Fix action destination middleware bug (#629)

* only transform destinations

* add changeset

* Add another test around mutating context

* Update comment

* Only add middleware to destination types

Author: danieljackins

.changeset/rich-icons-nail.md

@@ -0,0 +1,5 @@
+---
+'@segment/analytics-next': patch
+---
+
+Fix bug where destination middleware were applying to other plugin types

packages/browser/src/plugins/remote-loader/__tests__/index.test.ts

@@ -1,5 +1,5 @@
 import * as loader from '../../../lib/load-script'
-import { remoteLoader } from '..'
+import { ActionDestination, remoteLoader } from '..'
 import { AnalyticsBrowser, LegacySettings } from '../../../browser'
 import { InitOptions } from '../../../core/analytics'
 import { Context } from '../../../core/context'
@@ -597,4 +597,105 @@ describe('Remote Loader', () => {
       }
     `)
   })
+
+  it('only applies destination middleware to destination actions', async () => {
+    const validPlugin = {
+      name: 'valid',
+      version: '1.0.0',
+      type: 'enrichment',
+      load: () => {},
+      isLoaded: () => true,
+      track: (ctx: Context) => ctx,
+    }
+
+    const cdnSettings: LegacySettings = {
+      integrations: {},
+      middlewareSettings: {
+        routingRules: [
+          {
+            matchers: [
+              {
+                ir: '["=","event",{"value":"Item Impression"}]',
+                type: 'fql',
+              },
+            ],
+            scope: 'destinations',
+            target_type: 'workspace::project::destination::config',
+            transformers: [[{ type: 'drop' }]],
+            destinationName: 'oldValidName',
+          },
+        ],
+      },
+      remotePlugins: [
+        {
+          name: 'valid',
+          creationName: 'oldValidName',
+          url: 'valid',
+          libraryName: 'valid',
+          settings: { foo: true },
+        },
+      ],
+    }
+
+    // @ts-expect-error not gonna return a script tag sorry
+    jest.spyOn(loader, 'loadScript').mockImplementation((url: string) => {
+      if (url === 'valid') {
+        window['valid'] = jest.fn().mockImplementation(() => validPlugin)
+      }
+
+      return Promise.resolve(true)
+    })
+
+    const middleware = jest.fn().mockImplementation(() => true)
+
+    const plugins = await remoteLoader(cdnSettings, {}, {}, false, middleware)
+    const plugin = plugins[0] as ActionDestination
+    plugin.addMiddleware(middleware)
+    await plugin.track(new Context({ type: 'track' }))
+    expect(middleware).not.toHaveBeenCalled()
+  })
+
+  it('non destination type plugins can modify the context', async () => {
+    const validPlugin = {
+      name: 'valid',
+      version: '1.0.0',
+      type: 'enrichment',
+      load: () => {},
+      isLoaded: () => true,
+      track: (ctx: Context) => {
+        ctx.event.name += 'bar'
+        return ctx
+      },
+    }
+
+    const cdnSettings: LegacySettings = {
+      integrations: {},
+      remotePlugins: [
+        {
+          name: 'valid',
+          creationName: 'valid',
+          url: 'valid',
+          libraryName: 'valid',
+          settings: { foo: true },
+        },
+      ],
+    }
+
+    // @ts-expect-error not gonna return a script tag sorry
+    jest.spyOn(loader, 'loadScript').mockImplementation((url: string) => {
+      if (url === 'valid') {
+        window['valid'] = jest.fn().mockImplementation(() => validPlugin)
+      }
+
+      return Promise.resolve(true)
+    })
+
+    const plugins = await remoteLoader(cdnSettings, {}, {}, false)
+    const plugin = plugins[0] as ActionDestination
+    const newCtx = await plugin.track(
+      new Context({ type: 'track', name: 'foo' })
+    )
+
+    expect(newCtx.event.name).toEqual('foobar')
+  })
 })

packages/browser/src/plugins/remote-loader/index.ts

@@ -44,7 +44,9 @@ export class ActionDestination implements Plugin {
   }
 
   addMiddleware(...fn: DestinationMiddlewareFunction[]): void {
-    this.middleware.push(...fn)
+    if (this.type === 'destination') {
+      this.middleware.push(...fn)
+    }
   }
 
   private async transform(ctx: Context): Promise<Context> {
@@ -72,7 +74,12 @@ export class ActionDestination implements Plugin {
     return async (ctx: Context): Promise<Context> => {
       if (!this.action[methodName]) return ctx
 
-      const transformedContext = await this.transform(ctx)
+      let transformedContext: Context = ctx
+      // Transformations only allowed for destination plugins. Other plugin types support mutating events.
+      if (this.type === 'destination') {
+        transformedContext = await this.transform(ctx)
+      }
+
       await this.action[methodName]!(transformedContext)
 
       return ctx