fix: add types and updated docs for 'preRewrite'. (#442)

Author: mn4367

README.md

@@ -203,6 +203,18 @@ A function that will be executed before rewriting the URL. It receives the URL,
 
 The function cannot return a promise.
 
+```javascript
+// `/api/abc` will be proxied to `http://api-upstream.com/api2/xyz`
+fastify.register(proxy, {
+  upstream: `http://api-upstream.com`,
+  prefix: '/api',
+  rewritePrefix: '/api2/',
+  preRewrite (url, params, prefix) {
+    return url.replace('abc', 'xyz');
+  }
+})
+```
+
 ### `websocket`
 
 This module has _partial_ support for forwarding websockets by passing a

types/index.d.ts

@@ -77,6 +77,12 @@ type FastifyHttpProxy = FastifyPluginCallback<
 >
 
 declare namespace fastifyHttpProxy {
+  type ProxyPreRewriteHookHandler = (
+    url: string,
+    params: unknown,
+    prefix: string
+  ) => string
+
   type QueryStringFunction = (
     search: string | undefined,
     reqUrl: string,
@@ -91,6 +97,7 @@ declare namespace fastifyHttpProxy {
     preHandler?: ProxyPreHandlerHookHandler;
     beforeHandler?: ProxyPreHandlerHookHandler;
     preValidation?: ProxyPreValidationHookHandler;
+    preRewrite?: ProxyPreRewriteHookHandler;
     config?: Object;
     replyOptions?: FastifyReplyFromHooks;
     wsClientOptions?: ClientOptions & { queryString?: { [key: string]: unknown } | QueryStringFunction; };

types/index.test-d.ts

@@ -41,6 +41,12 @@ app.register(fastifyHttpProxy, {
     expectType<unknown>(result.options)
     expectType<string>(result.url)
   },
+  preRewrite: (url, params, prefix): string => {
+    expectType<string>(url)
+    expectType<unknown>(params)
+    expectType<string>(prefix)
+    return ''
+  },
   base: 'whatever',
   cacheURLs: 10,
   undici: {