如何：连接到 HTTP 服务器 (C++ REST SDK)
通过 C++ REST SDK (codename "Casablanca")，你可以从 C++ 应用更加轻松地连接到 HTTP 服务器。 此页显示三个示例。 第一个示例显示创建 HTTP GET 请求和接收响应的基本方法。 第二个示例与第一个示例类似，但生成了一个使用自定义标头值的 HTTP 请求。 第三个示例显示如何使用 HTTP PUT 将文件上载到服务器。
在这些示例之后，有一个更完整的示例显示 #include 和 using 语句。
警告
本主题包含有关 C++ REST SDK 1.0 (codename "Casablanca") 的信息。如果你正在从 Codeplex Casablanca 网页 使用更高版本，则使用 http://casablanca.codeplex.com/documentation 上的本地文档。
创建 HTTP GET 请求和接收响应
以下是使用 web::http::client::http_client 类创建 HTTP GET 请求的方法。 web::http::client::http_response 类表示服务器的响应。 有关将 HTTP 响应作为 JSON 数据进行处理的类似示例，请参阅如何：使用 JSON 数据。
// 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.
*/
}
创建使用自定义标头值的 HTTP GET 请求
此示例类似于前一个示例，但此示例使用 web::http::client::http_request 类手动构建请求标头。
// 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.
*/
}
使用 HTTP PUT 将文件上载到服务器
此示例与第一个示例类型，但此示例使用 concurrency::streams::file_stream 类从磁盘异步读取文件。 concurrency::streams::basic_istream 对象保存文件内容。 此示例使用 web::http::methods::PUT 将操作指定为 HTTP PUT 操作。 有关使用流的详细信息，请参阅如何：使用异步流。
// 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
*/
}
完整示例
以下是完整示例。
// 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();
}