Hi, I am trying to use boost::asio for a project where we currently use ACE. The way it currently works, the data that is passed between the server and client is preceded by a header with the data length. Currently with ACE when data is ready to be read at the socket, the handler function is invoked, and we invoke a ioctl with FIONREAD to read the number of bytes ready to be read and then allocate a buffer of that length to read the data. The reason we do this way is because the data may be sent in chunks. Internally we keep track of how much data we have received etc. I am at a loss to know how to do this using boost::asio. All the read methods expect a buffer where data will be read and it also needs the size of the buffer. Is there a way we get notified when data is ready to be read, and do similar operation. ie read the number of bytes available to read and then allocate buffers to read the data? Are there any other methods to accomplish the same? Thanks, Ram
From: boost-users-bounces@lists.boost.org [mailto:boost-users-bounces@lists.boost.org] On Behalf Of Ram Sundar Sent: Thursday, June 02, 2011 9:27 AM To: boost-users@lists.boost.org Subject: [Boost-users] Using boost::asio Hi, I am trying to use boost::asio for a project where we currently use ACE. The way it currently works, the data that is passed between the server and client is preceded by a header with the data length. Currently with ACE when data is ready to be read at the socket, the handler function is invoked, and we invoke a ioctl with FIONREAD to read the number of bytes ready to be read and then allocate a buffer of that length to read the data. The reason we do this way is because the data may be sent in chunks. Internally we keep track of how much data we have received etc. I am at a loss to know how to do this using boost::asio. All the read methods expect a buffer where data will be read and it also needs the size of the buffer. Is there a way we get notified when data is ready to be read, and do similar operation. ie read the number of bytes available to read and then allocate buffers to read the data? Are there any other methods to accomplish the same? Thanks, Ram Hi Ram. We have a similar situation (fixed size header + variable length body following). We happily use boost::asio with a very big buffer that can hold the biggest possible message. We accumulate bytes, check the headers, and eventually process the body. Can't you just use a big buffer and do the rest as you're doing now? Thanks, Benedetto
On Thursday, June 02, 2011 12:27 PM, Ram Sundar wrote:
I am trying to use boost::asio for a project where we currently use ACE. The way it currently works, the data that is passed between the server and client is preceded by a header with the data length. Currently with ACE when data is ready to be read at the socket, the handler function is invoked, and we invoke a ioctl with FIONREAD to read the number of bytes ready to be read and then allocate a buffer of that length to read the data. The reason we do this way is because the data may be sent in chunks. Internally we keep track of how much data we have received etc. I am at a loss to know how to do this using boost::asio. All the read methods expect a buffer where data will be read and it also needs the size of the buffer. Is there a way we get notified when data is ready to be read, and do similar operation. ie read the number of bytes available to read and then allocate buffers to read the data? Are there any other methods to accomplish the same?
There should be no reason to worry about whatever chunks TCP creates when it sends data. Try the following method: 1: Allocate a buffer just big enough for the header. 2: Call async_read to read the header. In the ReadHandler: 2a: Check for errors 2b: Extract the data length from the header. 2c: Allocate a buffer of exactly that size. 2d: Call async_read to read the data. In the ReadHandler: 2d1: Check for read errors. 2d2: Process the data knowing that you have the whole message. 2d3: Allocate a buffer for the next header (or reuse the existing header buffer) and call async_read with the same ReadHandler as described in step 2.
On 06/02/2011 09:26 AM, Ram Sundar wrote:
Hi, I am trying to use boost::asio for a project where we currently use ACE. The way it currently works, the data that is passed between the server and client is preceded by a header with the data length. Currently with ACE when data is ready to be read at the socket, the handler function is invoked, and we invoke a ioctl with FIONREAD to read the number of bytes ready to be read and then allocate a buffer of that length to read the data. The reason we do this way is because the data may be sent in chunks. Internally we keep track of how much data we have received etc. I am at a loss to know how to do this using boost::asio. All the read methods expect a buffer where data will be read and it also needs the size of the buffer. Is there a way we get notified when data is ready to be read, and do similar operation. ie read the number of bytes available to read and then allocate buffers to read the data? Are there any other methods to accomplish the same?
Thanks, Ram
Hi Ram - async_read_some is your friend. It will allow you to stitch together messages based on what is available at any particular time. You could use the read_some method to initially get the header and then use async_read afterward to read the remaining bytes. With the read_some you would likely end up (at some point) with the header and part of the body. Just make sure you take that into account when you initiate the read. Since you are coming from a reactor implementation, keep in mind that a proactor has a few important differences. These are outlined in the ASIO documentation. You may also find my BoostCon'10 presentation on ASIO useful to get going: slides: http://objectmodelingdesigns.com/boostcon10/ video : http://wipkip.nikhef.nl/events/BoostCon/2010/Boostcon-MichaelCaisseAnAsioBas... hth - michael -- Michael Caisse Object Modeling Designs www.objectmodelingdesigns.com
Thanks to everyone for your suggestions. It seems, I could do similar to reactor using null_buffers. I am going to try both techniques.(reading header and using null_buffers). Thanks, Ram
participants (4)
-
Andrew Holden -
Benedetto Proietti -
Michael Caisse -
Ram Sundar