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Let PostHog see that ingestion is proxied #24

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Merged
msmfa merged 1 commit into from
Sep 11, 2026
Merged

Let PostHog see that ingestion is proxied #24

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3 changes: 3 additions & 0 deletions src/analytics.js
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Original file line number Diff line number Diff line change
Expand Up @@ -27,6 +27,9 @@ export function sanitizePosthogEvent(event) {
'$lib','$lib_version','$browser','$browser_version','$os','$os_version','$device_type',
'$screen_height','$screen_width','$viewport_height','$viewport_width','$timezone',
'$host','$pathname','$title','$is_identified','$process_person_profile','page_path','page_title',
// How PostHog recognises that ingestion is proxied. It holds our own
// public origin, and without it the reverse proxy check never passes.
'$lib_custom_api_host',
'concept','placement','destination',...campaignKeys,
...webVitalsMetrics.map(name => `$web_vitals_${name}_value`)]);
const properties = Object.fromEntries(Object.entries(event.properties || {}).filter(([key,value]) => keep.has(key) && ['string','number','boolean'].includes(typeof value)));
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2 changes: 2 additions & 0 deletions test/analytics.test.mjs
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Expand Up @@ -77,6 +77,8 @@ test('PostHog loads and ingests through the same origin so blockers cannot drop
const options = h.win.posthog._i[0][1];
assert.equal(options.api_host,'https://www.javascriptin30words.com/e30');
assert.equal(options.ui_host,'https://eu.posthog.com','Links into PostHog still point at the real app');
assert.ok(sanitizePosthogEvent({event:'$pageview',properties:{$lib_custom_api_host:'https://www.javascriptin30words.com/e30'}}).properties.$lib_custom_api_host,
'PostHog detects the proxy from this property, so it has to survive sanitizing');
const loader = h.scripts.map(element=>element.src).find(src=>src.includes('/e30/'));
assert.equal(loader,'https://www.javascriptin30words.com/e30/static/array.js');
assert.ok(!h.scripts.some(element=>element.src.includes('posthog.com')),'No request reveals the vendor hostname');
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