Replace greenwave message consumer with resultsdb and waiverdb message consumers

[AdamWill]

As detailed in #4219 (comment) , I feel like the current design where Greenwave publishes 'decision change' messages and Bodhi listens for them to update the gating status for updates is fundamentally problematic. It requires greenwave to duplicate logic and knowledge from greenwave clients (Bodhi, in this case) which it should not do.

I think a more fundamentally sensible design would be for Bodhi to replace its greenwave 'decision change' message consumer with a resultsdb message consumer which would listen out for results that might potentially change a decision, and query Greenwave for an updated decision when they see one. And, I guess, a waiverdb consumer that would look out for waiver changes similarly.

Bodhi already has a lot of knowledge about what kinds of results and waivers are significant and what decisions to ask Greenwave for; this consumer would only have to reuse that. And it would allow us to throw away all the duplication of that knowledge on the Greenwave side.

@hluk @mattiaverga for comment.

[AdamWill]

Worth noting that I'm kind of filing this as an alternative to filing several issues for making the current design work properly with openQA test gating. It currently does not work properly for several reasons, which would require changes on both Bodhi and Greenwave sides to fix. If others agree that the current design is kind of not the best idea, I would rather work on replacing it than work on digging the hole even deeper. :D

[AdamWill]

So I decided to just go ahead and write the ResultsDB handler as a PoC. It didn't seem very hard. This isn't tested yet, but I think it should more or less work (typos, thinkos etc. excepted) and do the job:

# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License along with
# this program; if not, write to the Free Software Foundation, Inc., 51
# Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
"""
The "resultsdb handler".

This module is responsible for listening for messages from resultsdb.
If a message seems like it might be a result change for an update or
build from an update, we re-check the gating decision for that update.
"""

import logging

import fedora_messaging

from bodhi.server.models import Build, TestGatingStatus, Update
from bodhi.server.util import transactional_session_maker

log = logging.getLogger(__name__)


class ResultsdbHandler:
    """
    The Bodhi ResultsDB Handler.

    A fedora-messaging listener waiting for messages from resultsdb that may
    affect gating status for an update.
    """

    def __init__(self):
        """Initialize the handler."""
        self.db_factory = transactional_session_maker()

    def __call__(self, message: fedora_messaging.api.Message):
        """Handle messages arriving with the configured topic."""
        msg = message.body
        if not msg:
            log.debug("Ignoring message without body.")
            return

        restype = msg.get("data", {}).get("type")

        if restype is None:
            log.debug("Couldn't find result type in ResultsDB message")
            return
        if restype not in ("koji_build", "bodhi_update"):
            log.debug(f"Irrelevant result type {restype}")
            return

        passed = False
        if msg["outcome"] in ("PASSED", "INFO"):
            passed = True

        with self.db_factory():
            # find the update
            if restype == "bodhi_update":
                updateid = msg["data"]["item"]
                update = Update.get(updateid)
            else:
                nvr = msg["data"]["nvr"]
                build = Build.get(nvr)
                if build is None:
                    log.debug(f"Couldn't find build {subject_identifier} in DB")
                    return
                update = build.update

            # update the gating status if there's a chance it changed
            status = update.test_gating_status
            if (
                passed and status in (TestGatingStatus.waiting, TestGatingStatus.failed) or
                not passed and status == TestGatingStatus.passed
            ):
                log.info(f"Updating the test_gating_status for: {update.alias}")
                update.update_test_gating_status()

I'll maybe polish it up into a full PR (and add a waiverdb handler) tomorrow.