Refactor: Split reqResMapper into createRequest/ResponseObject

Split the reqResMapper function into two separate files. One for
creating the request object and one for creating the response object.
This is easier to read and understand.

Author: FinnWoelm

lib/helpers/setupNetlifyFunctionForPage.js

@@ -24,7 +24,12 @@ const setupNetlifyFunctionForPage = ({ filePath, functionsPath }) => {
   });
 
   // Copy function helpers
-  ["renderNextPage.js", "reqResMapper.js"].forEach((helper) => {
+  const functionHelpers = [
+    "renderNextPage.js",
+    "createRequestObject.js",
+    "createResponseObject.js",
+  ];
+  functionHelpers.forEach((helper) => {
     copySync(join(TEMPLATES_DIR, helper), join(functionDirectory, helper), {
       overwrite: false,
       errorOnExist: true,

lib/templates/createRequestObject.js

@@ -0,0 +1,81 @@
+const Stream = require("stream");
+const queryString = require("querystring");
+const http = require("http");
+
+// Mock a HTTP IncomingMessage object from the Netlify Function event parameters
+// 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 {
+    requestContext = {},
+    path = "",
+    multiValueQueryStringParameters,
+    pathParameters,
+    httpMethod,
+    multiValueHeaders = {},
+    body,
+    isBase64Encoded,
+  } = event;
+
+  const newStream = new Stream.Readable();
+  const req = Object.assign(newStream, http.IncomingMessage.prototype);
+  req.url =
+    (requestContext.path || path || "").replace(
+      new RegExp("^/" + requestContext.stage),
+      ""
+    ) || "/";
+
+  let qs = "";
+
+  if (multiValueQueryStringParameters) {
+    qs += queryString.stringify(multiValueQueryStringParameters);
+  }
+
+  if (pathParameters) {
+    const pathParametersQs = queryString.stringify(pathParameters);
+
+    if (qs.length > 0) {
+      qs += `&${pathParametersQs}`;
+    } else {
+      qs += pathParametersQs;
+    }
+  }
+
+  const hasQueryString = qs.length > 0;
+
+  if (hasQueryString) {
+    req.url += `?${qs}`;
+  }
+
+  req.method = httpMethod;
+  req.rawHeaders = [];
+  req.headers = {};
+
+  for (const key of Object.keys(multiValueHeaders)) {
+    for (const value of multiValueHeaders[key]) {
+      req.rawHeaders.push(key);
+      req.rawHeaders.push(value);
+    }
+    req.headers[key.toLowerCase()] = multiValueHeaders[key].toString();
+  }
+
+  req.getHeader = (name) => {
+    return req.headers[name.toLowerCase()];
+  };
+  req.getHeaders = () => {
+    return req.headers;
+  };
+
+  req.connection = {};
+
+  if (body) {
+    req.push(body, isBase64Encoded ? "base64" : undefined);
+  }
+
+  req.push(null);
+
+  return req;
+};
+
+module.exports = createRequestObject;

lib/templates/createResponseObject.js

@@ -0,0 +1,81 @@
+const Stream = require("stream");
+
+// Mock a HTTP ServerResponse object that returns a Netlify Function-compatible
+// response via the onResEnd callback when res.end() is called.
+// 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 createResponseObject = ({ onResEnd }) => {
+  const response = {
+    isBase64Encoded: true,
+    multiValueHeaders: {},
+  };
+
+  const res = new Stream();
+  Object.defineProperty(res, "statusCode", {
+    get() {
+      return response.statusCode;
+    },
+    set(statusCode) {
+      response.statusCode = statusCode;
+    },
+  });
+  res.headers = {};
+  res.writeHead = (status, headers) => {
+    response.statusCode = status;
+    if (headers) res.headers = Object.assign(res.headers, headers);
+  };
+  res.write = (chunk) => {
+    if (!response.body) {
+      response.body = Buffer.from("");
+    }
+
+    response.body = Buffer.concat([
+      Buffer.isBuffer(response.body)
+        ? response.body
+        : Buffer.from(response.body),
+      Buffer.isBuffer(chunk) ? chunk : Buffer.from(chunk),
+    ]);
+  };
+  res.setHeader = (name, value) => {
+    res.headers[name.toLowerCase()] = value;
+  };
+  res.removeHeader = (name) => {
+    delete res.headers[name.toLowerCase()];
+  };
+  res.getHeader = (name) => {
+    return res.headers[name.toLowerCase()];
+  };
+  res.getHeaders = () => {
+    return res.headers;
+  };
+  res.hasHeader = (name) => {
+    return !!res.getHeader(name);
+  };
+  res.end = (text) => {
+    if (text) res.write(text);
+    if (!res.statusCode) {
+      res.statusCode = 200;
+    }
+
+    if (response.body) {
+      response.body = Buffer.from(response.body).toString("base64");
+    }
+    response.multiValueHeaders = res.headers;
+    res.writeHead(response.statusCode);
+
+    // Convert all multiValueHeaders into arrays
+    for (const key of Object.keys(response.multiValueHeaders)) {
+      if (!Array.isArray(response.multiValueHeaders[key])) {
+        response.multiValueHeaders[key] = [response.multiValueHeaders[key]];
+      }
+    }
+
+    // Call onResEnd handler with the response object
+    onResEnd(response);
+  };
+
+  return res;
+};
+
+module.exports = createResponseObject;

lib/templates/renderNextPage.js

@@ -1,6 +1,7 @@
 // Load the NextJS page
 const nextPage = require("./nextPage");
-const reqResMapper = require("./reqResMapper");
+const createRequestObject = require("./createRequestObject");
+const createResponseObject = require("./createResponseObject");
 
 // Render the Next.js page
 const renderNextPage = (event) => {
@@ -10,8 +11,10 @@ const renderNextPage = (event) => {
     // 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 callback = (_null, response) => resolve(response);
-    const { req, res } = reqResMapper(event, callback);
+    const req = createRequestObject({ event });
+    const res = createResponseObject({
+      onResEnd: (response) => resolve(response),
+    });
 
     // Check if page is a Next.js page or an API route
     const isNextPage = nextPage.render instanceof Function;