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--fingerprint dropped deviceScaleFactor, so the identity contradicted itself #26

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Merged
jehrr merged 1 commit into from
Sep 11, 2026
+23 −1
Merged

--fingerprint dropped deviceScaleFactor, so the identity contradicted itself #26

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14 changes: 14 additions & 0 deletions fingerprint_client.py
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Original file line number Diff line number Diff line change
Expand Up @@ -241,6 +241,20 @@ def playwright_context_kwargs(fp: dict) -> dict:
kwargs["viewport"] = {"width": outer_w, "height": max(400, outer_h)}
kwargs["screen"] = {"width": width, "height": height}

# The device pixel ratio, which Playwright takes as its own context
# option and which was previously dropped on the floor. Measured
# 2026-09-11 against the live API and a live browser: a fingerprint
# stating `deviceScaleFactor: 1.25` produced a browser reporting
# `window.devicePixelRatio === 1`, so the identity contradicted itself
# on an axis any fingerprinter reads for free -- and a contradiction is
# exactly what this flag exists to avoid. Same shape as the three
# defects the family notes already list for this file: a key the API
# returns that nothing applies. Found by comparing a live browser
# against the fingerprint rather than by reading the code.
scale = (fp.get("screen") or {}).get("deviceScaleFactor")
if isinstance(scale, (int, float)) and not isinstance(scale, bool) and scale > 0:
kwargs["device_scale_factor"] = float(scale)

intl = fp.get("intl") or {}
# The fingerprint's OWN locale. This used to be built as
# f"en-{country}", which produced "en-DE" for a German fingerprint — an
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10 changes: 9 additions & 1 deletion smoke_test.py
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Expand Up @@ -1407,7 +1407,8 @@ def wait_for_timeout(self, ms): pass
from fingerprint_client import playwright_context_kwargs, playwright_init_script

FP = {"id": "fp_test", "country": "us",
"screen": {"width": 1920, "height": 1080},
"screen": {"width": 1920, "height": 1080,
"deviceScaleFactor": 1},
"userAgent": {"value": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) Chrome/145.0.0.0"},
"navigator": {"platform": "Win32", "hardwareConcurrency": 8, "deviceMemory": 8},
"webgl": {"vendor": 'Google Inc. "quoted"', "renderer": "ANGLE (RTX 3060)"}}
Expand All @@ -1421,6 +1422,13 @@ def wait_for_timeout(self, ms): pass
and kw["screen"]["width"] == 1920)

js = playwright_init_script(FP)
# The device pixel ratio, which Playwright takes as its own option
# and which was dropped on the floor until a live browser was
# compared against the fingerprint: one stating 1.25 produced a
# browser reporting `devicePixelRatio === 1`, an identity
# contradicting itself on an axis a fingerprinter reads for free.
ok &= check("fingerprint: the device scale factor is carried",
kw.get("device_scale_factor") == 1)
ok &= check("fingerprint: values are JSON-encoded, so a quote in an API string "
"cannot break out of the script",
'\\"quoted\\"' in js and "Google Inc. \"quoted\"" not in js)
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