added support for dynamical upstream configuration

index.js

@@ -117,7 +117,7 @@ function generateRewritePrefix (prefix, opts) {
     return ''
   }
 
-  let rewritePrefix = opts.rewritePrefix || new URL(opts.upstream).pathname
+  let rewritePrefix = opts.rewritePrefix || (opts.upstream ? new URL(opts.upstream).pathname : '/')
 
   if (!prefix.endsWith('/') && rewritePrefix.endsWith('/')) {
     rewritePrefix = rewritePrefix.slice(0, -1)
@@ -127,7 +127,7 @@ function generateRewritePrefix (prefix, opts) {
 }
 
 async function httpProxy (fastify, opts) {
-  if (!opts.upstream) {
+  if (!opts.upstream && !(opts.upstream === '' && opts.replyOptions && typeof opts.replyOptions.getUpstream === 'function')) {
     throw new Error('upstream must be specified')
   }
 

test/test.js

@@ -62,6 +62,31 @@ async function run () {
     t.equal(resultA.body, 'this is a')
   })
 
+  test('dynamic upstream for basic proxy', async t => {
+    const server = Fastify()
+    server.register(proxy, {
+      upstream: '',
+      replyOptions: {
+        getUpstream: function (original, base) {
+          return `http://localhost:${origin.server.address().port}`
+        }
+      }
+    })
+
+    await server.listen(0)
+    t.teardown(server.close.bind(server))
+
+    const resultRoot = await got(
+      `http://localhost:${server.server.address().port}`
+    )
+    t.equal(resultRoot.body, 'this is root')
+
+    const resultA = await got(
+      `http://localhost:${server.server.address().port}/a`
+    )
+    t.equal(resultA.body, 'this is a')
+  })
+
   test('redirects passthrough', async t => {
     const server = Fastify()
     server.register(proxy, {
@@ -83,6 +108,32 @@ async function run () {
     t.equal(statusCode, 302)
   })
 
+  test('dynamic upstream for redirects passthrough', async t => {
+    const server = Fastify()
+    server.register(proxy, {
+      upstream: '',
+      replyOptions: {
+        getUpstream: function (original, base) {
+          return `http://localhost:${origin.server.address().port}`
+        }
+      }
+    })
+
+    await server.listen(0)
+    t.teardown(server.close.bind(server))
+
+    const {
+      headers: { location },
+      statusCode
+    } = await got(
+      `http://localhost:${server.server.address().port}/redirect`, {
+        followRedirect: false
+      }
+    )
+    t.equal(location, 'https://fastify.io')
+    t.equal(statusCode, 302)
+  })
+
   test('no upstream will throw', async t => {
     const server = Fastify()
     server.register(proxy)
@@ -121,6 +172,37 @@ async function run () {
     t.equal(resultA.body, 'this is a')
   })
 
+  test('dynamic upstream for prefixed proxy', async t => {
+    const server = Fastify()
+    server.register(proxy, {
+      upstream: '',
+      prefix: '/my-prefix',
+      replyOptions: {
+        getUpstream: function (original, base) {
+          return `http://localhost:${origin.server.address().port}`
+        }
+      }
+    })
+
+    await server.listen(0)
+    t.teardown(server.close.bind(server))
+
+    const resultRoot = await got(
+      `http://localhost:${server.server.address().port}/my-prefix/`
+    )
+    t.equal(resultRoot.body, 'this is root')
+
+    const withoutSlash = await got(
+      `http://localhost:${server.server.address().port}/my-prefix`
+    )
+    t.equal(withoutSlash.body, 'this is root')
+
+    const resultA = await got(
+      `http://localhost:${server.server.address().port}/my-prefix/a`
+    )
+    t.equal(resultA.body, 'this is a')
+  })
+
   test('posting stuff', async t => {
     const server = Fastify()
     server.register(proxy, {
@@ -141,6 +223,31 @@ async function run () {
     t.same(resultRoot.body, { something: 'posted' })
   })
 
+  test('dynamic upstream for posting stuff', async t => {
+    const server = Fastify()
+    server.register(proxy, {
+      upstream: '',
+      replyOptions: {
+        getUpstream: function (original, base) {
+          return `http://localhost:${origin.server.address().port}`
+        }
+      }
+    })
+
+    await server.listen(0)
+    t.teardown(server.close.bind(server))
+
+    const resultRoot = await got(
+      `http://localhost:${server.server.address().port}/this-has-data`,
+      {
+        method: 'POST',
+        json: { hello: 'world' },
+        responseType: 'json'
+      }
+    )
+    t.same(resultRoot.body, { something: 'posted' })
+  })
+
   test('skip proxying the incoming payload', async t => {
     const server = Fastify()
     server.register(proxy, {