According to the documentation the answer is Yes. If the named pipe is used with PIPE_NOWAIT and PIPE_TYPE_BYTE, WriteFile should write the bytes to the buffer until it fills up or all the requested bytes are written.
A WriteFile operation is affected by the wait mode of a pipe handle when there is insufficient space in the pipe's buffer. With a blocking-wait handle, the write operation cannot succeed until sufficient space is created in the buffer by a thread reading from the other end of the pipe. With a nonblocking-wait handle, the write operation returns a nonzero value immediately, without writing any bytes (for a message-type pipe) or after writing as many bytes as the buffer holds (for a byte-type pipe).
But, my experiments contradict this statement. When I use WriteFile in PIPE_NOWAIT mode, regardless of the type mode (PIPE_TYPE_BYTE or PIPE_TYPE_MESSAGE), the lpNumberOfBytesWritten is always equal to nNumberOfBytesToWrite when the pipe buffer space is larger than nNumberOfBytesToWrite, and equal to 0 when the pipe buffer space is smaller than nNumberOfBytesToWrite.
I'm only expecting this behavior with PIPE_TYPE_MESSAGE, not with PIPE_TYPE_BYTE.
Am I misreading the documentation?
