feat: Add preRewrite option.

Signed-off-by: Paolo Insogna <[email protected]>

Author: ShogunPanda

README.md

@@ -197,6 +197,12 @@ An array that contains the types of the methods. Default: `['DELETE', 'GET', 'HE
 
 An array that contains the routes to handle. Default: `['/', '/*']`.
 
+### `preRewrite`
+
+A function that will be executed before rewriting the URL. It receives the URL, the request parameters and the prefix and must return the new URL. 
+
+The function cannot return a promise.
+
 ### `websocket`
 
 This module has _partial_ support for forwarding websockets by passing a

index.js

@@ -83,6 +83,10 @@ function isExternalUrl (url) {
 
 function noop () { }
 
+function noopPreRewrite (url) {
+  return url
+}
+
 function createContext (logger) {
   return { log: logger }
 }
@@ -519,6 +523,7 @@ async function fastifyHttpProxy (fastify, opts) {
   opts = validateOptions(opts)
 
   const preHandler = opts.preHandler || opts.beforeHandler
+  const preRewrite = typeof opts.preRewrite === 'function' ? opts.preRewrite : noopPreRewrite
   const rewritePrefix = generateRewritePrefix(fastify.prefix, opts)
 
   const fromOpts = Object.assign({}, opts)
@@ -585,6 +590,8 @@ async function fastifyHttpProxy (fastify, opts) {
   }
 
   function fromParameters (url, params = {}, prefix = '/') {
+    url = preRewrite(url, params, prefix)
+
     const { path, queryParams } = extractUrlComponents(url)
     let dest = path
 

test/test.js

@@ -981,6 +981,30 @@ async function run () {
       t.assert.strictEqual(body, 'this is a')
     }
   })
+
+  test('preRewrite handler', async t => {
+    const proxyServer = Fastify()
+
+    proxyServer.register(proxy, {
+      upstream: `http://localhost:${origin.server.address().port}`,
+      prefix: '/api',
+      rewritePrefix: '/api2/',
+      preRewrite (url) {
+        return url.replace('abc', 'a')
+      }
+    })
+
+    await proxyServer.listen({ port: 0 })
+
+    t.after(() => {
+      proxyServer.close()
+    })
+
+    const firstProxyPrefix = await got(
+      `http://localhost:${proxyServer.server.address().port}/api/abc`
+    )
+    t.assert.strictEqual(firstProxyPrefix.body, 'this is /api2/a')
+  })
 }
 
 run()