使用 javascript 和 websockets 显示 blob 中的图像

Display image from blob using javascript and websockets

提问by guitio2002

I'm currently working on a WebSocket application that is displaying images send by a C++ server. I've seen a couple of topics around there but I can't seem to get rid of this error in Firefox:

我目前正在开发一个 WebSocket 应用程序，该应用程序显示由 C++ 服务器发送的图像。我在那里看到了几个主题，但我似乎无法摆脱 Firefox 中的这个错误：

Image corrupt or truncated: data:image/png;base64,[some data]

图像损坏或截断：data:image/png;base64,[some data]

Here's the Javascript code I'm using to display my blob:

这是我用来显示我的 blob 的 Javascript 代码：

socket.onmessage = function(msg) {
    var blob = msg.data;

    var reader = new FileReader();
    reader.onloadend = function() {
        var string = reader.result;
        var buffer = Base64.encode(string);
        var data = "data:image/png;base64,"+buffer;

        var image = document.getElementById('image');
        image.src = data;
    };
    reader.readAsBinaryString(blob);
}

I'm using the image of a red dot that I found on this topic: https://stackoverflow.com/a/4478878/1464608And the Base64 class is from here: https://stackoverflow.com/a/246813/1464608

我正在使用我在此主题上找到的红点图像：https://stackoverflow.com/a/4478878/1464608 Base64 类来自此处：https: //stackoverflow.com/a/246813/ 1464608

But the base64 outcome I get doesn't match and Firefox retrieves me an error of the image being corrupted.

但是我得到的 base64 结果不匹配，Firefox 检索到我的图像已损坏的错误。

I know this ain't much informations but I don't have a clue where to look :/ Any help is more than welcome!!

我知道这不是很多信息，但我不知道在哪里看：/任何帮助都非常受欢迎！！

回答by Stefan Haustein

I think the cleanest solution would be to change the base64 encoder to operate directly on a Uint8Array instead of a string.

我认为最干净的解决方案是将 base64 编码器更改为直接在 Uint8Array 而不是字符串上操作。

Important: You'll need to set the binaryType of the web socket to "arraybuffer" for this.

重要提示：为此，您需要将 Web 套接字的 binaryType 设置为“arraybuffer”。

The onmessage method should look like this:

onmessage 方法应如下所示：

socket.onmessage = function(msg) {
    var arrayBuffer = msg.data;
    var bytes = new Uint8Array(arrayBuffer);

    var image = document.getElementById('image');
    image.src = 'data:image/png;base64,'+encode(bytes);
};

The converted encoder should then look like this (based on https://stackoverflow.com/a/246813/1464608):

转换后的编码器应如下所示（基于https://stackoverflow.com/a/246813/1464608）：

// public method for encoding an Uint8Array to base64
function encode (input) {
    var keyStr = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
    var output = "";
    var chr1, chr2, chr3, enc1, enc2, enc3, enc4;
    var i = 0;

    while (i < input.length) {
        chr1 = input[i++];
        chr2 = i < input.length ? input[i++] : Number.NaN; // Not sure if the index 
        chr3 = i < input.length ? input[i++] : Number.NaN; // checks are needed here

        enc1 = chr1 >> 2;
        enc2 = ((chr1 & 3) << 4) | (chr2 >> 4);
        enc3 = ((chr2 & 15) << 2) | (chr3 >> 6);
        enc4 = chr3 & 63;

        if (isNaN(chr2)) {
            enc3 = enc4 = 64;
        } else if (isNaN(chr3)) {
            enc4 = 64;
        }
        output += keyStr.charAt(enc1) + keyStr.charAt(enc2) +
                  keyStr.charAt(enc3) + keyStr.charAt(enc4);
    }
    return output;
}

回答by Nikita Koksharov

You may write it much simpler:

你可以写得更简单：

socket.onmessage = function(msg) {
   var arrayBuffer = msg.data;
   var bytes = new Uint8Array(arrayBuffer);
   var blob        = new Blob([bytes.buffer]);

   var image = document.getElementById('image');

   var reader = new FileReader();
   reader.onload = function(e) {
       image.src = e.target.result;
   };
   reader.readAsDataURL(blob);
};

回答by guitio2002

Thanks, it's working great!!

谢谢，效果很好！！

So I figure I'd share my final javascript code:

所以我想我会分享我的最终 javascript 代码：

var socket = new WebSocket('ws://'+host+':'+port, protocol);
socket.binaryType = 'arraybuffer';

try {
    socket.onopen = function() {
        document.getElementById('status').style.backgroundColor = '#40ff40';
        document.getElementById('status').textContent = 'Connection opened';
    }

    socket.onmessage = function(msg) {
        var arrayBuffer = msg.data;
        var bytes = new Uint8Array(arrayBuffer);

        var image = document.getElementById('image');
        image.src = 'data:image/png;base64,'+encode(bytes);
    }

    socket.onclose = function(){
        document.getElementById('status').style.backgroundColor = '#ff4040';
        document.getElementById('status').textContent = 'Connection closed';
    }
} catch(exception) {
    alert('Error:'+exception);
}

don't really understand why the blob version is so tricky but this did the trick!

真的不明白为什么 blob 版本如此棘手，但这确实成功了！

回答by Walle Cyril

Another alternative

另一种选择

let urlObject;

socket.onmessage = function(msg) {
    const arrayBuffer = msg.data;
    const image = document.getElementById('image');

    if (urlObject) {
        URL.revokeObjectURL(urlObject) // only required if you do that multiple times
    }
    urlObject = URL.createObjectURL(new Blob([arrayBuffer]));

    image.src = urlObject;

};

回答by J.Jacobs-VP

Thanks to the other answers, I managed to receive a jpeg image by websocket and display it in a new window :

感谢其他答案，我设法通过 websocket 接收 jpeg 图像并将其显示在新窗口中：

socket.binaryType = "arraybuffer";                 
socket.onmessage = function (msg) 
               {    var bytes = new Uint8Array(msg.data);
                    var blob = new Blob([bytes.buffer]);
                    window.open(URL.createObjectURL(blob),'Name','resizable=1');
                };