Procedura: connettersi a server HTTP (C++ REST SDK)
Con C++ REST SDK (nome in codice "Casablanca"), è possibile connettersi più facilmente ai server HTTP da un'applicazione C++. In questa pagina vengono illustrati tre esempi. Nel primo viene illustrato un metodo di base per creare una richiesta HTTP GET e ricevere la risposta. Il secondo esempio è simile al primo, ma genera una richiesta HTTP che usa valori delle intestazioni personalizzati. Nel terzo esempio viene illustrato come usare HTTP PUT per caricare un file su un server.
Un esempio più completo che illustra le istruzioni #include e using segue questi esempi.
Avviso
In questo argomento vengono fornite informazioni per C++ REST SDK 1.0 (nome in codice "Casablanca").Se si sta usando una versione più recente dalla pagina Web di Codeplex Casablanca, usare la documentazione locale all'indirizzo http://casablanca.codeplex.com/documentation.
Per creare una richiesta HTTP GET e ricevere la risposta
Di seguito viene illustrato come usare la classe web::http::client::http_client per creare una richiesta HTTP GET. La classe web::http::client::http_response rappresenta la risposta del server. Per un esempio simile che elabora la risposta HTTP come dati JSON, vedere Procedura: usare i dati JSON.
// Creates an HTTP request and prints the length of the response stream.
pplx::task<void> HTTPStreamingAsync()
{
http_client client(L"https://www.fourthcoffee.com");
// Make the request and asynchronously process the response.
return client.request(methods::GET).then([](http_response response)
{
// Print the status code.
std::wostringstream ss;
ss << L"Server returned returned status code " << response.status_code() << L'.' << std::endl;
std::wcout << ss.str();
// TODO: Perform actions here reading from the response stream.
auto bodyStream = response.body();
// In this example, we print the length of the response to the console.
ss.str(std::wstring());
ss << L"Content length is " << response.headers().content_length() << L" bytes." << std::endl;
std::wcout << ss.str();
});
/* Sample output:
Server returned returned status code 200.
Content length is 63803 bytes.
*/
}
Per creare una richiesta HTTP GET che usa i valori di intestazione personalizzati
Questo esempio è simile a quello precedente, ma usa la classe web::http::client::http_request per creare manualmente le intestazioni di richiesta.
// Builds an HTTP request that uses custom header values.
pplx::task<void> HTTPRequestCustomHeadersAsync()
{
http_client client(L"https://www.fourthcoffee.com");
// Manually build up an HTTP request with header and request URI.
http_request request(methods::GET);
request.headers().add(L"MyHeaderField", L"MyHeaderValue");
request.set_request_uri(L"requestpath");
return client.request(request).then([](http_response response)
{
// Print the status code.
std::wostringstream ss;
ss << L"Server returned returned status code " << response.status_code() << L"." << std::endl;
std::wcout << ss.str();
});
/* Sample output:
Server returned returned status code 200.
*/
}
Per usare HTTP PUT per caricare un file su un server
Questo esempio è simile al primo, ma usa la classe concurrency::streams::file_stream per leggere in modo asincrono un file dal disco. L'oggetto concurrency::streams::basic_istream contiene il contenuto del file. Questo esempio usa web::http::methods::PUT per specificare l'operazione come operazione HTTP PUT. Per altri esempi di uso dei flussi, vedere Procedura: usare flussi asincroni.
// Upload a file to an HTTP server.
pplx::task<void> UploadFileToHttpServerAsync()
{
using concurrency::streams::file_stream;
using concurrency::streams::basic_istream;
// To run this example, you must have a file named myfile.txt in the current folder.
// Alternatively, you can use the following code to create a stream from a text string.
// std::string s("abcdefg");
// auto ss = concurrency::streams::stringstream::open_istream(s);
// Open stream to file.
return file_stream<unsigned char>::open_istream(L"myfile.txt").then([](pplx::task<basic_istream<unsigned char>> previousTask)
{
try
{
auto fileStream = previousTask.get();
// Make HTTP request with the file stream as the body.
http_client client(L"https://www.fourthcoffee.com");
return client.request(methods::PUT, L"myfile", fileStream).then([fileStream](pplx::task<http_response> previousTask)
{
fileStream.close();
std::wostringstream ss;
try
{
auto response = previousTask.get();
ss << L"Server returned returned status code " << response.status_code() << L"." << std::endl;
}
catch (const http_exception& e)
{
ss << e.what() << std::endl;
}
std::wcout << ss.str();
});
}
catch (const std::system_error& e)
{
std::wostringstream ss;
ss << e.what() << std::endl;
std::wcout << ss.str();
// Return an empty task.
return pplx::task_from_result();
}
});
/* Sample output:
The request must be resent
*/
}
Esempio completo
Ecco un esempio completo.
// basic-http-client.cpp
#include <http_client.h>
#include <filestream.h>
#include <iostream>
#include <sstream>
using namespace web::http;
using namespace web::http::client;
// Creates an HTTP request and prints the length of the response stream.
pplx::task<void> HTTPStreamingAsync()
{
http_client client(L"https://www.fourthcoffee.com");
// Make the request and asynchronously process the response.
return client.request(methods::GET).then([](http_response response)
{
// Print the status code.
std::wostringstream ss;
ss << L"Server returned returned status code " << response.status_code() << L'.' << std::endl;
std::wcout << ss.str();
// TODO: Perform actions here reading from the response stream.
auto bodyStream = response.body();
// In this example, we print the length of the response to the console.
ss.str(std::wstring());
ss << L"Content length is " << response.headers().content_length() << L" bytes." << std::endl;
std::wcout << ss.str();
});
/* Sample output:
Server returned returned status code 200.
Content length is 63803 bytes.
*/
}
// Builds an HTTP request that uses custom header values.
pplx::task<void> HTTPRequestCustomHeadersAsync()
{
http_client client(L"https://www.fourthcoffee.com");
// Manually build up an HTTP request with header and request URI.
http_request request(methods::GET);
request.headers().add(L"MyHeaderField", L"MyHeaderValue");
request.set_request_uri(L"requestpath");
return client.request(request).then([](http_response response)
{
// Print the status code.
std::wostringstream ss;
ss << L"Server returned returned status code " << response.status_code() << L"." << std::endl;
std::wcout << ss.str();
});
/* Sample output:
Server returned returned status code 200.
*/
}
// Upload a file to an HTTP server.
pplx::task<void> UploadFileToHttpServerAsync()
{
using concurrency::streams::file_stream;
using concurrency::streams::basic_istream;
// To run this example, you must have a file named myfile.txt in the current folder.
// Alternatively, you can use the following code to create a stream from a text string.
// std::string s("abcdefg");
// auto ss = concurrency::streams::stringstream::open_istream(s);
// Open stream to file.
return file_stream<unsigned char>::open_istream(L"myfile.txt").then([](pplx::task<basic_istream<unsigned char>> previousTask)
{
try
{
auto fileStream = previousTask.get();
// Make HTTP request with the file stream as the body.
http_client client(L"https://www.fourthcoffee.com");
return client.request(methods::PUT, L"myfile", fileStream).then([fileStream](pplx::task<http_response> previousTask)
{
fileStream.close();
std::wostringstream ss;
try
{
auto response = previousTask.get();
ss << L"Server returned returned status code " << response.status_code() << L"." << std::endl;
}
catch (const http_exception& e)
{
ss << e.what() << std::endl;
}
std::wcout << ss.str();
});
}
catch (const std::system_error& e)
{
std::wostringstream ss;
ss << e.what() << std::endl;
std::wcout << ss.str();
// Return an empty task.
return pplx::task_from_result();
}
});
/* Sample output:
The request must be resent
*/
}
int wmain()
{
// This example uses the task::wait method to ensure that async operations complete before the app exits.
// In most apps, you typically don�t wait for async operations to complete.
std::wcout << L"Calling HTTPStreamingAsync..." << std::endl;
HTTPStreamingAsync().wait();
std::wcout << L"Calling HTTPRequestCustomHeadersAsync..." << std::endl;
HTTPRequestCustomHeadersAsync().wait();
std::wcout << L"Calling UploadFileToHttpServerAsync..." << std::endl;
UploadFileToHttpServerAsync().wait();
}