javascript - Android Native 浏览器中上传的空文件

Question

我正在为手机创建一个可以调整照片大小并上传照片的网站。

$('#ImgPreview canvas').each(function(pIndex) {
    vFormData.append(pIndex, canvasToJpegBlob($(this)[0]), vIssueId +'-attachment0'+ pIndex +'.jpg');
});

$.ajax({
    url: '/api/ob/issuefileupload',
    data: vFormData,
    processData: false,
    contentType: false,
    type: 'POST'
}).done(function(pData) {
    window.location = '/issue?id='+ vIssueId;
}).fail(function(pJqXHR) {
    alert(My.Strings.UploadFailed);
});

这适用于 Android 版 Chrome 和 iOS 版 Safari，但在原生 Android 浏览器中，文件的内容长度为 0，名称为 Blob + 一个 UID。当文件被添加到表单数据时，大小似乎也相当大(900k 而不是 Chrome 中的 50k)。

canvasToJpegBlob 函数:

function canvasToJpegBlob(pCanvas) {
    var vMimeType = "image/jpeg",
        vDataURI,
        vByteString,
        vBlob,
        vArrayBuffer,
        vUint8Array, i,
        vBlobBuilder;

    vDataURI = pCanvas.toDataURL(vMimeType, 0.8);
    vByteString = atob(vDataURI.split(',')[1]);

    vArrayBuffer = new ArrayBuffer(vByteString.length);
    vUint8Array = new Uint8Array(vArrayBuffer);
    for (i = 0; i < vByteString.length; i++) {
        vUint8Array[i] = vByteString.charCodeAt(i);
    }

    try {
        vBlob = new Blob([vUint8Array.buffer], {type : vMimeType});
    } catch(e) {
        window.BlobBuilder = window.BlobBuilder ||
                             window.WebKitBlobBuilder ||
                             window.MozBlobBuilder ||
                             window.MSBlobBuilder;

        if (e.name === 'TypeError' && window.BlobBuilder) {
            vBlobBuilder = new BlobBuilder();
            vBlobBuilder.append(vUint8Array.buffer);
            vBlob = vBlobBuilder.getBlob(vMimeType);
        } else if (e.name === 'InvalidStateError') {
            vBlob = new Blob([vUint8Array.buffer], {type : vMimeType});
        } else {
            alert(My.Strings.UnsupportedFile);
        }
    }

    return vBlob;
}

有什么方法可以让它在原生 Android 浏览器中运行吗？

Answer 1

我也遇到了这个问题，需要想出一个更通用的解决方案，因为在某些情况下我无法控制服务器端代码。

最终我找到了一个几乎完全透明的解决方案。该方法是用一个 blob 填充损坏的 FormData，该 blob 以 multipart/form-data 的必要格式附加数据。它使用将 blob 读入缓冲区的版本覆盖 XHR 的 send()，该缓冲区在请求中发送。

主要代码如下:

var
    // Android native browser uploads blobs as 0 bytes, so we need a test for that
    needsFormDataShim = (function () {
        var bCheck = ~navigator.userAgent.indexOf('Android')
                        && ~navigator.vendor.indexOf('Google')
                        && !~navigator.userAgent.indexOf('Chrome');

        return bCheck && navigator.userAgent.match(/AppleWebKit\/(\d+)/).pop() <= 534;
    })(),

    // Test for constructing of blobs using new Blob()
    blobConstruct = !!(function () {
        try { return new Blob(); } catch (e) {}
    })(),

    // Fallback to BlobBuilder (deprecated)
    XBlob = blobConstruct ? window.Blob : function (parts, opts) {
        var bb = new (window.BlobBuilder || window.WebKitBlobBuilder || window.MSBlobBuilder);
        parts.forEach(function (p) {
            bb.append(p);
        });

        return bb.getBlob(opts ? opts.type : undefined);
    };

function FormDataShim () {
    var
        // Store a reference to this
        o = this,

        // Data to be sent
        parts = [],

        // Boundary parameter for separating the multipart values
        boundary = Array(21).join('-') + (+new Date() * (1e16*Math.random())).toString(36),

        // Store the current XHR send method so we can safely override it
        oldSend = XMLHttpRequest.prototype.send;

    this.append = function (name, value, filename) {
        parts.push('--' + boundary + '\nContent-Disposition: form-data; name="' + name + '"');

        if (value instanceof Blob) {
            parts.push('; filename="'+ (filename || 'blob') +'"\nContent-Type: ' + value.type + '\n\n');
            parts.push(value);
        }
        else {
            parts.push('\n\n' + value);
        }
        parts.push('\n');
    };

    // Override XHR send()
    XMLHttpRequest.prototype.send = function (val) {
        var fr,
            data,
            oXHR = this;

        if (val === o) {
            // Append the final boundary string
            parts.push('--' + boundary + '--');

            // Create the blob
            data = new XBlob(parts);

            // Set up and read the blob into an array to be sent
            fr = new FileReader();
            fr.onload = function () { oldSend.call(oXHR, fr.result); };
            fr.onerror = function (err) { throw err; };
            fr.readAsArrayBuffer(data);

            // Set the multipart content type and boudary
            this.setRequestHeader('Content-Type', 'multipart/form-data; boundary=' + boundary);
            XMLHttpRequest.prototype.send = oldSend;
        }
        else {
            oldSend.call(this, val);
        }
    };
}

然后像这样使用它，然后像往常一样调用 fd.append(name, value):

var fd = needsFormDataShim ? new FormDataShim() : new FormData();