[Boost-users] Buffering and ASIO
Vadim Shmelev
boost::asio::async_read_until(m_socket, m_headerBuffer,
"\r\n\r\n", boost::bind(&CAXISParser::read_header, this, boost::asio::placeholders::error,boost::asio::placeholders::bytes_transferred));, where m_headerBuffer is asio::streambuf object. During header parsing i can get video sample length. Now I want to read all video data in one function call, for example:
boost::asio::async_read(m_socket, boost::asio::buffer(pSample->GetBody(), m_currentSampleLength),boost::bind(&CAXISParser::read_body,
this, pSample, boost::asio::placeholders::error, boost::asio::placeholders::bytes_transferred));, where pSample is object with buffer for video data. There is problem that async_read_until captures some data from video data, and that call's behavior is incorrect. How can i fight that problem? For example, how can i figure out number of bytes left in streambuf and copy them to my buffer, and then read rest with async_read? I'm will very appreciate for any advices.
Thanks in advance, Vadim
Scott Gifford
[...]
> Now I want to read all video data in one function call, for example:
>
> boost::asio::async_read(m_socket, boost::asio::buffer(pSample->GetBody(),
> m_currentSampleLength),boost::bind(&CAXISParser::read_body, this, pSample,
> boost::asio::placeholders::error,
> boost::asio::placeholders::bytes_transferred));
>
> , where pSample is object with buffer for video data. There is problem that
> async_read_until captures some data from video data, and that call's behavior
> is incorrect. How can i fight that problem? For example, how can i figure out
> number of bytes left in streambuf and copy them to my buffer, and
> then read rest with async_read? I'm will very appreciate for any advices.
Hello Vadim,
It's not clear to me exactly what you're asking here. From what I can
tell, you have created a buffer of size m_currentSampleLength, and
asked ASIO to call CAXISParser::read_body when it has received this
many bytes. Is that what you intended to do? Is that what boost is
doing? Or is the problem something else?
-----Scott.
_______________________________________________
Boost-users mailing list
Boost...@lists.boost.org
http://lists.boost.org/mailman/listinfo.cgi/boost-users
Vadim Shmelev
header:boost::asio::async_read_until(m_socket, m_headerBuffer, "\r\n\r\n",
boost::bind(&CAXISParser::read_header, this,
boost::asio::placeholders::bytes_transferred));, where m_headerBuffer is
example:boost::asio::async_read(m_socket,
boost::asio::buffer(pSample->GetBody(), m_currentSampleLength),
boost::bind(&CAXISParser::read_body, this, pSample,
boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred));, where pSample is object
with buffer for video data. There is problem that async_read_until captures
some data from video data, and that call's behavior is incorrect. How can i
fight that problem? For example, how can i figure out number of bytes left
in streambuf and copy them to my buffer, and then read rest with async_read?
> tell, you have created a buffer of size m_currentSampleLength, and
> asked ASIO to call CAXISParser::read_body when it has received this
> many bytes. Is that what you intended to do? Is that what boost is
> doing? Or is the problem something else?
>
> -----Scott.
Hello, Scott.
Sorry for bad english, i'm will try explain.
Yep, there is problem. When i'm read HTTP header with acync_read_until, it
consume header and some bytes from video data (i think). After i'm
calculate video data length from header and trying read data with
async_read. But it works incorrect as previous call async_read_until
captures some bytes from video data and video data readed with async_read
have wrong offset.
How can i understand, the problem that async_read_until and async_read
used different buffers for reading (asio::streambuf and custom buffer),
and some video data consumed by streambuf.
Question: how to get video data captured with async_read_until and read
rest from tcp buffer?There is is code sample:void read_header(PSample
pSample, const boost::system::error_code& error, size_t
bytes_transferred){ // Calculate data length with regex
boost::asio::const_buffer data = m_headerBuffer.data(); const char* beg =
boost::asio::buffer_cast<const char*>(data); const char* end = beg +
bytes_transferred; CalculateDataLength(beg, end); // Clear buffer
std::vector<char> vec(bytes_transferred); m_headerBuffer.sgetn(&vec[0],
bytes_transferred); ReadBody();}Before ReadBody call, i reject streambuf
content with sgetn. But i think there ismore data in streambuf that is video
data. How can i get it? Below non working sample, but it describe my
wishes:// Add before read bodysize_t restBytes = m_headerBuffer.size() -
bytes_transferred;if (0 != restBytes){
m_headerBuffer.sgetn(pSample->GetBody(), restBytes);}Then in ReadBody i can
to read rest video data with single async_readcall. There is implementation
sample:void ReadBody(NMMSS::PSample&
pSample){1)//boost::asio::async_read(m_socket,
m_headerBuffer.prepare(m_currentSampleLength),2)//boost::asio::async_read_until(m_socket,
m_headerBuffer, "\r\n",3)//boost::asio::async_read(m_socket,
boost::asio::buffer(pSample->GetBody(), m_currentSampleLength),
boost::bind(&CAXISParser::read_body, this, pSample,
boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred));}I trying use 3 variants
there:1) Trying read to buffer all video data (dont understand why it
doesn't work)2) Very slow variant, as video data is big.3) Preferrable
variant
P.S. One question more: how can i correctly reject data consumed by
streambuf? Now i used the following strategy:
streambuf buf;
.....
std::vector<char> vec(size);
buf.sgetn(&vec[0], size);
Is there another strategy for that? For example, commit and consume
strategy? I dont need streambuf content in some
cases.
Best regards,
Vadim
Vadim Shmelev
2)//boost::asio::async_read_until(m_socket, m_headerBuffer, "\r\n",
3)//boost::asio::async_read(m_socket, boost::asio::buffer(pSample->GetBody(), m_currentSampleLength),
Cliff Green
Emil Mieilica
Hello Vadim,
This is a piece of code from an application that inadvertently does what your application appears to be doing: receives a stream of images over a HTTP connection.
We had the same problems and you have in bold the solution we found: we call in_avail() on the read-buffer of the stream that tells us the amount of data already read but left in the buffer and then we readsome to get the actual data.
void onConnect(boost::system::error_code ErrorCode,unsigned int fps)
{
boost::asio::streambuf response;
boost::asio::read_until(*Socket, response, "\r\n");
std::istream response_stream(&response);
response_stream >> http_version;
response_stream >> status_code;
std::getline(response_stream, status_message);
if (!response_stream || http_version.substr(0, 5) != "HTTP/")
{
THROW_EXCEPTION(logic_error("Invalid HTTP response"));
}
// Read the response headers, which are terminated by a blank line.
boost::asio::read_until(*Socket, response, "\r\n\r\n");
while (std::getline(response_stream, header) && header != "\r")
{
LOG_DEBUG(log,"Got http header: "<<header);
}
//Get the number of bytes we have received after the HTTP header
size_t avail = response_stream.rdbuf()->in_avail();
//Read that data into the buffer
response_stream.readsome(Buffer.data(), avail );
LOG_DEBUG(log,"Connection succeded. Already received "<<avail);
//Call the asynchronous receive handler as if an read operation was completed with avail bytes of data
onReadComplete(ErrorCode,avail ,fps);
}
void onReadComplete(const boost::system::error_code& ErrorCode,size_t bytesTransfered,unsigned int fps)
{
if (!ErrorCode) {
boost::asio::async_read(
*Socket,
boost::asio::buffer(Buffer),
boost::asio::transfer_all(),
boost::bind(
& onReadComplete,
this,
boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred,
fps
)
);
}
}
Best regards,
----
Emil Mieilica
IT Manager
Office and mailing : Calea Bucuresti no 3A,
Otopeni, Ilfov, Romania
Tel: +40 21 350 40 57 ; +40 21 350 40 54 ; +40 21 350 40 55 ;
+40 21 350 40 56 ; +4031.620.0212; +4031.620.0213; +4743.26.4142
Fax: +40 21 350 15 80
E-mail:
From:
boost-use...@lists.boost.org
[mailto:boost-use...@lists.boost.org] On Behalf Of Vadim Shmelev
Sent: Monday, December 15, 2008 1:55 PM
To: boost...@lists.boost.org
Subject: Re: [Boost-users] Buffering and ASIO
> Good day.
> I'm trying to read video data transferred by HTTP. I use the following function in order
> to read HTTP header:
[sip]