将base64字符串转换为字节数组

Question

On the page you need to load in the input type file, as well as display this image in img. And then ajax request to transfer the base64 string to the server and there translate it into an array of bytes. Here is my view code:

$('#modalWindow').on('click', '#send', function () {
    var file = $('#autoPicture').attr('src');

    var formData = new FormData();
    formData.append("base64img", file);

    $.ajax({
        type: "POST",
        url: "/Home/LoadImage",
        data: $('form').serialize() + "&base64img=" + formData.get('base64img'),
        success: function (data) {
            alert('Success');
        },
        error: function (error) {
            alert(error.responseText);
        }
    });
});

Controller code:

public ActionResult LoadImage(Car car, string base64img)
    {
        var base64arr = base64img.Split(',');
        byte[] picture = Convert.FromBase64String(base64arr[1]);
        return View();
    }

But when you try to convert crashes with the text:

The input is not a valid Base-64 string because it contains a character in an encoding other than Base 64, more than two padding characters, or an invalid character among the padding characters

Although if you use the site to translate base64 to image convert normally. https://codebeautify.org/base64-to-image-converter

If you need an example base64 code write, I will give. It's just very big. I can give, for example, the beginning and the end of the code, according to my definition it is suitable or not. Well, in general, if you need an example, I will give. I do not understand why c # does not convert.

the second picture for which the method did not fit:

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And the first picture has a very big base64 line, is it also off?

Answer 1

The problem seem originated from this line:

byte[] picture = Convert.FromBase64String(base64img);

If the base64img contains some header like data:image/png;base64 , then Convert.FromBase64String() fails because the string is not fully formatted in Base64 format. Consider using string.Split() before converting from string parameter to remove corresponding Base64 header:

[HttpPost]
public ActionResult LoadImage(Car car, string base64img)
{
    // split the header and content, separated by comma
    var base64arr = base64img.Split(',');
    byte[] picture = Convert.FromBase64String(base64arr[1]);

    // do something with the image

    return View();
}

If the content string contains characters other than ASCII or trailing padding ones, you should remove them like this:

string base64str = base64arr[1];
string processed = base64str.Replace('_', '/').Replace('-', '+');

switch (base64str.Length % 4) 
{
    case 2: 
       processed += "=="; 
       break;
    case 3: 
       processed += "="; 
       break;
}

byte[] picture = Convert.FromBase64String(processed);

Also consider using FormData object when passing image formatted with Base64 string:

$('#modalWindow').on('click', '#send', function () {
    var file = $('#autoPicture').attr('src');

    // note: if you send other form data, use 'serializeArray()' or 'serialize()'

    var formData = new FormData();
    // append other form contents here
    formData.append("base64img", file);

    $.ajax({
        type: "POST",
        url: "/Home/LoadImage",
        data: formData,
        success: function (data) {
            alert('Привет');
        },
        error: function (error) {
            alert(error.responseText);
        }
    });
});

Note:

The equals sign like = or == at the end of Base64 encoded string serves as trailing padding characters and not all Base64 encoded strings ended with them. You can see the reason behind padding here .