将Canvas保存为服务器上的图像时出现setRequestHeader错误

Question

I have a highcharts svg which I have converted to a png via canvg and displayed on the webpage. I would like to then send this png to the server to create a link to the image. I was following the answer code on another topic:

Renaming an image created from an HTML5 canvas

My javascript code is the following:

var timeout = window.setTimeout(function() {
    canvg(document.getElementById('canvas'), chart.getSVG());
}, 10000);

var canvas = document.getElementById("canvas");

var img = canvas.toDataURL("images/png");
document.write('<img src="'+img+'"/>');

saveDataURL(img)

function saveDataURL(canvas) {
    var request = new XMLHttpRequest();
    request.onreadystatechange = function () {
        if (request.readyState === 4 && request.status === 200) {
            window.location.href = request.responseText;
        }
    };
    request.setRequestHeader("Content-type","application/x-www-form-urlencoded");
    request.open("POST", "saveDataURL.php", true);
    request.send("dataURL=" + canvas.toDataURL());
}

My php called saveDataURL.php is then:

$dataURL = $_POST["dataURL"];
$encodedData = explode(',', $dataURL)[1];
$decodedData = base64_decode($encodedData);
file_put_contents("temp/faizan.png", $decodedData);
echo "http://whichchart.com/temp/faizan.png";

In firefox 12 the following error is thrown up at the "request.setRequestHeader" line:

Component returned failure code: 0x804b000f (NS_ERROR_IN_PROGRESS) [nsIXMLHttpRequest.setRequestHeader] http://whichchart.com/oil.js Line 102

In chrome the error on the same line is:

Uncaught Error: INVALID_STATE_ERR: DOM Exception 11 saveDataURLoil.js:106 (anonymous function)

The example can be viewed here: whichchart.com. Can you help? Thanks.

Answer 1

Ok, so I found a different solution after much searching. The link is here:

http://permadi.com/blog/2010/10/html5-saving-canvas-image-data-using-php-and-ajax/

Assuming you have a canvas called testCanvas, this javascript and php will work:

var canvasData = testCanvas.toDataURL("image/png");
var ajax = new XMLHttpRequest();
ajax.open("POST",'testSave.php',false);
ajax.setRequestHeader('Content-Type', 'application/upload');
ajax.send(canvasData );  

<?php
if (isset($GLOBALS["HTTP_RAW_POST_DATA"]))
{
    // Get the data
    $imageData=$GLOBALS['HTTP_RAW_POST_DATA'];

    // Remove the headers (data:,) part. 
    // A real application should use them according to needs such as to check image type
    $filteredData=substr($imageData, strpos($imageData, ",")+1);

    // Need to decode before saving since the data we received is already base64 encoded
    $unencodedData=base64_decode($filteredData);

    //echo "unencodedData".$unencodedData;

    // Save file.  This example uses a hard coded filename for testing,
    // but a real application can specify filename in POST variable
    $fp = fopen( 'test.png', 'wb' );
    fwrite( $fp, $unencodedData);
    fclose( $fp );
}
?>