WebAPI IE8、IE9 跨域问题

关于WebAPI跨域的问题，网上已经很多了，以下方案可以解决很多跨域问题，但是都不支持IE8、IE9浏览器，JSONP也只能支持Get请求

1. 通过dll配置 Install-Package Microsoft.AspNet.WebApi.Cors
2. 配置 Web.config

IE8，IE9跨域是通过XDomainRequest这个对象去实现，和XMLHttpRequest类似，可以参考下面文档

https://msdn.microsoft.com/zh-cn/library/dd573303(v=vs.85).aspx

使用jQuery.ajax的基础上，在jQuery下面再引用

https://github.com/MoonScript/jQuery-ajaxTransport-XDomainRequest/blob/master/jQuery.XDomainRequest.js

这样IE8、IE9跨域成功了

        public Response<string> Post()
        {
            Response<string> rs = new Response<string>
            {
                head = new ResponseHeader { errcode = 0, errmessage = "post" },
                data = "hello"
            };
            return rs;
        }

这样IE8、IE9跨域失败了

        public Response<string> Post(Request<Message> request)
        {
            Response<string> rs = new Response<string>
            {
                head = new ResponseHeader { errcode = 0, errmessage = "post" },
                data = request.data.content
            };
            return rs;
        }

后来通过排查，有对象形参的WebAPI就会遇到反序列化问题，（IE8,IE9）转换为request对象的時候报错

试了很多次，前端帶不过來Content-Type,就想到了用參数传递到后端，也修改了jQuery.XDOmainRequest.js这个文件

/*!
 * jQuery-ajaxTransport-XDomainRequest - v1.0.4 - 2015-03-05
 * https://github.com/MoonScript/jQuery-ajaxTransport-XDomainRequest
 * Copyright (c) 2015 Jason Moon (@JSONMOON)
 * Licensed MIT (/blob/master/LICENSE.txt)
 */
(function (factory) {
    if (typeof define === 'function' && define.amd) {
        // AMD. Register as anonymous module.
        define(['jquery'], factory);
    } else if (typeof exports === 'object') {
        // CommonJS
        module.exports = factory(require('jquery'));
    } else {
        // Browser globals.
        factory(jQuery);
    }
}(function ($) {

    // Only continue if we're on IE8/IE9 with jQuery 1.5+ (contains the ajaxTransport function)
    if ($.support.cors || !$.ajaxTransport || !window.XDomainRequest) {
        return $;
    }

    var httpRegEx = /^(https?:)?///i;
    var getOrPostRegEx = /^get|post$/i;
    var sameSchemeRegEx = new RegExp('^(//|' + location.protocol + ')', 'i');

    // ajaxTransport exists in jQuery 1.5+
    $.ajaxTransport('* text html xml json', function (options, userOptions, jqXHR) {

        // Only continue if the request is: asynchronous, uses GET or POST method, has HTTP or HTTPS protocol, and has the same scheme as the calling page
        if (!options.crossDomain || !options.async || !getOrPostRegEx.test(options.type) || !httpRegEx.test(options.url) || !sameSchemeRegEx.test(options.url)) {
            return;
        }

        var xdr = null;

        return {
            send: function (headers, complete) {
                var postData = '';
                var userType = (userOptions.dataType || '').toLowerCase();

                xdr = new XDomainRequest();
                if (/^d+$/.test(userOptions.timeout)) {
                    xdr.timeout = userOptions.timeout;
                }

                xdr.ontimeout = function () {
                    complete(500, 'timeout');
                };

                xdr.onload = function () {
                    var allResponseHeaders = 'Content-Length: ' + xdr.responseText.length + '
Content-Type: ' + xdr.contentType;
                    var status = {
                        code: 200,
                        message: 'success'
                    };
                    var responses = {
                        text: xdr.responseText
                    };
                    try {
                        if (userType === 'html' || /text/html/i.test(xdr.contentType)) {
                            responses.html = xdr.responseText;
                        } else if (userType === 'json' || (userType !== 'text' && //json/i.test(xdr.contentType))) {
                            try {
                                responses.json = $.parseJSON(xdr.responseText);
                            } catch (e) {
                                status.code = 500;
                                status.message = 'parseerror';
                                //throw 'Invalid JSON: ' + xdr.responseText;
                            }
                        } else if (userType === 'xml' || (userType !== 'text' && //xml/i.test(xdr.contentType))) {
                            var doc = new ActiveXObject('Microsoft.XMLDOM');
                            doc.async = false;
                            try {
                                doc.loadXML(xdr.responseText);
                            } catch (e) {
                                doc = undefined;
                            }
                            if (!doc || !doc.documentElement || doc.getElementsByTagName('parsererror').length) {
                                status.code = 500;
                                status.message = 'parseerror';
                                throw 'Invalid XML: ' + xdr.responseText;
                            }
                            responses.xml = doc;
                        }
                    } catch (parseMessage) {
                        throw parseMessage;
                    } finally {
                        complete(status.code, status.message, responses, allResponseHeaders);
                    }
                };

                // set an empty handler for 'onprogress' so requests don't get aborted
                xdr.onprogress = function () { };
                xdr.onerror = function () {
                    complete(500, 'error', {
                        text: xdr.responseText
                    });
                };

                if (userOptions.data) {
                    postData = ($.type(userOptions.data) === 'string') ? userOptions.data : $.param(userOptions.data);
                }
                if (options.contentType && options.contentType.length > 0) {
                    if (options.url.indexOf('?') > -1) {
                        options.url = options.url + '&_contentType=' + options.contentType;
                    } else {
                        options.url = options.url + '?_contentType=' + options.contentType;
                    }
                }
                xdr.open(options.type, options.url);
                xdr.send(postData);
            },
            abort: function () {
                if (xdr) {
                    xdr.abort();
                }
            }
        };
    });

    return $;

}));

加上消息处理就可以解决

 public class CrossDomainFixIEHandler : DelegatingHandler
    {
        protected override System.Threading.Tasks.Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, System.Threading.CancellationToken cancellationToken)
        {
            if (request.Method == HttpMethod.Options)
            {
                HttpResponseMessage response = request.CreateResponse<string>(HttpStatusCode.OK, null);
                TaskCompletionSource<HttpResponseMessage> tcs = new TaskCompletionSource<HttpResponseMessage>();
                tcs.SetResult(response);
                return tcs.Task;
            }
            if (request.Content.Headers.ContentType == null || string.IsNullOrWhiteSpace(request.Content.Headers.ContentType.MediaType))
            {
                string contentType = this.GetContentType(string.Concat(request.RequestUri.Query, "&"));
                if (string.IsNullOrWhiteSpace(contentType))
                {
                    contentType = "application/json";
                }
                request.Content.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue(contentType);
            }
            return base.SendAsync(request, cancellationToken);
        }

        /// <summary>
        /// 獲取ContentType
        /// </summary>
        /// <param name="source"></param>
        /// <returns></returns>
        private string GetContentType(string source)
        {
            if (string.IsNullOrWhiteSpace(source))
            {
                return string.Empty;
            }
            Regex regex = new Regex("[&?]_contentType=(?<contentType>(.*?))&", RegexOptions.IgnoreCase);
            Match match = regex.Match(source);
            if (match.Success)
            {
                return match.Groups["contentType"].Value;
            }
            else
            {
                return string.Empty;
            }
        }

完