MITM Not Receiving MessageChannel on writer.close()

Hmm, not sure what it is. can’t reproduce.

• localhost is considered secure. so you shouldn’t see any popup.
• safari don’t use workers/mitm at all cuz it can’t download content generated on the client side, it switches to just download the url behind it and avoiding the hole respondWith (resulting in a 404 error). instead it generates a blob and use a[download] #69
• the MITM shouldn’t receive any such event - it should just accept a postmessage event, pass it along to the service worker and be done with it. the rest of the communication happens throught MessageChannel.

if the download is doing just fine then maybe you don’t have anything to worry about. it could be that something else is posting messages to any iframe that exist in the DOM tree. you could try putting a breakpoint at the message event at look what the message data look like.

I have this very same problem on mac using Firefox and Chrome. The download works ok, only this message appears on console after the download is completed. I use this in a Vue.js app.

Here is the code I use to download:

            fetch(this.getApi(),
                {
                    headers: {
                        'Accept': '*/*',
                        'Content-Type': 'application/x-www-form-urlencoded'
                    },
                    credentials: "include",
                    method: "GET",
                }).then(response => download(response))


// here is the download method:
        download: function ( response ) {
            const streamSaver = window.streamSaver;
            // if you decide to host mitm + sw yourself
            streamSaver.mitm = 'downloadutil.html'

            const fileStream = streamSaver.createWriteStream('relatorio.csv', {});
            return response.body
                .pipeTo(fileStream)
                .then(() => console.info("Sucesso"), (erro) => console.error(erro));
        },