ios.read_nonblock(maxlen)              → string
ios.read_nonblock(maxlen, outbuf)      → outbuf

Reads at most maxlen bytes from ios using read(2) system call after O_NONBLOCK is set for the underlying file descriptor.

If the optional outbuf argument is present, it must reference a String, which will receive the data.

read_nonblock just calls read(2). It causes all errors read(2) causes: EAGAIN, EINTR, etc. The caller should care such errors.

read_nonblock causes EOFError on EOF.

If the read buffer is not empty, read_nonblock reads from the buffer like readpartial. In this case, read(2) is not called.

Source Code

/*
*  call-seq:
*     ios.read_nonblock(maxlen)              => string
*     ios.read_nonblock(maxlen, outbuf)      => outbuf
*
*  Reads at most <i>maxlen</i> bytes from <em>ios</em> using
*  read(2) system call after O_NONBLOCK is set for
*  the underlying file descriptor.
*
*  If the optional <i>outbuf</i> argument is present,
*  it must reference a String, which will receive the data.
*
*  read_nonblock just calls read(2).
*  It causes all errors read(2) causes: EAGAIN, EINTR, etc.
*  The caller should care such errors.
*
*  read_nonblock causes EOFError on EOF.
*
*  If the read buffer is not empty,
*  read_nonblock reads from the buffer like readpartial.
*  In this case, read(2) is not called.
*
*/

static VALUE
io_read_nonblock(int argc, VALUE *argv, VALUE io)
{
   VALUE ret;

   ret = io_getpartial(argc, argv, io, 1);
   if (NIL_P(ret))
       rb_eof_error();
   else
       return ret;
}