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.TH io_tryread 3
.SH NAME
io_tryread \- read from a descriptor without blocking
.SH SYNTAX
.B #include <libowfat/io.h>
int \fBio_tryread\fP(int64 fd,char* buf,int64 len);
.SH DESCRIPTION
io_tryread tries to read \fIlen\fR bytes of data from descriptor
\fIfd\fR into buf[0], buf[1], ..., buf[len-1]. (The effects are
undefined if \fIlen\fR is 0 or smaller.) There are several possible
results:
.RS 0
.IP \[bu] 3
o_tryread returns an integer between 1 and \fIlen\fR: This number of bytes was
available for immediate reading; the bytes were read into the beginning
of \fIbuf\fR. Note that this number can be, and often is, smaller than \fIlen\fR;
you must not assume that io_tryread always succeeds in reading exactly
\fIlen\fR bytes.
.IP \[bu]
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.
.IP \[bu]
io_tryread returns -1, setting \fIerrno\fR 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.
.IP \[bu]
io_tryread returns -3, setting \fIerrno\fR 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).
.RE
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().
.SH "SEE ALSO"
io_nonblock(3), io_waitread(3), io_tryreadtimeout(3)