From 733cbd57abc63dcd279526b3666020754bace765 Mon Sep 17 00:00:00 2001
From: Sam Chung <samc@seek.com.au>
Date: Fri, 27 May 2022 10:22:38 +1000
Subject: [PATCH] fix(RequestLogging.createContextStorage): Shallow copy
 context store for the `mixin` function (#155)

---
 src/requestLogging/requestLogging.test.ts | 33 +++++++++++++++++++++++
 src/requestLogging/requestLogging.ts      |  4 +--
 2 files changed, 35 insertions(+), 2 deletions(-)

diff --git a/src/requestLogging/requestLogging.test.ts b/src/requestLogging/requestLogging.test.ts
index 80d352d..ed71775 100644
--- a/src/requestLogging/requestLogging.test.ts
+++ b/src/requestLogging/requestLogging.test.ts
@@ -341,5 +341,38 @@ describe('RequestLogging', () => {
         'x-session-id': '8f859d2a-46a7-4b2d-992b-3da4a18b7ab5',
       });
     });
+
+    it('should not mutate the current context if surface level fields are changed', async () => {
+      const { createContextMiddleware, mixin } = createContextStorage();
+
+      const contextMiddleware = createContextMiddleware();
+
+      // We need to grab the result from within the run() chain
+      let result: Fields = {};
+      const setResultMiddleware = jest.fn(async (_ctx: Context, next: Next) => {
+        const tempResult = mixin();
+        tempResult.abcd = 'extra';
+        result = mixin();
+        await next();
+      });
+
+      const handler = jest.fn((ctx: Context) => {
+        ctx.status = 201;
+      });
+
+      await createAgent(contextMiddleware, setResultMiddleware, handler)
+        .post('/my/test/service')
+        .set('Authenticated-User', 'somesercret')
+        .set('user-agent', 'Safari')
+        .set('x-session-id', '8f859d2a-46a7-4b2d-992b-3da4a18b7ab5')
+        .expect(201);
+
+      expect(result).toStrictEqual({
+        method: 'POST',
+        url: '/my/test/service',
+        'x-request-id': expect.any(String),
+        'x-session-id': '8f859d2a-46a7-4b2d-992b-3da4a18b7ab5',
+      });
+    });
   });
 });
diff --git a/src/requestLogging/requestLogging.ts b/src/requestLogging/requestLogging.ts
index 8618cc7..ec432e6 100644
--- a/src/requestLogging/requestLogging.ts
+++ b/src/requestLogging/requestLogging.ts
@@ -193,8 +193,8 @@ export const createContextStorage = () => {
         await loggerContext.run(getFieldsFn(ctx, contextFields(ctx)), next);
       },
     /**
-     * Returns fields from the logger context store
+     * Returns a shallow copy of fields from the logger context store. For performance reason we only copy the surface level fields.
      */
-    mixin: () => loggerContext.getStore() ?? {},
+    mixin: () => ({ ...loggerContext.getStore() }),
   };
 };