feat: add property so we can check if a client is using a proxy

src/__tests__/posthog-core.js

@@ -405,6 +405,7 @@ describe('posthog core', () => {
                 persistent: 'prop',
                 $window_id: 'windowId',
                 $session_id: 'sessionId',
+                $using_proxy: false,
             })
         })
 
@@ -417,6 +418,7 @@ describe('posthog core', () => {
                 distinct_id: 'abc',
                 $window_id: 'windowId',
                 $session_id: 'sessionId',
+                $using_proxy: false,
             })
         })
 
@@ -439,6 +441,7 @@ describe('posthog core', () => {
                 $session_id: 'sessionId',
                 $window_id: 'windowId',
                 token: 'testtoken',
+                $using_proxy: false,
             })
         })
 

src/__tests__/utils/request-router.test.ts

@@ -1,3 +1,4 @@
+import { defaultConfig } from '../../posthog-core'
 import { RequestRouter, RequestRouterTarget } from '../../utils/request-router'
 
 describe('request-router', () => {
@@ -75,4 +76,16 @@ describe('request-router', () => {
         mockPostHog.config.api_host = 'https://eu.posthog.com'
         expect(router.endpointFor('api')).toEqual('https://eu.i.posthog.com')
     })
+
+    it('should check this api_host for a proxy', () => {
+        const mockPostHog = { config: {} }
+        const router = new RequestRouter(mockPostHog as any)
+        expect(router.isUsingProxy()).toEqual(false)
+
+        mockPostHog.config['api_host'] = defaultConfig().api_host
+        expect(router.isUsingProxy()).toEqual(false)
+
+        mockPostHog.config['api_host'] = 'https://z.example.com'
+        expect(router.isUsingProxy()).toEqual(true)
+    })
 })

src/posthog-core.ts

@@ -813,6 +813,8 @@ export class PostHog {
             properties['$window_id'] = windowId
         }
 
+        properties['$using_proxy'] = this.requestRouter.isUsingProxy()
+
         if (
             this.sessionPropsManager &&
             this.config.__preview_send_client_session_params &&

src/utils/request-router.ts

@@ -1,4 +1,4 @@
-import { PostHog } from '../posthog-core'
+import { PostHog, defaultConfig } from '../posthog-core'
 
 /**
  * The request router helps simplify the logic to determine which endpoints should be called for which things
@@ -43,6 +43,10 @@ export class RequestRouter {
         return this._regionCache[this.apiHost]
     }
 
+    isUsingProxy(): boolean {
+        return this.instance.config.api_host != null && this.instance.config.api_host !== defaultConfig().api_host
+    }
+
     endpointFor(target: RequestRouterTarget, path: string = ''): string {
         if (path) {
             path = path[0] === '/' ? path : `/${path}`