cowboy/manual/cowboy_middleware.md

cowboy_middleware

The cowboy_middleware behaviour defines the interface used by Cowboy middleware modules.

Middlewares process the request sequentially in the order they are configured.

Types

env() = [{atom(), any()}]

The environment variable.

One is created for every request. It is passed to each middleware module executed and subsequently returned, optionally with its contents modified.

Callbacks

execute(Req, Env)

-> {ok, Req, Env}
| {suspend, Module, Function, Args}
| {halt, Req}
| {error, StatusCode, Req}

Types:

• Req = cowboy_req:req()
• Env = env()
• Module = module()
• Function = atom()
• Args = [any()]
• StatusCode = cowboy:http_status()

Execute the middleware.

The ok return value indicates that everything went well and that Cowboy should continue processing the request. A response may or may not have been sent.

The suspend return value will hibernate the process until an Erlang message is received. Note that when resuming, any previous stacktrace information will be gone.

The halt return value stops Cowboy from doing any further processing of the request, even if there are middlewares that haven't been executed yet. The connection may be left open to receive more requests from the client.

The error return value sends an error response identified by the StatusCode and then proceeds to terminate the connection. Middlewares that haven't been executed yet will not be called.