cf-detect-chrome/background.js

const iconColorAndDesc = {
    0: { color: "grey",   desc: "Detect Cloudflare" },
    1: { color: "green",  desc: "This page doesn't seem to use Cloudflare." },
    2: { color: "orange", desc: "External resources on this page use Cloudflare." },
    3: { color: "red",    desc: "This page uses Cloudflare!" }
};

function Counter() {
    this.counts = new Map();
    this.setCount = function(key,val) {
        this.counts.set(key, val);
    };
    this.getCount = function(key) {
        if (!this.counts.has(key)) { return 0; }
        else { return this.counts.get(key); }
    };
    this.incCount = function(key) {
        if (!this.counts.has(key)) { this.counts.set(key,1); }
        else { this.counts.set(key, this.counts.get(key)+1); }
    };
    this.delCount = function(key) {
        this.counts.delete(key);
    };
}

function mapToObject( map ) {
    obj = {};
    map.forEach( function(val,key) { obj[key]=val; } );
    return obj;
}

function CFInfo() {
    this.domainCounter = new Counter();
    this.result = 0;
    // maybe more in the future
}

function CFInfoByTab() {
    this.info = new Map(); 
    this.getInfo = function(id) {
        return this.info.get(id);
    }
    this.getOrCreate = function(id) {
        if (!this.info.has(id)) { this.info.set(id, new CFInfo()); }
        return this.info.get(id);
    };
    this.delInfo = function(id) {
        this.info.delete(id);
    };
}

var cfInfo = new CFInfoByTab();

function onError(e) {
    console.log(`CF-Detect-Background: ${e}`);
}

function getDomainFromURL( urltxt ) {
    try {
        var url = new URL(urltxt);
        return url.hostname;
    } catch(err) {
        return null;
    }
}

function updateStatus( tabId ) {
    var info = cfInfo.getInfo(tabId);
    if (info) {
        if (info.result >= 3) return; // no need for further updates
        var counts = info.domainCounter.counts;
        if (counts.size == 0) {
            info.result = 1;
            updateIcon( tabId, 1 );
        } else {
            chrome.tabs.get(tabId, function(tab) {
                try {
                    var domain = getDomainFromURL(tab.url);
                    if (counts.has(domain)) {
                        info.result = 3;
                        updateIcon( tabId, 3 );
                    } else {
                        info.result = 2;
                        updateIcon( tabId, 2 );
                    }
                } catch (error) {
                    onError(error);
                }
            });
        }
    } else {
        updateIcon( tabId, 0 );
    }
}

function updateIcon( tabId, result ) {
    var cd = iconColorAndDesc[result];
    var color = cd.color;
    var title = cd.desc;
    chrome.browserAction.setTitle({
        tabId: tabId,
        title: title
    });
    chrome.browserAction.setIcon({
        tabId: tabId,
        path: {
            16: `icons/cf-${color}-16.png` ,
            32: `icons/cf-${color}-32.png` ,
            64: `icons/cf-${color}-64.png`
        }
    });
}

function cfdetect( details ) {
    var headers = details.responseHeaders;
    var cf = false;
    for (var i=0; i<headers.length; i++) {
        var h = headers[i];
        var hname = h.name.toLowerCase();
        if ((hname === "cf-ray") ||
            (hname === "server" && h.value === "cloudflare-nginx")) {
            cf = true;
            break;
        }
    }
    var tabId = details.tabId;
    if (tabId == -1) return;
    var info = cfInfo.getOrCreate(tabId);
    if (cf) {
        var ctr = info.domainCounter;
        var domain = getDomainFromURL( details.url );
        ctr.incCount(domain);
    }
    updateStatus(tabId);
}

function handleBeforeNavigate( details ) {
    if (details.frameId == 0) {
        cfInfo.delInfo( details.tabId );
        updateStatus( details.tabId );
    }
}

function handleTabUpdate( tabId, changeInfo, tabInfo ) {
    if ("url" in changeInfo) {
        updateStatus( tabId );
    }
}

function handleTabClose( tabId, removeInfo ) {
    cfInfo.delInfo(tabId);
}

function handleTabReplace( newId, oldId ) {
    cfInfo.delInfo(oldId);
}

// triggered by popup script
function handleConnect(port) {
    port.onMessage.addListener( function(tabId) {
        var info = cfInfo.getInfo(tabId);
        var msg;
        if (info) {
            msg = {
                result: info.result,
                counts: mapToObject(info.domainCounter.counts)
            };
        } else {
            msg = null;
        }
        port.postMessage(msg);
    });
}

chrome.webRequest.onHeadersReceived.addListener(
    cfdetect,
    { urls: [ "<all_urls>" ] },
    [ "responseHeaders" ]
);

chrome.webNavigation.onBeforeNavigate.addListener( handleBeforeNavigate );

chrome.tabs.onUpdated.addListener( handleTabUpdate );
chrome.tabs.onRemoved.addListener( handleTabClose );
chrome.tabs.onReplaced.addListener( handleTabReplace );

chrome.runtime.onConnect.addListener( handleConnect );

// vim: set expandtab ts=4 sw=4 :