core(uses-text-compression): ignore percent threshold for large savings (#16165)

Author: connorjclark

core/audits/byte-efficiency/uses-text-compression.js

@@ -59,12 +59,18 @@ class ResponsesAreCompressed extends ByteEfficiencyAudit {
       const gzipSize = record.gzipSize;
       const gzipSavings = originalSize - gzipSize;
 
-      // we require at least 10% savings off the original size AND at least 1400 bytes
-      // if the savings is smaller than either, we don't care
-      if (1 - gzipSize / originalSize < IGNORE_THRESHOLD_IN_PERCENT ||
-          gzipSavings < IGNORE_THRESHOLD_IN_BYTES ||
-          record.transferSize < gzipSize
-      ) {
+      // Not every resource is smaller when compressed.
+      if (record.transferSize < gzipSize) {
+        return;
+      }
+
+      // If savings is small, let's be generous and not surface the minor savings.
+      if (gzipSavings < IGNORE_THRESHOLD_IN_BYTES) {
+        return;
+      }
+
+      // Require at least 20kb of savings ... or some percentage of total resource size.
+      if (gzipSavings < 20_000 && 1 - gzipSize / originalSize < IGNORE_THRESHOLD_IN_PERCENT) {
         return;
       }
 

core/test/audits/byte-efficiency/uses-text-compression-test.js

@@ -4,44 +4,36 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-const KB = 1024;
-import assert from 'assert/strict';
-
 import ResponsesAreCompressedAudit from '../../../audits/byte-efficiency/uses-text-compression.js';
 
+const KB = 1024;
+const MB = 1024 * KB;
+
 function generateResponse(options) {
-  return Object.assign({
+  return {
     url: `http://google.com/${options.file}`,
     transferSize: options.resourceSize || 0,
     resourceSize: 0,
     gzipSize: 0,
-  }, options);
+    ...options,
+  };
 }
 
 describe('Page uses optimized responses', () => {
-  it('fails when responses are collectively unoptimized', () => {
-    const auditResult = ResponsesAreCompressedAudit.audit_({
-      ResponseCompression: [
-        generateResponse({file: 'index.js', resourceSize: 100 * KB, gzipSize: 90 * KB}), // 10kb & 10%
-        generateResponse({file: 'index.css', resourceSize: 50 * KB, gzipSize: 37 * KB}), //  13kb & 26% (hit)
-        generateResponse({file: 'index.json', resourceSize: 2048 * KB, gzipSize: 1024 * KB}), // 1024kb & 50% (hit)
-      ],
-    });
-
-    assert.equal(auditResult.items.length, 2);
-  });
-
-  it('passes when all responses are sufficiently optimized', () => {
+  it('applies a threshold', () => {
     const auditResult = ResponsesAreCompressedAudit.audit_({
       ResponseCompression: [
-        generateResponse({file: 'index.js', resourceSize: 1000 * KB, gzipSize: 910 * KB}), // 90kb & 9%
-        generateResponse({file: 'index.css', resourceSize: 6 * KB, gzipSize: 4.5 * KB}), // 1,5kb & 25% (hit)
-        generateResponse({file: 'index.json', resourceSize: 10 * KB, gzipSize: 10 * KB}), // 0kb & 0%
+        generateResponse({file: 'index.js', resourceSize: 1000 * KB, gzipSize: 910 * KB}), // 90kb (hit)
+        generateResponse({file: 'index.css', resourceSize: 6 * KB, gzipSize: 4.8 * KB}), // 1.2kb
+        generateResponse({file: 'index2.css', resourceSize: 50 * KB, gzipSize: 37 * KB}), //  13kb (hit)
+        generateResponse({file: 'index.json', resourceSize: 10 * KB, gzipSize: 10 * KB}), // 0kb
+        generateResponse({file: 'uncompressed.xcustom', resourceSize: 11 * MB, gzipSize: 10 * MB}), // 1mb (hit)
         generateResponse({file: 'compressed.json', resourceSize: 10 * KB, transferSize: 3 * KB,
-          gzipSize: 6 * KB}), // 0kb & 0%
+          gzipSize: 6 * KB}), // 0kb
       ],
     });
 
-    assert.equal(auditResult.items.length, 1);
+    expect(auditResult.items.map(item => item.url)).toEqual(
+      ['http://google.com/index.js', 'http://google.com/index2.css', 'http://google.com/uncompressed.xcustom']);
   });
 });