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-rw-r--r--guide/handlers.md22
1 files changed, 19 insertions, 3 deletions
diff --git a/guide/handlers.md b/guide/handlers.md
index dac5460..e2c1264 100644
--- a/guide/handlers.md
+++ b/guide/handlers.md
@@ -33,7 +33,23 @@ init(_Any, _Req, _Opts) ->
{upgrade, protocol, my_protocol}.
```
-The `my_protocol` module will be used for further processing of the
-request. It requires only one callback, `upgrade/4`.
+Cowboy comes with two protocol upgrades: `cowboy_rest` and
+`cowboy_websocket`. Use these values in place of `my_protocol`
+to use them.
-@todo Describe `upgrade/4` when the middleware code gets pushed.
+Custom protocol upgrades
+------------------------
+
+The `my_protocol` module above will be used for further processing
+of the request. It requires only one callback, `upgrade/4`.
+
+It receives the request object, the middleware environment, and
+the handler this request has been routed to along with its options.
+
+``` erlang
+upgrade(Req, Env, Handler, HandlerOpts) ->
+ %% ...
+```
+
+This callback is expected to behave like any middleware. Please
+see the corresponding chapter for more information.