How to convert a base64 image into a image file and upload it with an asynchronous form using jQuery

The first solution that you may implement and probably the only idea that will occur to everybody, when you need to upload a Base64 image into the server, is to upload this file as a string and then convert it to a file in the server side. This implementation works like a charm, however there's another implementation that you may want to know if you don't want to make that your server does all the hard job for the user.

In this article, you are going to learn how to convert a Base64 string into a Blob to upload it as a file to our server. This approach will be equivalent to the action that an user does when he drags and drop a file into a file input.

Implementation

To get started, we need to convert a base64 string into a "file" using Javascript, to do that, we are going to convert a Base64 string to a Blob and that will be interpreted as a File in our server.

We are going to use the following method to convert a base64 string into a blob:

/**
 * Convert a base64 string in a Blob according to the data and contentType.
 * 
 * @param b64Data {String} Pure base64 string without contentType
 * @param contentType {String} the content type of the file i.e (image/jpeg - image/png - text/plain)
 * @param sliceSize {Int} SliceSize to process the byteCharacters
 * @see http://stackoverflow.com/questions/16245767/creating-a-blob-from-a-base64-string-in-javascript
 * @return Blob
 */
function b64toBlob(b64Data, contentType, sliceSize) {
        contentType = contentType || '';
        sliceSize = sliceSize || 512;

        var byteCharacters = atob(b64Data);
        var byteArrays = [];

        for (var offset = 0; offset < byteCharacters.length; offset += sliceSize) {
            var slice = byteCharacters.slice(offset, offset + sliceSize);

            var byteNumbers = new Array(slice.length);
            for (var i = 0; i < slice.length; i++) {
                byteNumbers[i] = slice.charCodeAt(i);
            }

            var byteArray = new Uint8Array(byteNumbers);

            byteArrays.push(byteArray);
        }

      var blob = new Blob(byteArrays, {type: contentType});
      return blob;
}

Now, as you simply can't attach a blob to a visible file input, we need to make it with an asynchronous form using a Post request. We are going to use the following form:

<form id="myAwesomeForm" method="post" action="/php-code-that-handles-fileupload.php">
    <input type="text" id="filename" name="filename" /> <!-- Filename -->
    <input type="submit" id="submitButton" name="submitButton" /> <!-- Submit -->
</form>

The submit of the previous form, would only send the filename text parameter but not any file. Use Javascript to retrieve the form and pass it as first parameter to a new instance of FormData, that will include the text input to our asynchronous form, besides, process your Base64 string to fit the format required by the b64toblob function (first parameter only the base64 string without content type and as second parameter only the datatype):

// Get the form element withot jQuery
var form = document.getElementById("myAwesomeForm");

var ImageURL = "data:image/gif;base64,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";
// Split the base64 string in data and contentType
var block = ImageURL.split(";");
// Get the content type of the image
var contentType = block[0].split(":")[1];// In this case "image/gif"
// get the real base64 content of the file
var realData = block[1].split(",")[1];// In this case "R0lGODlhPQBEAPeoAJosM...."

// Convert it to a blob to upload
var blob = b64toBlob(realData, contentType);

// Create a FormData and append the file with "image" as parameter name
var formDataToUpload = new FormData(form);
formDataToUpload.append("image", blob);

Now that the FormData has a file you only need to submit it asynchronously using jQuery:

/**
 * The following code should send 2 post parameters:
 * filename: providen by the text input
 * image: a file, dinamically added from a base64 string using javascript
 *
 * Is up to you how to receive the file in the Server side.
 */
$.ajax({
    url:"/php-code-that-handles-fileupload.php",
    data: formDataToUpload,// Add as Data the Previously create formData
    type:"POST",
    contentType:false,
    processData:false,
    cache:false,
    dataType:"json", // Change this according to your response from the server.
    error:function(err){
        console.error(err);
    },
    success:function(data){
        console.log(data);
    },
    complete:function(){
        console.log("Request finished.");
    }
});

Is up to you how to handle the previous code, you can prevent the submit event of the form and then execute the code as shown in the following example:

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <title>Base64 string to a file in form</title>
    </head>
    <body>
        <form id="myAwesomeForm" method="post" action="endpoint.php">
            <input type="text" id="filename" name="filename" /> <!-- Filename -->
            <input type="submit" id="submitButton" name="submitButton" /> <!-- Submit -->
        </form>
        <script>
            function b64toBlob(b64Data, contentType, sliceSize) {
                contentType = contentType || '';
                sliceSize = sliceSize || 512;

                var byteCharacters = atob(b64Data);
                var byteArrays = [];

                for (var offset = 0; offset < byteCharacters.length; offset += sliceSize) {
                    var slice = byteCharacters.slice(offset, offset + sliceSize);

                    var byteNumbers = new Array(slice.length);
                    for (var i = 0; i < slice.length; i++) {
                        byteNumbers[i] = slice.charCodeAt(i);
                    }

                    var byteArray = new Uint8Array(byteNumbers);

                    byteArrays.push(byteArray);
                }

              var blob = new Blob(byteArrays, {type: contentType});
              return blob;
            }

            $("#myAwesomeForm").submit(function(e){
                e.preventDefault();
                appendFileAndSubmit();
            });

            function appendFileAndSubmit(){
                // Get the form
                var form = document.getElementById("myAwesomeForm");

                var ImageURL = "data:image/gif;base64,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";
                // Split the base64 string in data and contentType
                var block = ImageURL.split(";");
                // Get the content type
                var contentType = block[0].split(":")[1];// In this case "image/gif"
                // get the real base64 content of the file
                var realData = block[1].split(",")[1];// In this case "iVBORw0KGg...."

                // Convert to blob
                var blob = b64toBlob(realData, contentType);

                // Create a FormData and append the file
                var fd = new FormData(form);
                fd.append("image", blob);

                // Submit Form and upload file
                $.ajax({
                    url:"endpoint.php",
                    data: fd,// the formData function is available in almost all new browsers.
                    type:"POST",
                    contentType:false,
                    processData:false,
                    cache:false,
                    dataType:"json", // Change this according to your response from the server.
                    error:function(err){
                        console.error(err);
                    },
                    success:function(data){
                        console.log(data);
                    },
                    complete:function(){
                        console.log("Request finished.");
                    }
                });
            }
        </script>
    </body>
</html>

Retrieve the file in the server side

Is up to you how to receive the file in the server side, as we don't know if you're using PHP, a framework, django or other languages, however, we provide 2 examples with PHP that could be useful to understand what we've just do.

Symfony 2

<?php
// Important to use these statemenets, the json response is optional for our response.
use Symfony\Component\HttpFoundation\Request;

public function retrieveAction(Request $request){
   // retrieve the file with the name given in the form.
   // do var_dump($request->files->all()); if you need to know if the file is being uploaded.
   $file = $request->files->get('image');
   $nameInTextInput = $request->request->get("filename");
}

Plain PHP

// Do something with the gif image
$file = $_FILES['image']['tmp_name'];

Happy coding !