feat: use resolved ports in dns interceptor

lib/interceptor/dns.js

@@ -63,11 +63,20 @@ class DNSInstance {
           newOpts.affinity
         )
 
+        let port
+        if (typeof ip.port === 'number') {
+          port = `:${ip.port}`
+        } else if (origin.port !== '') {
+          port = `:${origin.port}`
+        } else {
+          port = ''
+        }
+
         cb(
           null,
           `${origin.protocol}//${
             ip.family === 6 ? `[${ip.address}]` : ip.address
-          }${origin.port === '' ? '' : `:${origin.port}`}`
+          }${port}`
         )
       })
     } else {
@@ -85,11 +94,20 @@ class DNSInstance {
         return
       }
 
+      let port
+      if (typeof ip.port === 'number') {
+        port = `:${ip.port}`
+      } else if (origin.port !== '') {
+        port = `:${origin.port}`
+      } else {
+        port = ''
+      }
+
       cb(
         null,
         `${origin.protocol}//${
           ip.family === 6 ? `[${ip.address}]` : ip.address
-        }${origin.port === '' ? '' : `:${origin.port}`}`
+        }${port}`
       )
     }
   }

test/interceptors/dns.js

@@ -1366,6 +1366,79 @@ test('Should prefer affinity (dual stack - 6)', async t => {
   t.equal(lookupCounter, 1)
 })
 
+test('Should use resolved ports', async t => {
+  t = tspl(t, { plan: 5 })
+
+  let lookupCounter = 0
+  const server1 = createServer()
+  const server2 = createServer()
+  const requestOptions = {
+    method: 'GET',
+    path: '/',
+    headers: {
+      'content-type': 'application/json'
+    }
+  }
+
+  server1.on('request', (req, res) => {
+    res.writeHead(200, { 'content-type': 'text/plain' })
+    res.end('hello world!')
+  })
+
+  server1.listen(0)
+
+  server2.on('request', (req, res) => {
+    res.writeHead(200, { 'content-type': 'text/plain' })
+    res.end('hello world! (x2)')
+  })
+  server2.listen(0)
+
+  await Promise.all([once(server1, 'listening'), once(server2, 'listening')])
+
+  const client = new Agent().compose([
+    dispatch => {
+      return (opts, handler) => {
+        return dispatch(opts, handler)
+      }
+    },
+    dns({
+      lookup (origin, opts, cb) {
+        lookupCounter++
+        cb(null, [
+          { address: '127.0.0.1', family: 4, port: server1.address().port },
+          { address: '127.0.0.1', family: 4, port: server2.address().port }
+        ])
+      }
+    })
+  ])
+
+  after(async () => {
+    await client.close()
+    server1.close()
+    server2.close()
+
+    await Promise.all([once(server1, 'close'), once(server2, 'close')])
+  })
+
+  const response = await client.request({
+    ...requestOptions,
+    origin: 'http://localhost'
+  })
+
+  t.equal(response.statusCode, 200)
+  t.equal(await response.body.text(), 'hello world!')
+
+  const response2 = await client.request({
+    ...requestOptions,
+    origin: 'http://localhost'
+  })
+
+  t.equal(response2.statusCode, 200)
+  t.equal(await response2.body.text(), 'hello world! (x2)')
+
+  t.equal(lookupCounter, 1)
+})
+
 test('Should handle max cached items', async t => {
   t = tspl(t, { plan: 9 })