fix(#3937): respect correct host header

lib/interceptor/dns.js

@@ -358,7 +358,7 @@ module.exports = interceptorOpts => {
           servername: origin.hostname, // For SNI on TLS
           origin: newOrigin,
           headers: {
-            host: origin.hostname,
+            host: origin.host,
             ...origDispatchOpts.headers
           }
         }

test/interceptors/dns.js

@@ -124,7 +124,7 @@ test('Should respect DNS origin hostname for SNI on TLS', async t => {
   }
 
   server.on('request', (req, res) => {
-    t.equal(req.headers.host, 'localhost')
+    t.equal(req.headers.host, `localhost:${server.address().port}`)
     res.writeHead(200, { 'content-type': 'text/plain' })
     res.end('hello world!')
   })
@@ -1731,3 +1731,86 @@ test('Should handle max cached items', async t => {
   t.equal(response3.statusCode, 200)
   t.equal(await response3.body.text(), 'hello world! (x2)')
 })
+
+test('#3937 - Handle host correctly', async t => {
+  t = tspl(t, { plan: 10 })
+
+  const hostsnames = []
+  const server = createServer()
+  const requestOptions = {
+    method: 'GET',
+    path: '/',
+    headers: {
+      'content-type': 'application/json'
+    }
+  }
+
+  server.on('request', (req, res) => {
+    t.equal(req.headers.host, `localhost:${server.address().port}`)
+
+    res.writeHead(200, { 'content-type': 'text/plain' })
+    res.end('hello world!')
+  })
+
+  server.listen(0)
+
+  await once(server, 'listening')
+
+  const client = new Agent().compose([
+    dispatch => {
+      return (opts, handler) => {
+        const url = new URL(opts.origin)
+
+        t.equal(hostsnames.includes(url.hostname), false)
+
+        if (url.hostname[0] === '[') {
+          // [::1] -> ::1
+          t.equal(isIP(url.hostname.slice(1, 4)), 6)
+        } else {
+          t.equal(isIP(url.hostname), 4)
+        }
+
+        hostsnames.push(url.hostname)
+
+        return dispatch(opts, handler)
+      }
+    },
+    dns({
+      lookup: (_origin, _opts, cb) => {
+        cb(null, [
+          {
+            address: '::1',
+            family: 6
+          },
+          {
+            address: '127.0.0.1',
+            family: 4
+          }
+        ])
+      }
+    })
+  ])
+
+  after(async () => {
+    await client.close()
+    server.close()
+
+    await once(server, 'close')
+  })
+
+  const response = await client.request({
+    ...requestOptions,
+    origin: `http://localhost:${server.address().port}`
+  })
+
+  t.equal(response.statusCode, 200)
+  t.equal(await response.body.text(), 'hello world!')
+
+  const response2 = await client.request({
+    ...requestOptions,
+    origin: `http://localhost:${server.address().port}`
+  })
+
+  t.equal(response2.statusCode, 200)
+  t.equal(await response2.body.text(), 'hello world!')
+})