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| -rw-r--r-- | README.md | 45 |
1 files changed, 34 insertions, 11 deletions
@@ -94,7 +94,6 @@ Following is an example of a "Hello World!" HTTP handler. ``` erlang -module(my_handler). --behaviour(cowboy_http_handler). -export([init/3, handle/2, terminate/2]). init({tcp, http}, Req, Opts) -> @@ -107,14 +106,46 @@ handle(Req, State) -> terminate(Req, State) -> ok. ``` + +You can also write handlers that do not reply directly. Instead, such handlers +will wait for an Erlang message from another process and only reply when +receiving such message, or timeout if it didn't arrive in time. + +This is especially useful for long-polling functionality, as Cowboy will handle +process hibernation and timeouts properly, preventing mistakes if you were to +write the code yourself. An handler of that kind can be defined like this: + +``` erlang +-module(my_loop_handler). +-export([init/3, info/3, terminate/2]). + +-define(TIMEOUT, 60000). + +init({tcp, http}, Req, Opts) -> + {loop, Req, undefined_state, ?TIMEOUT, hibernate}. + +info({reply, Body}, Req, State) -> + {ok, Req2} = cowboy_http_req:reply(200, [], Body, Req), + {ok, Req2, State}; +info(Message, Req, State) -> + {loop, Req, State, hibernate}. + +terminate(Req, State) -> + ok. +``` + +It is of course possible to combine both type of handlers together as long as +you return the proper tuple from init/3. + **Note**: versions prior to `0.4.0` used the [quoted](https://github.com/klaar/quoted.erl) library instead of the built in `cowboy_http:urldecode/2` function. If you want to retain this you must add it as a dependency to your application and add the following cowboy_http_protocol option: +``` erlang {urldecode, {fun quoted:from_url/2, quoted:make([])}} - +``` Continue reading to learn how to dispatch rules and handle requests. @@ -187,21 +218,13 @@ Websocket would look like this: ``` erlang -module(my_ws_handler). --behaviour(cowboy_http_handler). --behaviour(cowboy_http_websocket_handler). --export([init/3, handle/2, terminate/2]). +-export([init/3]). -export([websocket_init/3, websocket_handle/3, websocket_info/3, websocket_terminate/3]). init({tcp, http}, Req, Opts) -> {upgrade, protocol, cowboy_http_websocket}. -handle(Req, State) -> - error(foo). %% Will never be called. - -terminate(Req, State) -> - error(foo). %% Same for that one. - websocket_init(TransportName, Req, _Opts) -> erlang:start_timer(1000, self(), <<"Hello!">>), {ok, Req, undefined_state}. |