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copied!<p>One <a href="http://gruffcode.com/2010/10/28/detecting-the-file-download-dialog-in-the-browser/" rel="noreferrer">possible solution</a> uses JavaScript on the client.</p> <p>The client algorithm:</p> <ol> <li>Generate a random unique token.</li> <li>Submit the download request, and include the token in a GET/POST field.</li> <li>Show the "waiting" indicator.</li> <li>Start a timer, and every second or so, look for a cookie named "fileDownloadToken" (or whatever you decide).</li> <li>If the cookie exists, and its value matches the token, hide the "waiting" indicator.</li> </ol> <p>The server algorithm:</p> <ol> <li>Look for the GET/POST field in the request.</li> <li>If it has a non-empty value, drop a cookie (e.g. "fileDownloadToken"), and set its value to the token's value.</li> </ol> <hr> <p>Client source code (JavaScript):</p> <pre><code>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; } </code></pre> <p>Example server code (PHP):</p> <pre><code>$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(); </code></pre> <p>Where:</p> <pre><code>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 ); } </code></pre>

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