readIntFd

fn readIntFd(fd: posix.fd_t) !ErrInt {
    var buffer: [8]u8 = undefined;
    var i: usize = 0;
    while (true) {
        const rc = posix.system.read(fd, buffer[i..].ptr, buffer.len - i);
        switch (posix.errno(rc)) {
            .SUCCESS => {
                const n: usize = @intCast(rc);
                if (n == 0) break;
                i += n;
                continue;
            },
            .INTR => continue,
            else => |err| return posix.unexpectedErrno(err),
        }
    }
    if (buffer.len - i != 0) return error.EndOfStream;
    return @intCast(std.mem.readInt(u64, &buffer, .little));
}