问题
I have a page that allows the user to download a dynamically-generated file. It takes a long time to generate, so I\'d like to show a \"waiting\" indicator. The problem is, I can\'t figure out how to detect when the browser has received the file, so I can hide the indicator.
I\'m making the request in a hidden form, which POSTs to the server, and targets a hidden iframe for its results. This is so I don\'t replace the entire browser window with the result. I listen for a \"load\" event on the iframe, in the hope that it will fire when the download is complete.
I return a \"Content-Disposition: attachment\" header with the file, which causes the browser to show the \"Save\" dialog. But the browser doesn\'t fire a \"load\" event in the iframe.
One approach I tried is using a multi-part response. So it would send an empty HTML file, as well as the attached downloadable file. For example:
Content-type: multipart/x-mixed-replace;boundary=\"abcde\"
--abcde
Content-type: text/html
--abcde
Content-type: application/vnd.fdf
Content-Disposition: attachment; filename=foo.fdf
file-content
--abcde
This works in Firefox; it receives the empty HTML file, fires the \"load\" event, then shows the \"Save\" dialog for the downloadable file. But it fails on IE and Safari; IE fires the \"load\" event but doesn\'t download the file, and Safari downloads the file (with the wrong name and content-type), and doesn\'t fire the \"load\" event.
A different approach might be to make a call to start the file creation, then poll the server until it\'s ready, then download the already-created file. But I\'d rather avoid creating temporary files on the server.
Does anyone have a better idea?
回答1:
One possible solution uses JavaScript on the client.
The client algorithm:
- Generate a random unique token.
- Submit the download request, and include the token in a GET/POST field.
- Show the "waiting" indicator.
- Start a timer, and every second or so, look for a cookie named "fileDownloadToken" (or whatever you decide).
- If the cookie exists, and its value matches the token, hide the "waiting" indicator.
The server algorithm:
- Look for the GET/POST field in the request.
- If it has a non-empty value, drop a cookie (e.g. "fileDownloadToken"), and set its value to the token's value.
Client source code (JavaScript):
function getCookie( name ) {
var parts = document.cookie.split(name + "=");
if (parts.length == 2) return parts.pop().split(";").shift();
}
function expireCookie( cName ) {
document.cookie =
encodeURIComponent(cName) + "=deleted; expires=" + new Date( 0 ).toUTCString();
}
function setCursor( docStyle, buttonStyle ) {
document.getElementById( "doc" ).style.cursor = docStyle;
document.getElementById( "button-id" ).style.cursor = buttonStyle;
}
function setFormToken() {
var downloadToken = new Date().getTime();
document.getElementById( "downloadToken" ).value = downloadToken;
return downloadToken;
}
var downloadTimer;
var attempts = 30;
// Prevents double-submits by waiting for a cookie from the server.
function blockResubmit() {
var downloadToken = setFormToken();
setCursor( "wait", "wait" );
downloadTimer = window.setInterval( function() {
var token = getCookie( "downloadToken" );
if( (token == downloadToken) || (attempts == 0) ) {
unblockSubmit();
}
attempts--;
}, 1000 );
}
function unblockSubmit() {
setCursor( "auto", "pointer" );
window.clearInterval( downloadTimer );
expireCookie( "downloadToken" );
attempts = 30;
}
Example server code (PHP):
$TOKEN = "downloadToken";
// Sets a cookie so that when the download begins the browser can
// unblock the submit button (thus helping to prevent multiple clicks).
// The false parameter allows the cookie to be exposed to JavaScript.
$this->setCookieToken( $TOKEN, $_GET[ $TOKEN ], false );
$result = $this->sendFile();
Where:
public function setCookieToken(
$cookieName, $cookieValue, $httpOnly = true, $secure = false ) {
// See: http://stackoverflow.com/a/1459794/59087
// See: http://shiflett.org/blog/2006/mar/server-name-versus-http-host
// See: http://stackoverflow.com/a/3290474/59087
setcookie(
$cookieName,
$cookieValue,
2147483647, // expires January 1, 2038
"/", // your path
$_SERVER["HTTP_HOST"], // your domain
$secure, // Use true over HTTPS
$httpOnly // Set true for $AUTH_COOKIE_NAME
);
}
回答2:
A very simple (and lame) one line solution is to use the window.onblur() event to close the loading dialog. Of course, if it takes too long and the user decides to do something else (like reading emails) the loading dialog will close.
回答3:
old thread, i know...
but those, that are lead here by google might be interested in my solution. it is very simple, yet reliable. and it makes it possible to display real progress messages (and can be easily plugged in to existing processes):
the script that processes (my problem was: retrieving files via http and deliver them as zip) writes the status to the session.
the status is polled and displayed every second. thats all (ok, its not. you have to take care of a lot of details [eg concurrent downloads], but its a good place to start ;-)).
the downloadpage:
<a href="download.php?id=1" class="download">DOWNLOAD 1</a>
<a href="download.php?id=2" class="download">DOWNLOAD 2</a>
...
<div id="wait">
Please wait...
<div id="statusmessage"></div>
</div>
<script>
//this is jquery
$('a.download').each(function()
{
$(this).click(
function(){
$('#statusmessage').html('prepare loading...');
$('#wait').show();
setTimeout('getstatus()', 1000);
}
);
});
});
function getstatus(){
$.ajax({
url: "/getstatus.php",
type: "POST",
dataType: 'json',
success: function(data) {
$('#statusmessage').html(data.message);
if(data.status=="pending")
setTimeout('getstatus()', 1000);
else
$('#wait').hide();
}
});
}
</script>
getstatus.php
<?php
session_start();
echo json_encode($_SESSION['downloadstatus']);
?>
download.php
<?php
session_start();
$processing=true;
while($processing){
$_SESSION['downloadstatus']=array("status"=>"pending","message"=>"Processing".$someinfo);
session_write_close();
$processing=do_what_has_2Bdone();
session_start();
}
$_SESSION['downloadstatus']=array("status"=>"finished","message"=>"Done");
//and spit the generated file to the browser
?>
回答4:
i use the following to download blobs and revoke the object-url after the download. it works in chrome and firefox!
function download(blob){
var url = URL.createObjectURL(blob);
console.log('create ' + url);
window.addEventListener('focus', window_focus, false);
function window_focus(){
window.removeEventListener('focus', window_focus, false);
URL.revokeObjectURL(url);
console.log('revoke ' + url);
}
location.href = url;
}
after the file download dialog is closed, the window gets her focus back so the focus event is triggered.
回答5:
Based on Elmer's example I've prepared my own solution. After elements click with defined download class it lets to show custom message on the screen. I've used focus trigger to hide the message.
JavaScript
$(function(){$('.download').click(function() { ShowDownloadMessage(); }); })
function ShowDownloadMessage()
{
$('#message-text').text('your report is creating, please wait...');
$('#message').show();
window.addEventListener('focus', HideDownloadMessage, false);
}
function HideDownloadMessage(){
window.removeEventListener('focus', HideDownloadMessage, false);
$('#message').hide();
}
HTML
<div id="message" style="display: none">
<div id="message-screen-mask" class="ui-widget-overlay ui-front"></div>
<div id="message-text" class="ui-dialog ui-widget ui-widget-content ui-corner-all ui-front ui-draggable ui-resizable waitmessage">please wait...</div>
</div>
Now you should implement any element to download:
<a class="download" href="file://www.ocelot.com.pl/prepare-report">Download report</a>
or
<input class="download" type="submit" value="Download" name="actionType">
After each download click you will see message your report is creating, please wait...
回答6:
I wrote a simple JavaScript class that implements a technique similar to the one described in bulltorious answer. I hope it can be useful to someone here. The GitHub project is called response-monitor.js
By default it uses spin.js as the waiting indicator but it also provides a set of callbacks for implementation of a custom indicator.
JQuery is supported but not required.
Notable features
- Simple integration
- No dependencies
- JQuery plug-in (optional)
- Spin.js Integration (optional)
- Configurable callbacks for monitoring events
- Handles multiple simultaneous requests
- Server-side error detection
- Timeout detection
- Cross browser
Example usage
HTML
<!-- the response monitor implementation -->
<script src="response-monitor.js"></script>
<!-- optional JQuery plug-in -->
<script src="response-monitor.jquery.js"></script>
<a class="my_anchors" href="/report?criteria1=a&criteria2=b#30">Link 1 (Timeout: 30s)</a>
<a class="my_anchors" href="/report?criteria1=b&criteria2=d#10">Link 2 (Timeout: 10s)</a>
<form id="my_form" method="POST">
<input type="text" name="criteria1">
<input type="text" name="criteria2">
<input type="submit" value="Download Report">
</form>
Client (plain JavaScript)
//registering multiple anchors at once
var my_anchors = document.getElementsByClassName('my_anchors');
ResponseMonitor.register(my_anchors); //clicking on the links initiates monitoring
//registering a single form
var my_form = document.getElementById('my_form');
ResponseMonitor.register(my_form); //the submit event will be intercepted and monitored
Client (JQuery)
$('.my_anchors').ResponseMonitor();
$('#my_form').ResponseMonitor({timeout: 20});
Client with callbacks (JQuery)
//when options are defined, the default spin.js integration is bypassed
var options = {
onRequest: function(token){
$('#cookie').html(token);
$('#outcome').html('');
$('#duration').html('');
},
onMonitor: function(countdown){
$('#duration').html(countdown);
},
onResponse: function(status){
$('#outcome').html(status==1?'success':'failure');
},
onTimeout: function(){
$('#outcome').html('timeout');
}
};
//monitor all anchors in the document
$('a').ResponseMonitor(options);
Server (PHP)
$cookiePrefix = 'response-monitor'; //must match the one set on the client options
$tokenValue = $_GET[$cookiePrefix];
$cookieName = $cookiePrefix.'_'.$tokenValue; //ex: response-monitor_1419642741528
//this value is passed to the client through the ResponseMonitor.onResponse callback
$cookieValue = 1; //for ex, "1" can interpret as success and "0" as failure
setcookie(
$cookieName,
$cookieValue,
time()+300, // expire in 5 minutes
"/",
$_SERVER["HTTP_HOST"],
true,
false
);
header('Content-Type: text/plain');
header("Content-Disposition: attachment; filename=\"Response.txt\"");
sleep(5); //simulate whatever delays the response
print_r($_REQUEST); //dump the request in the text file
For more examples check the examples folder on the repository.
回答7:
If you're streaming a file that you're generating dynamically, and also have a realtime server-to-client messaging library implemented, you can alert your client pretty easily.
The server-to-client messaging library I like and recommend is Socket.io (via Node.js). After your server script is done generating the file that is being streamed for download your last line in that script can emit a message to Socket.io which sends a notification to the client. On the client, Socket.io listens for incoming messages emitted from the server and allows you to act on them. The benefit of using this method over others is that you are able to detect a "true" finish event after the streaming is done.
For example, you could show your busy indicator after a download link is clicked, stream your file, emit a message to Socket.io from the server in the last line of your streaming script, listen on the client for a notification, receive the notification and update your UI by hiding the busy indicator.
I realize most people reading answers to this question might not have this type of a setup, but I've used this exact solution to great effect in my own projects and it works wonderfully.
Socket.io is incredibly easy to install and use. See more: http://socket.io/
回答8:
When the user triggers the generation of the file, you could simply assign a unique ID to that "download", and send the user to a page which refreshes (or checks with AJAX) every few seconds. Once the file is finished, save it under that same unique ID and...
- If the file is ready, do the download.
- If the file is not ready, show the progress.
Then you can skip the whole iframe/waiting/browserwindow mess, yet have a really elegant solution.
回答9:
If you don't want to generate and store the file on the server, are you willing to store the status, e.g. file-in-progress, file-complete? Your "waiting" page could poll the server to know when the file generation is complete. You wouldn't know for sure that the browser started the download but you'd have some confidence.
回答10:
I'm very late to the party but I'll put this up here if anyone else would like to know my solution:
I had a real struggle with this exact problem but I found a viable solution using iframes (I know, I know. It's terrible but it works for a simple problem that I had)
I had an html page that launched a separate php script that generated the file and then downloaded it. On the html page, i used the following jquery in the html header (you'll need to include a jquery library as well):
<script>
$(function(){
var iframe = $("<iframe>", {name: 'iframe', id: 'iframe',}).appendTo("body").hide();
$('#click').on('click', function(){
$('#iframe').attr('src', 'your_download_script.php');
});
$('iframe').load(function(){
$('#iframe').attr('src', 'your_download_script.php?download=yes'); <!--on first iframe load, run script again but download file instead-->
$('#iframe').unbind(); <!--unbinds the iframe. Helps prevent against infinite recursion if the script returns valid html (such as echoing out exceptions) -->
});
});
</script>
On your_download_script.php, have the following:
function downloadFile($file_path) {
if (file_exists($file_path)) {
header('Content-Description: File Transfer');
header('Content-Type: text/csv');
header('Content-Disposition: attachment; filename=' . basename($file_path));
header('Expires: 0');
header('Cache-Control: must-revalidate');
header('Pragma: public');
header('Content-Length: ' . filesize($file_path));
ob_clean();
flush();
readfile($file_path);
exit();
}
}
$_SESSION['your_file'] = path_to_file; //this is just how I chose to store the filepath
if (isset($_REQUEST['download']) && $_REQUEST['download'] == 'yes') {
downloadFile($_SESSION['your_file']);
} else {
*execute logic to create the file*
}
To break this down, jquery first launches your php script in an iframe. The iframe is loaded once the file is generated. Then jquery launches the script again with a request variable telling the script to download the file.
The reason that you can't do the download and file generation all in one go is due to the php header() function. If you use header(), you're changing the script to something other than a web page and jquery will never recognize the download script as being 'loaded'. I know this may not necessarily be detecting when a browser receives a file but your issue sounded similar to mine.
回答11:
"How to detect when browser receives file download?"
I faced the same problem with that config:
struts 1.2.9
jquery-1.3.2.
jquery-ui-1.7.1.custom
IE 11
java 5
My solution with a cookie:
- Client side:
When submitting your form, call your javascript function to hide your page and load your waiting spinner
function loadWaitingSpinner(){
... hide your page and show your spinner ...
}
Then, call a function that will check every 500ms whether a cookie is coming from server.
function checkCookie(){
var verif = setInterval(isWaitingCookie,500,verif);
}
If the cookie is found, stop checking every 500ms, expire the cookie and call your function to come back to your page and remove the waiting spinner (removeWaitingSpinner()). It is important to expire the cookie if you want to be able to download another file again!
function isWaitingCookie(verif){
var loadState = getCookie("waitingCookie");
if (loadState == "done"){
clearInterval(verif);
document.cookie = "attenteCookie=done; expires=Tue, 31 Dec 1985 21:00:00 UTC;";
removeWaitingSpinner();
}
}
function getCookie(cookieName){
var name = cookieName + "=";
var cookies = document.cookie
var cs = cookies.split(';');
for (var i = 0; i < cs.length; i++){
var c = cs[i];
while(c.charAt(0) == ' ') {
c = c.substring(1);
}
if (c.indexOf(name) == 0){
return c.substring(name.length, c.length);
}
}
return "";
}
function removeWaitingSpinner(){
... come back to your page and remove your spinner ...
}
- Server side:
At the end of your server process, add a cookie to the response. That cookie will be sent to the client when your file will be ready for download.
Cookie waitCookie = new Cookie("waitingCookie", "done");
response.addCookie(waitCookie);
I hope to help someone!
回答12:
I just had this exact same problem. My solution was to use temporary files since I was generating a bunch of temporary files already. The form is submitted with:
var microBox = {
show : function(content) {
$(document.body).append('<div id="microBox_overlay"></div><div id="microBox_window"><div id="microBox_frame"><div id="microBox">' +
content + '</div></div></div>');
return $('#microBox_overlay');
},
close : function() {
$('#microBox_overlay').remove();
$('#microBox_window').remove();
}
};
$.fn.bgForm = function(content, callback) {
// Create an iframe as target of form submit
var id = 'bgForm' + (new Date().getTime());
var $iframe = $('<iframe id="' + id + '" name="' + id + '" style="display: none;" src="about:blank"></iframe>')
.appendTo(document.body);
var $form = this;
// Submittal to an iframe target prevents page refresh
$form.attr('target', id);
// The first load event is called when about:blank is loaded
$iframe.one('load', function() {
// Attach listener to load events that occur after successful form submittal
$iframe.load(function() {
microBox.close();
if (typeof(callback) == 'function') {
var iframe = $iframe[0];
var doc = iframe.contentWindow.document;
var data = doc.body.innerHTML;
callback(data);
}
});
});
this.submit(function() {
microBox.show(content);
});
return this;
};
$('#myForm').bgForm('Please wait...');
At the end of the script that generates the file I have:
header('Refresh: 0;url=fetch.php?token=' . $token);
echo '<html></html>';
This will cause the load event on the iframe to be fired. Then the wait message is closed and the file download will then start. Tested on IE7 and Firefox.
回答13:
If you have download a file, which is saved, as opposed to being in the document, there's no way to determine when the download is complete, since it is not in the scope of the current document, but a separate process in the browser.
回答14:
The question is to have a ‘waiting’ indicator while a file is generated and then return to normal once the file is downloading. The way I like todo this is using a hidden iFrame and hook the frame’s onload event to let my page know when download starts. BUT onload does not fire in IE for file downloads (like with the attachment header token). Polling the server works, but I dislike the extra complexity. So here is what I do:
- Target the hidden iFrame as usual.
- Generate the content. Cache it with an absolute timeout in 2 minutes.
- Send a javascript redirect back to the calling client, essentially calling the generator page a second time. NOTE: this will cause the onload event to fire in IE because it's acting like a regular page.
- Remove the content from the cache and send it to the client.
Disclaimer, don’t do this on a busy site, because of the caching could add up. But really, if your sites that busy the long running process will starve you of threads anyways.
Here is what the codebehind looks like, which is all you really need.
public partial class Download : System.Web.UI.Page
{
protected System.Web.UI.HtmlControls.HtmlControl Body;
protected void Page_Load( object sender, EventArgs e )
{
byte[ ] data;
string reportKey = Session.SessionID + "_Report";
// Check is this page request to generate the content
// or return the content (data query string defined)
if ( Request.QueryString[ "data" ] != null )
{
// Get the data and remove the cache
data = Cache[ reportKey ] as byte[ ];
Cache.Remove( reportKey );
if ( data == null )
// send the user some information
Response.Write( "Javascript to tell user there was a problem." );
else
{
Response.CacheControl = "no-cache";
Response.AppendHeader( "Pragma", "no-cache" );
Response.Buffer = true;
Response.AppendHeader( "content-disposition", "attachment; filename=Report.pdf" );
Response.AppendHeader( "content-size", data.Length.ToString( ) );
Response.BinaryWrite( data );
}
Response.End();
}
else
{
// Generate the data here. I am loading a file just for an example
using ( System.IO.FileStream stream = new System.IO.FileStream( @"C:\1.pdf", System.IO.FileMode.Open ) )
using ( System.IO.BinaryReader reader = new System.IO.BinaryReader( stream ) )
{
data = new byte[ reader.BaseStream.Length ];
reader.Read( data, 0, data.Length );
}
// Store the content for retrieval
Cache.Insert( reportKey, data, null, DateTime.Now.AddMinutes( 5 ), TimeSpan.Zero );
// This is the key bit that tells the frame to reload this page
// and start downloading the content. NOTE: Url has a query string
// value, so that the content isn't generated again.
Body.Attributes.Add("onload", "window.location = 'binary.aspx?data=t'");
}
}
回答15:
A quick solution if you only want to display a message or a loader gif until the download dialog is displayed is to put the message in a hidden container and when you click on the button that generate the file to be downloaded you make the container visible. Then use jquery or javascript to catch the focusout event of the button to hide the container that contain the message
回答16:
If Xmlhttprequest with blob is not an option then you can open your file in new window and check if eny elements get populated in that window body with interval.
var form = document.getElementById("frmDownlaod");
form.setAttribute("action","downoad/url");
form.setAttribute("target","downlaod");
var exportwindow = window.open("", "downlaod", "width=800,height=600,resizable=yes");
form.submit();
var responseInterval = setInterval(function(){
var winBody = exportwindow.document.body
if(winBody.hasChildNodes()) // or 'downoad/url' === exportwindow.document.location.href
{
clearInterval(responseInterval);
// do your work
// if there is error page configured your application for failed requests, check for those dom elemets
}
}, 1000)
//Better if you specify maximun no of intervals回答17:
In my experience, there are two ways to handle this:
- Set a short-lived cookie on the download, and have JavaScript continually check for its existence. Only real issue is getting the cookie lifetime right - too short and the JS can miss it, too long and it might cancel the download screens for other downloads. Using JS to remove the cookie upon discovery usually fixes this.
- Download the file using fetch/XHR. Not only do you know exactly when the file download finishes, if you use XHR you can use progress events to show a progress bar! Save the resulting blob with msSaveBlob in IE/Edge and a download link (like this one) in Firefox/Chrome. The problem with this method is that iOS Safari doesn't seem to handle downloading blobs right - you can convert the blob into a data URL with a FileReader and open that in a new window, but that's opening the file, not saving it.
回答18:
Create an iframe when button/link is clicked and append this to body.
$('<iframe />')
.attr('src', url)
.attr('id','iframe_download_report')
.hide()
.appendTo('body');
Create an iframe with delay and delete it after download.
var triggerDelay = 100;
var cleaningDelay = 20000;
var that = this;
setTimeout(function() {
var frame = $('<iframe style="width:1px; height:1px;" class="multi-download-frame"></iframe>');
frame.attr('src', url+"?"+ "Content-Disposition: attachment ; filename="+that.model.get('fileName'));
$(ev.target).after(frame);
setTimeout(function() {
frame.remove();
}, cleaningDelay);
}, triggerDelay);
来源：https://stackoverflow.com/questions/1106377/detect-when-browser-receives-file-download