaults to `16_384`
* `max_connections_retry_wait`: How long to wait during each iteration as described in
`num_connectors` above, in milliseconds. Defaults to `1000`
* `max_connections_retry_count`: How many iterations to wait as described in `num_connectors`
above. Defaults to `5`
* `read_timeout`: How long to wait for client data before closing the connection, in
milliseconds. Defaults to 60_000
* `shutdown_timeout`: How long to wait for existing client connections to complete before
forcibly shutting those connections down at server shutdown time, in milliseconds. Defaults to
15_000. May also be `:infinity` or `:brutal_kill` as described in the `Supervisor`
documentation
"""
@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(),
num_connections: non_neg_integer() | :infinity,
max_connections_retry_count: non_neg_integer(),
max_connections_retry_wait: timeout(),
read_timeout: timeout(),
shutdown_timeout: timeout()
]
@typedoc "A module implementing `ThousandIsland.Transport` behaviour"
@type transport_module :: ThousandIsland.Transports.TCP | ThousandIsland.Transports.SSL
@typedoc "A keyword list of options to be passed to the transport module's `listen/2` function"
@type transport_options() ::
ThousandIsland.Transports.TCP.options() | ThousandIsland.Transports.SSL.options()
@doc false
@spec child_spec(options()) :: Supervisor.child_spec()
def child_spec(opts) do
%{
id: {__MODULE__, make_ref()},
start: {__MODULE__, :start_link, [opts]},
type: :supervisor,
restart: :permanent
}
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
|> ThousandIsland.ServerConfig.new()
|> ThousandIsland.Server.start_link()
end
@doc """
Returns information about the address and port that the server is listening on
"""
@spec listener_info(Supervisor.supervisor()) ::
{:ok, ThousandIsland.Transport.socket_info()} | :error
def listener_info(supervisor) do
case ThousandIsland.Server.listener_pid(supervisor) do
nil -> :error
pid -> {:ok, ThousandIsland.Listener.listener_info(pid)}
end
end
@doc """
Gets a list of active connection processes. This is inherently a bit of a leaky notion in the
face of concurrency, as there may be connections coming and going during the period that this
function takes to run. Callers should account for the possibility that new connections may have
been made since / during this call, and that processes returned by this call may have since
completed. The order that connection processes are returned in is not specified
"""
@spec connection_pids(Supervisor.supervisor()) :: {:ok, [pid()]} | :error
def connection_pids(supervisor) do
case ThousandIsland.Server.acceptor_pool_supervisor_pid(supervisor) do
nil -> :error
acceptor_pool_pid -> {:ok, collect_connection_pids(acceptor_pool_pid)}
end
end
@doc """
Suspend the server. This will close the listening port, and will stop the acceptance of new
connections. Existing connections will stay connected and will continue to be processed.
The server can later be resumed by calling `resume/1`, or shut down via standard supervision
patterns.
If this function returns `:error`, it is unlikely that the server is in a useable state
Note that if you do not explicitly set a port (or if you set port to `0`), then the server will
bind to a different port when you resume it. This new port can be obtained as usual via the
`listener_info/1` function. This is not a concern if you explicitly set a port value when first
instantiating the server
"""
defdelegate suspend(supervisor), to: ThousandIsland.Server
@doc """
Resume a suspended server. This will reopen the listening port, and resume the acceptance of new
connections
"""
defdelegate resume(supervisor), to: ThousandIsland.Server
defp collect_connection_pids(acceptor_pool_pid) do
acceptor_pool_pid
|> ThousandIsland.AcceptorPoolSupervisor.acceptor_supervisor_pids()
|> Enum.reduce([], fn acceptor_sup_pid, acc ->
case ThousandIsland.AcceptorSupervisor.connection_sup_pid(acceptor_sup_pid) do
nil -> acc
connection_sup_pid -> connection_pids(connection_sup_pid, acc)
end
end)
end
defp connection_pids(connection_sup_pid, acc) do
connection_sup_pid
|> DynamicSupervisor.which_children()
|> Enum.reduce(acc, fn
{_, connection_pid, _, _}, acc when is_pid(connection_pid) ->
[connection_pid | acc]
_, acc ->
acc
end)
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(Supervisor.supervisor(), timeout()) :: :ok
def stop(supervisor, connection_wait \\ 15_000) do
Supervisor.stop(supervisor, :normal, connection_wait)
end
end
