Dev: Fix false positives for Netlify Forms (#973)

* Dev: Fix false positives for Netlify Forms

* Add test for Netlify Form false positive

* Formatting

src/commands/dev/index.js

@@ -22,6 +22,7 @@ const Command = require('../../utils/command')
 const chalk = require('chalk')
 const jwtDecode = require('jwt-decode')
 const open = require('open')
+const contentType = require('content-type')
 const { NETLIFYDEV, NETLIFYDEVLOG, NETLIFYDEVWARN, NETLIFYDEVERR } = require('../../utils/logo')
 const boxen = require('boxen')
 const { createTunnel, connectTunnel } = require('../../utils/live-tunnel')
@@ -211,7 +212,12 @@ async function startProxy(settings = {}, addonUrls, configPath, projectDir, func
 
       if (match) return serveRedirect(req, res, proxy, match, options)
 
-      if (req.method === 'POST' && !isInternal(req.url)) {
+      const ct = req.headers['content-type'] ? contentType.parse(req) : {}
+      if (
+        req.method === 'POST' &&
+        !isInternal(req.url) &&
+        (ct.type.endsWith('/x-www-form-urlencoded') || ct.type === 'multipart/form-data')
+      ) {
         return proxy.web(req, res, { target: functionsServer })
       }
 
@@ -329,7 +335,13 @@ async function serveRedirect(req, res, proxy, match, options) {
       return handler(req, res, {})
     }
 
-    if (req.method === 'POST' && !isInternal(req.url) && !isInternal(destURL)) {
+    const ct = req.headers['content-type'] ? contentType.parse(req) : {}
+    if (
+      req.method === 'POST' &&
+      !isInternal(req.url) &&
+      !isInternal(destURL) &&
+      (ct.type.endsWith('/x-www-form-urlencoded') || ct.type === 'multipart/form-data')
+    ) {
       return proxy.web(req, res, { target: options.functionsServer })
     }
 

tests/dev.test.js

@@ -192,6 +192,18 @@ test('Netlify Forms support', async t => {
   })
 })
 
+test('Netlify Forms: False positive', async t => {
+  const response = await fetch(`http://${host}/?ding=dong`, {
+    method: 'POST',
+    body: 'Something',
+    headers: {
+      'content-type': 'text/plain',
+    },
+  }).then(r => r.text())
+
+  t.deepEqual(response, 'Method Not Allowed')
+})
+
 test('functions env file overriding prod var', async t => {
   const response = await fetch(`http://${host}/.netlify/functions/override-process-env`).then(r => r.text())