defmodule Phoenix.Socket do
@moduledoc ~S"""
A socket implementation that multiplexes messages over channels.
`Phoenix.Socket` is used as a module for establishing and maintaining
the socket state via the `Phoenix.Socket` struct.
Once connected to a socket, incoming and outgoing events are routed to
channels. The incoming client data is routed to channels via transports.
It is the responsibility of the socket to tie transports and channels
together.
Phoenix supports `websocket` and `longpoll` options when invoking
`Phoenix.Endpoint.socket/3` in your endpoint. `websocket` is set by default
and `longpoll` can also be configured explicitly.
socket "/socket", MyAppWeb.Socket, websocket: true, longpoll: false
The command above means incoming socket connections can be made via
a WebSocket connection. Events are routed by topic to channels:
channel "room:lobby", MyAppWeb.LobbyChannel
See `Phoenix.Channel` for more information on channels.
## Socket Behaviour
Socket handlers are mounted in Endpoints and must define two callbacks:
* `connect/3` - receives the socket params, connection info if any, and
authenticates the connection. Must return a `Phoenix.Socket` struct,
often with custom assigns
* `id/1` - receives the socket returned by `connect/3` and returns the
id of this connection as a string. The `id` is used to identify socket
connections, often to a particular user, allowing us to force disconnections.
For sockets requiring no authentication, `nil` can be returned
## Examples
defmodule MyAppWeb.UserSocket do
use Phoenix.Socket
channel "room:*", MyAppWeb.RoomChannel
def connect(params, socket, _connect_info) do
{:ok, assign(socket, :user_id, params["user_id"])}
end
def id(socket), do: "users_socket:#{socket.assigns.user_id}"
end
# Disconnect all user's socket connections and their multiplexed channels
MyAppWeb.Endpoint.broadcast("users_socket:" <> user.id, "disconnect", %{})
## Socket fields
* `:id` - The string id of the socket
* `:assigns` - The map of socket assigns, default: `%{}`
* `:channel` - The current channel module
* `:channel_pid` - The channel pid
* `:endpoint` - The endpoint module where this socket originated, for example: `MyAppWeb.Endpoint`
* `:handler` - The socket module where this socket originated, for example: `MyAppWeb.UserSocket`
* `:joined` - If the socket has effectively joined the channel
* `:join_ref` - The ref sent by the client when joining
* `:ref` - The latest ref sent by the client
* `:pubsub_server` - The registered name of the socket's pubsub server
* `:topic` - The string topic, for example `"room:123"`
* `:transport` - An identifier for the transport, used for logging
* `:transport_pid` - The pid of the socket's transport process
* `:serializer` - The serializer for socket messages
## Using options
On `use Phoenix.Socket`, the following options are accepted:
* `:log` - the default level to log socket actions. Defaults
to `:info`. May be set to `false` to disable it
* `:partitions` - each channel is spawned under a supervisor.
This option controls how many supervisors will be spawned
to handle channels. Defaults to the number of cores.
## Garbage collection
It's possible to force garbage collection in the transport process after
processing large messages. For example, to trigger such from your channels,
run:
send(socket.transport_pid, :garbage_collect)
Alternatively, you can configure your endpoint socket to trigger more
fullsweep garbage collections more frequently, by setting the `:fullsweep_after`
option for websockets. See `Phoenix.Endpoint.socket/3` for more info.
## Client-server communication
The encoding of server data and the decoding of client data is done
according to a serializer, defined in `Phoenix.Socket.Serializer`.
By default, JSON encoding is used to broker messages to and from clients.
The serializer `decode!` function must return a `Phoenix.Socket.Message`
which is forwarded to channels except:
* `"heartbeat"` events in the "phoenix" topic - should just emit an OK reply
* `"phx_join"` on any topic - should join the topic
* `"phx_leave"` on any topic - should leave the topic
Each message also has a `ref` field which is used to track responses.
The server may send messages or replies back. For messages, the
ref uniquely identifies the message. For replies, the ref matches
the original message. Both data-types also include a join_ref that
uniquely identifies the currently joined channel.
The `Phoenix.Socket` implementation may also send special messages
and replies:
* `"phx_error"` - in case of errors, such as a channel process
crashing, or when attempting to join an already joined channel
* `"phx_close"` - the channel was gracefully closed
Phoenix ships with a JavaScript implementation of both websocket
and long polling that interacts with Phoenix.Socket and can be
used as reference for those interested in implementing custom clients.
## Custom sockets and transports
See the `Phoenix.Socket.Transport` documentation for more information on
writing your own socket that does not leverage channels or for writing
your own transports that interacts with other sockets.
## Custom channels
You can list any module as a channel as long as it implements
a `child_spec/1` function. The `child_spec/1` function receives
the caller as argument and it must return a child spec that
initializes a process.
Once the process is initialized, it will receive the following
message:
{Phoenix.Channel, auth_payload, from, socket}
A custom channel implementation MUST invoke
`GenServer.reply(from, {:ok | :error, reply_payload})` during its
initialization with a custom `reply_payload` that will be sent as
a reply to the client. Failing to do so will block the socket forever.
A custom channel receives `Phoenix.Socket.Message` structs as regular
messages from the transport. Replies to those messages and custom
messages can be sent to the socket at any moment by building an
appropriate `Phoenix.Socket.Reply` and `Phoenix.Socket.Message`
structs, encoding them with the serializer and dispatching the
serialized result to the transport.
For example, to handle "phx_leave" messages, which is recommended
to be handled by all channel implementations, one may do:
def handle_info(
%Message{topic: topic, event: "phx_leave"} = message,
%{topic: topic, serializer: serializer, transport_pid: transport_pid} = socket
) do
send transport_pid, serializer.encode!(build_leave_reply(message))
{:stop, {:shutdown, :left}, socket}
end
We also recommend all channels to monitor the `transport_pid`
on `init` and exit if the transport exits. We also advise to rewrite
`:normal` exit reasons (usually due to the socket being closed)
to the `{:shutdown, :closed}` to guarantee links are broken on
the channel exit (as a `:normal` exit does not break links):
def handle_info({:DOWN, _, _, transport_pid, reason}, %{transport_pid: transport_pid} = socket) do
reason = if reason == :normal, do: {:shutdown, :closed}, else: reason
{:stop, reason, socket}
end
Any process exit is treated as an error by the socket layer unless
a `{:socket_close, pid, reason}` message is sent to the socket before
shutdown.
Custom channel implementations cannot be tested with `Phoenix.ChannelTest`
and are currently considered experimental. The underlying API may be
changed at any moment.
"""
require Logger
require Phoenix.Endpoint
alias Phoenix.Socket
alias Phoenix.Socket.{Broadcast, Message, Reply}
@doc """
Receives the socket params and authenticates the connection.
## Socket params and assigns
Socket params are passed from the client and can
be used to verify and authenticate a user. After
verification, you can put default assigns into
the socket that will be set for all channels, ie
{:ok, assign(socket, :user_id, verified_user_id)}
To deny connection, return `:error`.
See `Phoenix.Token` documentation for examples in
performing token verification on connect.
"""
@callback connect(params :: map, Socket.t) :: {:ok, Socket.t} | {:error, term} | :error
@callback connect(params :: map, Socket.t, connect_info :: map) :: {:ok, Socket.t} | {:error, term} | :error
@doc ~S"""
Identifies the socket connection.
Socket IDs are topics that allow you to identify all sockets for a given user:
def id(socket), do: "users_socket:#{socket.assigns.user_id}"
Would allow you to broadcast a `"disconnect"` event and terminate
all active sockets and channels for a given user:
MyAppWeb.Endpoint.broadcast("users_socket:" <> user.id, "disconnect", %{})
Returning `nil` makes this socket anonymous.
"""
@callback id(Socket.t) :: String.t | nil
@optional_callbacks connect: 2, connect: 3
defmodule InvalidMessageError do
@moduledoc """
Raised when the socket message is invalid.
"""
defexception [:message]
end
defstruct assigns: %{},
channel: nil,
channel_pid: nil,
endpoint: nil,
handler: nil,
id: nil,
joined: false,
join_ref: nil,
private: %{},
pubsub_server: nil,
ref: nil,
serializer: nil,
topic: nil,
transport: nil,
transport_pid: nil
@type t :: %Socket{
assigns: map,
channel: atom,
channel_pid: pid,
endpoint: atom,
handler: atom,
id: String.t | nil,
joined: boolean,
ref: term,
private: map,
pubsub_server: atom,
serializer: atom,
topic: String.t,
transport: atom,
transport_pid: pid,
}
defmacro __using__(opts) do
quote do
## User API
import Phoenix.Socket
@behaviour Phoenix.Socket
@before_compile Phoenix.Socket
Module.register_attribute(__MODULE__, :phoenix_channels, accumulate: true)
@phoenix_socket_options unquote(opts)
## Callbacks
@behaviour Phoenix.Socket.Transport
@doc false
def child_spec(opts) do
Phoenix.Socket.__child_spec__(__MODULE__, opts, @phoenix_socket_options)
end
@doc false
def connect(map), do: Phoenix.Socket.__connect__(__MODULE__, map, @phoenix_socket_options)
@doc false
def init(state), do: Phoenix.Socket.__init__(state)
@doc false
def handle_in(message, state), do: Phoenix.Socket.__in__(message, state)
@doc false
def handle_info(message, state), do: Phoenix.Socket.__info__(message, state)
@doc false
def terminate(reason, state), do: Phoenix.Socket.__terminate__(reason, state)
end
end
## USER API
@doc """
Adds key-value pairs to socket assigns.
A single key-value pair may be passed, a keyword list or map
of assigns may be provided to be merged into existing socket
assigns.
## Examples
iex> assign(socket, :name, "Elixir")
iex> assign(socket, name: "Elixir", logo: "💧")
"""
def assign(%Socket{} = socket, key, value) do
assign(socket, [{key, value}])
end
def assign(%Socket{} = socket, attrs)
when is_map(attrs) or is_list(attrs) do
%{socket | assigns: Map.merge(socket.assigns, Map.new(attrs))}
end
@doc """
Defines a channel matching the given topic and transports.
* `topic_pattern` - The string pattern, for example `"room:*"`, `"users:*"`,
or `"system"`
* `module` - The channel module handler, for example `MyAppWeb.RoomChannel`
* `opts` - The optional list of options, see below
## Options
* `:assigns` - the map of socket assigns to merge into the socket on join
## Examples
channel "topic1:*", MyChannel
## Topic Patterns
The `channel` macro accepts topic patterns in two flavors. A splat (the `*`
character) argument can be provided as the last character to indicate a
`"topic:subtopic"` match. If a plain string is provided, only that topic will
match the channel handler. Most use-cases will use the `"topic:*"` pattern to
allow more versatile topic scoping.
See `Phoenix.Channel` for more information
"""
defmacro channel(topic_pattern, module, opts \\ []) do
module = expand_alias(module, __CALLER__)
opts =
if Macro.quoted_literal?(opts) do
Macro.prewalk(opts, &expand_alias(&1, __CALLER__))
else
opts
end
quote do
@phoenix_channels {unquote(topic_pattern), unquote(module), unquote(opts)}
end
end
defp expand_alias({:__aliases__, _, _} = alias, env),
do: Macro.expand(alias, %{env | function: {:channel, 3}})
defp expand_alias(other, _env), do: other
@doc false
@deprecated "transport/3 in Phoenix.Socket is deprecated and has no effect"
defmacro transport(_name, _module, _config \\ []) do
:ok
end
defmacro __before_compile__(env) do
channels = Module.get_attribute(env.module, :phoenix_channels)
channel_defs =
for {topic_pattern, module, opts} <- channels do
topic_pattern
|> to_topic_match()
|> defchannel(module, opts)
end
quote do
unquote(channel_defs)
def __channel__(_topic), do: nil
end
end
defp to_topic_match(topic_pattern) do
case String.split(topic_pattern, "*") do
[prefix, ""] -> quote do: <<unquote(prefix) <> _rest>>
[bare_topic] -> bare_topic
_ -> raise ArgumentError, "channels using splat patterns must end with *"
end
end
defp defchannel(topic_match, channel_module, opts) do
quote do
def __channel__(unquote(topic_match)), do: unquote({channel_module, Macro.escape(opts)})
end
end
## CALLBACKS IMPLEMENTATION
def __child_spec__(handler, opts, socket_options) do
endpoint = Keyword.fetch!(opts, :endpoint)
opts = Keyword.merge(socket_options, opts)
partitions = Keyword.get(opts, :partitions, System.schedulers_online())
args = {endpoint, handler, partitions}
Supervisor.child_spec({Phoenix.Socket.PoolSupervisor, args}, id: handler)
end
def __connect__(user_socket, map, socket_options) do
%{
endpoint: endpoint,
options: options,
transport: transport,
params: params,
connect_info: connect_info
} = map
vsn = params["vsn"] || "1.0.0"
options = Keyword.merge(socket_options, options)
start = System.monotonic_time()
case negotiate_serializer(Keyword.fetch!(options, :serializer), vsn) do
{:ok, serializer} ->
result = user_connect(user_socket, endpoint, transport, serializer, params, connect_info)
metadata = %{
endpoint: endpoint,
transport: transport,
params: params,
connect_info: connect_info,
vsn: vsn,
user_socket: user_socket,
log: Keyword.get(options, :log, :info),
result: result(result),
serializer: serializer
}
duration = System.monotonic_time() - start
:telemetry.execute([:phoenix, :socket_connected], %{duration: duration}, metadata)
result
:error ->
:error
end
end
defp result({:ok, _}), do: :ok
defp result(:error), do: :error
defp result({:error, _}), do: :error
def __init__({state, %{id: id, endpoint: endpoint} = socket}) do
_ = id && endpoint.subscribe(id, link: true)
{:ok, {state, %{socket | transport_pid: self()}}}
end
def __in__({payload, opts}, {state, socket}) do
%{topic: topic} = message = socket.serializer.decode!(payload, opts)
handle_in(Map.get(state.channels, topic), message, state, socket)
end
def __info__({:DOWN, ref, _, pid, reason}, {state, socket}) do
case state.channels_inverse do
%{^pid => {topic, join_ref}} ->
state = delete_channel(state, pid, topic, ref)
{:push, encode_on_exit(socket, topic, join_ref, reason), {state, socket}}
%{} ->
{:ok, {state, socket}}
end
end
def __info__(%Broadcast{event: "disconnect"}, state) do
{:stop, {:shutdown, :disconnected}, state}
end
def __info__({:socket_push, opcode, payload}, state) do
{:push, {opcode, payload}, state}
end
def __info__({:socket_close, pid, _reason}, {state, socket}) do
socket_close(pid, {state, socket})
end
def __info__(:garbage_collect, state) do
:erlang.garbage_collect(self())
{:ok, state}
end
def __info__(_, state) do
{:ok, state}
end
def __terminate__(_reason, _state_socket) do
:ok
end
defp negotiate_serializer(serializers, vsn) when is_list(serializers) do
case Version.parse(vsn) do
{:ok, vsn} ->
serializers
|> Enum.find(:error, fn {_serializer, vsn_req} -> Version.match?(vsn, vsn_req) end)
|> case do
{serializer, _vsn_req} ->
{:ok, serializer}
:error ->
Logger.error "The client's requested transport version \"#{vsn}\" " <>
"does not match server's version requirements of #{inspect serializers}"
:error
end
:error ->
Logger.error "Client sent invalid transport version \"#{vsn}\""
:error
end
end
defp user_connect(handler, endpoint, transport, serializer, params, connect_info) do
# The information in the Phoenix.Socket goes to userland and channels.
socket = %Socket{
handler: handler,
endpoint: endpoint,
pubsub_server: endpoint.config(:pubsub_server),
serializer: serializer,
transport: transport
}
# The information in the state is kept only inside the socket process.
state = %{
channels: %{},
channels_inverse: %{}
}
connect_result =
if function_exported?(handler, :connect, 3) do
handler.connect(params, socket, connect_info)
else
handler.connect(params, socket)
end
case connect_result do
{:ok, %Socket{} = socket} ->
case handler.id(socket) do
nil ->
{:ok, {state, socket}}
id when is_binary(id) ->
{:ok, {state, %{socket | id: id}}}
invalid ->
Logger.error "#{inspect handler}.id/1 returned invalid identifier " <>
"#{inspect invalid}. Expected nil or a string."
:error
end
:error ->
:error
{:error, _reason} = err ->
err
invalid ->
connect_arity = if function_exported?(handler, :connect, 3), do: "connect/3", else: "connect/2"
Logger.error "#{inspect handler}. #{connect_arity} returned invalid value #{inspect invalid}. " <>
"Expected {:ok, socket}, {:error, reason} or :error"
:error
end
end
defp handle_in(_, %{ref: ref, topic: "phoenix", event: "heartbeat"}, state, socket) do
reply = %Reply{
ref: ref,
topic: "phoenix",
status: :ok,
payload: %{}
}
{:reply, :ok, encode_reply(socket, reply), {state, socket}}
end
defp handle_in(nil, %{event: "phx_join", topic: topic, ref: ref, join_ref: join_ref} = message, state, socket) do
case socket.handler.__channel__(topic) do
{channel, opts} ->
case Phoenix.Channel.Server.join(socket, channel, message, opts) do
{:ok, reply, pid} ->
reply = %Reply{join_ref: join_ref, ref: ref, topic: topic, status: :ok, payload: reply}
state = put_channel(state, pid, topic, join_ref)
{:reply, :ok, encode_reply(socket, reply), {state, socket}}
{:error, reply} ->
reply = %Reply{join_ref: join_ref, ref: ref, topic: topic, status: :error, payload: reply}
{:reply, :error, encode_reply(socket, reply), {state, socket}}
end
_ ->
Logger.warn fn -> "Ignoring unmatched topic \"#{topic}\" in #{inspect(socket.handler)}" end
{:reply, :error, encode_ignore(socket, message), {state, socket}}
end
end
defp handle_in({pid, _ref, status}, %{event: "phx_join", topic: topic} = message, state, socket) do
receive do
{:socket_close, ^pid, _reason} -> :ok
after
0 ->
if status != :leaving do
Logger.debug(fn ->
"Duplicate channel join for topic \"#{topic}\" in #{inspect(socket.handler)}. " <>
"Closing existing channel for new join."
end)
end
end
:ok = shutdown_duplicate_channel(pid)
{:push, {opcode, payload}, {new_state, new_socket}} = socket_close(pid, {state, socket})
send(self(), {:socket_push, opcode, payload})
handle_in(nil, message, new_state, new_socket)
end
defp handle_in({pid, _ref, _status}, message, state, socket) do
send(pid, message)
{:ok, {maybe_put_status(state, pid, message), socket}}
end
defp handle_in(nil, %{event: "phx_leave", ref: ref, topic: topic, join_ref: join_ref}, state, socket) do
reply = %Reply{
ref: ref,
join_ref: join_ref,
topic: topic,
status: :ok,
payload: %{}
}
{:reply, :ok, encode_reply(socket, reply), {state, socket}}
end
defp handle_in(nil, message, state, socket) do
# This clause can happen if the server drops the channel
# and the client sends a message meanwhile
{:reply, :error, encode_ignore(socket, message), {state, socket}}
end
defp put_channel(state, pid, topic, join_ref) do
%{channels: channels, channels_inverse: channels_inverse} = state
monitor_ref = Process.monitor(pid)
%{
state |
channels: Map.put(channels, topic, {pid, monitor_ref, :joined}),
channels_inverse: Map.put(channels_inverse, pid, {topic, join_ref})
}
end
defp delete_channel(state, pid, topic, monitor_ref) do
%{channels: channels, channels_inverse: channels_inverse} = state
Process.demonitor(monitor_ref, [:flush])
%{
state |
channels: Map.delete(channels, topic),
channels_inverse: Map.delete(channels_inverse, pid)
}
end
defp encode_on_exit(socket, topic, ref, _reason) do
message = %Message{join_ref: ref, ref: ref, topic: topic, event: "phx_error", payload: %{}}
encode_reply(socket, message)
end
defp encode_ignore(socket, %{ref: ref, topic: topic}) do
reply = %Reply{ref: ref, topic: topic, status: :error, payload: %{reason: "unmatched topic"}}
encode_reply(socket, reply)
end
defp encode_reply(%{serializer: serializer}, message) do
{:socket_push, opcode, payload} = serializer.encode!(message)
{opcode, payload}
end
defp encode_close(socket, topic, join_ref) do
message = %Message{join_ref: join_ref, ref: join_ref, topic: topic, event: "phx_close", payload: %{}}
encode_reply(socket, message)
end
defp shutdown_duplicate_channel(pid) do
ref = Process.monitor(pid)
Process.exit(pid, {:shutdown, :duplicate_join})
receive do
{:DOWN, ^ref, _, _, _} -> :ok
after
5_000 ->
Process.exit(pid, :kill)
receive do: ({:DOWN, ^ref, _, _, _} -> :ok)
end
end
defp socket_close(pid, {state, socket}) do
case state.channels_inverse do
%{^pid => {topic, join_ref}} ->
{^pid, monitor_ref, _status} = Map.fetch!(state.channels, topic)
state = delete_channel(state, pid, topic, monitor_ref)
{:push, encode_close(socket, topic, join_ref), {state, socket}}
%{} ->
{:ok, {state, socket}}
end
end
defp maybe_put_status(state, pid, %{event: "phx_leave", topic: topic}) do
update_channel_status(state, pid, topic, :leaving)
end
defp maybe_put_status(state, _pid, %{} = _msg) do
state
end
defp update_channel_status(state, pid, topic, status) do
new_channels = Map.update!(state.channels, topic, fn {^pid, ref, _} -> {pid, ref, status} end)
%{state | channels: new_channels}
end
end
