From 69c8a05ca8904f092fb994a4fd43c942d8ccd971 Mon Sep 17 00:00:00 2001
From: RYN BSD <rynbsd04@gmail.com>
Date: Tue, 18 Nov 2025 14:36:55 +0100
Subject: [PATCH] feat: add transform method to request context

- Add `transform` method that allows functional updates to context values
- Method takes a key and transformation function for immutable updates
- Support complex data structures and object transformations
- Maintain request isolation and work with default store values
- Add TypeScript definitions for type-safe transformations
- Include comprehensive test coverage for various use cases
---
 index.js                                  |   8 +-
 test-tap/requestContextPlugin.e2e.test.js | 123 ++++++++++++++++++++++
 types/index.d.ts                          |   4 +
 3 files changed, 132 insertions(+), 3 deletions(-)

diff --git a/index.js b/index.js
index cb86172..1554337 100644
--- a/index.js
+++ b/index.js
@@ -15,9 +15,11 @@ const requestContext = {
   },
   set: (key, value) => {
     const store = asyncLocalStorage.getStore()
-    if (store) {
-      store[key] = value
-    }
+    if (store) store[key] = value
+  },
+  transform: (key, fn) => {
+    const store = asyncLocalStorage.getStore()
+    if (store) store[key] = fn(store[key])
   },
   getStore: () => {
     return asyncLocalStorage.getStore()
diff --git a/test-tap/requestContextPlugin.e2e.test.js b/test-tap/requestContextPlugin.e2e.test.js
index 36e0fa5..d01c274 100644
--- a/test-tap/requestContextPlugin.e2e.test.js
+++ b/test-tap/requestContextPlugin.e2e.test.js
@@ -367,6 +367,129 @@ test('passing a custom resource factory function when create as AsyncResource',
   })
 })
 
+test('transform method correctly updates context values using transformation function', (t) => {
+  t.plan(1)
+
+  const route = (req) => {
+    // Set initial value
+    req.requestContext.set('counter', 5)
+
+    // Use transform to increment the value
+    req.requestContext.transform('counter', (oldValue) => oldValue + 3)
+
+    const finalValue = req.requestContext.get('counter')
+    return Promise.resolve({ value: finalValue })
+  }
+
+  app = initAppGetWithDefaultStoreValues(route, undefined)
+
+  return app.listen({ port: 0, host: '127.0.0.1' }).then(() => {
+    const { address, port } = app.server.address()
+    const url = `http://${address}:${port}`
+
+    return request('GET', url).then((response) => {
+      t.assert.strictEqual(response.body.value, 8)
+    })
+  })
+})
+
+test('transform method works with objects and complex data structures', (t) => {
+  t.plan(2)
+
+  const route = (req) => {
+    req.requestContext.set('user', { id: 'system', permissions: ['read'] })
+
+    // Add a new permission using transform
+    req.requestContext.transform('user', (oldUser) => ({
+      ...oldUser,
+      permissions: [...oldUser.permissions, 'write'],
+    }))
+
+    const user = req.requestContext.get('user')
+    return Promise.resolve({
+      id: user.id,
+      permissions: user.permissions,
+    })
+  }
+
+  app = initAppGetWithDefaultStoreValues(route, undefined)
+
+  return app.listen({ port: 0, host: '127.0.0.1' }).then(() => {
+    const { address, port } = app.server.address()
+    const url = `http://${address}:${port}`
+
+    return request('GET', url).then((response) => {
+      t.assert.strictEqual(response.body.id, 'system')
+      t.assert.deepStrictEqual(response.body.permissions, ['read', 'write'])
+    })
+  })
+})
+
+test('transform method preserves values within single request without affecting others', (t) => {
+  t.plan(2)
+
+  const route = (req) => {
+    const { action } = req.query
+
+    if (action === 'increment') {
+      req.requestContext.transform('counter', (oldValue = 0) => oldValue + 1)
+    }
+
+    return Promise.resolve({ count: req.requestContext.get('counter') })
+  }
+
+  app = initAppGetWithDefaultStoreValues(route, undefined)
+
+  return app.listen({ port: 0, host: '127.0.0.1' }).then(() => {
+    const { address, port } = app.server.address()
+    const url = `http://${address}:${port}`
+
+    // First request with increment
+    return request('GET', url)
+      .query({ action: 'increment' })
+      .then((response1) => {
+        t.assert.strictEqual(response1.body.count, 1)
+
+        // Second request without increment should not see first request's value
+        return request('GET', url).then((response2) => {
+          t.assert.ok(!response2.body.count)
+        })
+      })
+  })
+})
+
+test('transform method works with default store values', (t) => {
+  t.plan(2)
+
+  const route = (req) => {
+    // Transform the default value
+    req.requestContext.transform('user', (oldUser) => ({
+      ...oldUser,
+      status: 'active',
+    }))
+
+    const user = req.requestContext.get('user')
+    return Promise.resolve({
+      id: user.id,
+      status: user.status,
+    })
+  }
+
+  app = initAppGetWithDefaultStoreValues(route, {
+    user: { id: 'system', status: 'inactive' },
+  })
+
+  return app.listen({ port: 0, host: '127.0.0.1' }).then(() => {
+    const { address, port } = app.server.address()
+    const url = `http://${address}:${port}`
+
+    return request('GET', url).then((response) => {
+      t.assert.strictEqual(response.body.id, 'system')
+      t.assert.strictEqual(response.body.status, 'active')
+    })
+  })
+})
+
 test('returns the store', (t) => {
   t.plan(2)
 
diff --git a/types/index.d.ts b/types/index.d.ts
index 303cedc..0b2c3a5 100644
--- a/types/index.d.ts
+++ b/types/index.d.ts
@@ -22,6 +22,10 @@ declare namespace fastifyRequestContext {
   export interface RequestContext {
     get<K extends keyof RequestContextData>(key: K): RequestContextData[K] | undefined
     set<K extends keyof RequestContextData>(key: K, value: RequestContextData[K]): void
+    transform<K extends keyof RequestContextData>(
+      key: K,
+      fn: (oldValue: RequestContextData[K]) => RequestContextData[K],
+    ): void
     getStore(): RequestContextData | undefined
   }