Może być łatwiej zwizualizować programowanie asynchroniczne niż łańcuch funkcji zamiast pętli. Rozbijając łańcuchy, uważam, że pomocne jest podzielenie operacji na dwie części (inicjowanie i kończenie), a następnie zilustrowanie potencjalnych ścieżek wywołania.Oto przykład ilustracji, które asynchronicznie czyta niektórych danych z body_stream_
, a następnie zapisuje go do gniazda za pomocą HTTP Chunked Transfer Encoding:
void connection::start()
{
socket.async_receive_from(..., &handle_read); --.
} |
.----------------------------------------------'
| .-----------------------------------------.
V V |
void connection::handle_read(...) |
{ |
if (result) |
{ |
body_stream_.assign(open(...)) |
|
write_header(); --------------------------------|-----.
} | |
else if (!result) | |
boost::asio::async_write(..., &handle_write); --|--. |
else | | |
socket_.async_read_some(..., &handle_read); ----' | |
} | |
.---------------------------------------------------' |
| |
V |
void connection::handle_write() |
{} |
.------------------------------------------------------'
|
V
void connection::write_header()
{
// Start chunked transfer coding. Write http headers:
// HTTP/1.1. 200 OK\r\n
// Transfer-Encoding: chunked\r\n
// Content-Type: text/plain\r\n
// \r\n
boost::asio::async_write(socket_, ...,
&handle_write_header); --.
} .-------------------------'
|
V
void connection::handle_write_header(...)
{
if (error) return;
read_chunk(); --.
} .-------------'
| .--------------------------------------------.
V V |
void connection::read_chunk() |
{ |
boost::asio::async_read(body_stream_, ..., |
&handle_read_chunk); --. |
} .-----------------------' |
| |
V |
void connection::handle_read_chunk(...) |
{ |
bool eof = error == boost::asio::error::eof; |
|
// On non-eof error, return early. |
if (error && !eof) return; |
|
write_chunk(bytes_transferred, eof); --. |
} .-------------------------------------' |
| |
V |
void connection::write_chunk(...) |
{ |
// Construct chunk based on rfc2616 section 3.6.1 |
// If eof has been reached, then append last-chunk. |
boost::asio::async_write(socket_, ..., |
&handle_write_chunk); --. |
} .------------------------' |
| |
V |
void connection::handle_write_chunk(...) |
{ |
// If an error occured or no more data is available, |
// then return early. |
if (error || eof) return; |
|
// Read more data from body_stream_. |
read_chunk(); ---------------------------------------'
}
Jak pokazano powyżej, dzielenie na porcje odbywa się za pomocą asynchronicznego łańcuchu, w którym dane są odczytywane z body_stream_
, przygotowane do pisania na podstawie specyfikacji HTTP Chunked Transfer Encoding, a następnie zapisywane w gnieździe. Jeśli body_stream_
nadal zawiera dane, następuje kolejna iteracja.
nie mam środowisku Windows, aby przetestować, ale tutaj jest podstawowym kompletny przykład na Linuksie, że kawałki danych 10 bajtów na raz.
#include <iostream>
#include <sstream>
#include <string>
#include <vector>
#include <boost/array.hpp>
#include <boost/asio.hpp>
#include <boost/bind.hpp>
using boost::asio::ip::tcp;
namespace posix = boost::asio::posix;
// Constant strings.
const std::string http_chunk_header =
"HTTP/1.1 200 OK\r\n"
"Transfer-Encoding: chunked\r\n"
"Content-Type: text/html\r\n"
"\r\n";
const char crlf[] = { '\r', '\n' };
const char last_chunk[] = { '0', '\r', '\n' };
std::string to_hex_string(std::size_t value)
{
std::ostringstream stream;
stream << std::hex << value;
return stream.str();
}
class chunk_connection
{
public:
chunk_connection(
boost::asio::io_service& io_service,
const std::string& pipe_name)
: socket_(io_service),
body_stream_(io_service),
pipe_name_(pipe_name)
{}
/// Get the socket associated with the connection
tcp::socket& socket() { return socket_; }
/// Start asynchronous http chunk coding.
void start(const boost::system::error_code& error)
{
// On error, return early.
if (error)
{
close();
return;
}
std::cout << "Opening pipe." << std::endl;
int pipe = open(pipe_name_.c_str(), O_RDONLY);
if (-1 == pipe)
{
std::cout << "Failed to open pipe." << std::endl;
close();
return;
}
// Assign native descriptor to Asio's stream_descriptor.
body_stream_.assign(pipe);
// Start writing the header.
write_header();
}
private:
// Write http header.
void write_header()
{
std::cout << "Writing http header." << std::endl;
// Start chunked transfer coding. Write http headers:
// HTTP/1.1. 200 OK\r\n
// Transfer-Encoding: chunked\r\n
// Content-Type: text/plain\r\n
// \r\n
boost::asio::async_write(socket_,
boost::asio::buffer(http_chunk_header),
boost::bind(&chunk_connection::handle_write_header, this,
boost::asio::placeholders::error));
}
/// Handle writing of http header.
void handle_write_header(const boost::system::error_code& error)
{
// On error, return early.
if (error)
{
close();
return;
}
read_chunk();
}
// Read a file chunk.
void read_chunk()
{
std::cout << "Reading from body_stream_...";
std::cout.flush();
// Read body_stream_ into chunk_data_ buffer.
boost::asio::async_read(body_stream_,
boost::asio::buffer(chunk_data_),
boost::bind(&chunk_connection::handle_read_chunk, this,
boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred));
}
// Handle reading a file chunk.
void handle_read_chunk(const boost::system::error_code& error,
std::size_t bytes_transferred)
{
bool eof = error == boost::asio::error::eof;
// On non-eof error, return early.
if (error && !eof)
{
close();
return;
}
std::cout << bytes_transferred << " bytes read." << std::endl;
write_chunk(bytes_transferred, eof);
}
// Prepare chunk and write to socket.
void write_chunk(std::size_t bytes_transferred, bool eof)
{
std::vector<boost::asio::const_buffer> buffers;
// If data was read, create a chunk-body.
if (bytes_transferred)
{
// Convert bytes transferred count to a hex string.
chunk_size_ = to_hex_string(bytes_transferred);
// Construct chunk based on rfc2616 section 3.6.1
buffers.push_back(boost::asio::buffer(chunk_size_));
buffers.push_back(boost::asio::buffer(crlf));
buffers.push_back(boost::asio::buffer(chunk_data_, bytes_transferred));
buffers.push_back(boost::asio::buffer(crlf));
}
// If eof, append last-chunk to outbound data.
if (eof)
{
buffers.push_back(boost::asio::buffer(last_chunk));
buffers.push_back(boost::asio::buffer(crlf));
}
std::cout << "Writing chunk..." << std::endl;
// Write to chunk to socket.
boost::asio::async_write(socket_, buffers,
boost::bind(&chunk_connection::handle_write_chunk, this,
boost::asio::placeholders::error,
eof));
}
// Handle writing a chunk.
void handle_write_chunk(const boost::system::error_code& error,
bool eof)
{
// If eof or error, then shutdown socket and return.
if (eof || error)
{
// Initiate graceful connection closure.
boost::system::error_code ignored_ec;
socket_.shutdown(tcp::socket::shutdown_both, ignored_ec);
close();
return;
}
// Otherwise, body_stream_ still has data.
read_chunk();
}
// Close the socket and body_stream.
void close()
{
boost::system::error_code ignored_ec;
socket_.close(ignored_ec);
body_stream_.close(ignored_ec);
}
private:
// Socket for the connection.
tcp::socket socket_;
// Stream file being chunked.
posix::stream_descriptor body_stream_;
// Buffer to read part of the file into.
boost::array<char, 10> chunk_data_;
// Buffer holds hex encoded value of chunk_data_'s valid size.
std::string chunk_size_;
// Name of pipe.
std::string pipe_name_;
};
int main()
{
boost::asio::io_service io_service;
// Listen to port 80.
tcp::acceptor acceptor_(io_service, tcp::endpoint(tcp::v4(), 80));
// Asynchronous accept connection.
chunk_connection connection(io_service, "example_pipe");
acceptor_.async_accept(connection.socket(),
boost::bind(&chunk_connection::start, &connection,
boost::asio::placeholders::error));
// Run the service.
io_service.run();
}
Mam mały plik HTML, który będzie służył nad pakietowego kodowania, 10 bajtów na raz:
<html>
<body>
Test transfering html over chunked encoding.
</body>
</html>
uruchomienia serwera:
$ mkfifo example_pipe
$ sudo ./a.out &
[1] 28963
<open browser and connected to port 80>
$ cat html > example_pipe
Wyjście z serwera:
Opening pipe.
Writing http header.
Reading from body_stream_...10 bytes read.
Writing chunk...
Reading from body_stream_...10 bytes read.
Writing chunk...
Reading from body_stream_...10 bytes read.
Writing chunk...
Reading from body_stream_...10 bytes read.
Writing chunk...
Reading from body_stream_...10 bytes read.
Writing chunk...
Reading from body_stream_...10 bytes read.
Writing chunk...
Reading from body_stream_...10 bytes read.
Writing chunk...
Reading from body_stream_...7 bytes read.
Writing chunk...
The wiresha Wyjście rk nie wykazuje-nieprawidłowy dane:
0000 48 54 54 50 2f 31 2e 31 20 32 30 30 20 4f 4b 0d HTTP/1.1 200 OK.
0010 0a 54 72 61 6e 73 66 65 72 2d 45 6e 63 6f 64 69 .Transfe r-Encodi
0020 6e 67 3a 20 63 68 75 6e 6b 65 64 0d 0a 43 6f 6e ng: chun ked..Con
0030 74 65 6e 74 2d 54 79 70 65 3a 20 74 65 78 74 2f tent-Typ e: text/
0040 68 74 6d 6c 0d 0a 0d 0a 61 0d 0a 3c 68 74 6d 6c html.... a..<html
0050 3e 0a 3c 62 6f 0d 0a 61 0d 0a 64 79 3e 0a 20 20 >.<bo..a ..dy>.
0060 54 65 73 74 0d 0a 61 0d 0a 20 74 72 61 6e 73 66 Test..a. . transf
0070 65 72 69 0d 0a 61 0d 0a 6e 67 20 68 74 6d 6c 20 eri..a.. ng html
0080 6f 76 0d 0a 61 0d 0a 65 72 20 63 68 75 6e 6b 65 ov..a..e r chunke
0090 64 0d 0a 61 0d 0a 20 65 6e 63 6f 64 69 6e 67 2e d..a.. e ncoding.
00a0 0d 0a 61 0d 0a 0a 3c 2f 62 6f 64 79 3e 0a 3c 0d ..a...</ body>.<.
00b0 0a 37 0d 0a 2f 68 74 6d 6c 3e 0a 0d 0a 30 0d 0a .7../htm l>...0..
00c0 0d 0a ..
Dobry opis! Jest bardzo podobny do tego, co wymyśliłem, choć w moim przypadku potrzebuję całej wiadomości http, zanim będę mógł zacząć odpowiadać, ponieważ odpowiedź zależy od wiadomości. – Rollie