ProjectEvergreen · thescientist13 · Mar 5, 2022 · Oct 9, 2021 · Oct 9, 2021 · Oct 10, 2021
diff --git a/packages/cli/package.json b/packages/cli/package.json
@@ -31,7 +31,7 @@
     "acorn-walk": "^8.0.0",
     "commander": "^2.20.0",
     "cssnano": "^5.0.11",
-    "es-module-shims": "^0.5.2",
+    "es-module-shims": "^1.2.0",
     "front-matter": "^4.0.2",
     "koa": "^2.13.0",
     "livereload": "^0.9.1",

diff --git a/packages/cli/src/lib/hashing-utils.js b/packages/cli/src/lib/hashing-utils.js
@@ -0,0 +1,14 @@
+// https://gist.github.com/hyamamoto/fd435505d29ebfa3d9716fd2be8d42f0#gistcomment-2775538
+function hashString(inputString) {
+  let h = 0;
+
+  for (let i = 0; i < inputString.length; i += 1) {
+    h = Math.imul(31, h) + inputString.charCodeAt(i) | 0; // eslint-disable-line no-bitwise
+  }
+
+  return Math.abs(h).toString();
+}
+
+export {
+  hashString
+};
diff --git a/packages/cli/src/lifecycles/serve.js b/packages/cli/src/lifecycles/serve.js
@@ -1,5 +1,6 @@
 import { BrowserRunner } from '../lib/browser.js';
 import fs from 'fs';
+import { hashString } from '../lib/hashing-utils.js';
 import path from 'path';
 import Koa from 'koa';
 import { ResourceInterface } from '../lib/resource-interface.js';
@@ -88,7 +89,7 @@ async function getDevServer(compilation) {
   });
 
   // allow intercepting of urls (response)
-  app.use(async (ctx) => {
+  app.use(async (ctx, next) => {
     const responseAccumulator = {
       body: ctx.body,
       contentType: ctx.response.headers['content-type']
@@ -120,6 +121,36 @@ async function getDevServer(compilation) {
 
     ctx.set('Content-Type', reducedResponse.contentType);
     ctx.body = reducedResponse.body;
+
+    await next();
+  });
+
+  // ETag Support - https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/ETag
+  // https://stackoverflow.com/questions/43659756/chrome-ignores-the-etag-header-and-just-uses-the-in-memory-cache-disk-cache
+  app.use(async (ctx) => {
+    const body = ctx.response.body;
+    const { url } = ctx;
+
+    // don't interfere with external requests or API calls
+    // and only run in development
+    if (process.env.__GWD_COMMAND__ === 'develop' && path.extname(url) !== '' && url.indexOf('http') !== 0) { // eslint-disable-line no-underscore-dangle
+      if (Buffer.isBuffer(body)) {
+        // console.warn(`no body for => ${ctx.url}`);
+      } else {
+        const inm = ctx.headers['if-none-match'];
+        const etagHash = hashString(body);
+
+        if (inm && inm === etagHash) {
+          ctx.status = 304;
+          ctx.body = null;
+          ctx.set('Etag', etagHash);
+          ctx.set('Cache-Control', 'no-cache');
+        } else if (!inm || inm !== etagHash) {
+          ctx.set('Etag', etagHash);
+        }
+      }
+    }
+
   });
 
   return Promise.resolve(app);

diff --git a/packages/cli/src/plugins/resource/plugin-node-modules.js b/packages/cli/src/plugins/resource/plugin-node-modules.js
@@ -306,7 +306,9 @@ class NodeModulesResource extends ResourceInterface {
         // for each entry found in dependencies, find its entry point
         // then walk its entry point (e.g. index.js) for imports / exports to add to the importMap
         // and then walk its package.json for transitive dependencies and all those import / exports
-        await walkPackageJson(userPackageJson);
+        if (Object.keys(importMap).length === 0) {
+          await walkPackageJson(userPackageJson);
+        }
 
         // apply import map and shim for users
         newContents = newContents.replace('<head>', `

diff --git a/packages/plugin-graphql/src/core/common.js b/packages/plugin-graphql/src/core/common.js
@@ -1,13 +1,4 @@
-// https://gist.github.com/hyamamoto/fd435505d29ebfa3d9716fd2be8d42f0#gistcomment-2775538
-function hashString(queryKeysString) {
-  let h = 0;
-
-  for (let i = 0; i < queryKeysString.length; i += 1) {
-    h = Math.imul(31, h) + queryKeysString.charCodeAt(i) | 0; // eslint-disable-line no-bitwise
-  }
-
-  return Math.abs(h).toString();
-}
+import { hashString } from '@greenwood/cli/src/lib/hashing-utils.js';
 
 function getQueryHash(query, variables = {}) {
   const queryKeys = query;

diff --git a/packages/plugin-graphql/src/index.js b/packages/plugin-graphql/src/index.js
@@ -43,6 +43,7 @@ class GraphQLResource extends ResourceInterface {
           : ',';
         const shimmedBody = body.replace('"imports": {', `
           "imports": {
+            "@greenwood/cli/src/lib/hashing-utils.js": "/node_modules/@greenwood/cli/src/lib/hashing-utils.js",
             "@greenwood/plugin-graphql/core/client": "/node_modules/@greenwood/plugin-graphql/src/core/client.js",
             "@greenwood/plugin-graphql/core/common": "/node_modules/@greenwood/plugin-graphql/src/core/common.js",
             "@greenwood/plugin-graphql/queries/children": "/node_modules/@greenwood/plugin-graphql/src/queries/children.gql",

diff --git a/www/pages/about/how-it-works.md b/www/pages/about/how-it-works.md
@@ -24,6 +24,7 @@ During _development_ the CLI will:
 - Process requests on the fly only for the content or code you need for a given page.
 - Supports loading dependencies from _node_modules_ using an [`importMap`](https://github.com/WICG/import-maps) to avoid bundling.
 - While Greenwood is ESM first, we have a [plugin](/plugins/custom-plugins/) to transform CommonJS into ESM (🤞)
+- Leverage `E-Tag` headers to apply [caching techniques for unchanged assets](/blog/release/v0-24-0/#local-development-enhancements)
 
 For _production_ builds:
 - Combine all your code and dependencies into efficient modern bundles including minifying your JavaScript and CSS.

diff --git a/yarn.lock b/yarn.lock
@@ -5173,10 +5173,12 @@ es-abstract@^1.18.0-next.2:
     string.prototype.trimstart "^1.0.4"
     unbox-primitive "^1.0.0"
 
-es-module-shims@^0.5.2:
-  version "0.5.2"
-  resolved "https://registry.yarnpkg.com/es-module-shims/-/es-module-shims-0.5.2.tgz#9bea003e84a11bdc052b9f52464671176509f520"
-  integrity sha512-cXSy7EPyZc6Iq4AjyWXMqMURXgFguduPN7nxtfI0WsV4C83wNHrdxf0oxhzDPZU/8zB6YFllR24HMG/EBVN/GQ==
+es-module-shims@^1.2.0:
+  version "1.2.0"
+  resolved "https://registry.yarnpkg.com/es-module-shims/-/es-module-shims-1.2.0.tgz#f3b447826c4f4b9d9597b24a7aaa0c639893de2f"
+  integrity sha512-Kupc9HFwmScot1v8vO/3CX9MjNprarG4wdlBk2bv5R76SD63UBhXG53MUTjg8USgHaCMLBOQyGSl7lAEqGUb1g==
+  dependencies:
+    rimraf "^3.0.2"
 
 es-to-primitive@^1.2.1:
   version "1.2.1"