Phoenix v1.1.4 Phoenix.Endpoint
Defines a Phoenix endpoint.
The endpoint is the boundary where all requests to your web application start. It is also the interface your application provides to the underlying web servers.
Overall, an endpoint has three responsibilities:
to provide a wrapper for starting and stopping the endpoint as part of a supervision tree;
to define an initial plug pipeline where requests are sent through;
- to host web specific configuration for your application.
Endpoints
An endpoint is simply a module defined with the help
of Phoenix.Endpoint
. If you have used the mix phoenix.new
generator, an endpoint was automatically generated as
part of your application:
defmodule YourApp.Endpoint do
use Phoenix.Endpoint, otp_app: :your_app
# plug ...
# plug ...
plug YourApp.Router
end
Before being used, an endpoint must be explicitly started as part of your application supervision tree too (which is again done by default in generated applications):
supervisor(YourApp.Endpoint, [])
Endpoint configuration
All endpoints are configured in your application environment. For example:
config :your_app, YourApp.Endpoint,
secret_key_base: "kjoy3o1zeidquwy1398juxzldjlksahdk3"
Endpoint configuration is split into two categories. Compile-time configuration means the configuration is read during compilation and changing it at runtime has no effect. The compile-time configuration is mostly related to error handling and instrumentation.
Runtime configuration, instead, is accessed during or
after your application is started and can be read and written through the
config/2
function:
YourApp.Endpoint.config(:port)
YourApp.Endpoint.config(:some_config, :default_value)
Compile-time configuration
:code_reloader
- whentrue
, enables code reloading functionality:debug_errors
- whentrue
, usesPlug.Debugger
functionality for debugging failures in the application. Recommended to be set totrue
only in development as it allows listing of the application source code during debugging. Defaults tofalse
.:render_errors
- responsible for rendering templates whenever there is a failure in the application. For example, if the application crashes with a 500 error during a HTML request,render("500.html", assigns)
will be called in the view given to:render_errors
. Defaults to:[view: MyApp.ErrorView, accepts: ~w(html)]
The default format is used when none is set in the connection.
:instrumenters
- a list of instrumenters modules whose callbacks will be fired on instrumentation events. Read more on instrumentation in the “Instrumentation” section below.
Runtime configuration
:root
- the root of your application for running external commands. This is only required if the watchers or code reloading functionality are enabled.:cache_static_manifest
- a path to a json manifest file that contains static files and their digested version. This is typically set to “priv/static/manifest.json” which is the file automatically generated bymix phoenix.digest
.:check_origin
- configure transports to check origins or not. May be false, true or a list of hosts that are allowed.:http
- the configuration for the HTTP server. Currently uses cowboy and accepts all options as defined byPlug.Adapters.Cowboy
. Defaults tofalse
.:https
- the configuration for the HTTPS server. Currently uses cowboy and accepts all options as defined byPlug.Adapters.Cowboy
. Defaults tofalse
.:force_ssl
- ensures no data is ever sent via http, always redirecting to https. It expects a list of options which are forwarded toPlug.SSL
. By default, it redirects http requests and sets the “strict-transport-security” header for https ones.:secret_key_base
- a secret key used as a base to generate secrets to encode cookies, session and friends. Defaults tonil
as it must be set per application.:server
- whentrue
, starts the web server when the endpoint supervision tree starts. Defaults tofalse
. Themix phoenix.server
task automatically sets this totrue
.:url
- configuration for generating URLs throughout the app. Accepts the:host
,:scheme
,:path
and:port
options. All keys except:path
can be changed at runtime. Defaults to:[host: "localhost", path: "/"]
The
:port
option requires either an integer, string, or{:system, "ENV_VAR"}
. When given a tuple like{:system, "PORT"}
, the port will be referenced fromSystem.get_env("PORT")
at runtime as a workaround for releases where environment specific information is loaded only at compile-time.:static_url
- configuration for generating URLs for static files. It will fallback tourl
if no option is provided. Accepts the same options asurl
.:watchers
- a set of watchers to run alongside your server. It expects a list of tuples containing the executable and its arguments. Watchers are guaranteed to run in the application directory but only when the server is enabled. For example, the watcher below will run the “watch” mode of the brunch build tool when the server starts. You can configure it to whatever build tool or command you want:[node: ["node_modules/brunch/bin/brunch", "watch"]]
:live_reload
- configuration for the live reload option. Configuration requires a:paths
option which should be a list of files to watch. When these files change, it will trigger a reload. If you are using a tool like pow in development, you may need to set the:url
option appropriately.[url: "ws://localhost:4000", paths: [Path.expand("priv/static/js/phoenix.js")]]
:pubsub
- configuration for this endpoint’s pubsub adapter. Configuration either requires a:name
of the registered pubsub server or a:name
and:adapter
pair. The given adapter and name pair will be started as part of the supervision tree. if no adapter is specified, the pubsub system will work by sending events and subscribing to the given name. Defaults to:[adapter: Phoenix.PubSub.PG2, name: MyApp.PubSub]
It also supports custom adpater configuration:
[name: :my_pubsub, adapter: Phoenix.PubSub.Redis, host: "192.168.100.1"]
Endpoint API
In the previous section, we have used the config/2
function which is
automatically generated in your endpoint. Here is a summary of all the
functions that are automatically defined in your endpoint.
Paths and URLs
url()
- generates the endpoint base URL without any path informationstatic_url()
- generates the static URL without any path informationstruct_url()
- generates the endpoint base URL but as aURI
structpath(path)
- generates the path information when routing to this endpointstatic_path(path)
- generates a route to a static file inpriv/static
Channels
subscribe(pid, topic, opts)
- subscribes the pid to the given topic. SeePhoenix.PubSub.subscribe/4
for options.unsubscribe(pid, topic)
- unsubscribes the pid from the given topic.broadcast(topic, event, msg)
- broadcasts amsg
with asevent
in the giventopic
.broadcast!(topic, event, msg)
- broadcasts amsg
with asevent
in the giventopic
. Raises in case of failures.broadcast_from(from, topic, event, msg)
- broadcasts amsg
from the givenfrom
asevent
in the giventopic
.broadcast_from!(from, topic, event, msg)
- broadcasts amsg
from the givenfrom
asevent
in the giventopic
. Raises in case of failures.
Endpoint configuration
start_link()
- starts the Endpoint supervision tree, including its configuration cache and possibly the servers for handling requestsconfig(key, default)
- access the endpoint configuration given by keyconfig_change(changed, removed)
- reload the endpoint configuration on application upgrades
Plug API
init(opts)
- invoked when starting the endpoint servercall(conn, opts)
- invoked on every request (simply dispatches to the defined plug pipeline)
Instrumentation API
instrument(event, runtime_metadata \ nil, function)
- read more about instrumentation in the “Instrumentation” section
Instrumentation
Phoenix supports instrumentation through an extensible API. Each endpoint
defines an instrument/3
macro that both users and Phoenix internals can call
to instrument generic events. This macro is responsible for measuring the time
it takes for the event to happen and for notifying a list of interested
instrumenter modules of this measurement.
You can configure this list of instrumenter modules in the compile-time
configuration of your endpoint. (see the :instrumenters
option above). The
way these modules express their interest in events is by exporting public
functions where the name of each function is the name of an event. For
example, if someone instruments the :render_view
event, then each
instrumenter module interested in that event will have to export
render_view/3
.
Note: since the configuration for the list of instrumenters is specified at compile time but it’s used inside Phoenix itself, if you change this configuration you’ll have to recompile Phoenix manually:
$ mix deps.compile phoenix
$ mix compile
Callbacks cycle
The way event callbacks are called is the following.
- The event callback is called before the event happens (in this case,
before the view is rendered) with the atom
:start
as the first argument; see the “Before clause” section below. - The event happens (in this case, the view is rendered).
- The same event callback is called again, this time with the atom
:stop
as the first argument; see the “After clause” section below.
The second and third argument that each event callback takes depend on the
callback being an “after” or a “before” callback (i.e., they depend on the
value of the first argument, :start
or :stop
). For this reason, most of
the time you will want to define (at least) two separate clauses for each
event callback, one for the “before” and one for the “after” callbacks.
All event callbacks are run in the same process that calls the instrument/3
macro; hence, instrumenters should be careful in performing blocking actions.
If an event callback fails in any way (exits, throws, or raises), it won’t
affect anything (the error is caught) but the failure will be logged. Note
that “after” callbacks are not guaranteed to be called as, for example, a link
may break before they’ve been called.
“Before” clause
When the first argument to an event callback is :start
, the signature of
that callback is:
event_callback(:start, compile_metadata, runtime_metadata)
where:
compile_metadata
is a map of compile-time metadata about the environment whereinstrument/3
has been called. It contains the module where the instrumentation is happening (under the:module
key), the file and line (:file
and:line
), and the function inside which the instrumentation is happening (under:function
). This information can be used arbitrarely by the callback.runtime_metadata
is a map of runtime data that the instrumentation passes to the callbacks. This can be used for any purposes: for example, when instrumenting the rendering of a view, the name of the view could be passed in these runtime data so that instrumenters know which view is being rendered (`instrument(:view_render, %{view: “index.html”}, fn …)`).
“After” clause
When the first argument to an event callback is :stop
, the signature of that
callback is:
event_callback(:stop, time_diff, result_of_before_callback)
where:
time_diff
is an integer representing the time it took to execute the instrumented function in microseconds.result_of_before_callback
is the return value of the “before” clause of the sameevent_callback
. This is a means of passing data from the “before” clause to the “after” clause when instrumenting. For example, an instrumenter can implement custom time measuring with this:defmodule MyInstrumenter do def event_callback(:start, _compile, _runtime) do :erlang.monotonic_time(:micro_seconds) end def event_callback(:stop, _time_diff, start_time) do stop_time = :erlang.monotonic_time(:micro_seconds) do_something_with_diff(stop_time - start_time) end end
The return value of each “before” event callback will be stored and passed to the corresponding “after” callback.
Using instrumentation
Each Phoenix endpoint defines its own instrument/3
macro. This macro is
called like this:
require MyApp.Endpoint
MyApp.Endpoint.instrument :render_view, %{view: "index.html"}, fn ->
# actual view rendering
end
All the instrumenter modules that export a render_view/3
function will be
notified of the event so that they can perform their respective actions.
Phoenix default events
By default, Phoenix instruments the following events:
:phoenix_controller_call
- it’s the whole controller pipeline. No runtime metadata is passed to the instrumentation here.:phoenix_controller_render
- the rendering of a view from a controller. The map of runtime metadata passed to instrumentation callbacks has the:template
key - for the name of the template, e.g.,"index.html"
- and the:format
key - for the format of the template.
Dynamic instrumentation
If you want to instrument a piece of code but the endpoint that should
instrument it (the one that contains the instrument/3
macro you want to use)
is not known at compile time, but only at runtime, then you can use the
Phoenix.Endpoint.instrument/4
macro. Refer to its documentation for more
information.
Summary
Functions
Checks if Endpoint’s web server has been configured to start
Macros
Instruments the given function using the instrumentation provided by the given endpoint
Stores a plug to be executed as part of the pipeline
Defines a mount-point for a Socket module to handle channel definitions
Functions
Macros
Instruments the given function using the instrumentation provided by the given endpoint.
To specify the endpoint that will provide instrumentation, the first argument can be:
- a module name - the endpoint itself
- a
Plug.Conn
struct - this macro will look for the endpoint module in the:private
field of the connection; if it’s not there,fun
will be executed with no instrumentation - a
Phoenix.Socket
struct - this macro will look for the endpoint module in the:endpoint
field of the socket; if it’s not there,fun
will be executed with no instrumentation
Usually, users should prefer to instrument events using the instrument/3
macro defined in every Phoenix endpoint. This macro should only be used for
cases when the endpoint is dynamic and not known at compile time instead.
Examples
endpoint = MyApp.Endpoint
Phoenix.Endpoint.instrument endpoint, :render_view, fn -> ... end
Defines a mount-point for a Socket module to handle channel definitions.
Examples
socket "/ws", MyApp.UserSocket
socket "/ws/admin", MyApp.AdminUserSocket
By default, the given path is a websocket upgrade endpoint,
with long-polling fallback. The transports can be configured
within the Socket handler. See Phoenix.Socket
for more information
on defining socket handlers.