Expose event + context of Netlify Functions on the req object

When a page is being SSR-ed by a Netlify Function, allow users to access
the function's event and context parameters. These can be accessed as
a property on the `req` object in all SSR-ed pages and in API routes:
- req.netlifyFunction.event
- req.netlifyFunction.context

This allows users to access/leverage Netlify identity for their Next.js
page.
See: #20

It also allows users to modify the callbackWaitsForEmptyEventLoop
behavior.
See: #66 (comment))

Author: FinnWoelm

cypress/fixtures/pages/api/context.js

@@ -0,0 +1,3 @@
+export default async function context(req, res) {
+  res.json({ req, res });
+}

cypress/fixtures/pages/getServerSideProps/context.js

@@ -0,0 +1,11 @@
+const Context = ({ context }) => <pre>{JSON.stringify(context, 2, " ")}</pre>;
+
+export const getServerSideProps = async (context) => {
+  return {
+    props: {
+      context,
+    },
+  };
+};
+
+export default Context;

cypress/integration/default_spec.js

@@ -136,6 +136,31 @@ describe("getInitialProps", () => {
 });
 
 describe("getServerSideProps", () => {
+  it("exposes function context on the req object", () => {
+    cy.visit("/getServerSideProps/context");
+
+    cy.get("pre")
+      .first()
+      .then((json) => {
+        const {
+          req: {
+            netlifyFunction: { event, context },
+          },
+        } = JSON.parse(json.html());
+
+        expect(event).to.have.property("path", "/getServerSideProps/context");
+        expect(event).to.have.property("httpMethod", "GET");
+        expect(event).to.have.property("headers");
+        expect(event).to.have.property("multiValueHeaders");
+        expect(event).to.have.property("isBase64Encoded");
+        expect(context.done).to.be.undefined;
+        expect(context.getRemainingTimeInMillis).to.be.undefined;
+        expect(context).to.have.property("awsRequestId");
+        expect(context).to.have.property("callbackWaitsForEmptyEventLoop");
+        expect(context).to.have.property("clientContext");
+      });
+  });
+
   context("with static route", () => {
     it("loads TV shows", () => {
       cy.visit("/getServerSideProps/static");
@@ -534,6 +559,27 @@ describe("API endpoint", () => {
     cy.get("h1").should("contain", "Show #999");
     cy.get("p").should("contain", "Flash Gordon");
   });
+
+  it("exposes function context on the req object", () => {
+    cy.request("/api/context").then((response) => {
+      const {
+        req: {
+          netlifyFunction: { event, context },
+        },
+      } = response.body;
+
+      expect(event).to.have.property("path", "/api/context");
+      expect(event).to.have.property("httpMethod", "GET");
+      expect(event).to.have.property("headers");
+      expect(event).to.have.property("multiValueHeaders");
+      expect(event).to.have.property("isBase64Encoded");
+      expect(context.done).to.be.undefined;
+      expect(context.getRemainingTimeInMillis).to.be.undefined;
+      expect(context).to.have.property("awsRequestId");
+      expect(context).to.have.property("callbackWaitsForEmptyEventLoop");
+      expect(context).to.have.property("clientContext");
+    });
+  });
 });
 
 describe("Preview Mode", () => {

lib/templates/createRequestObject.js

@@ -6,7 +6,7 @@ const http = require("http");
 // Based on API Gateway Lambda Compat
 // Source: https://github.com/serverless-nextjs/serverless-next.js/blob/master/packages/compat-layers/apigw-lambda-compat/lib/compatLayer.js
 
-const createRequestObject = ({ event }) => {
+const createRequestObject = ({ event, context }) => {
   const {
     requestContext = {},
     path = "",
@@ -52,6 +52,14 @@ const createRequestObject = ({ event }) => {
   req.rawHeaders = [];
   req.headers = {};
 
+  // Expose Netlify Function event and callback on request object.
+  // This makes it possible to access the clientContext, for example.
+  // See: https://github.com/netlify/next-on-netlify/issues/20
+  // It also allows users to change the behavior of waiting for empty event
+  // loop.
+  // See: https://github.com/netlify/next-on-netlify/issues/66#issuecomment-719988804
+  req.netlifyFunction = { event, context };
+
   for (const key of Object.keys(multiValueHeaders)) {
     for (const value of multiValueHeaders[key]) {
       req.rawHeaders.push(key);

lib/templates/netlifyFunction.js

@@ -16,9 +16,7 @@ exports.handler = async (event, context, callback) => {
   console.log("[request]", path);
 
   // Render the Next.js page
-  const response = await renderNextPage({
-    ...event,
-  });
+  const response = await renderNextPage({ event, context });
 
   // Convert header values to string. Netlify does not support integers as
   // header values. See: https://github.com/netlify/cli/issues/451

lib/templates/renderNextPage.js

@@ -4,14 +4,14 @@ const createRequestObject = require("./createRequestObject");
 const createResponseObject = require("./createResponseObject");
 
 // Render the Next.js page
-const renderNextPage = (event) => {
+const renderNextPage = ({ event, context }) => {
   // The Next.js page is rendered inside a promise that is resolved when the
   // Next.js page ends the response via `res.end()`
   const promise = new Promise((resolve) => {
     // Create a Next.js-compatible request and response object
     // These mock the ClientRequest and ServerResponse classes from node http
     // See: https://nodejs.org/api/http.html
-    const req = createRequestObject({ event });
+    const req = createRequestObject({ event, context });
     const res = createResponseObject({
       onResEnd: (response) => resolve(response),
     });