Read from a descriptor without blocking
#include <io.h>
int io_tryread(int64 fd,char* buf,int64 len);
io_tryread tries to read len bytes of data from descriptor fd into buf[0], buf[1], ..., buf[len-1]. (The effects are undefined if len is 0 or smaller.) There are several possible results:
o_tryread returns an integer between 1 and len: This number of bytes was available for immediate reading; the bytes were read into the beginning of buf. Note that this number can be, and often is, smaller than len; you must not assume that io_tryread always succeeds in reading exactly len bytes.
io_tryread returns 0: No bytes were read, because the descriptor is at end of file. For example, this descriptor has reached the end of a disk file, or is reading an empty pipe that has been closed by all writers.
io_tryread returns -1, setting errno to EAGAIN: No bytes were read, because the descriptor is not ready. For example, the descriptor is reading an empty pipe that could still be written to.
io_tryread returns -3, setting errno to something other than EAGAIN: No bytes were read, because the read attempt encountered a persistent error, such as a serious disk failure (EIO), an unreachable network (ENETUNREACH), or an invalid descriptor number (EBADF).
io_tryread does not pause waiting for a descriptor that is not ready. If you want to pause, use io_waitread or io_wait.
You can make io_tryread faster and more efficient by making the socket non-blocking with io_nonblock().