Routes
Routes define what happens when your client connects to a certain URL.
Macro¶
CROW_ROUTE(app, url)
Can be replaced with app.route<crow::black_magick::get_parameter_tag(url)>(url) or app.route_dynamic(url) if you're using VS2013 or want runtime URL evaluation. Although this usage is NOT recommended.
App¶
Which app class to assign the route to.
Path (URL)¶
Which relative path is assigned to the route.
Using /hello means the client will need to access http://example.com/hello in order to access the route.
A path can have parameters, for example /hello/<int> will allow a client to input an int into the url which will be in the handler (something like http://example.com/hello/42).
Parameters can be <int>, <uint>, <double>, <string>, or <path>.
It's worth noting that the parameters also need to be defined in the handler, an example of using parameters would be to add 2 numbers based on input:
CROW_ROUTE(app, "/add/<int>/<int>")
([](int a, int b)
{
return std::to_string(a+b);
});
<int> is defined as a and the second as b. If you were to run this and call http://example.com/add/1/2, the result would be a page with 3. Exciting!
Methods¶
You can change the HTTP methods the route uses from just the default GET by using method(), your route macro should look like CROW_ROUTE(app, "/add/<int>/<int>").methods(crow::HTTPMethod::GET, crow::HTTPMethod::PATCH) or CROW_ROUTE(app, "/add/<int>/<int>").methods("GET"_method, "PATCH"_method).
Note
Crow handles OPTIONS method automatically. The HEAD method is handled automatically unless defined in a route.
Adding OPTIONS to a route's methods has no effect.
Crow defines the following methods:
DELETE
GET
HEAD
POST
PUT
CONNECT
OPTIONS
TRACE
PATCH
PURGE
COPY
LOCK
MKCOL
MOVE
PROPFIND
PROPPATCH
SEARCH
UNLOCK
BIND
REBIND
UNBIND
ACL
REPORT
MKACTIVITY
CHECKOUT
MERGE
SEARCH
NOTIFY
SUBSCRIBE
UNSUBSCRIBE
MKCALENDAR
LINK
UNLINK
SOURCE
Handler¶
Basically a piece of code that gets executed whenever the client calls the associated route, usually in the form of a lambda expression. It can be as simple as ([](){return "Hello World"}).
Request¶
Handlers can also use information from the request by adding it as a parameter ([](const crow::request& req){...}).
You can also access the URL parameters in the handler using req.url_params.get("param_name");. If the parameter doesn't exist, nullptr is returned.
Note master
parameters inside the body can be parsed using req.get_body_params();. which is useful for requests of type application/x-www-form-urlencoded. Its format is similar to url_params.
For more information on crow::request go here.
Response¶
Crow also provides the ability to define a response in the parameters by using ([](crow::response& res){...}).
Please note that in order to return a response defined as a parameter you'll need to use res.end();.
Alternatively, you can define the response in the body and return it (([](){return crow::response()})).
For more information on crow::response go here.
Crow defines the following status codes:
100 Continue
101 Switching Protocols
200 OK
201 Created
202 Accepted
203 Non-Authoritative Information
204 No Content
205 Reset Content
206 Partial Content
300 Multiple Choices
301 Moved Permanently
302 Found
303 See Other
304 Not Modified
307 Temporary Redirect
308 Permanent Redirect
400 Bad Request
401 Unauthorized
403 Forbidden
404 Not Found
405 Method Not Allowed
406 Not Acceptable
407 Proxy Authentication Required
409 Conflict
410 Gone
413 Payload Too Large
415 Unsupported Media Type
416 Range Not Satisfiable
417 Expectation Failed
428 Precondition Required
429 Too Many Requests
451 Unavailable For Legal Reasons
500 Internal Server Error
501 Not Implemented
502 Bad Gateway
503 Service Unavailable
504 Gateway Timeout
506 Variant Also Negotiates
Note
If your status code is not defined in the list above (e.g. crow::response(123)) Crow will return 500 Internal Server Error instead.
Return statement¶
A crow::response is very strictly tied to a route. If you can have something in a response constructor, you can return it in a handler.
The main return type is std::string, although you could also return a crow::json::wvalue or crow::multipart::message directly.
For more information on the specific constructors for a crow::response go here.
Returning custom classes¶
If you have your own class you want to return (without converting it to string and returning that), you can use the crow::returnable class.
to use the returnable class, you only need your class to publicly extend crow::returnable, add a dump() method that returns your class as an std::string, and add a constructor that has a Content-Type header as a string argument.
Your class should look like the following:
class a : public crow::returnable
{
a() : returnable("text/plain"){};
...
...
...
std::string dump() const override
{
return this.as_string();
}
}
Response codes¶
Instead of assigning a response code, you can use the crow::status enum, for example you can replace crow::response(200) with crow::response(crow::status::OK)
Catchall routes¶
By default, any request that Crow can't find a route for will return a simple 404 response. You can change that to return a default route using the CROW_CATCHALL_ROUTE(app) macro. Defining it is identical to a normal route, even when it comes to the const crow::request& and crow::response& parameters being optional.
Note
For versions higher than 0.3 (excluding patches), Catchall routes handle 404 and 405 responses. The default response will contain the code 404 or 405.