Handling streamed data via pipes

Question

A Win32 application (the "server") is sending a continuous stream of data over a named pipe. GetNamedPipeInfo() tells me that input and output buffer sizes are automatically allocated as needed. The pipe is operating in byte mode (although it is sending data units that are bigger than 1 byte (doubles, to be precise)).

Now, my question is this: Can I somehow verify that my application (the "client") is not missing any data when reading from the pipe? I know that those read/write operations are buffered, but I suppose the buffers will not grow indefinitely if the client doesn't fetch the data quickly enough. How do I know if I missed something? Does the server (or the pipe?) silently discard data that is not read in time by the client?

BTW, can I rely on proper alignment of the data the client reads using ReadFile()? As far as I understood, ReadFile() may return with less bytes read than specified, i.e. NumberOfBytesRead <= NumberOfBytesToRead. Do I have to check every time that NumberOfBytesRead is a multiple of sizeof(double)?

Answer 1

The write operation will block if there is no more room in the pipe's buffers. This is from my (old) copy of the SDK manual:

When an application uses the WriteFile function to write to a pipe, the write operation may not finish if the pipe buffer is full. The write operation is completed when a read operation (using the ReadFile function) makes more buffer space available.

Answer 2

Sorry, didn't find out how to comment on your post, Neil.

The write operation will block if there is no more room in the pipe's buffers.

I just discovered that Sysinternals' FileMon can also monitor pipe operations. For testing purposes I connected the client to the named pipe and did no read operations, just waiting. The server writes a few hundred kB to the pipe every 4--5 seconds, even though nobody is fetching the data from the pipe on the client side. No blocking write operation ... And so far no limits in buffer-size seem to have been reached.

This is either a very big buffer ... or the server does some magic additional to just using WriteFile() and waiting for the client to read.