Use headless chrome to intercept image request data - node.js

Question

I have a use case that needs to use Headless Chrome Network (https://chromedevtools.github.io/devtools-protocol/tot/Network/) to intercept all images requests and find out the image size before saving it (basically discard small images such as icons).
However, I am unable to figure out a way to load the image data in memory before saving it. I need to load it in Img object to get width and height. The Network.getResponseBody is taking requestId which I don't have access in Network.requestIntercepted. Also Network.loadingFinished always gives me "0" in encodedDataLength variable. I have no idea why. So my questions are:
How to intercept all responses from jpg/png request and get the image data? Without saving the file via URL string to the disk and load back.
BEST: how to get image dimension from header response? Then I don't have to read the data into memory at all.
My code is below:
const chromeLauncher = require('chrome-launcher');
const CDP = require('chrome-remote-interface');
const file = require('fs');
(async function() {
async function launchChrome() {
return await chromeLauncher.launch({
chromeFlags: [
'--disable-gpu',
'--headless'
]
});
}
const chrome = await launchChrome();
const protocol = await CDP({
port: chrome.port
});
const {
DOM,
Network,
Page,
Emulation,
Runtime
} = protocol;
await Promise.all([Network.enable(), Page.enable(), Runtime.enable(), DOM.enable()]);
await Network.setRequestInterceptionEnabled({enabled: true});
Network.requestIntercepted(({interceptionId, request, resourceType}) => {
if ((request.url.indexOf('.jpg') >= 0) || (request.url.indexOf('.png') >= 0)) {
console.log(JSON.stringify(request));
console.log(resourceType);
if (request.url.indexOf("/unspecified.jpg") >= 0) {
console.log("FOUND unspecified.jpg");
console.log(JSON.stringify(interceptionId));
// console.log(JSON.stringify(Network.getResponseBody(interceptionId)));
}
}
Network.continueInterceptedRequest({interceptionId});
});
Network.loadingFinished(({requestId, timestamp, encodedDataLength}) => {
console.log(requestId);
console.log(timestamp);
console.log(encodedDataLength);
});
Page.navigate({
url: 'https://www.yahoo.com/'
});
Page.loadEventFired(async() => {
protocol.close();
chrome.kill();
});
})();

Answer 1

This should get you 90% of the way there. It gets the body of each image request. You'd still need to base64decode, check size and save etc...
const CDP = require('chrome-remote-interface');
const sizeThreshold = 1024;
async function run() {
try {
var client = await CDP();
const { Network, Page } = client;
// enable events
await Promise.all([Network.enable(), Page.enable()]);
// commands
const _url = "https://google.co.za";
let _pics = [];
Network.responseReceived(async ({requestId, response}) => {
let url = response ? response.url : null;
if ((url.indexOf('.jpg') >= 0) || (url.indexOf('.png') >= 0)) {
const {body, base64Encoded} = await Network.getResponseBody({ requestId }); // throws promise error returning null/undefined so can't destructure. Must be different in inspect shell to app?
_pics.push({ url, body, base64Encoded });
console.log(url, body, base64Encoded);
}
});
await Page.navigate({ url: _url });
await sleep(5000);
// TODO: process _pics - base64Encoded, check body.length > sizeThreshold, save etc...
} catch (err) {
if (err.message && err.message === "No inspectable targets") {
console.error("Either chrome isn't running or you already have another app connected to chrome - e.g. `chrome-remote-interface inspect`")
} else {
console.error(err);
}
} finally {
if (client) {
await client.close();
}
}
}
function sleep(miliseconds = 1000) {
if (miliseconds == 0)
return Promise.resolve();
return new Promise(resolve => setTimeout(() => resolve(), miliseconds))
}
run();