[英]How to get if there is any data avaliable on socket to read in boost::asio?
[英]Unable to get all the data with boost asio read()
我正在開發一個 RTSP 客戶端。 它是一個簡單的基於文本的協議。 服務器向我發送了一個響應,我可以在 Wireshark 上看到該響應,但是當我嘗試閱讀它時並沒有得到所有響應。
發送的數據是這樣的(來自wireshark):
RTSP/1.0 200 OK
CSeq: 1
Date: Thu, Aug 11 2022 12:09:54 GMT
Content-Base: rtsp://10.45.231.24:559/pint.sdp/
Content-Type: application/sdp
Content-Length: 590
v=0
o=- 1660140466387175 1 IN IP4 10.1.23.23
s=Session streamed by Pinkman
i=pint.sdp
t=0 0
a=tool:LIVE555 Streaming Media v2017.10.28
a=type:broadcast
a=control:*
a=range:npt=0-
a=x-qt-text-nam:Session streamed by Pinkman
a=x-qt-text-pint.sdp
m=video 0 RTP/AVP 96
c=IN IP4 0.0.0.0
b=AS:2000
a=rtpmap:96 H264/90000
a=fmtp:96 packetization-mode=1;profile-level-id=640015;sprop-parameter-sets=Z2QAFazkBQfoQAAAAwBAAAAPA8WLRIA=,aOvssiw=
a=control:track1
m=application 0 RTP/AVP 97
c=IN IP4 0.0.0.0
b=AS:1000
a=rtpmap:97 vnd.onvif.metadata/10000
a=control:track2
我的閱讀策略是首先“read_until”內容長度,然后使用內容長度讀取數據的 rest。
相反,當我嘗試它時,我只得到了大約一半的數據。 第二次讀取只是掛起。 我認為這與套接字緩沖區的大小有關,但事實並非如此。
這是代碼:
boost::asio::streambuf receive_buffer;
std::size_t bytes_transferred;
receive_buffer.prepare(2048);
std::string delimeter{ "\r\n\r\n" };
std::string message = "DESCRIBE " + m_rtspServerURI + " RTSP/1.0\nCSeq: 1\r\n\r\n";
boost::asio::write(*m_socket, boost::asio::buffer(message), error);
if (error)
return false;
std::this_thread::sleep_for(std::chrono::milliseconds(maxResponseWaitingTime_ms));
bytes_transferred = boost::asio::read_until(*m_socket, receive_buffer, delimeter.c_str(), error);
if (error && error != boost::asio::error::eof)
{
std::cout << "receive failed: " << error.message() << std::endl;
return false;
}
else
{
std::cout << "\n Bytes Transferred :: " << bytes_transferred << "\n";
std::string describeHeaders{
boost::asio::buffers_begin(receive_buffer.data()),
boost::asio::buffers_begin(receive_buffer.data()) +
bytes_transferred - delimeter.size() };
receive_buffer.consume(bytes_transferred);
std::size_t sdpSize = extractContentLength(describeHeaders);
std::cout << "Describe Headers:: \n" << describeHeaders << "\n\n" << "Sdp Size: " << sdpSize << "\n";
bytes_transferred = boost::asio::read(*m_socket, receive_buffer,
boost::asio::transfer_exactly(sdpSize), error);
std::string sdpInfo{
boost::asio::buffers_begin(receive_buffer.data()),
boost::asio::buffers_begin(receive_buffer.data()) + bytes_transferred };
receive_buffer.consume(bytes_transferred);
std::cout << "sdpinfo :: \n" << sdpInfo << "\n";
我究竟做錯了什么?
內容長度錯誤。 它是 580 字節。 您將無限期地等待另外 10 個字節。
此外,當使用transfer_exactly
時,已經緩沖的字節不計算在內。 這是不幸的:
#include <boost/asio.hpp>
#include <iostream>
namespace net = boost::asio;
using boost::system::error_code;
struct DummyStream {
size_t read_some(auto) const { return 0; }
size_t read_some(auto, error_code& ec) const { ec = {}; return 0; }
};
int main() {
net::io_context io;
error_code ec;
DummyStream s;
net::streambuf buf;
std::ostream(&buf) << "HEADERS\r\n\r\nBODY";
auto n = net::read_until(s, buf, "\r\n\r\n", ec);
std::cout << "n:" << n << " ec:" << ec.message() << " buf.size():" << buf.size() << "\n";
buf.consume(n);
n = net::read(s, buf, net::transfer_exactly(1), ec); // not even 1
std::cout << "n:" << n << " ec:" << ec.message() << " buf.size():" << buf.size() << "\n";
}
即使是這個極小化的測試程序也會掛起,因為transfer_exactly(1)
沒有考慮緩沖區中已經存在的 4 個剩余字節。
相反,您應該創建一個將現有緩沖區內容考慮在內的功能完成條件,或者手動進行數學運算:
static constexpr auto expected_content_length = 4;
buf.consume(n);
n = buf.size();
if (n < expected_content_length) {
n += net::read(s, buf,
net::transfer_exactly(expected_content_length - n), ec);
}
現在它正確打印:
n:11 ec:Success buf.size():15
n:4 ec:Success buf.size():4
我個人傾向於使用現有的解析庫。 遺憾的是,RTSP 不是標准 HTTP,所以我破解了一個基於 Beast 的實用程序 function:
#include <boost/beast/http.hpp>
size_t extractContentLength(std::string_view res) {
namespace http = boost::beast::http;
http::response_parser<http::empty_body> p;
p.eager(false);
error_code ec;
// replacing non-HTTP status line
if (!ec || ec == http::error::need_more) p.put(net::buffer("HTTP/1.1 200 OK\r\n", 17), ec);
if (!ec || ec == http::error::need_more) p.put(net::buffer(res.substr(res.find_first_of("\n") + 1)), ec);
//if (!ec || ec == http::error::need_more) p.put(net::buffer("\r\n\r\n", 4), ec);
assert(p.is_header_done());
auto const& msg = p.get();
return msg.has_content_length()
? std::stoull(msg.at(http::field::content_length))
: 0;
}
在這里,我們通過用虛擬 HTTP 狀態行替換 RTSP 狀態行來安撫 HTTP 解析器。 然后我們可以使用現有的頭部解析和驗證來提取內容長度 header 字段值。
現在,我們可以實現您的 function 工作:
#undef NDEBUG
#define REPRO
#include <boost/asio.hpp>
#include <fstream>
#include <iostream>
namespace net = boost::asio;
using boost::system::error_code;
using net::ip::tcp;
using net::buffers_begin;
using namespace std::chrono_literals;
static std::string const m_rtspServerURI = "/stream";
static auto const maxResponseWaitingTime_ms = 100ms;
extern std::string const sample590;
extern std::string const sample580;
struct DummyStream {
size_t read_some(auto) const { return 0; }
size_t read_some(auto, error_code& ec) const { ec = {}; return 0; }
};
#include <boost/beast/http.hpp>
size_t extractContentLength(std::string_view res) {
namespace http = boost::beast::http;
http::response_parser<http::empty_body> p;
p.eager(false);
error_code ec;
// replacing non-HTTP status line
if (!ec || ec == http::error::need_more) p.put(net::buffer("HTTP/1.1 200 OK\r\n", 17), ec);
if (!ec || ec == http::error::need_more) p.put(net::buffer(res.substr(res.find_first_of("\n") + 1)), ec);
//if (!ec || ec == http::error::need_more) p.put(net::buffer("\r\n\r\n", 4), ec);
assert(p.is_header_done());
auto const& msg = p.get();
return msg.has_content_length()
? std::stoull(msg.at(http::field::content_length).data())
: 0;
}
bool foo(std::string_view sample) {
net::io_context io;
error_code ec;
std::string_view const delimiter{"\r\n\r\n"};
#ifdef REPRO
DummyStream s;
auto* m_socket = &s;
#else
tcp::socket s(io);
auto* m_socket = &s;
s.connect({{}, 80});
std::string const message =
"DESCRIBE " + m_rtspServerURI + " RTSP/1.0\nCSeq: 1\r\n\r\n";
net::write(*m_socket, net::buffer(message), error);
#endif
if (ec)
return false;
net::streambuf receive_buffer;
#ifdef REPRO
//std::ostream(&receive_buffer)
//<< std::ifstream("input.txt", std::ios::binary).rdbuf();
std::ostream(&receive_buffer) << sample;
#else
receive_buffer.prepare(2048);
#endif
std::this_thread::sleep_for(maxResponseWaitingTime_ms);
auto bytes_transferred =
net::read_until(*m_socket, receive_buffer, delimiter, ec);
if (ec && ec != net::error::eof) {
std::cout << "receive failed: " << ec.message() << std::endl;
return false;
} else {
std::cout << "Bytes Transferred: " << bytes_transferred << " ("
<< ec.message() << ")" << std::endl;
auto consume = [&receive_buffer](size_t n) {
auto b = buffers_begin(receive_buffer.data()), e = b + n;
assert(n <= receive_buffer.size());
auto s = std::string{b, e};
receive_buffer.consume(n);
return s;
};
auto headers = consume(bytes_transferred);
size_t sdpSize = extractContentLength(headers);
std::cout << "Describe Headers: " << headers << "Sdp Size: " << sdpSize
<< std::endl;
bytes_transferred = receive_buffer.size();
std::cout << "Pre-buffer: " << bytes_transferred << std::endl;
if (bytes_transferred < sdpSize) {
bytes_transferred += net::read(
*m_socket, receive_buffer,
net::transfer_exactly(sdpSize - bytes_transferred), ec);
}
auto sdpInfo = consume(bytes_transferred);
std::cout << "sdpinfo: " << sdpInfo << "\n";
// note theoretically receive_buffer may still contain data received
// *after* the body
}
return true;
}
int main() {
foo(sample580);
//foo(sample590); // would hang
}
std::string const sample590 =
"RTSP/1.0 200 OK\r\nCSeq: 1\r\nDate: Thu, Aug 11 2022 12:09:54 "
"GMT\r\nContent-Base: rtsp://10.45.231.24:559/pint.sdp/\r\nContent-Type: "
"application/sdp\r\nContent-Length: 590\r\n\r\nv=0\r\no=- 1660140466387175 "
"1 IN IP4 10.1.23.23\r\ns=Session streamed by Pinkman\r\ni=pint.sdp\r\nt=0 "
"0\r\na=tool:LIVE555 Streaming Media "
"v2017.10.28\r\na=type:broadcast\r\na=control:*\r\na=range:npt=0-\r\na=x-"
"qt-text-nam:Session streamed by "
"Pinkman\r\na=x-qt-text-pint.sdp\r\nm=video 0 RTP/AVP 96\r\nc=IN IP4 "
"0.0.0.0\r\nb=AS:2000\r\na=rtpmap:96 H264/90000\r\na=fmtp:96 "
"packetization-mode=1;profile-level-id=640015;sprop-parameter-sets="
"Z2QAFazkBQfoQAAAAwBAAAAPA8WLRIA=,aOvssiw=\r\na=control:track1\r\nm="
"application 0 RTP/AVP 97\r\nc=IN IP4 0.0.0.0\r\nb=AS:1000\r\na=rtpmap:97 "
"vnd.onvif.metadata/10000\r\na=control:track2\r\n";
std::string const sample580 =
"RTSP/1.0 200 OK\r\nCSeq: 1\r\nDate: Thu, Aug 11 2022 12:09:54 "
"GMT\r\nContent-Base: rtsp://10.45.231.24:559/pint.sdp/\r\nContent-Type: "
"application/sdp\r\nContent-Length: 580\r\n\r\nv=0\r\no=- 1660140466387175 "
"1 IN IP4 10.1.23.23\r\ns=Session streamed by Pinkman\r\ni=pint.sdp\r\nt=0 "
"0\r\na=tool:LIVE555 Streaming Media "
"v2017.10.28\r\na=type:broadcast\r\na=control:*\r\na=range:npt=0-\r\na=x-"
"qt-text-nam:Session streamed by "
"Pinkman\r\na=x-qt-text-pint.sdp\r\nm=video 0 RTP/AVP 96\r\nc=IN IP4 "
"0.0.0.0\r\nb=AS:2000\r\na=rtpmap:96 H264/90000\r\na=fmtp:96 "
"packetization-mode=1;profile-level-id=640015;sprop-parameter-sets="
"Z2QAFazkBQfoQAAAAwBAAAAPA8WLRIA=,aOvssiw=\r\na=control:track1\r\nm="
"application 0 RTP/AVP 97\r\nc=IN IP4 0.0.0.0\r\nb=AS:1000\r\na=rtpmap:97 "
"vnd.onvif.metadata/10000\r\na=control:track2\r\n";
印刷
Bytes Transferred: 166 (Success)
Describe Headers: RTSP/1.0 200 OK
CSeq: 1
Date: Thu, Aug 11 2022 12:09:54 GMT
Content-Base: rtsp://10.45.231.24:559/pint.sdp/
Content-Type: application/sdp
Content-Length: 580
Sdp Size: 580
Pre-buffer: 580
sdpinfo: v=0
o=- 1660140466387175 1 IN IP4 10.1.23.23
s=Session streamed by Pinkman
i=pint.sdp
t=0 0
a=tool:LIVE555 Streaming Media v2017.10.28
a=type:broadcast
a=control:*
a=range:npt=0-
a=x-qt-text-nam:Session streamed by Pinkman
a=x-qt-text-pint.sdp
m=video 0 RTP/AVP 96
c=IN IP4 0.0.0.0
b=AS:2000
a=rtpmap:96 H264/90000
a=fmtp:96 packetization-mode=1;profile-level-id=640015;sprop-parameter-sets=Z2QAFazkBQfoQAAAAwBAAAAPA8WLRIA=,aOvssiw=
a=control:track1
m=application 0 RTP/AVP 97
c=IN IP4 0.0.0.0
b=AS:1000
a=rtpmap:97 vnd.onvif.metadata/10000
a=control:track2
現在,如果您的服務器實際上發送了錯誤的 Content-Length 並且您希望maxResponseWaitingTime_ms
有意義,則必須使用async_read
接口並使用計時器來取消異步操作。 此時,我將使用 go 完整的野獸模式:
#include <boost/algorithm/string/find.hpp>
#include <boost/asio.hpp>
#include <boost/beast.hpp>
#include <fstream>
#include <iostream>
namespace net = boost::asio;
using boost::system::error_code;
using net::ip::tcp;
using net::buffers_begin;
namespace beast = boost::beast;
namespace http = beast::http;
using namespace std::chrono_literals;
static std::string const m_rtspServerURI = "/stream";
static auto const maxResponseWaitingTime = 100ms;
extern std::string const sample590;
extern std::string const sample580;
bool foo() {
net::thread_pool io(1);
try {
beast::tcp_stream s(io);
s.expires_after(3s);
s.async_connect({{}, 65200}, net::use_future)
.get(); // TODO connect to your host
{
s.expires_after(1s);
std::string const message =
"DESCRIBE " + m_rtspServerURI + " RTSP/1.0\nCSeq: 1\r\n\r\n";
net::async_write(s, net::buffer(message), net::use_future).get();
}
net::streambuf buf;
s.expires_after(maxResponseWaitingTime);
auto n =
net::async_read_until(s, buf, "\r\n\r\n", net::use_future).get();
std::cout << "Initial read " << n << std::endl;
{
// hack RTSP status line:
auto firstbuf = *buf.data().begin();
auto b = const_cast<char*>(net::buffer_cast<char const*>(firstbuf)),
e = b + std::min(n, firstbuf.size());
auto i = boost::make_iterator_range(b, e);
auto o = boost::algorithm::find_first(i, "RTSP/1.0");
if (o.size() == 8)
std::copy_n("HTTP/1.1", 8, o.begin());
}
http::response<http::string_body> res;
http::async_read(s, buf, res, net::use_future).get();
std::cout << "Describe headers: " << res.base() << std::endl;
std::cout << "sdpInfo: " << res.body() << std::endl;
// note buf may still contain data received *after* the body
return true;
} catch (boost::system::system_error const& se) {
std::cout << "Error: " << se.code().message() << std::endl;
return false;
}
io.join();
}
int main() {
foo();
}
有一些更有趣的現場演示:
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