HTTP Client API =============== General ------- :mod:`cpp-netlib` includes and implements a number of HTTP clients that you can use and embed in your own applications. All of the HTTP client implementations: * **Cannot be copied.** This means you may have to store instances of the clients in dynamic memory if you intend to use them as function parameters or pass them around in smart pointers or by reference. * **Assume that requests made are independent of each other.** There currently is no cookie or session management system built-in to cpp-netlib's HTTP client implementations. * **Are header-only and are compiled-into your application.** Future releases in case you want to upgrade the implementation you are using in your application will be distributed as header-only implementations, which means you have to re-compile your application to use a newer version of the implementations. The HTTP clients all share the same API, but the internals are documented in terms of what is different and what to expect with the different implementations. As of 0.9.1 the default implementation for the :mod:`cpp-netlib` HTTP client is asynchronous. Implementations --------------- There is a single user-facing template class named ``basic_client`` which takes three template parameters: * **Tag** - which static tag you choose that defines the behavior of the client. * **http_version_major** - an unsigned int that defines the HTTP major version number, this directly affects the HTTP messages sent by the client. * **http_version_minor** - an unsigned int that defines the HTTP minor version number. There are two major different class of implementations of the ``basic_client`` template that depend on which tag you choose: `Synchronous Clients`_ and `Asynchronous Clients`_. These two different classes are described in their own sections following this one. What follows is a table of all tags supported by the HTTP client implementation provided by :mod:`cpp-netlib`. --------------- .. include:: ../in_depth/http_client_tags.rst In the above table the tags follow a pattern for describing the behavior introduced by the tags. This pattern is shown below: ___ For example, the tag ``http_default_8bit_tcp_resolve`` indicates the protocol ``http``, a modifier ``default``, a character width of ``8bit``, and a resolve strategy of ``tcp_resolve``. Synchronous Clients ~~~~~~~~~~~~~~~~~~~ Of the client tags shown in the table, the following makes the ``basic_client`` behave as a fully synchronous client. * **http_default_8bit_tcp_resolve** * **http_default_8bit_udp_resolve** * **http_keepalive_8bit_tcp_resolve** * **http_keepalive_8bit_udp_resolve** The synchronous client implements all the operations of the client underneath the interface all block to wait for I/O to finish. All the member methods are synchronous and will block until the response object is ready or throws if erros are encountered in the performance of the HTTP requests. .. warning:: The synchronous clients are **NOT** thread safe. You will need to do external synchronization to use synchronous client implementations. Asynchronous Clients ~~~~~~~~~~~~~~~~~~~~ The following tags specify the ``basic_client`` to behave in an asynchronous manner: * **http_async_8bit_tcp_resolve** * **http_async_8bit_udp_resolve** An asynchronous client implementation means that``basic_client<...>`` is an `Active Object`_. This means that the client has and manages its own lifetime thread, and returns values that are asynchronously filled in. The response object encapsulates Boost.Thread_ futures which get filled in once the values are available. .. _Boost.Thread: http://www.boost.org/libs/thread .. _`Active Object`: http://en.wikipedia.org/wiki/Active_object The asynchronous clients implement all operations asynchronously which are hidden from the user. The interface is still synchronous but the fetching of data happens on a different thread. .. note:: The asynchronous clients are thread safe, and can be shared across many threads. Each request starts a sequence of asynchronous operations dedicated to that request. The client does not re-cycle connections and uses a one-request-one-connection model. Member Functions ---------------- In this section we assume that the following typedef is in effect: .. code-block:: c++ typedef boost::network::http::basic_client< boost::network::http::tags::http_default_8bit_udp_resolve , 1 ,1 > client; Also, that code using the HTTP client will have use the following header: .. code-block:: c++ #include .. note:: Starting version 0.9, cpp-netlib clients and server implementations by default now have an externally-linked component. This is a breaking change for code that used to rely on cpp-netlib being a header-only library, but can inhibited by defining the ``BOOST_NETWORK_NO_LIB`` preprocessor macro before including any cpp-netlib header. Constructors ~~~~~~~~~~~~ The client implementation can be default constructed, or customized at initialization. ``client()`` Default constructor. ``client(boost::asio::io_service & io_service)`` Construct a client to use an existing Boost.Asio ``io_service`` instance. ``template client(ArgPack const & args)`` Pass in an argument pack. See supported parameters in the table below. +----------------------+-------------------------------+-------------------------+ | Parameter Name | Type | Description | +======================+===============================+=========================+ | _follow_redirects | ``bool`` | Boolean to specify | | | | whether the client | | | | should follow HTTP | | | | redirects. Default is | | | | ``false``. | +----------------------+-------------------------------+-------------------------+ | _cache_resolved | ``bool`` | Boolean to specify | | | | whether the client | | | | should cache resolved | | | | endpoints. The default | | | | is ``false``. | +----------------------+-------------------------------+-------------------------+ | _io_service | ``boost::asio::io_service &`` | Reference to an | | | | instance of a | | | | Boost.Asio | | | | ``io_service``. | +----------------------+-------------------------------+-------------------------+ | _openssl_certificate | string | The filename of the | | | | certificate to load for | | | | the SSL connection for | | | | verification. | +----------------------+-------------------------------+-------------------------+ | _openssl_verify_path | string | The directory from | | | | which the certificate | | | | authority files are | | | | located. | +----------------------+-------------------------------+-------------------------+ To use the above supported named parameters, you'll have code that looks like the following: .. code-block:: c++ using namespace boost::network::http; // parameters are in this namespace boost::asio::io_service my_io_service; client client_(_follow_redirects=true, _cache_resolved=true, _io_service=my_io_service , _openssl_certificate="/tmp/my-cert" , _openssl_verify_path="/tmp/ca-certs/"); // use client_ as normal from here on out. HTTP Methods ~~~~~~~~~~~~ The client implementation supports various HTTP methods. The following constructs assume that a client has been properly constructed named ``client_`` and that there is an appropriately constructed request object named ``request_`` and that there is an appropriately constructed response object named ``response_`` like the following: .. code-block:: c++ using namespace boost::network::http; // parameters are here client client_(); client::request request_("http://cpp-netib.github.com/"); client::response response_; ``response_ = client_.get(request_)`` Perform an HTTP GET request. ``response_ = client_.get(request_, _body_handler=callback)`` Perform an HTTP GET request, and have the body chunks be handled by the ``callback`` parameter. The signature of ``callback`` should be the following: ``void(iterator_range const &, boost::system::error_code const &)``. ``response_ = client_.head(request_)`` Perform an HTTP HEAD request. ``response_ = client_.post(request_)`` Perform an HTTP POST, use the data already set in the request object which includes the headers, and the body. ``response_ = client_.post(request_, _body_handler=callback)`` Perform an HTTP POST request, and have the body chunks be handled by the ``callback`` parameter. The signature of ``callback`` should be the following: ``void(iterator_range const &, boost::system::error_code const &)``. ``response_ = client_.post(request_, body)`` Body is a string of type ``boost::network::string::type`` where ``Tag`` is the HTTP Client's ``Tag``. The default content-type used is ``x-application/octet-stream``. ``response_ = client_.post(request_, body, _body_handler=callback)`` Body is a string of type ``boost::network::string::type`` where ``Tag`` is the HTTP Client's ``Tag``. The default content-type used is ``x-application/octet-stream``. Have the response body chunks be handled by the ``callback`` parameter. The signature of ``callback`` should be the following: ``void(iterator_range const &, boost::system::error_code const &)``. ``response_ = client_.post(request_, content_type, body)`` The body and content_type parameters are of type ``boost::network::string::type`` where ``Tag`` is the HTTP Client's ``Tag``. This uses the request object's other headers. ``response_ = client_.post(request_, content_type, body, _body_handler=callback)`` The body and content_type parameters are of type ``boost::network::string::type`` where ``Tag`` is the HTTP Client's ``Tag``. This uses the request object's other headers. Have the response body chunks be handled by the ``callback`` parameter. The signature of ``callback`` should be the following: ``void(iterator_range const &, boost::system::error_code const &)``. ``response_ = client_.put(request_)`` Perform an HTTP PUT, use the data already set in the request object which includes the headers, and the body. ``response_ = client_.put(request_, _body_handler=callback)`` Perform an HTTP PUT request, and have the body chunks be handled by the ``callback`` parameter. The signature of ``callback`` should be the following: ``void(iterator_range const &, boost::system::error_code const &)``. ``response_ = client_.put(request_, body)`` Body is a string of type ``boost::network::string::type`` where ``Tag`` is the HTTP Client's ``Tag``. The default content-type used is ``x-application/octet-stream``. ``response_ = client_.put(request_, body, _body_handler=callback)`` Body is a string of type ``boost::network::string::type`` where ``Tag`` is the HTTP Client's ``Tag``. The default content-type used is ``x-application/octet-stream``. Have the response body chunks be handled by the ``callback`` parameter. The signature of ``callback`` should be the following: ``void(iterator_range const &, boost::system::error_code const &)``. ``response_ = client_.put(request_, content_type, body)`` The body and content_type parameters are of type ``boost::network::string::type`` where ``Tag`` is the HTTP Client's ``Tag``. This uses the request object's other headers. ``response_ = client_.put(request_, content_type, body, _body_handler=callback)`` The body and content_type parameters are of type ``boost::network::string::type`` where ``Tag`` is the HTTP Client's ``Tag``. This uses the request object's other headers. Have the response body chunks be handled by the ``callback`` parameter. The signature of ``callback`` should be the following: ``void(iterator_range const &, boost::system::error_code const &)``. ``response_ = client_.delete_(request_)`` Perform an HTTP DELETE request. ``response_ = client_.delete_(request_, _body_handler=callback)`` Perform an HTTP DELETE request, and have the response body chunks be handled by the ``callback`` parameter. The signature of ``callback`` should be the following: ``void(iterator_range const &, boost::system::error_code const &)``. Client-Specific ~~~~~~~~~~~~~~~ ``client_.clear_resolved_cache()`` Clear the cache of resolved endpoints. Streaming Body Handler ~~~~~~~~~~~~~~~~~~~~~~ As of v0.9.1 the library now offers a way to support a streaming body callback function in all HTTP requests that expect a body part (GET, PUT, POST, DELETE). A convenience macro is also provided to make callback handlers easier to write. This macro is called ``BOOST_NETWORK_HTTP_BODY_CALLBACK`` which allows users to write the following code to easily create functions or function objects that are compatible with the callback function requirements. An example of how to use the macro is shown below: .. code-block:: c++ struct body_handler { explicit body_handler(std::string & body) : body(body) {} BOOST_NETWORK_HTTP_BODY_CALLBACK(operator(), range, error) { // in here, range is the Boost.Range iterator_range, and error is // the Boost.System error code. if (!error) body.append(boost::begin(range), boost::end(range)); } std::string & body; }; // somewhere else std::string some_string; response_ = client_.get(request("http://cpp-netlib.github.com/"), _body_handler=body_handler(some_string)); You can also use if for standalone functions instead if you don't want or need to create a function object. .. code-block:: c++ BOOST_NETWORK_HTTP_BODY_CALLBACK(print_body, range, error) { if (!error) std::cout << "Received " << boost::distance(range) << "bytes." << std::endl; else std::cout << "Error: " << error << std::endl; } // somewhere else response_ = client_.get(request("http://cpp-netlib.github.com/"), _body_handler=print_body); The ``BOOST_NETWORK_HTTP_BODY_CALLBACK`` macro is defined in ``boost/network/protocol/http/client/macros.hpp``.