Re: [Boost-users] Buffering and ASIO

Subject: Re: [Boost-users] Buffering and ASIO
From: Cliff Green (cliffg_at_[hidden])
Date: 2008-12-15 13:20:51

IIUC, you're trying to mix and match calls to async_read_until (with a streambuf) and calls to async_read (with a buffer parameter), but having problems with "extra data past the length data". If you keep the same design, you will need to first extract the "extra data" out of the streambuf, place it in to the buffer you want to use, then call async_read or async_read_at with the partially filled buffer. While I haven't done anything similar, I can't think of a reason this won't work.

However, I think it would be easier to use async_read_until calls only, and keep all data in the streambuf. Create a match_condition function object, track the state of the HTTP transfer in the function object, and then return a true condition when the full buffer has been received. This encapsulates all of your "buffer filling logic" into one small place and I think is the simplest code of everything I'm writing in this e-mail.

If you cannot use a streambuf for the full transfer for whatever reason, then I would not use async_read_until and instead use async_read or async_read_at with a single buffer for everything. It shouldn't be hard to manage the "two states" of the transfer ("need length header", "have length header, getting rest of data"). Your handler will be called multiple times (most likely) while in the second state (and it's possible it will get called multiple times while in the first state, depending on how congested the TCP incoming buffers are). I think your design of trying to mix the two models is more complicated than it needs to be.

Cliff