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Recommended way to check file size on upload

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南笙
南笙 2021-02-04 10:33

I am working on a web application which supports file uploading. I am already familiar checking the size in server side, but i wanted to check the file size in a client side.

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  • 盖世英雄少女心
    2021-02-04 10:57

    You may take a look at the File API which is a draft for HTML 5. Here's a nice article. That's what Gmail uses if the browser supports it of course. But there's no way to ensure this will work across all browsers.

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  • 既然无缘
    2021-02-04 10:59

    It is possible to determine the size of the file that is on uploading even before the uploaded file has been transfered completely. Even when using Internet Explorer. By using the HTTP's content-length header!
    In java world:
    First of all the if you handle the request that arrive to the server in the first servlet/filter/controller before any previous thread mass with it, you'll be albe to get the total file size in the content-length header (request.getContentLength()).

    second- have a look in an ajax implementation that prove that it is possible: http://www.ajaxfilebrowser.com/

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  • 一整个雨季
    2021-02-04 11:07

    You can have the following Code to get Gmail feature: 

    <html>
<head>
<script type="text/javascript">
$(function()
{

$('#btnSubmit').click(function()
{
if (typeof (input.files) != 'undefined') {  // this will work in firefox,chrome.
   if (input.files[0].fileSize > MAX_FILE_SIZE) {
        alert("file size exceeded");
         return false;
      }
 }
else
{
//this approach will work for ie 8.
$('iframe').bind('load'),function()
{
try
{
var text = $('iframe')[0].contentWindow.document.body ? $('iframe')[0].contentWindow.document.body.innerHTML : null;
}
catch(e)
{
alert('Server error occurred');
}
}
});
});

});
</script>
</head>
<body>
<form method="post" enctype="multipart/form-data" name="fileUpload" action="Default.aspx" target="responseFrame">
<input type="file"/>
<input type="submit" value="upload" id="btnSubmit"/>
</form>
<iframe src='' name='responseFrame' id='responseFrame' style='width:0px;height:0px;border:0;'></iframe>
</body>
</html>

    Hope this help.

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  • 忘掉有多难
    2021-02-04 11:10

    I actually asked this very question (more or less) a few days ago and the general answer seems to be: It can't be done.

    For reference: Ensure file size of uploaded file is lower than maxRequestLength before the upload occurs?

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  • 醉酒成梦
    2021-02-04 11:11

    I haven't tested this, but isn't there a "Content-Length" header on the request? It will include more than just the file being uploaded, but you can use it as a benchmark to determine if the POST is too large to handle.

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  • 猫巷女王i
    2021-02-04 11:13

    I believe file upload is based on RFC 1867, although HTML5 supersedes all this. You can perfectly reimplement this RFC, server side, and check the size of the cumulated incoming stream.

    In the most general cases, I don't think you can safely rely on the content-length as it may not represent the size of the file, but just the size of a chunk.

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