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core(image-usage): use min of resourceSize/transferSize #4968

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Apr 19, 2018
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core(image-usage): use min of resourceSize/transferSize #4968

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5 changes: 3 additions & 2 deletions lighthouse-core/gather/gatherers/dobetterweb/optimized-images.js
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Original file line number Diff line number Diff line change
Expand Up @@ -79,14 +79,15 @@ class OptimizedImages extends Gatherer {
const isSameOrigin = URL.originsMatch(pageUrl, record._url);
const isBase64DataUri = /^data:.{2,40}base64\s*,/.test(record._url);

if (isOptimizableImage && record._resourceSize > MINIMUM_IMAGE_SIZE) {
const actualResourceSize = Math.min(record._resourceSize, record._transferSize);
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can _transferSize be larger than _resourceSize? Seems possible, especially with image data, but even in that case wouldn't we still want to use the transfer size because they're sending too many bytes (it's just in that case one of the culprits is a bad choice to gzip?)

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@patrickhulce patrickhulce Apr 14, 2018 •
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in every case I've seen with my own two 👀 for images transferSize = resourceSize + size of headers, highly irregular to try to gzip/brotli/etc an image since images are always compressed with their own domain-specific method that is way more effective, but apparently the tweet ran into that case with a 30MB image 😆

if (isOptimizableImage && actualResourceSize > MINIMUM_IMAGE_SIZE) {
prev.push({
isSameOrigin,
isBase64DataUri,
requestId: record._requestId,
url: record._url,
mimeType: record._mimeType,
resourceSize: record._resourceSize,
resourceSize: actualResourceSize,
});
}

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2 changes: 1 addition & 1 deletion lighthouse-core/gather/gatherers/image-usage.js
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Expand Up @@ -130,7 +130,7 @@ class ImageUsage extends Gatherer {
if (/^image/.test(record._mimeType) && record.finished) {
map[record._url] = {
url: record.url,
resourceSize: record.resourceSize,
resourceSize: Math.min(record.resourceSize, record.transferSize),
startTime: record.startTime,
endTime: record.endTime,
responseReceivedTime: record.responseReceivedTime,
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11 changes: 10 additions & 1 deletion lighthouse-core/test/gather/gatherers/dobetterweb/optimized-images-test.js
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Expand Up @@ -23,41 +23,47 @@ const traceData = {
_url: 'http://google.com/image.jpg',
_mimeType: 'image/jpeg',
_resourceSize: 10000,
_transferSize: 20000,
_resourceType: {_name: 'image'},
finished: true,
},
{
_url: 'http://google.com/transparent.png',
_mimeType: 'image/png',
_resourceSize: 11000,
_transferSize: 20000,
_resourceType: {_name: 'image'},
finished: true,
},
{
_url: 'http://google.com/image.bmp',
_mimeType: 'image/bmp',
_resourceSize: 12000,
_transferSize: 9000, // bitmap was compressed another way
_resourceType: {_name: 'image'},
finished: true,
},
{
_url: 'http://google.com/image.bmp',
_mimeType: 'image/bmp',
_resourceSize: 12000,
_transferSize: 20000,
_resourceType: {_name: 'image'},
finished: true,
},
{
_url: 'http://google.com/vector.svg',
_mimeType: 'image/svg+xml',
_resourceSize: 13000,
_transferSize: 20000,
_resourceType: {_name: 'image'},
finished: true,
},
{
_url: 'http://gmail.com/image.jpg',
_mimeType: 'image/jpeg',
_resourceSize: 15000,
_transferSize: 20000,
_resourceType: {_name: 'image'},
finished: true,
},
Expand All @@ -66,20 +72,23 @@ const traceData = {
_mimeType: 'image/jpeg',
_resourceType: {_name: 'image'},
_resourceSize: 14000,
_transferSize: 20000,
finished: true,
},
{
_url: 'http://google.com/big-image.bmp',
_mimeType: 'image/bmp',
_resourceType: {_name: 'image'},
_resourceSize: 12000,
_transferSize: 20000,
finished: false, // ignore for not finishing
},
{
_url: 'http://google.com/not-an-image.bmp',
_mimeType: 'image/bmp',
_resourceType: {_name: 'document'}, // ignore for not really being an image
_resourceSize: 12000,
_transferSize: 20000,
finished: true,
},
],
Expand Down Expand Up @@ -125,7 +134,7 @@ describe('Optimized images', () => {
assert.equal(artifact.length, 4);
checkSizes(artifact[0], 10000, 60, 80);
checkSizes(artifact[1], 11000, 60, 80);
checkSizes(artifact[2], 12000, 60, 80);
checkSizes(artifact[2], 9000, 60, 80);
// skip cross-origin for now
// checkSizes(artifact[3], 15000, 60, 80);
checkSizes(artifact[3], 20, 80, 100); // uses base64 data
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