def getdescfromdrev(drev):
    """get description (commit message) from "Differential Revision"

    This is similar to differential.getcommitmessage API. But we only care
    about limited fields: title, summary, test plan, and URL.
    """
    title = drev[b'title']
    summary = drev[b'summary'].rstrip()
    testplan = drev[b'testPlan'].rstrip()
    if testplan:
        testplan = b'Test Plan:\n%s' % testplan
    uri = b'Differential Revision: %s' % drev[b'uri']
    return b'\n\n'.join(filter(None, [title, summary, testplan, uri]))
