add nice warning message if body omitted

Author: sw-yx

Diff for: lib/serve.js

@@ -1,16 +1,16 @@
-var express = require("express");
-var bodyParser = require("body-parser");
-var expressLogging = require("express-logging");
-var queryString = require("querystring");
-var path = require("path");
-var conf = require("./config");
-var jwtDecode = require("jwt-decode")
+var express = require('express');
+var bodyParser = require('body-parser');
+var expressLogging = require('express-logging');
+var queryString = require('querystring');
+var path = require('path');
+var conf = require('./config');
+var jwtDecode = require('jwt-decode');
 
 function handleErr(err, response) {
   response.statusCode = 500;
-  response.write("Function invocation failed: " + err.toString());
+  response.write('Function invocation failed: ' + err.toString());
   response.end();
-  console.log("Error during invocation: ", err);
+  console.log('Error during invocation: ', err);
   return;
 }
 
@@ -28,22 +28,35 @@ function createCallback(response) {
     if (lambdaResponse.body) {
       response.write(
         lambdaResponse.isBase64Encoded
-          ? Buffer.from(lambdaResponse.body, "base64")
+          ? Buffer.from(lambdaResponse.body, 'base64')
           : lambdaResponse.body
       );
+    } else {
+      if (
+        process.env.CONTEXT !== 'production' ||
+        !process.env.SILENCE_EMPTY_LAMBDA_WARNING
+      )
+        console.log(
+          `Your lambda function didn't return a body, which may be a mistake. Check our Usage docs for examples (https://github.com/netlify/netlify-lambda#usage). 
+          If this is intentional, you can silence this warning by setting process.ENV.SILENCE_EMPTY_LAMBDA_WARNING to a truthy value or process.env.CONTEXT to 'production'`
+        );
     }
     response.end();
-  }
+  };
 }
 
 function promiseCallback(promise, callback) {
   if (!promise) return;
-  if (typeof promise.then !== "function") return;
-  if (typeof callback !== "function") return;
+  if (typeof promise.then !== 'function') return;
+  if (typeof callback !== 'function') return;
 
   promise.then(
-    function(data) {callback(null, data)},
-    function(err) {callback(err, null)}
+    function(data) {
+      callback(null, data);
+    },
+    function(err) {
+      callback(err, null);
+    }
   );
 }
 
@@ -56,7 +69,10 @@ function buildClientContext(headers) {
 
   try {
     return {
-      identity: { url: 'NETLIFY_LAMBDA_LOCALLY_EMULATED_IDENTITY_URL', token: 'NETLIFY_LAMBDA_LOCALLY_EMULATED_IDENTITY_TOKEN' },
+      identity: {
+        url: 'NETLIFY_LAMBDA_LOCALLY_EMULATED_IDENTITY_URL',
+        token: 'NETLIFY_LAMBDA_LOCALLY_EMULATED_IDENTITY_TOKEN'
+      },
       user: jwtDecode(parts[1])
     };
   } catch (e) {
@@ -67,14 +83,14 @@ function buildClientContext(headers) {
 function createHandler(dir, static) {
   return function(request, response) {
     // handle proxies without path re-writes (http-servr)
-    var cleanPath = request.path.replace(/^\/.netlify\/functions/, "")
+    var cleanPath = request.path.replace(/^\/.netlify\/functions/, '');
 
-    var func = cleanPath.split("/").filter(function(e) {
+    var func = cleanPath.split('/').filter(function(e) {
       return e;
     })[0];
     var module = path.join(process.cwd(), dir, func);
-    if(static) {
-      delete require.cache[require.resolve(module)]
+    if (static) {
+      delete require.cache[require.resolve(module)];
     }
     var handler;
     try {
@@ -86,19 +102,27 @@ function createHandler(dir, static) {
 
     var isBase64 =
       request.body &&
-      !(request.headers["content-type"] || "").match(/text|application|multipart\/form-data/);
+      !(request.headers['content-type'] || '').match(
+        /text|application|multipart\/form-data/
+      );
     var lambdaRequest = {
       path: request.path,
       httpMethod: request.method,
       queryStringParameters: queryString.parse(request.url.split(/\?(.+)/)[1]),
       headers: request.headers,
-      body: isBase64 ? Buffer.from(request.body.toString(), "utf8").toString("base64") : request.body,
+      body: isBase64
+        ? Buffer.from(request.body.toString(), 'utf8').toString('base64')
+        : request.body,
       isBase64Encoded: isBase64
     };
 
     var callback = createCallback(response);
 
-    var promise = handler.handler(lambdaRequest, { clientContext: buildClientContext(request.headers) || {} }, callback);
+    var promise = handler.handler(
+      lambdaRequest,
+      { clientContext: buildClientContext(request.headers) || {} },
+      callback
+    );
     promiseCallback(promise, callback);
   };
 }
@@ -107,20 +131,22 @@ exports.listen = function(port, static) {
   var config = conf.load();
   var app = express();
   var dir = config.build.functions || config.build.Functions;
-  app.use(bodyParser.raw({limit: "6mb"}));
-  app.use(bodyParser.text({limit: "6mb", type: "*/*"}));
-  app.use(expressLogging(console, {
-    blacklist: ["/favicon.ico"],
-  }));
+  app.use(bodyParser.raw({ limit: '6mb' }));
+  app.use(bodyParser.text({ limit: '6mb', type: '*/*' }));
+  app.use(
+    expressLogging(console, {
+      blacklist: ['/favicon.ico']
+    })
+  );
 
-  app.get("/favicon.ico", function(req, res) {
+  app.get('/favicon.ico', function(req, res) {
     res.status(204).end();
   });
-  app.all("*", createHandler(dir, static));
+  app.all('*', createHandler(dir, static));
 
   app.listen(port, function(err) {
     if (err) {
-      console.error("Unable to start lambda server: ", err);
+      console.error('Unable to start lambda server: ', err);
       process.exit(1);
     }