Right. The most simple way to accomplish this is to use asio::streambuf as a buffer. When you process the input data, you call consume() function only for the amout you've really processed, and the rest of the data remains unused in the streambuf - until the next time you get something from the server (look at the asio examples with streambuf).

Yes, I'm using the streambuf, and then constructing an istream from the streambuf, and then calling getline on the istream. (The chat client/server was the primary example that I used to build my app.) If I have 2.5 lines in the buffer then the first two calls to getline will give me the first two lines, but won't the third call to getline get me the half line, and consume that half line from the streambuf? Do I need to process the streambuf in a more manual fashion rather than calling getline on the istream? Also to make sure I understand it how it works with the streambuf, that I am understanding you correctly: if I was just processing one line in the async_handler, and the first time the server sends me 3 lines, then the handler is called and will process the first line sent. Then the server sends another 3 lines, the async handler is called and the client will process the 2nd line that it received, not the 4th line, right? Thanks for your help, -Sameer