Re: Inspecting a read buffer

Hello all,

I am talking to a device over a serial port. The messages sent to me by
the device are of varying length, but they all start with a uniform
header which contains, among other things, a field indicating the
number of bytes in the message body (i.e. the part of the message after
the header).

1. I call ClearCommError() to find out the number of bytes available in
the read buffer (aside: is there a better way to do this?).

2. If there are at least as many bytes as there are in the smallest
message we ever expect to receive (8 bytes), I go ahead and read the
number of bytes in a header (6 bytes).

3. I extract the message body size from the header. Call it N bytes.

4. I call ClearCommError() again to find out if there are at least N
bytes in the read buffer. (If there are not, that simply means that the
whole message has not arrived yet.)

5. If there are at least N bytes available, I read the rest of the
message and process it.

6. If there are not at least N bytes available, I'm in trouble since I
now have a corrupt buffer (having extracted the header but nothing
else). Once the rest of the message arrives, it will exist in the
buffer without a header. It's a partial message.

Given this, I would like to either:

1. Inspect the buffer without taking anything out of it. This would
allow me to check the header and see if all the bytes I need are
available yet without actually taking anything out of the buffer until
I know I've got a full message.

2. If I can't do the above, I'd like to insert the header bytes back
into the front of the buffer, just as if I had never touched the
buffer.

Is it possible to do either of these things? MSDN (and my coworkers)
have not shown that it is possible.

Thanks,
Dave