Download Multiple Files Without Using Zip File

Question

I have a generic handler Document.ashx that creates Word documents on the fly by reading information from the querystring like this Document.ashx?clientid=123&documentid=10 and it works perfectly.

I need to create an interface with a list of checkboxes and a Download All button. The best idea I've had so far is to use something like this to make the calls to the handler.

$("body").append("<iframe src='Document.ashx?clientid=123&documentid=10'></iframe>
                  <iframe src='Document.ashx?clientid=123&documentid=11'></iframe>")

Chrome and Firefox handle this as expected, though IE9 prompts the user to ask if they want to save the first file but ignores the following files.

How do I initiate downloading of multiple files from the client?

This is for an intranet site so the files are always generated in ~1 second, users would be selecting ~3-5 documents at a time. The vast majority of users are using IE9. I can tell everyone they have to use Firefox or Chrome but I'd rather find a solution that works in all modern browsers.

I don't want to create a zip file server side because then they always have to unzip it first (which will be too difficult for some to understand) and it slows them down.

Answer 1

So this is propably overkill but works in IE9, FF7, and Chrome 16:

Inspired by this SO post

jQuery Plugins:

• json2.js
• $.cookie()
• $.bbq()

C# in handler:

public void ProcessRequest (HttpContext context) {

    ...

    if (!string.IsNullOrEmpty(context.Request.QueryString["downloadid"])) 
          Response.Cookies[context.Request.QueryString["downloadid"]].Value = "complete";
}

Javascript/jQuery:

function downloadFile(url, downloadid) {
    //set a cookie with a unique download id
    $.cookie(downloadid, 'pending', { path: '/' });

    //create a new url
    var newurl = $.param.querystring(url, { downloadid: downloadid });

    //append an iframe with new url
    $("body").append("<iframe style='height:0;width:0;' data-downloadid='" + downloadid + "' src='" + newurl + "'></iframe>");
}

function downloadComplete(downloadid) {
    //check if download is pending
    return $.cookie(downloadid) == "complete";
}

function downloadManager(arrDownloads) {
    //loop through download items backwards
    var allComplete = false;
    for (var i = arrDownloads.length; i > 0; i--) {
        if (downloadComplete(arrDownloads[i - 1].downloadid)) {
            //download the next one if it exists
            if (i == arrDownloads.length) {
                allComplete = true;
            }
            else {
                downloadFile(arrDownloads[i].url, arrDownloads[i].downloadid);
            }
            //stop checking for completed downloads
            break;
        }
    }

    if (allComplete) {
        //remove cookies
        for (var i = arrDownloads.length; i > 0; i--) {
            $.cookie(arrDownloads[i - 1].downloadid, null, { path: '/' });
        }

        //remove iframes
        $("iframe[data-downloadid]").remove();
    }
    else {
        setTimeout("downloadManager(" + JSON.stringify(arrDownloads) + ");", 500);
    }
}

function downloadFiles(arrurls) {
    var arrDownloads = [];

    for (var i = 0; i < arrurls.length; i++) {
        var item = new Object();
        item.url = arrurls[i];
        item.downloadid = newGuid();
        arrDownloads.push(item);
    }

    //start the first download
    downloadFile(arrDownloads[0].url, arrDownloads[0].downloadid);
    //initiate the manager
    downloadManager(arrDownloads);
}

$(function () {
    var arrurls = [];
    arrurls.push("Document.ashx?clientid=123&documentid=10");
    arrurls.push("Document.ashx?clientid=123&documentid=11");
    arrurls.push("Document.ashx?clientid=123&documentid=12");
    arrurls.push("Document.ashx?clientid=123&documentid=13");
    arrurls.push("Document.ashx?clientid=123&documentid=14");
    downloadFiles(arrurls);
});

Answer 2

jQuery plugin which will do the work for you:

github.com/biesiad/multiDownload