2022年10月21日dom-to-image iOS端线上版本跨域问题

背景：dom中img src 为项目本地路径，本地调试时调用dom-to-image toPng方法时，可以正常生成截图，但线上调试时提示：Cross origin requests are only supported for HTTP.
XMLHttpRequest cannot load file:///var/mobxxxxxxx

按照提示，这个应该是跨域问题，但在调用方法时，我明明已经开启了useCORS: true
断点查看调用栈显示在XMLHttpRequest这里出了问题：

cannot load file:///var/mobile/Containers/Data/Application/3AD80DAD-368A-4F7A-A553-EDD9CBFA3028/Documents/xxxx/mPaaS/xxxx/xxxx/static/media/xxxx.17ad6194.png due to access control checks.

 function getAndEncode(url) {
            var TIMEOUT = 30000;
            if(domtoimage.impl.options.cacheBust) {
                // Cache bypass so we dont have CORS issues with cached images
                // Source: https://developer.mozilla.org/en/docs/Web/API/XMLHttpRequest/Using_XMLHttpRequest#Bypassing_the_cache
                url += ((/\?/).test(url) ? "&" : "?") + (new Date()).getTime();
            }

            return new Promise(function (resolve) {
                var request = new XMLHttpRequest();

                request.onreadystatechange = done;
                request.ontimeout = timeout;
                request.responseType = 'blob';
                request.timeout = TIMEOUT;
                request.open('GET', url, true);
                request.send();

                var placeholder;
                if(domtoimage.impl.options.imagePlaceholder) {
                    var split = domtoimage.impl.options.imagePlaceholder.split(/,/);
                    if(split && split[1]) {
                        placeholder = split[1];
                    }
                }

                function done() {
                    if (request.readyState !== 4) return;

                    if (request.status !== 200) {
                        if(placeholder) {
                            resolve(placeholder);
                        } else {
                            fail('cannot fetch resource: ' + url + ', status: ' + request.status);
                        }

                        return;
                    }

                    var encoder = new FileReader();
                    encoder.onloadend = function () {
                        var content = encoder.result.split(/,/)[1];
                        resolve(content);
                    };
                    encoder.readAsDataURL(request.response);
                }

                function timeout() {
                    if(placeholder) {
                        resolve(placeholder);
                    } else {
                        fail('timeout of ' + TIMEOUT + 'ms occured while fetching resource: ' + url);
                    }
                }

                function fail(message) {
                    console.error(message);
                    resolve('');
                }
            });
        }

解决方案1:img标签里的图片改为url加载

解决方案2:img标签里的图片改为base64加载

原理
方案1：通过http链接加载，正常完成XMLHttpRequest请求逻辑
方案2：让newImage 方法在进入isDataUrl判断后，直接返回，不在进入XMLHttpRequest逻辑

function newImage(element) {
            return {
                inline: inline
            };

            function inline(get) {
                if (util.isDataUrl(element.src)) return Promise.resolve();

                return Promise.resolve(element.src)
                    .then(get || util.getAndEncode)
                    .then(function (data) {
                        return util.dataAsUrl(data, util.mimeType(element.src));
                    })
                    .then(function (dataUrl) {
                        return new Promise(function (resolve, reject) {
                            element.onload = resolve;
                            element.onerror = reject;
                            element.src = dataUrl;
                        });
                    });
            }
        }