allow rewritePrefix without prefix

Author: StevenMatchett

README.md

@@ -62,6 +62,13 @@ server.register(proxy, {
   http2: false // optional
 })
 
+// /user will be proxied to http://single-signon.example.com/signon/user
+server.register(proxy, {
+  upstream: 'http://single-signon.example.com',
+  rewritePrefix: '/signon', // optional
+  http2: false // optional
+})
+
 server.listen(3000)
 ```
 

index.js

@@ -120,11 +120,7 @@ function setupWebSocketProxy (fastify, options, rewritePrefix) {
   }
 }
 
-function generateRewritePrefix (prefix, opts) {
-  if (!prefix) {
-    return ''
-  }
-
+function generateRewritePrefix (prefix = '', opts) {
   let rewritePrefix = opts.rewritePrefix || (opts.upstream ? new URL(opts.upstream).pathname : '/')
 
   if (!prefix.endsWith('/') && rewritePrefix.endsWith('/')) {

test/test.js

@@ -424,6 +424,26 @@ async function run () {
     t.equal(firstProxyPrefix.body, 'this is /api2/a')
   })
 
+  test('rewritePrefix without prefix', async t => {
+    const proxyServer = Fastify()
+
+    proxyServer.register(proxy, {
+      upstream: `http://localhost:${origin.server.address().port}`,
+      rewritePrefix: '/api2'
+    })
+
+    await proxyServer.listen({ port: 0 })
+
+    t.teardown(() => {
+      proxyServer.close()
+    })
+
+    const firstProxyPrefix = await got(
+      `http://localhost:${proxyServer.server.address().port}/a`
+    )
+    t.equal(firstProxyPrefix.body, 'this is /api2/a')
+  })
+
   test('rewrite location headers', async t => {
     const proxyServer = Fastify()