Feature: Custom handler (#57)

* feat: add support for custom handlers

README.md

@@ -22,6 +22,7 @@ The plugin targets [Next 8 serverless mode](https://nextjs.org/blog/next-8/#serv
 - [Overriding page configuration](#overriding-page-configuration)
 - [Custom page routing](#custom-page-routing)
 - [Custom error page](#custom-error-page)
+- [Custom handler](#custom-handler)
 - [Examples](#examples)
 - [Contributing](#contributing)
 
@@ -267,6 +268,36 @@ class Error extends React.Component {
 export default Error;
 ```
 
+### Custom handler
+
+If you need to customize the lambda handler you can do so by providing a path to your own handler in the `customHandler` field. Note that it resolves the path to the custom handler relative to your `next.config.js`.
+
+```yml
+plugins:
+  - serverless-nextjs-plugin
+
+custom:
+  serverless-nextjs:
+    nextConfigDir: ./
+    customHandler: ./handler.js
+```
+
+The custom handler needs to look something like this:
+
+```js
+const compat = require('serverless-nextjs-plugin/aws-lambda-compat');
+
+module.exports = (page) => {
+  const handler = (event, context, callback) => {
+    // do any stuff you like
+    // make sure the next page renders etc.
+    compat(page)(event, context, callback);
+    // do any other stuff you like
+  };
+  return handler;
+};
+```
+
 ## Examples
 
 See the `examples/` directory.

__tests__/index.test.js

@@ -103,7 +103,8 @@ describe("ServerlessNextJsPlugin", () => {
       return plugin.buildNextPages().then(() => {
         expect(build).toBeCalledWith(
           new PluginBuildDir(nextConfigDir),
-          pageConfig
+          pageConfig,
+          undefined
         );
       });
     });

aws-lambda-compat.js

@@ -0,0 +1,8 @@
+const reqResMapper = require("./lib/compatLayer");
+
+const handlerFactory = page => (event, _context, callback) => {
+  const { req, res } = reqResMapper(event, callback);
+  page.render(req, res);
+};
+
+module.exports = handlerFactory;

index.js

@@ -56,9 +56,12 @@ class ServerlessNextJsPlugin {
     servicePackage.include.push(
       path.posix.join(pluginBuildDir.posixBuildDir, "**")
     );
-    return build(pluginBuildDir, this.getPluginConfigValue("pageConfig")).then(
-      nextPages => this.setNextPages(nextPages)
-    );
+
+    return build(
+      pluginBuildDir,
+      this.getPluginConfigValue("pageConfig"),
+      this.getPluginConfigValue("customHandler")
+    ).then(nextPages => this.setNextPages(nextPages));
   }
 
   setNextPages(nextPages) {

lib/__tests__/build.test.js

@@ -130,30 +130,8 @@ describe("build", () => {
       nextPages => {
         expect(getNextPagesFromBuildDir).toBeCalledWith(
           new PluginBuildDir(nextConfigDir).buildDir,
-          pageConfig
-        );
-        expect(nextPages).toEqual(mockNextPages);
-      }
-    );
-  });
-
-  it("should call getNextPagesFromBuildDir and return NextPage instances for each nextPage copied", () => {
-    expect.assertions(2);
-
-    const parsedConfig = parsedNextConfigurationFactory();
-    parseNextConfiguration.mockResolvedValueOnce(parsedConfig);
-    const mockNextPages = [new NextPage("/foo/bar"), new NextPage("/foo/baz")];
-    getNextPagesFromBuildDir.mockResolvedValueOnce(mockNextPages);
-
-    const nextConfigDir = "path/to/next-app";
-
-    const pageConfig = {};
-
-    return build(new PluginBuildDir(nextConfigDir), pageConfig).then(
-      nextPages => {
-        expect(getNextPagesFromBuildDir).toBeCalledWith(
-          new PluginBuildDir(nextConfigDir).buildDir,
-          pageConfig
+          pageConfig,
+          undefined
         );
         expect(nextPages).toEqual(mockNextPages);
       }
@@ -174,7 +152,7 @@ describe("build", () => {
     getNextPagesFromBuildDir.mockResolvedValueOnce(nextPages);
 
     return build(new PluginBuildDir(nextConfigDir)).then(() => {
-      expect(rewritePageHandlers).toBeCalledWith(nextPages);
+      expect(rewritePageHandlers).toBeCalledWith(nextPages, undefined);
     });
   });
 });

lib/__tests__/copyBuildFiles.test.js

@@ -54,7 +54,10 @@ describe("copyBuildFiles", () => {
     it("should call fs copy with the compatLayer file", () => {
       expect(fse.copy).toBeCalledWith(
         path.join(__dirname, "..", `compatLayer.js`),
-        path.join(pluginBuildDir, "compatLayer.js")
+        path.join(
+          pluginBuildDir,
+          "./node_modules/serverless-nextjs-plugin/lib/compatLayer.js"
+        )
       );
     });
   });

lib/__tests__/getCompatLayerCode.test.js → lib/__tests__/getFactoryHandlerCode.test.js

@@ -1,38 +1,44 @@
 const path = require("path");
-const getCompatLayerCode = require("../getCompatLayerCode");
+const getFactoryHandlerCode = require("../getFactoryHandlerCode");
 const PluginBuildDir = require("../../classes/PluginBuildDir");
 
-describe("getCompatLayerCode", () => {
+describe("getFactoryHandlerCode", () => {
   it("should require compatLayer", () => {
-    const compatHandlerContent = getCompatLayerCode(
+    const compatHandlerContent = getFactoryHandlerCode(
       path.join(PluginBuildDir.BUILD_DIR_NAME, "my-page.js")
     );
-    expect(compatHandlerContent).toContain('require("./compatLayer")');
+    expect(compatHandlerContent).toContain(
+      'require("serverless-nextjs-plugin/aws-lambda-compat")'
+    );
   });
 
   it("should require compatLayer with correct path when page is nested", () => {
-    const compatHandlerContent = getCompatLayerCode(
+    const compatHandlerContent = getFactoryHandlerCode(
       path.join(PluginBuildDir.BUILD_DIR_NAME, "categories/fridge/fridges.js")
     );
-    expect(compatHandlerContent).toContain('require("../../compatLayer")');
+    expect(compatHandlerContent).toContain(
+      'require("serverless-nextjs-plugin/aws-lambda-compat")'
+    );
   });
 
   it("should require compatLayer with correct path when buildDir is nested", () => {
-    const compatHandlerContent = getCompatLayerCode(
+    const compatHandlerContent = getFactoryHandlerCode(
       path.join(`app/${PluginBuildDir.BUILD_DIR_NAME}`, "page.js")
     );
-    expect(compatHandlerContent).toContain('require("./compatLayer")');
+    expect(compatHandlerContent).toContain(
+      'require("serverless-nextjs-plugin/aws-lambda-compat")'
+    );
   });
 
   it("should require next page provided", () => {
-    const compatHandlerContent = getCompatLayerCode(
+    const compatHandlerContent = getFactoryHandlerCode(
       path.join(PluginBuildDir.BUILD_DIR_NAME, "my-page.js")
     );
     expect(compatHandlerContent).toContain('require("./my-page.original.js")');
   });
 
   it("should export render method", () => {
-    const compatHandlerContent = getCompatLayerCode(
+    const compatHandlerContent = getFactoryHandlerCode(
       path.join(PluginBuildDir.BUILD_DIR_NAME, "my-page.js")
     );
     expect(compatHandlerContent).toContain("module.exports.render");

lib/__tests__/rewritePageHandlers.js

@@ -1,13 +1,13 @@
 const path = require("path");
 const fs = require("fs");
 const rewritePageHandlers = require("../rewritePageHandlers");
-const getCompatLayerCode = require("../getCompatLayerCode");
+const getFactoryHandlerCode = require("../getFactoryHandlerCode");
 const NextPage = require("../../classes/NextPage");
 const logger = require("../../utils/logger");
 
 jest.mock("fs");
 jest.mock("../../utils/logger");
-jest.mock("../getCompatLayerCode");
+jest.mock("../getFactoryHandlerCode");
 
 describe("rewritePageHandlers", () => {
   describe("when compat layer is injected successfully", () => {
@@ -20,7 +20,7 @@ describe("rewritePageHandlers", () => {
         cb(null, undefined);
       });
 
-      getCompatLayerCode.mockReturnValue("module.exports.render={...}");
+      getFactoryHandlerCode.mockReturnValue("module.exports.render={...}");
 
       rewritePageHandlersPromise = rewritePageHandlers([
         new NextPage(path.join(pagesDir, "home.js")),
@@ -43,10 +43,14 @@ describe("rewritePageHandlers", () => {
       );
     });
 
-    it("should call getCompatLayerCode with the next page path", () => {
-      expect(getCompatLayerCode).toBeCalledWith(path.join(pagesDir, "home.js"));
-      expect(getCompatLayerCode).toBeCalledWith(
-        path.join(pagesDir, "about.js")
+    it("should call getFactoryHandlerCode with the next page path", () => {
+      expect(getFactoryHandlerCode).toBeCalledWith(
+        path.join(pagesDir, "home.js"),
+        undefined
+      );
+      expect(getFactoryHandlerCode).toBeCalledWith(
+        path.join(pagesDir, "about.js"),
+        undefined
       );
     });
 

lib/build.js

@@ -1,5 +1,6 @@
 const nextBuild = require("next/dist/build").default;
 const path = require("path");
+const fse = require("fs-extra");
 const parseNextConfiguration = require("./parseNextConfiguration");
 const logger = require("../utils/logger");
 const copyBuildFiles = require("./copyBuildFiles");
@@ -17,7 +18,7 @@ const overrideTargetIfNotServerless = nextConfiguration => {
   }
 };
 
-module.exports = async (pluginBuildDir, pageConfig) => {
+module.exports = async (pluginBuildDir, pageConfig, customHandler) => {
   logger.log("Started building next app ...");
 
   const nextConfigDir = pluginBuildDir.nextConfigDir;
@@ -31,12 +32,21 @@ module.exports = async (pluginBuildDir, pageConfig) => {
     pluginBuildDir
   );
 
+  if (customHandler) {
+    // Copy custom handler
+    await fse.copy(
+      path.resolve(nextConfigDir, customHandler),
+      path.join(pluginBuildDir.buildDir, customHandler)
+    );
+  }
+
   const nextPages = await getNextPagesFromBuildDir(
     pluginBuildDir.buildDir,
-    pageConfig
+    pageConfig,
+    customHandler ? [path.basename(customHandler)] : undefined
   );
 
-  await rewritePageHandlers(nextPages);
+  await rewritePageHandlers(nextPages, customHandler);
 
   return nextPages;
 };

lib/copyBuildFiles.js

@@ -11,6 +11,16 @@ module.exports = async (nextBuildDir, pluginBuildDirObj) => {
   await fse.copy(pagesBuildDir, pluginBuildDirObj.buildDir);
   await fse.copy(
     path.join(__dirname, "./compatLayer.js"),
-    path.join(pluginBuildDirObj.buildDir, "./compatLayer.js")
+    path.join(
+      pluginBuildDirObj.buildDir,
+      "./node_modules/serverless-nextjs-plugin/lib/compatLayer.js"
+    )
+  );
+  await fse.copy(
+    path.join(__dirname, "../aws-lambda-compat.js"),
+    path.join(
+      pluginBuildDirObj.buildDir,
+      "./node_modules/serverless-nextjs-plugin/aws-lambda-compat.js"
+    )
   );
 };

lib/getFactoryHandlerCode.js

@@ -0,0 +1,23 @@
+const path = require("path");
+const PAGE_BUNDLE_PATH = "/*page_bundle_path_placeholder*/";
+const HANDLER_FACTORY_PATH = "/*handler_factory_path_placeholder*/";
+
+const lambdaHandlerWithFactory = `
+  const page = require("${PAGE_BUNDLE_PATH}");
+  const handlerFactory = require("${HANDLER_FACTORY_PATH}");
+
+  module.exports.render = (event, context, callback) => {
+    const handler = handlerFactory(page);
+    handler(event, context, callback);
+  };
+`;
+
+module.exports = (jsHandlerPath, customHandlerPath) => {
+  const basename = path.basename(jsHandlerPath, ".js");
+  return lambdaHandlerWithFactory
+    .replace(PAGE_BUNDLE_PATH, `./${basename}.original.js`)
+    .replace(
+      HANDLER_FACTORY_PATH,
+      customHandlerPath || "serverless-nextjs-plugin/aws-lambda-compat"
+    );
+};