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diff --git a/doc/src/guide/rest_handlers.asciidoc b/doc/src/guide/rest_handlers.asciidoc new file mode 100644 index 0000000..6bff18d --- /dev/null +++ b/doc/src/guide/rest_handlers.asciidoc @@ -0,0 +1,133 @@ +[[rest_handlers]] +== REST handlers + +REST is implemented in Cowboy as a sub protocol. The request +is handled as a state machine with many optional callbacks +describing the resource and modifying the machine's behavior. + +The REST handler is the recommended way to handle HTTP requests. + +=== Initialization + +First, the `init/2` callback is called. This callback is common +to all handlers. To use REST for the current request, this function +must return a `cowboy_rest` tuple. + +[source,erlang] +---- +init(Req, _Opts) -> + {cowboy_rest, Req, #state{}}. +---- + +Cowboy will then switch to the REST protocol and start executing +the state machine. + +After reaching the end of the flowchart, the `terminate/3` callback +will be called if it is defined. + +=== Methods + +The REST component has code for handling the following HTTP methods: +HEAD, GET, POST, PATCH, PUT, DELETE and OPTIONS. + +Other methods can be accepted, however they have no specific callback +defined for them at this time. + +=== Callbacks + +All callbacks are optional. Some may become mandatory depending +on what other defined callbacks return. The various flowcharts +in the next chapter should be a useful to determine which callbacks +you need. + +All callbacks take two arguments, the Req object and the State, +and return a three-element tuple of the form `{Value, Req, State}`. + +All callbacks can also return `{stop, Req, State}` to stop execution +of the request. + +The following table summarizes the callbacks and their default values. +If the callback isn't defined, then the default value will be used. +Please look at the flowcharts to find out the result of each return +value. + +In the following table, "skip" means the callback is entirely skipped +if it is undefined, moving directly to the next step. Similarly, +"none" means there is no default value for this callback. + +[cols="<,^",options="header"] +|=== +| Callback name | Default value +| allowed_methods | `[<<"GET">>, <<"HEAD">>, <<"OPTIONS">>]` +| allow_missing_post | `true` +| charsets_provided | skip +| content_types_accepted | none +| content_types_provided | `$$[{{<<"text">>, <<"html">>, '*'}, to_html}]$$` +| delete_completed | `true` +| delete_resource | `false` +| expires | `undefined` +| forbidden | `false` +| generate_etag | `undefined` +| is_authorized | `true` +| is_conflict | `false` +| known_methods | `[<<"GET">>, <<"HEAD">>, <<"POST">>, <<"PUT">>, <<"PATCH">>, <<"DELETE">>, <<"OPTIONS">>]` +| languages_provided | skip +| last_modified | `undefined` +| malformed_request | `false` +| moved_permanently | `false` +| moved_temporarily | `false` +| multiple_choices | `false` +| options | `ok` +| previously_existed | `false` +| resource_exists | `true` +| service_available | `true` +| uri_too_long | `false` +| valid_content_headers | `true` +| valid_entity_length | `true` +| variances | `[]` +|=== + +As you can see, Cowboy tries to move on with the request whenever +possible by using well thought out default values. + +In addition to these, there can be any number of user-defined +callbacks that are specified through `content_types_accepted/2` +and `content_types_provided/2`. They can take any name, however +it is recommended to use a separate prefix for the callbacks of +each function. For example, `from_html` and `to_html` indicate +in the first case that we're accepting a resource given as HTML, +and in the second case that we send one as HTML. + +=== Meta data + +Cowboy will set informative meta values at various points of the +execution. You can retrieve them using `cowboy_req:meta/{2,3}`. +The values are defined in the following table. + +[cols="<,<",options="header"] +|=== +| Meta key | Details +| media_type | The content-type negotiated for the response entity. +| language | The language negotiated for the response entity. +| charset | The charset negotiated for the response entity. +|=== + +They can be used to send a proper body with the response to a +request that used a method other than HEAD or GET. + +=== Response headers + +Cowboy will set response headers automatically over the execution +of the REST code. They are listed in the following table. + +[cols="<,<",options="header"] +|=== +| Header name | Details +| content-language | Language used in the response body +| content-type | Media type and charset of the response body +| etag | Etag of the resource +| expires | Expiration date of the resource +| last-modified | Last modification date for the resource +| location | Relative or absolute URI to the requested resource +| vary | List of headers that may change the representation of the resource +|=== |