We've noticed that when nodes have connection problems, they get full segments
with different hashes. Inspection of these segments shows that
they all have identical data up to a point.
Segments that fetched normally will then have the remainder of the data.
Segments that had issues will have a slightly corrupted end.
The data is still valid, and no errors are raised. It just doesn't have all the data.
We noticed that these corrupted segments all were cut off exactly 60sec after their requests
began. We believe this is a server-side timeout on the request that returns whatever data
it has, then closes the container file cleanly before returning successfully.
We detect segments that take > 59 seconds to recieve, and label them as "suspect".
Suspect segments are treated identically to partial segments, except they are always preferred
over partials.
Not only is this redundant, but it creates a race condition where
the worker fails before the latest_worker = workers[-1] check,
and we get an IndexError.
By carefully ensuring most of our dockerfiles are identical in their first few layers,
we only need to build those layers once instead of every time.
In particular, we move installing gevent to before installing common,
so that even when common changes gevent doesn't need to be reinstalled.
This is important because gevent takes ages to install.
Also fixes segment_coverage, which wasn't being installed.
In our usage, we have one channel where we really care / want to know if it's down,
but also a bunch of other channels where they're expected to not be streaming most/all of the time.
To prevent these extra channels making a ton of noise, we introduce the concept of an "important"
channel, indicated by appending a '!' to the channel name in the command line.
So for example, you might specify channels as "foo! foo_backup foo_behindthescenes".
Important channels have the same behaviour as previously.
Non-important channels:
* Have a 20-second retry on a master playlist fetch failure, instead of 5
* Log at debug when the stream is down, instead of info.
This gives us a "stream delay" metric.
Prom doesn't have any native way to check the current value of a metric,
in order to take max(). It only offers increment and set.
We reach into some internals to do this in a hacky way,
but the cleaner way would be to track the value ourselves and have a prom callback
that gets the value.
Sigh, I hate this prom library. I might write my own that's less dumb.
We wrap direct dateutil calls to handle two distinct cases:
* `common.dateutil.parse()`: We want to handle arbitrary timestamps including tz info,
then convert them to UTC.
This is used in HLS parsing, and for command line input for backfiller
* `common.dateutil.parse_utc_only()`: We want to only handle UTC timestamps,
but datetime.strptime isn't flexible enough (eg. can't handle missing fractional component).
This is used for restreamer request params.
* Checks for the SCTE35-OUT/SCTE35-IN marks in the HLS stream that indicate an ad start/end
* Ignores those segments completely
* Doesn't mark the StreamWorker as up until it sees the first non-ad segment
Some other operational notes:
* The main risk this adds is that re-connecting / refreshing master playlist takes longer.
If all downloaders are doing this at the same time (ie. because the stream only just came up,
or during a deployment rollout), all downloaders might be waiting for ads to finish and
you'll miss segments.
* We should run more downloaders to compensate. This also increases the chance at least one of
them won't get any ads, so we get everything right from stream-up.
* The other mitigation we can do is have geographically diverse downloaders. This decreases the risk
that they all get served an ad, and at least at time of writing it seems that no in-stream ads
are served outside of these regions:
> US, Canada, Germany, France, Sweden, Belgium, Poland, Norway, Finland, Denmark, Netherlands, Italy, Spain, Switzerland, Austria, Portugal, UK, Australia, New Zealand
In resource contention scenarios, all calls can start failing due to
not being able to read the response in a timely manner.
This means SegmentGetters never stop retrying, leading to further contention
and a feedback loop.
We attempt to put at least some cap on this scenario by giving up
if an amount of time has elapsed to the point that we know our URL couldn't be valid anymore.
Since we don't actually know how long segment URLs are valid, we are very conservative about
this time, for now setting it to 20min.
When we're under CPU or disk contention, doing other work
can become very slow. We want to avoid spurious errors in this situation
as this causes further retries and further contention.
One easy way to do this is to increase the time we have to finish fetching headers.
To preserve independence between workers and ensure that a
retry (a worker re-create) actually starts from scratch, we only pool connections
on a per-worker basis.
Furthermore, for the same reason, we only let SegmentGetters use the worker's
pool on their first attempt. After that, they create a new pool to ensure they have a clean retry.
Despite this, the result should be that we're almost always re-using an existing connection
when getting segments or media playlists, unless something goes wrong.
SSL connection setup was measured as almost half the CPU time used by the process,
so this change should result in a signifigant CPU usage reduction.
Backdoor allows the operator to telnet into the given port, and get a python shell
running inside the process, from which you can debug, modify state (eg. set the log level),
or whatever. This is extremely useful for debugging weird states that you encounter randomly
but can't easily reproduce, without restarting the process and needing to wait until it happens again.
This meant that old workers would never shut down, causing us to fetch the same media playlist
and same segments multiple times for no reason, and to never give up in face of (non-403/404) errors
even once we have something else working.
Also fix some logging.
When we're out of touch with twitch for long enough, our segment URL will get
so old that twitch stops returning 403 because our token is expired,
and start returning 404s, presumebly becasue the underlying resource has gone away.
We want to treat these the same.
I ran `pyflakes` on the repo and found these bugs:
```
./common/common.py:289: undefined name 'random'
./downloader/downloader/main.py:7: 'random' imported but unused
./backfiller/backfiller/main.py:150: undefined name 'variant'
./backfiller/backfiller/main.py:158: undefined name 'timedelta'
./backfiller/backfiller/main.py:171: undefined name 'sort'
./backfiller/backfiller/main.py:173: undefined name 'sort'
```
(ok, the "imported but unused" one isn't a bug, but the rest are)
This fixes those, as well as a further issue I saw with sorting of hours.
Iterables are not sortable. As an obvious example, what if your iterable was infinite?
As a result, any attempt to sort an iterable that is not already a friendly type like a list
or tuple will result in an error. We avoid this by coercing to list, fully realising the iterable
and putting it into a form that python will let us sort. It also avoids the nasty side-effect
of mutating the list that gets passed into us, which the caller may not expect. Consider this example:
```
>>> my_hours = ["one", "two", "three"]
>>> print my_hours
["one", "two", "three"]
>>> backfill_node(base_dir, node, stream, variants, hours=my_hours, order='forward')
>>> print my_hours
["one", "three", "two"]
```
Also, one of the linter errors was non-trivial to fix - we were trying to get a list of hours
(which is an api call for a particular variant), but at a time when we weren't dealing with a single
variant. My solution was to get a list of hours for ALL variants, and take the union.
Previously, downloader would put files under BASE_DIR/VARIANT/HOUR/FILE.ts
now, it will put files under BASE_DIR/STREAM/VARIANT/HOUR/FILE.ts
This brings downloader in line with restreamer's concept of base_dir
* Fix bug where soft timeout is not cancelled if an exception occurs
* Various logging tweaks
* Prevent master playlist wait time from going negative
* Stop gracefully if stream worker detects end of stream
* Don't treat master playlist 404 as an error, it just means the stream isn't up
* Set a reasonable log format
* Make soft timeouts not always fire
* Change soft_hard_timeout signature slightly for ease-of-use
* Make renames not fail if file already exists
* Misc typos
This makes the code crazy complicated and messy, but means we can be persistent about
not giving up, while still retrying at the same time, and trying multiple urls at once
until we find one that works.
See docstrings for a full discussion on some of the failures we're trying to work around.
This is a useful library and we might as well use it.
Copying it over and slightly modifying it to work was easier than importing all of streamlink.
The original version may be found at 30043408c7/src/streamlink/stream/hls_playlist.py
Mike Lang
Christopher Usher
Mike Lang