31

我目前正在开发一个显示由 C++ 服务器发送的图像的 WebSocket 应用程序。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:

图像损坏或截断:data:image/png;base64,[一些数据]

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);
}

我正在使用我在这个主题上找到的红点图像:https ://stackoverflow.com/a/4478878/1464608 Base64 类来自这里:https ://stackoverflow.com/a/246813/ 1464608

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

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!

4

6 回答 6

37

我认为最干净的解决方案是更改 base64 编码器以直接在 Uint8Array 而不是字符串上操作。

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

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);
};

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;
}
于 2012-06-18T23:12:33.997 回答
18

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);
};
于 2014-11-21T12:58:57.440 回答
14

谢谢,效果很好!!

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);
}

不太明白为什么 blob 版本如此棘手,但这成功了!

于 2012-06-19T14:06:49.770 回答
4

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');
};
于 2017-02-10T09:34:02.117 回答
3

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;

};
于 2016-10-29T16:45:51.113 回答
0

使用 Blob 非常简单:

// Small red dot image
const content = new Uint8Array([137, 80, 78, 71, 13, 10, 26, 10, 0, 0, 0, 13, 73, 72, 68, 82, 0, 0, 0, 5, 0, 0, 0, 5, 8, 6, 0, 0, 0, 141, 111, 38, 229, 0, 0, 0, 28, 73, 68, 65, 84, 8, 215, 99, 248, 255, 255, 63, 195, 127, 6, 32, 5, 195, 32, 18, 132, 208, 49, 241, 130, 88, 205, 4, 0, 14, 245, 53, 203, 209, 142, 14, 31, 0, 0, 0, 0, 73, 69, 78, 68, 174, 66, 96, 130]);

document.getElementById('my-img').src = URL.createObjectURL(
  new Blob([content.buffer], { type: 'image/png' } /* (1) */)
);
Should display a small red dot: <img id="my-img">

(1) 它也可以在不指定 MIME 类型的情况下工作。

于 2020-11-01T18:33:51.543 回答