fix: update TTL of cached results (#4)

To allow downstream users to know when a cached result will drop
out of the cache, update the TTL of returned cached results to
reflect time passing since the answer was cached.

src/utils/cache.ts

@@ -56,8 +56,9 @@ class CachedAnswers {
         .filter((entry) => {
           return entry.expires > Date.now()
         })
-        .map(({ value }) => ({
+        .map(({ expires, value }) => ({
           ...value,
+          TTL: Math.round((expires - Date.now()) / 1000),
           type: RecordType[value.type]
         }))
 

test/index.spec.ts

@@ -1,6 +1,7 @@
 import { expect } from 'aegir/chai'
 import Sinon from 'sinon'
 import { RecordType, dns } from '../src/index.js'
+import type { Answer } from '../src/index.js'
 
 describe('dns', () => {
   it('should query dns', async () => {
@@ -69,6 +70,40 @@ describe('dns', () => {
     expect(defaultResolver.calledOnce).to.be.true()
   })
 
+  it('should update the TTL of cached results', async () => {
+    const defaultResolver = Sinon.stub()
+
+    const answerA: Answer = {
+      name: 'result-with-update-ttl.com',
+      data: '123.123.123.123',
+      type: RecordType.A,
+      TTL: 60
+    }
+
+    defaultResolver.withArgs('result-with-update-ttl.com').resolves({
+      Answer: [answerA]
+    })
+
+    const resolver = dns({
+      resolvers: {
+        '.': defaultResolver
+      }
+    })
+    const resultA = await resolver.query('result-with-update-ttl.com')
+
+    // wait for long enough that TTL changes
+    await new Promise<void>((resolve) => {
+      setTimeout(() => {
+        resolve()
+      }, 5000)
+    })
+
+    const resultB = await resolver.query('result-with-update-ttl.com')
+
+    expect(defaultResolver.calledOnce).to.be.true()
+    expect(resultA.Answer[0].TTL).to.be.greaterThan(resultB.Answer[0].TTL)
+  })
+
   it('should use separate caches', async () => {
     const defaultResolver = Sinon.stub()