wasi: add nonblock_test.go from gotip, fix nonblock read on Unix-like

[evacchi]

Adapt and add the test from Go's WASI test suite nonblock.go for non-blocking I/O (pipes) to our own suite. Go (almost) straight to the syscall layer for read() on supported platforms; i.e., this is currently Unix-only. This also adds the field fd to the struct osFile because apparently f.file.Fd() resets the O_NONBLOCK flag on the fd /o.

Signed-off-by: Edoardo Vacchi evacchi@users.noreply.github.com

[achille-roussel]

👏

[evacchi]

ew, I guess this is a bad case of WorksOnMyMachine™️

[evacchi]

weird, on Linux it does set nonblock = true, but it still blocks on read??
EDIT: so it looks like it does return EAGAIN but then we are going through the Go runtime, which, probably as in the case of sockets (?) gets in the way of actually returning EAGAIN. In fact, the underlying syscall does return EAGAIN.

we can go straight to the syscall; in that case, EAGAIN is returned correctly and the runtime jumps through all the FDs, but apparently all of them have always no data and return EAGAIN. I guess I am going to debug this later/tomorrow.

EDIT2: well sure they had nothing to read, I was redirecting the pipe to screen instead :D so the syscall approach does work... let's see what I can do...

EDIT3: so that's why I had to setNonblock(fd) every time I called f.file.Fd()... 🤣

func (f *File) Fd() uintptr {
	if f == nil {
		return ^(uintptr(0))
	}

	// If we put the file descriptor into nonblocking mode,
	// then set it to blocking mode before we return it,
	// because historically we have always returned a descriptor
	// opened in blocking mode. The File will continue to work,
	// but any blocking operation will tie up a thread.
	if f.nonblock {
		f.pfd.SetBlocking()
	}

[evacchi]

OK I think I found a solution that is more solid; pretty much, again, like for sockets, going almost straight to the syscall layers for platforms that we support for nonblocking I/O (i.e. Unix for now). Probably better to add some specific test case before finalizing this, but this should make the gotip test work everywhere.

[evacchi]

ok apparently something I did (maybe the f.fd in place of f.file.Fd()) ? broke Windows. I guess it's a good time to call it a day :D

[evacchi]

Windows is fixed, but it looks like everything else is still broken... I'll investigate tomorrow, unless someone else wants to take over :)

[codefromthecrypt]

Thanks for the focused help on this stuff @evacchi!

[evacchi]

added tiny test case for readFd (all platforms) and nonblocking f.Read() (non-Windows)

[evacchi]

the timeouts are back, let's try to revert the commit with the build flags and see if it's related

[codefromthecrypt]

Thanks for fixing this!