Allow collecting signals even if edge function is not defined. (#1112)

Author: silesky

.changeset/yellow-camels-kiss.md

@@ -0,0 +1,5 @@
+---
+'@segment/analytics-signals': patch
+---
+
+Allow collecting signals from sources without an edge function written yet

packages/signals/signals/src/core/processor/__tests__/sandbox-settings.test.ts

@@ -0,0 +1,54 @@
+import { SandboxSettings, SandboxSettingsConfig } from '../sandbox'
+
+describe(SandboxSettings, () => {
+  const edgeFnResponseBody = `function processSignal() { console.log('hello world') }`
+  const baseSettings: SandboxSettingsConfig = {
+    functionHost: undefined,
+    processSignal: undefined,
+    edgeFnDownloadURL: 'http://example.com/download',
+    edgeFnFetchClient: jest.fn().mockReturnValue(
+      Promise.resolve({
+        text: () => edgeFnResponseBody,
+      })
+    ),
+  }
+  test('initializes with provided settings', async () => {
+    const sandboxSettings = new SandboxSettings({ ...baseSettings })
+    expect(baseSettings.edgeFnFetchClient).toHaveBeenCalledWith(
+      baseSettings.edgeFnDownloadURL
+    )
+    expect(await sandboxSettings.processSignal).toEqual(edgeFnResponseBody)
+  })
+
+  test('normalizes edgeFnDownloadURL when functionHost is provided', async () => {
+    const settings: SandboxSettingsConfig = {
+      ...baseSettings,
+      processSignal: undefined,
+      functionHost: 'newHost.com',
+      edgeFnDownloadURL: 'https://original.com/download',
+    }
+    new SandboxSettings(settings)
+    expect(baseSettings.edgeFnFetchClient).toHaveBeenCalledWith(
+      'https://newHost.com/download'
+    )
+  })
+
+  test('creates default processSignal when parameters are missing', async () => {
+    const consoleWarnSpy = jest
+      .spyOn(console, 'warn')
+      .mockImplementation(() => {})
+    const settings: SandboxSettingsConfig = {
+      ...baseSettings,
+      processSignal: undefined,
+      edgeFnDownloadURL: undefined,
+    }
+    const sandboxSettings = new SandboxSettings(settings)
+    expect(await sandboxSettings.processSignal).toEqual(
+      'globalThis.processSignal = function processSignal() {}'
+    )
+    expect(baseSettings.edgeFnFetchClient).not.toHaveBeenCalled()
+    expect(consoleWarnSpy).toHaveBeenCalledWith(
+      expect.stringContaining('processSignal')
+    )
+  })
+})

packages/signals/signals/src/core/processor/sandbox.ts

@@ -145,7 +145,14 @@ export class SandboxSettings {
         : settings.edgeFnDownloadURL
 
     if (!edgeFnDownloadURLNormalized && !settings.processSignal) {
-      throw new Error('edgeFnDownloadURL or processSignal must be defined')
+      // user may be onboarding and not have written a signal -- so do a noop so we can collect signals
+      this.processSignal = Promise.resolve(
+        `globalThis.processSignal = function processSignal() {}`
+      )
+      console.warn(
+        `No processSignal function found. Have you written a processSignal function on app.segment.com?`
+      )
+      return
     }
 
     const fetch = settings.edgeFnFetchClient ?? globalThis.fetch