How to access web service using Boost::Asio? - c++

Question

I wonder whether there is a possibility to access a web service using boost asio library.
I have tried following code (in IOS, C++11) which I got from boost asio documentation.
But it throws the following.
try
{
boost::asio::io_service io_service;
std::string address = "http://www.thomas-bayer.com/axis2/services/BLZService/";
// Get a list of endpoints corresponding to the server name.
tcp::resolver resolver(io_service);
tcp::resolver::query query(address,boost::asio::ip::resolver_query_base::numeric_service);
tcp::resolver::iterator endpoint_iterator = resolver.resolve(query);
endpoint_iterator->host_name() = "www.thomas-bayer.com/axis2/services/BLZService/";
std::cout<<"Print Query --"<<std::endl;
// Try each endpoint until we successfully establish a connection.
tcp::socket socket(io_service);
boost::asio::connect(socket, endpoint_iterator);
// Form the request. We specify the "Connection: close" header so that the
// server will close the socket after transmitting the response. This will
// allow us to treat all data up until the EOF as the content.
boost::asio::streambuf request;
std::ostream request_stream(&request);
request_stream << "POST: HTTP/1.0\r\n";
request_stream << "Host: " << address << "\r\n";
request_stream << "Accept: */*\r\n";
request_stream << "Connection: close\r\n\r\n";
// Send the request.
boost::asio::write(socket, request);
// Read the response status line. The response streambuf will automatically
// grow to accommodate the entire line. The growth may be limited by passing
// a maximum size to the streambuf constructor.
boost::asio::streambuf response;
boost::asio::read_until(socket, response, "\r\n");
// Check that response is OK.
std::istream response_stream(&response);
std::string http_version;
response_stream >> http_version;
unsigned int status_code;
response_stream >> status_code;
std::string status_message;
std::getline(response_stream, status_message);
if (!response_stream || http_version.substr(0, 5) != "HTTP/")
{
std::cout << "Invalid response\n";
return;
}
if (status_code != 200)
{
std::cout << "Response returned with status code " << status_code << "\n";
return;
}
// Read the response headers, which are terminated by a blank line.
boost::asio::read_until(socket, response, "\r\n\r\n");
// Process the response headers.
std::string header;
while (std::getline(response_stream, header) && header != "\r")
std::cout << header << "\n";
std::cout << "\n";
// Write whatever content we already have to output.
if (response.size() > 0)
std::cout << &response;
// Read until EOF, writing data to output as we go.
boost::system::error_code error;
while (boost::asio::read(socket, response,
boost::asio::transfer_at_least(1), error))
std::cout << &response;
if (error != boost::asio::error::eof)
throw boost::system::system_error(error);
}
catch (std::exception& e)
{
std::cout << "Exception: " << e.what() << "\n";
}
Exception: connect: Can't assign requested address
Or
Exception: resolve: Host not found (authoritative)
What is wrong with the code? Or I am doing completely wrong?
Thanks

Answer 1

The name resolution fails, because you are confusing what is a request, a URL, a protocol, hostname and an IP address.
Do the requestion on a FQDN. You need to supply a service unless you know it. The service in this case follows from the the protocol¹, `http:// is usually served on port 80:
std::string const address = "www.thomas-bayer.com";
tcp::resolver::query query(address, "80", boost::asio::ip::resolver_query_base::numeric_service);
Note that on most systems you can equivalently use:
std::string const address = "www.thomas-bayer.com";
tcp::resolver::query query(address, "http");
See where the http:// and www.thomas-bayer.com parts went?
Now /axis2/services/BLZService/ is the query path, as you would write in a GET request:
request_stream << "GET /axis2/services/BLZService/ HTTP/1.1\r\n";
Notes:
POST is not a header (so no colon!) it's a HTTP "verb" (GET, POST, DELETE, PUT...)
The "Host" header is a host name:
request_stream << "Host: " << address << "\r\n";
was correct iff address was really the logical name for the host
setting the hostname like this:
endpoint_iterator->host_name() = "www.thomas-bayer.com/axis2/services/BLZService/";
is something I've never seen before and I'm not sure what it should achieve. Perhaps it's just wrong?
¹ by convention, it could be other
Fixes
#include <boost/asio.hpp>
#include <iostream>
using boost::asio::ip::tcp;
void test() try {
boost::asio::io_service io_service;
std::string const address = "www.thomas-bayer.com";
// Get a list of endpoints corresponding to the server name.
tcp::resolver resolver(io_service);
tcp::resolver::query query(address, "80", boost::asio::ip::resolver_query_base::numeric_service);
tcp::resolver::iterator endpoint_iterator = resolver.resolve(query);
std::cout << "Print Query --" << std::endl;
// Try each endpoint until we successfully establish a connection.
tcp::socket socket(io_service);
boost::asio::connect(socket, endpoint_iterator);
// Form the request. We specify the "Connection: close" header so that the
// server will close the socket after transmitting the response. This will
// allow us to treat all data up until the EOF as the content.
boost::asio::streambuf request;
std::ostream request_stream(&request);
request_stream << "GET /axis2/services/BLZService HTTP/1.0\r\n";
request_stream << "Host: " << address << "\r\n";
request_stream << "Accept: */*\r\n";
request_stream << "Connection: close\r\n\r\n";
// Send the request.
boost::asio::write(socket, request);
// Read the response status line. The response streambuf will automatically
// grow to accommodate the entire line. The growth may be limited by
// passing a maximum size to the streambuf constructor.
boost::asio::streambuf response;
boost::asio::read_until(socket, response, "\r\n");
// Check that response is OK.
std::istream response_stream(&response);
std::string http_version, status_message;
unsigned int status_code;
std::getline(response_stream >> http_version >> status_code, status_message);
if (!response_stream || http_version.substr(0, 5) != "HTTP/") {
std::cout << "Invalid response\n";
return;
}
if (status_code != 200) {
std::cout << "Response returned with status code " << status_code << "\n";
return;
}
// Read the response headers, which are terminated by a blank line.
boost::asio::read_until(socket, response, "\r\n\r\n");
// Process the response headers.
std::string header;
while (std::getline(response_stream, header) && header != "\r")
std::cout << header << "\n";
std::cout << "\n";
// Write whatever content we already have to output.
if (response.size() > 0)
std::cout << &response;
// Read until EOF, writing data to output as we go.
boost::system::error_code error;
while (boost::asio::read(socket, response, boost::asio::transfer_at_least(1), error))
std::cout << &response;
if (error != boost::asio::error::eof)
throw boost::system::system_error(error);
} catch (std::exception &e) {
std::cout << "Exception: " << e.what() << "\n";
}
int main() { test(); }