siftlode/backend/tests/test_ytdlp_logging.py

"""E22.5 S4 — yt-dlp explains itself to our log, not to a stdout nobody reads.

`quiet: True` was doing more than quieting: with no `logger`, yt-dlp's whole account of a download
went to the child process's stdout, so "Requested format is not available", a signature-extraction
failure or a POT refusal reached us only as whatever text happened to end up in the raised
exception. A failed download's real reason was routinely one line the app never kept.

Measured against yt-dlp 2026.07.04 (the pinned version): with `logger` set, yt-dlp calls `debug`
for its extraction and progress lines and `warning`/`error` for the rest, and neither `quiet` nor
`no_warnings` gates those calls. The cases below pin what we do with them.
"""

import json
import logging

import pytest

from app import logs
from app.downloads import formats

URL = "https://www.youtube.com/watch?v=dQw4w9WgXcQ&list=PLsomething"


class _Sink(logging.Handler):
    """The stdout handler's own filter and formatter, so a case sees the bytes a deployment writes."""

    def __init__(self):
        super().__init__(level=logging.NOTSET)
        self.lines: list[str] = []
        self.setFormatter(logs.JsonFormatter())
        self.addFilter(logs.ContextFilter())

    def emit(self, record):
        self.lines.append(self.format(record))

    def objects(self) -> list[dict]:
        return [json.loads(line) for line in self.lines]


@pytest.fixture
def sink():
    logger = logging.getLogger("siftlode")
    handler = _Sink()
    previous = logger.level
    logger.addHandler(handler)
    logger.setLevel(logs.TRACE)
    try:
        yield handler
    finally:
        logger.removeHandler(handler)
        logger.setLevel(previous)


@pytest.mark.parametrize(
    ("method", "level"),
    [
        # Several lines per second during a download, and TRACE is the level a user turns on for
        # their own session — so the noisy half is exactly the half the consent gates.
        ("debug", "TRACE"),
        ("info", "DEBUG"),
        ("warning", "WARNING"),
        # yt-dlp calls `error` from `trouble()` just before it raises, on every failed ATTEMPT —
        # the pipeline's fallback client set then often succeeds. The job's verdict is the
        # pipeline's `download.job.failed`, not this.
        ("error", "WARNING"),
    ],
)
def test_each_ytdlp_level_lands_where_it_belongs(sink, method, level):
    getattr(formats._YDL_LOG, method)("something happened")

    (line,) = sink.objects()
    assert line["level"] == level
    assert line["event"] == "download.ytdlp"
    assert "something happened" in line["msg"]


def test_the_source_url_does_not_travel_with_the_explanation(sink):
    formats._YDL_LOG.error(f"ERROR: [youtube] {URL}: Requested format is not available")

    (line,) = sink.objects()
    # The host survives — it is what says which extractor is failing. The rest is a row of this
    # person's download history, and the job id already names the job on every one of these lines.
    assert "www.youtube.com/…" in line["msg"]
    assert "dQw4w9WgXcQ" not in json.dumps(line)
    assert "list=PLsomething" not in json.dumps(line)
    assert "Requested format is not available" in line["msg"]


@pytest.mark.parametrize(
    ("line", "kept", "gone"),
    [
        # The shape nearly every yt-dlp warning and error has: no URL, the id as a prefix.
        (
            "ERROR: [youtube] dQw4w9WgXcQ: Video unavailable",
            "ERROR: [youtube] …: Video unavailable",
            "dQw4w9WgXcQ",
        ),
        # The generic extractor's "id" is the URL's own basename.
        (
            "WARNING: [generic] my-private-holiday-clip: Falling back on generic information",
            "WARNING: [generic] …: Falling back on generic information",
            "my-private-holiday-clip",
        ),
        # `Destination` is yt-dlp's word, not an id; the path after it is built from the title.
        (
            "[download] Destination: /downloads/Some_Channel/Season_2024/A_Private_Title_a7.mp4",
            "[download] Destination: …",
            "A_Private_Title",
        ),
    ],
)
def test_what_names_the_download_comes_out_of_real_ytdlp_shapes(sink, line, kept, gone):
    formats._YDL_LOG.warning(line)

    (obj,) = sink.objects()
    assert obj["msg"] == kept
    assert gone not in json.dumps(obj)


def test_a_download_error_is_scrubbed_the_same_way_wherever_it_is_logged():
    """yt-dlp raises the text it has just logged, and the pipeline logs the exception again one
    line later (`download.job.failed`). The same scrub, or that line puts the URL back."""
    text = "ERROR: Unsupported URL: https://example.org/private/path?id=123"

    assert formats.log_safe(text) == "ERROR: Unsupported URL: example.org/…"


def test_a_line_with_no_url_is_left_alone(sink):
    formats._YDL_LOG.warning("nsig extraction failed: Some formats may be missing")

    (line,) = sink.objects()
    assert "nsig extraction failed: Some formats may be missing" in line["msg"]


def test_the_download_options_carry_the_logger():
    opts = formats.build_ydl_opts({}, "%(id)s.%(ext)s", lambda d: None)

    assert opts["logger"] is formats._YDL_LOG


def test_a_source_adapter_cannot_silence_it():
    """`extra` is the adapter's own options (YouTube's player-client/POT strategy), merged wholesale.
    The logger is set after that merge for the same reason `cookiefile` and the size cap are: an
    adapter must not be able to take away the one account of what went wrong that a failed job
    leaves behind."""
    opts = formats.build_ydl_opts(
        {}, "%(id)s.%(ext)s", lambda d: None, extra={"logger": None, "quiet": False}
    )

    assert opts["logger"] is formats._YDL_LOG