Re: [Libguestfs] [PATCH nbdkit v2 10/10] tests: Test the Python plugin thoroughly.

On Sat, Nov 23, 2019 at 3:10 PM Richard W.M. Jones <rjones(a)redhat.com&gt; wrote: > > On Sat, Nov 23, 2019 at 01:42:15AM +0200, Nir Soffer wrote: > > On Fri, Nov 22, 2019 at 9:55 PM Richard W.M. Jones <rjones(a)redhat.com&gt; wrote: > > > +def pread(h, count, offset, flags): > > > + assert flags == 0 > > > + return h['disk'][offset:offset+count] > > > > Very nice and simple test plugin! > > > > But this returns always a bytearray, which is also what nbdkit python plugin > > expects. But real code using HTTPConnection return bytes: > > > > >>> c = http.client.HTTPSConnection("www.python.org") > > >>> c.request("GET", "/") > > >>> r = c.getresponse() > > >>> r.read()[:10] > > b'<!doctype ' > > > > I think the plugin should support both bytearray, memoryview, or > > bytes. Supporting objects > > implementing the buffer protocol would be best. > > I thought bytearray & bytes were the same thing :-/ > > Would adding this break existing nbdkit Python scripts? Should this > be considered for v2 of the API? Are there performance implications / > improvements from doing this? There is performance implication for v1 plugins like rhv-upload-plugin that need to copy the bytes from imageio server on python side: r = http.getresponse() ... return bytearray(r.read()) This is sad because on the C side we mempcpy the data again. So with this patch we avoid one copy of the two. To avoid all unneeded copies, we need to change pread() to: def pread(h, buf, offset): So the python side we can do: f.readinto(buf) Or: sock.recv_info(buf) It does not work for HTTPResponse, so in this case we have to do: buf[:] = r.read() Since we work on v2 now, I think we should consider this change.

An uglier alternative is: def preadinto(h, buf, offset): Matching python read() and readinto() interface.

> > test-python-plugin.py > > > > This text can use python docstring: > > > > """ > > This tests ... > > """ > > Good point, I'll fix this. We could probably also have nbdkit do > something with the docstring, such as printing it in --help output, > although that's something for another patch series. > > > > + h = nbd.NBD () > > > + cfg = codecs.encode (pickle.dumps (cfg), "base64").decode() > > > > base64.b64encode() is better, avoiding unwanted newlines. > > Ah OK, I originally added strip(), but this is better. > > > > + cmd = ["nbdkit", "-v", "-s", "--exit-with-parent", > > > + "python", srcdir + "/test-python-plugin.py", > > > + "cfg=" + cfg] > > > + h.connect_command (cmd) > > > + return h > > > + > > > +# Test we can send an empty pickled test configuration and do nothing > > > +# else. This is just to ensure the machinery of the test works. > > > +h = test ({}) > > > > So we have now running nbdkit that will exit the python collects when h > > is implicitly closed when creating a new handle? > > > > This is fragile, but can be solved with the help of a testing framework. > [...] > > pytest test-python.py > > I'll probably use unittest though because it's built into Python and > because it's what we use in libguestfs, hivex etc but yes good idea. > > Thanks, > > Rich. > > -- > Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones > Read my programming and virtualization blog: http://rwmj.wordpress.com > Fedora Windows cross-compiler. Compile Windows programs, test, and > build Windows installers. Over 100 libraries supported. > http://fedoraproject.org/wiki/MinGW >