metamask-extension/app/scripts/lib/portalnetwork.js

const extension = require('extensionizer')
const resolver = require('./resolver.js');
module.exports = function (provider) {
    extension.webRequest.onBeforeRequest.addListener(details => {
        let name = details.url.substring(7, details.url.length - 1);
        extension.tabs.getSelected(null, tab => {
            extension.tabs.update(tab.id, { url: "loading.html" });

            setTimeout(() => {
                return extension.tabs.update(tab.id, { url: "404.html" });
            }, 60000);

            resolver.resolve(name, provider).then(ipfsHash => {
                let url = "https://gateway.ipfs.io/ipfs/" + ipfsHash;
                return fetch(url, {method: "HEAD"}).then(response => response.status).then(statusCode => {
                    if (statusCode !== 200) return "Local"
                    extension.tabs.update(tab.id, { url: url })
                })
                .catch(err => {
                    url = "https://gateway.ipfs.io/ipfs/" + ipfsHash
                    extension.tabs.update(tab.id, {url: url})
                    return err
                })
            })
            .catch(err => {
                let nameWithoutTld = name.substring(0, name.lastIndexOf('.'))
                let url = err === "no_mainnet" ? "no_mainnet" : "error"
                extension.tabs.update(tab.id, {url: `${url}.html?name=${name}`})
            })
        })
        return { cancel: true }
    }, {urls: ["*://*.eth/"]})
}