Basic idea

When describing RESTinio HTTP server there are three abstractions vital for an understanding of how to use it.

  • http_server_t<Traits> - a class representing HTTP server.
  • server_settings_t<Traits> - a class representing server settings.
  • Traits - a customization type for previous abstractions, that makes it possible to tune concrete server implementation.

Not less of importance is the fact that RESTinio runs on ASIO or Boost::ASIO See details here: ASIO Support. The rest of documentation assumes that a stand-alone ASIO is used.

An instance of asio::io_context is used to run the server. RESTinio can use its own privately created asio::io_context or it can make use of external io_context instance. The last case requires some assumptions to be fulfilled (see Using external io_context).


Main class http_server_t is a template class parameterized with a single template parameter: Traits. Traits class must specify a set of types used inside RESTinio, they are:


There is a helper classes for working with traits:

template <
    typename Timer_Manager,
    typename Logger,
    typename Request_Handler = default_request_handler_t,
    typename Strand = asio::strand< asio::executor >,
    typename Socket = asio::ip::tcp::socket >
struct traits_t; // Implementation omitted.

template <
    typename Timer_Manager,
    typename Logger,
    typename Request_Handler = default_request_handler_t >
using single_thread_traits_t =
  traits_t< Timer_Manager, Logger, Request_Handler, noop_strand_t >; // Implementation omitted.

Refer to Traits and restinio/traits.hpp for details.

Class http_server_t<Traits>

Class http_server_t<Traits> is a template class parameterized with a single template parameter: Traits. Its meaning is directly depicted in its name, http_server_t<Traits> represents HTTP-server. It is handy to consider http_server_t<Traits> class as a root class for the rest of RESTinio ecosystem running behind it, because pretty much all of them are also template types parameterized with the same Traits parameter.

Class http_server_t<Traits> has two constructors (simplified to omit verbose template stuff):

  io_context_holder_t io_context,
  server_settings_t<Traits> settings );

template < typename Configurator >
  io_context_holder_t io_context,
  Configurator && configurator );

The first is the main one. It obtains io_context as an asio::io_context back-end and server settings with the bunch of params.

The second constructor can simplify setting of parameters via generic lambda like this:

http_server_t< my_traits_t > http_server{
  []( auto & settings ){ // Omit concrete name of settings type.
      .port( 8080 )
      .read_next_http_message_timelimit( std::chrono::seconds( 1 ) )
      .handle_request_timeout( std::chrono::milliseconds( 3900 ) )
      .write_http_response_timelimit( std::chrono::milliseconds( 100 ) )
      .logger( /* logger params */ )
      .request_handler( /* request handler params */ );
  } };

But in the end, it delegates construction to the first constructor.

RESTinio runs its logic on asio::io_context, but its internal logic is separated from maintaining io_context directly, hence allowing to run restinio on external (specified by user) instance of asio::io_context (see Using external io_context). So there is a special class for wrapping io_context instance and pass it to http_server_t constructor: io_context_holder_t. To create such holder use one of the following functions:

  • restinio::own_io_context() – creates and uses its own instance of io_context;
  • restinio::external_io_context(asio::io_context&) – uses external instance of io_context.

Running server

To run server there are open()/close() methods :

class http_server_t
  // ...
    template <
        typename Server_Open_Ok_CB,
        typename Server_Open_Error_CB >
      Server_Open_Ok_CB && open_ok_cb,
      Server_Open_Error_CB && open_err_cb )


    template <
        typename Server_Close_Ok_CB,
        typename Server_Close_Error_CB >
      Server_Close_Ok_CB && close_ok_cb,
      Server_Close_Error_CB && close_err_cb );


There are sync methods for starting/stopping server and async. To choose the right method it is necessary to understand that RESTinio doesn’t start and run io_context that it runs on. So the user is responsible for running io_context. Sync versions of open()/close() methods assume they are called on the context of a running io_context. For example:

// Create and initialize object.
restinio::http_server_t< my_traits_t > server{
  [&]( auto & settings ){
      .port( args.port() )
      // .set_more_params( ... )
        []( restinio::request_handle_t req ){
            // Handle request.
        } );
  } };

// Post initial action to asio event loop.
asio::post( server.io_context(),
  [&] {
    // Starting the server in a sync way.
  } );

// Running server.

Async versions of open()/close() methods can be used from any thread. But it is not guaranteed that server is already started when method finishes. When using open_async() user provides two callbacks, the first one is called if the server starts successfully, and the second one is for handling an error. For example:

asio::io_context io_ctx;
restinio::http_server_t< my_traits_t > server{
    [&]( auto & settings ) { ... } };

// Launch thread on which server will work.
std::thread server_thread{ [&] {;
  } };

// Start server in async way. Actual start will be performed
// on the context of server_thread.
    // Ok callback. Nothing to do.
    // Error callback. Rethrow an exception.
    []( auto ex_ptr ) {
      std::rethrow_exception( ex_ptr );
    } );
// Wait while server_thread finishes its work.

Refer to restinio/http_server.hpp for details.

Class server_settings_t<Traits>

Class server_settings_t<Traits> serves to pass settings to http_server_t<Traits>. It is defined in restinio/settings.hpp).

For each parameter, a setter/getter pair is provided. While setting most of the parameters is pretty straightforward, there are some parameters with a bit tricky setter/getter semantics. They are request_handler, timer_factory, logger, acceptor_options_setter, socket_options_setter and cleanup_func.

For example setter for request_handler looks like this:

template< typename... PARAMS >
server_settings_t &
request_handler( PARAMS &&... params );

When called an instance of std::unique_ptr<Traits::request_handler_t> will be created with specified params. If no constructor with such parameters is available, then a compilation error will occur. If request_handler_t has a default constructor then it is not mandatory to call setter – the default constructed instance will be used. But there is an exception for std::function type because even though it has a default constructor it will be useless when constructed in such a way.

The request handler is constructed as unique_ptr, then getter returns unique_ptr value with ownership, so while manipulating server_settings_t object don’t use it.

The same applies to timer_factory, logger parameters, acceptor_options_setter, socket_options_setter and cleanup_func.

When http_server_t instance is created all the settings are checked in order to be properly instantiated.

Refer to Server settings and restinio/settings.hpp for details.