boost asio async_read：讀取的消息添加到自身

Question

我使用我的PC作爲服務器。客戶端發送如下消息：「PART1：Part2」，服務器執行必要的操作。我使用boost的asio服務器代碼。

void start_read() 
    { 
     boost::asio::async_read(socket_, input_buffer_, 
      boost::asio::transfer_at_least(1), 
      boost::bind(&tcp_connection::handle_read, shared_from_this(), 
      boost::asio::placeholders::error)); 
    } 

    // When stream is received handle the message from the client 
    void handle_read(const boost::system::error_code& error) 
    { 
     if (!error) 
     { 
      boost::asio::streambuf::const_buffers_type bufs = input_buffer_.data(); 
      std::string msgstr(boost::asio::buffers_begin(bufs), 
           boost::asio::buffers_begin(bufs) + 
           input_buffer_.size()); 

      std::vector<std::string> msgVector; 
      boost::split(msgVector, msgstr, boost::is_any_of(":")); 

      messageFromClient_ = msgVector[0]; 
      valueFromClient_ = msgVector[1]; 
}; 

消息發送到服務器的每秒發送所得msgstr看起來是這樣的：

PART1:part2a 
PART1:part2bPART1:part2b 
PART1:part2cPART1:part2cPART1:part2c 
PART1:part2dPART1:part2dPART1:part2dPART1:part2d 

這不是我想要的。我不想從以前的緩衝區包括數據，即我想這一點：

PART1:part2a 
PART1:part2b 
PART1:part2c 
PART1:part2d 

據我所知，這個問題很可能就出在這裏：

  std::string msgstr(boost::asio::buffers_begin(bufs), 
           boost::asio::buffers_begin(bufs) + 
           input_buffer_.size()); 

但是，我無法找到正確的代碼，將在我的情況下工作。

編輯： 嘗試做這個：

std::istream response_istream(&input_buffer_); 
std::string msgstr; 
response_istream >> msgstr; 

前三次，我得到了我所需要的，但隨後該消息被成倍增加。它總是這樣的：

PART1:part2a 
PART1:part2b 
PART1:part2c 
PART1:part2dPART1:part2d 
PART1:part2ePART1:part2e 
PART1:part2fPART1:part2fPART1:part2fPART1:part2f 
PART1:part2gPART1:part2g 

非常感謝提前。

Answer 1

streambuf::data()成員函數返回表示輸入序列的緩衝區。爲了避免再次訪問數據，可以使用streambuf::consume()成員函數從輸入序列的開頭刪除字符。

input_buffer_.consume(input_buffer_.size()); 

---

下面是一個完整的最小示例demonstrating的consume()行爲：：

#include <iostream> 
#include <boost/asio.hpp> 
#include <boost/bind.hpp> 
#include <boost/lexical_cast.hpp> 

// This example is not interested in the handlers, so provide a noop function 
// that will be passed to bind to meet the handler concept requirements. 
void noop() {} 

int main() 
{ 
    using boost::asio::ip::tcp; 
    boost::asio::io_service io_service; 

    // Create all I/O objects. 
    tcp::acceptor acceptor(io_service, tcp::endpoint(tcp::v4(), 0)); 
    tcp::socket server_socket(io_service); 
    tcp::socket client_socket(io_service); 

    // Connect client and server sockets. 
    acceptor.async_accept(server_socket, boost::bind(&noop)); 
    client_socket.async_connect(acceptor.local_endpoint(), boost::bind(&noop)); 
    io_service.run(); 

    // No-consuming case. 
    { 
    std::cout << "Non-consuming example" << std::endl; 
    boost::asio::streambuf streambuf; 
    for (int i = 0; i < 5; ++i) 
    { 
     std::string data = "test"; 
     data += boost::lexical_cast<std::string>(i); 

     // Write to server. 
     std::size_t bytes_transferred = 
      write(client_socket, boost::asio::buffer(data)); 

     // Read from client. 
     read(server_socket, streambuf, 
      boost::asio::transfer_exactly(bytes_transferred)); 

     // Print results. 
     std::string read_data(
     boost::asio::buffers_begin(streambuf.data()), 
     boost::asio::buffers_end(streambuf.data())); 
     std::cout << "size: " << streambuf.size() << ", " 
       << "read: " << read_data << std::endl; 
    } 
    } 

    // Consuming case. 
    { 
    std::cout << "Consuming example" << std::endl; 
    boost::asio::streambuf streambuf; 
    for (int i = 0; i < 5; ++i) 
    { 
     std::string data = "test"; 
     data += boost::lexical_cast<std::string>(i); 

     // Write to server. 
     std::size_t bytes_transferred = 
      write(client_socket, boost::asio::buffer(data)); 

     // Read from client. 
     read(server_socket, streambuf, 
      boost::asio::transfer_exactly(bytes_transferred)); 

     // Print results. 
     std::string read_data(
     boost::asio::buffers_begin(streambuf.data()), 
     boost::asio::buffers_end(streambuf.data())); 
     std::cout << "size: " << streambuf.size() << ", " 
       << "read: " << read_data << std::endl; 

     streambuf.consume(bytes_transferred); 
    } 
    } 
} 

在這種情況下，一旦數據已被從 input_buffer_複製到 msgstr，輸入序列可以與被清除

輸出：

Non-consuming example 
size: 5, read: test0 
size: 10, read: test0test1 
size: 15, read: test0test1test2 
size: 20, read: test0test1test2test3 
size: 25, read: test0test1test2test3test4 
Consuming example 
size: 5, read: test0 
size: 5, read: test1 
size: 5, read: test2 
size: 5, read: test3 
size: 5, read: test4 

請注意，在消費情況下，以前的數據將被丟棄。