import sys, os
import time
import errno

# This must match the initial buffersize used by fileobject.c,
# and the chunksize returned by fread().
BUFSIZE = 4096

def writer(filew):
    print "[write] sending exact buffer"
    filew.write("x"*BUFSIZE)
    filew.flush()
    print "[write] sleeping"
    time.sleep(5)
    print "[write] sending exact buffer"
    filew.write("x"*BUFSIZE)
    filew.flush()
    print "[write] sleeping"
    time.sleep(5)

def reader(filer):
    import fcntl
    fd = filer.fileno()
    flags = fcntl.fcntl (fd, fcntl.F_GETFL, 0)
    flags = flags | os.O_NONBLOCK
    fcntl.fcntl(fd, fcntl.F_SETFL, flags)
    print "[read] sleeping"
    time.sleep(2)
    readsize = 0
    while 1:
        try:
            print "[read] reading"
            data = filer.read()
            print "[read] success (%d)" % len(data)
            readsize += len(data)
            if not data:
                if readsize == 2*BUFSIZE:
                    print "[read] done!"
                    sys.exit(0)
                else:
                    print "[read] boom!"
                    sys.exit(0)
        except IOError, e:
            print "[read] exception:", str(e)
        print "[read] sleeping"
        time.sleep(5)

def main():
    r, w = os.pipe()
    fr, fw = os.fdopen(r, 'r'), os.fdopen(w, 'w')
    pid = os.fork()
    if pid == 0:
        os.close(r)
        writer(fw)
    else:
        os.close(w)
        reader(fr)

if __name__ == "__main__":
    main()