feat: add dns cache #2440

README.md

@@ -365,6 +365,52 @@ Returns: `URL`
 * **protocol** `string` (optional)
 * **search** `string` (optional)
 
+## DNS caching
+
+Undici provides DNS caching via the `DNSResolver` class.
+
+This functionality is coming from [cacheable-lookup](https://github.com/szmarczak/cacheable-lookup/tree/9e60c9f6e74a003692aec68f3ddad93afe613b8f) package.
+
+By default a global DNSResolver will be created and passed down by the agent to the pool.
+Here is an example of how to configure a custom DNSResolver:
+
+```js
+new Agent({
+    dnsResolverOptions: {
+      lookupOptions: { family: 6, hints: ALL }
+    }
+  })
+```
+
+To disable DNS caching for an agent:
+
+```js
+new Agent({
+  dnsResolverOptions: {
+    disable: true
+  }
+})
+```
+
+Provide your custom DNS resolver, it must implement the method `lookup`:
+
+```js
+new Agent({
+  dnsResolver: new MyCustomDNSResolver()
+})
+```
+
+All arguments match [`cacheable-lookup`](https://github.com/szmarczak/cacheable-lookup/tree/9e60c9f6e74a003692aec68f3ddad93afe613b8f) package
+
+Extra arguments available in Undici:
+
+* **lookupOptions**
+  * **family** `4 | 6 | 0` - Default: `0`
+  * **hints** [`getaddrinfo flags`](https://nodejs.org/api/dns.html#supported-getaddrinfo-flags)
+  * **all** `Boolean` - Default: `false`
+
+* **scheduling** `'first' | 'random'` - Default: `'first'`
+
 ## Specification Compliance
 
 This section documents parts of the HTTP/1.1 specification that Undici does
@@ -413,9 +459,9 @@ Refs: https://fetch.spec.whatwg.org/#atomic-http-redirect-handling
 
 If you experience problem when connecting to a remote server that is resolved by your DNS servers to a IPv6 (AAAA record)
 first, there are chances that your local router or ISP might have problem connecting to IPv6 networks. In that case
-undici will throw an error with code `UND_ERR_CONNECT_TIMEOUT`. 
+undici will throw an error with code `UND_ERR_CONNECT_TIMEOUT`.
 
-If the target server resolves to both a IPv6 and IPv4 (A records) address and you are using a compatible Node version 
+If the target server resolves to both a IPv6 and IPv4 (A records) address and you are using a compatible Node version
 (18.3.0 and above), you can fix the problem by providing the `autoSelectFamily` option (support by both `undici.request`
 and `undici.Agent`) which will enable the family autoselection algorithm when establishing the connection.
 

index.js

@@ -165,3 +165,6 @@ module.exports.MockClient = MockClient
 module.exports.MockPool = MockPool
 module.exports.MockAgent = MockAgent
 module.exports.mockErrors = mockErrors
+
+const DNSResolver = require('./lib/dns-resolver')
+module.exports.DNSResolver = DNSResolver

lib/agent.js

@@ -7,6 +7,7 @@ const Pool = require('./pool')
 const Client = require('./client')
 const util = require('./core/util')
 const createRedirectInterceptor = require('./interceptor/redirectInterceptor')
+const DNSResolver = require('./dns-resolver')
 
 const kOnConnect = Symbol('onConnect')
 const kOnDisconnect = Symbol('onDisconnect')
@@ -22,6 +23,18 @@ function defaultFactory (origin, opts) {
     : new Pool(origin, opts)
 }
 
+function getDNSResolver (options) {
+  if (options?.dnsResolverOptions?.disable) {
+    return
+  }
+
+  if (options.dnsResolver && typeof options.dnsResolver.lookup === 'function') {
+    return options.dnsResolver
+  }
+
+  return new DNSResolver(options.dnsResolverOptions)
+}
+
 class Agent extends DispatcherBase {
   constructor ({ factory = defaultFactory, maxRedirections = 0, connect, ...options } = {}) {
     super()
@@ -50,6 +63,7 @@ class Agent extends DispatcherBase {
     this[kOptions].interceptors = options.interceptors
       ? { ...options.interceptors }
       : undefined
+    this[kOptions].dnsResolver = getDNSResolver(options)
     this[kMaxRedirections] = maxRedirections
     this[kFactory] = factory
     this[kClients] = new Map()

lib/core/symbols.js

@@ -59,5 +59,7 @@ module.exports = {
   kHTTP2CopyHeaders: Symbol('http2 copy headers'),
   kHTTPConnVersion: Symbol('http connection version'),
   kRetryHandlerDefaultRetry: Symbol('retry agent default retry'),
-  kConstruct: Symbol('constructable')
+  kConstruct: Symbol('constructable'),
+  kDnsCacheSize: Symbol('dns cache size'),
+  kDnsHostnamesToFallback: Symbol('dns hostnames to fallback')
 }