AJAX（XMLHttpRequest）进行跨域请求方法详解（二）

2023-08-05 16:49:46

注意：以下代码请在Firefox 3.5、Chrome 3.0、Safari 4之后的版本中进行测试。IE8的实现方法与其他浏览不同。

2，预检请求

预检请求首先需要向另外一个域名的资源发送一个 HTTP OPTIONS 请求头，其目的就是为了判断实际发送的请求是否是安全的。下面的2种情况需要进行预检：
a，不是上面的简单请求，比如使用Content-Type 为 application/xml 或 text/xml 的 POST 请求
b，在请求中设置自定义头，比如 X-JSON、X-MENGXIANHUI 等

注意：在 iis 里进行测试，必须在“应用程序扩展”里面配置 .aspx 扩展的动作允许 OPTIONS。

下面我们举一个预检的请求：

  1. <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
  2. "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
  3. <htmlxmlns="http://www.w3.org/1999/xhtml">
  4. <head>
  5. <title>孟宪会之AJAX跨域请求测试</title>
  6. </head>
  7. <body>
  8. <inputtype='button'value='开始测试'onclick='crossDomainRequest()'/>
  9. <divid="content"></div>
  10. <mce:scripttype="text/javascript"><!--
  11. var xhr =new XMLHttpRequest();
  12. var url ='http://dotnet.aspx.cc/PreflightedRequests.aspx';
  13. function crossDomainRequest() {
  14. document.getElementById("content").innerHTML ="开始进行请求……";
  15. if (xhr) {
  16. var xml ="<root>测试</root>";
  17. xhr.open('POST', url, true);
  18. xhr.setRequestHeader("POWERED-BY-MENGXIANHUI", "Approve");
  19. xhr.setRequestHeader("Content-Type", "application/xml");
  20. xhr.onreadystatechange =handler;
  21. xhr.send(xml);
  22. } else {
  23. document.getElementById("content").innerHTML ="不能创建 XMLHttpRequest。";
  24. }
  25. }
  26. function handler(evtXHR) {
  27. if (xhr.readyState == 4) {
  28. if (xhr.status == 200) {
  29. var response =xhr.responseText;
  30. document.getElementById("content").innerHTML ="结果：" + response;
  31. } else {
  32. document.getElementById("content").innerHTML ="不能进行跨越访问。";
  33. }
  34. }
  35. else {
  36. document.getElementById("content").innerHTML += "<br/>执行状态 readyState：" + xhr.readyState;
  37. }
  38. }
  39. // --></mce:script>
  40. </body>
  41. </html>
  1. <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
  2. "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
  3. <html xmlns="http://www.w3.org/1999/xhtml">
  4. <head>
  5. <title>孟宪会之AJAX跨域请求测试</title>
  6. </head>
  7. <body>
  8. <input type='button' value='开始测试' onclick='crossDomainRequest()' />
  9. <div id="content"></div>
  10. <mce:script type="text/javascript"><!--
  11. var xhr = new XMLHttpRequest();
  12. var url = 'http://dotnet.aspx.cc/PreflightedRequests.aspx';
  13. function crossDomainRequest() {
  14. document.getElementById("content").innerHTML = "开始进行请求……";
  15. if (xhr) {
  16. var xml = "<root>测试</root>";
  17. xhr.open('POST', url, true);
  18. xhr.setRequestHeader("POWERED-BY-MENGXIANHUI", "Approve");
  19. xhr.setRequestHeader("Content-Type", "application/xml");
  20. xhr.onreadystatechange = handler;
  21. xhr.send(xml);
  22. } else {
  23. document.getElementById("content").innerHTML = "不能创建 XMLHttpRequest。";
  24. }
  25. }
  26. function handler(evtXHR) {
  27. if (xhr.readyState == 4) {
  28. if (xhr.status == 200) {
  29. var response = xhr.responseText;
  30. document.getElementById("content").innerHTML = "结果：" + response;
  31. } else {
  32. document.getElementById("content").innerHTML = "不能进行跨越访问。";
  33. }
  34. }
  35. else {
  36. document.getElementById("content").innerHTML += "<br/>执行状态 readyState：" + xhr.readyState;
  37. }
  38. }
  39. // --></mce:script>
  40. </body>
  41. </html>

上面的例子我们发送 xml 格式的数据，并且，发送一个非标准的HTTP头 POWERED-BY-MENGXIANHUI 来说明服务器端该如何设置响应头的。

在服务器端，PreflightedRequests.aspx 的内容如下：

  1. <%@ PageLanguage="C#" %>
  2. <mce:scriptrunat="server"><!--
  3. protected void Page_Load(object sender, EventArgs e)
  4. {
  5. if (Request.HttpMethod.Equals("GET"))
  6. {
  7. Response.Write("这个页面是用来测试跨域 POST 请求的，直接浏览意义不大。");
  8. }
  9. else if (Request.HttpMethod.Equals("OPTIONS"))
  10. {
  11. //通知客户端允许预检请求。并设置缓存时间
  12. Response.ClearContent();
  13. Response.AddHeader("Access-Control-Allow-Origin", "http://www.meng_xian_hui.com:801");
  14. Response.AddHeader("Access-Control-Allow-Methods", "POST, GET, OPTIONS");
  15. Response.AddHeader("Access-Control-Allow-Headers", "POWERED-BY-MENGXIANHUI");
  16. Response.AddHeader("Access-Control-Max-Age", "30");
  17. //此过程无需返回数据
  18. Response.End();
  19. }
  20. else if (Request.HttpMethod.Equals("POST"))
  21. {
  22. if (Request.Headers["Origin"].Equals("http://www.meng_xian_hui.com:801"))
  23. {
  24. System.Xml.XmlDocument doc =new System.Xml.XmlDocument();
  25. doc.Load(Request.InputStream);
  26. Response.AddHeader("Access-Control-Allow-Origin", "http://www.meng_xian_hui.com:801");
  27. Response.Write("您提交的数据是：<br/><br/>" + Server.HtmlEncode(doc.OuterXml));
  28. }
  29. else
  30. {
  31. Response.Write("不允许你的网站请求。");
  32. }
  33. }
  34. }
  35. // --></mce:script>
  1. <%@ Page Language="C#" %>
  2. <mce:script runat="server"><!--
  3. protected void Page_Load(object sender, EventArgs e)
  4. {
  5. if (Request.HttpMethod.Equals("GET"))
  6. {
  7. Response.Write("这个页面是用来测试跨域 POST 请求的，直接浏览意义不大。");
  8. }
  9. else if (Request.HttpMethod.Equals("OPTIONS"))
  10. {
  11. //通知客户端允许预检请求。并设置缓存时间
  12. Response.ClearContent();
  13. Response.AddHeader("Access-Control-Allow-Origin", "http://www.meng_xian_hui.com:801");
  14. Response.AddHeader("Access-Control-Allow-Methods", "POST, GET, OPTIONS");
  15. Response.AddHeader("Access-Control-Allow-Headers", "POWERED-BY-MENGXIANHUI");
  16. Response.AddHeader("Access-Control-Max-Age", "30");
  17. //此过程无需返回数据
  18. Response.End();
  19. }
  20. else if (Request.HttpMethod.Equals("POST"))
  21. {
  22. if (Request.Headers["Origin"].Equals("http://www.meng_xian_hui.com:801"))
  23. {
  24. System.Xml.XmlDocument doc = new System.Xml.XmlDocument();
  25. doc.Load(Request.InputStream);
  26. Response.AddHeader("Access-Control-Allow-Origin", "http://www.meng_xian_hui.com:801");
  27. Response.Write("您提交的数据是：<br/><br/>" + Server.HtmlEncode(doc.OuterXml));
  28. }
  29. else
  30. {
  31. Response.Write("不允许你的网站请求。");
  32. }
  33. }
  34. }
  35. // --></mce:script>

点击“开始测试”按钮，将会执行下面的一系列请求。

  1. OPTIONS /PreflightedRequests.aspx HTTP/1.1
  2. Host: dotnet.aspx.cc
  3. User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.2; zh-CN; rv:1.9.1.7) Gecko/20091221 Firefox/3.5.7 (.NET CLR 3.5.30729)
  4. Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
  5. Accept-Language: zh-cn,zh;q=0.5
  6. Accept-Encoding: gzip,deflate
  7. Accept-Charset: GB2312,utf-8;q=0.7,*;q=0.7
  8. Keep-Alive: 300
  9. Connection: keep-alive
  10. Origin: http://www.meng_xian_hui.com:801
  11. Access-Control-Request-Method: POST
  12. Access-Control-Request-Headers: powered-by-mengxianhui
  13. HTTP/1.x 200 OK
  14. Date: Sun, 10 Jan 2010 14:00:34 GMT
  15. Server: Microsoft-IIS/6.0
  16. X-Powered-By: ASP.NET
  17. X-AspNet-Version: 2.0.50727
  18. Access-Control-Allow-Origin: http://www.meng_xian_hui.com:801
  19. Access-Control-Allow-Methods: POST, GET, OPTIONS
  20. Access-Control-Allow-Headers: POWERED-BY-MENGXIANHUI
  21. Access-Control-Max-Age: 30
  22. Set-Cookie: ASP.NET_SessionId=5npqri55dl1k1zvij1tlw3re;path=/; HttpOnly
  23. Cache-Control: private
  24. Content-Length: 0
  25. POST /PreflightedRequests.aspx HTTP/1.1
  26. Host: dotnet.aspx.cc
  27. User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.2; zh-CN; rv:1.9.1.7) Gecko/20091221 Firefox/3.5.7 (.NET CLR 3.5.30729)
  28. Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
  29. Accept-Language: zh-cn,zh;q=0.5
  30. Accept-Encoding: gzip,deflate
  31. Accept-Charset: GB2312,utf-8;q=0.7,*;q=0.7
  32. Keep-Alive: 300
  33. Connection: keep-alive
  34. POWERED-BY-MENGXIANHUI: Approve
  35. Content-Type: application/xml; charset=UTF-8
  36. Referer: http://www.meng_xian_hui.com:801/CrossDomainAjax/PreflightedRequests.html
  37. Content-Length: 19
  38. Origin: http://www.meng_xian_hui.com:801
  39. Pragma: no-cache
  40. Cache-Control: no-cache
  41. <root>测试</root>
  42. HTTP/1.x 200 OK
  43. Date: Sun, 10 Jan 2010 14:00:34 GMT
  44. Server: Microsoft-IIS/6.0
  45. X-Powered-By: ASP.NET
  46. X-AspNet-Version: 2.0.50727
  47. Access-Control-Allow-Origin: http://www.meng_xian_hui.com:801
  48. Set-Cookie: ASP.NET_SessionId=byvose45zmtbqy45d2a1jf2i;path=/; HttpOnly
  49. Cache-Control: private
  50. Content-Type: text/html; charset=utf-8
  51. Content-Length: 65
  1. OPTIONS /PreflightedRequests.aspx HTTP/1.1
  2. Host: dotnet.aspx.cc
  3. User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.2; zh-CN; rv:1.9.1.7) Gecko/20091221 Firefox/3.5.7 (.NET CLR 3.5.30729)
  4. Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
  5. Accept-Language: zh-cn,zh;q=0.5
  6. Accept-Encoding: gzip,deflate
  7. Accept-Charset: GB2312,utf-8;q=0.7,*;q=0.7
  8. Keep-Alive: 300
  9. Connection: keep-alive
  10. Origin: http://www.meng_xian_hui.com:801
  11. Access-Control-Request-Method: POST
  12. Access-Control-Request-Headers: powered-by-mengxianhui
  13. HTTP/1.x 200 OK
  14. Date: Sun, 10 Jan 2010 14:00:34 GMT
  15. Server: Microsoft-IIS/6.0
  16. X-Powered-By: ASP.NET
  17. X-AspNet-Version: 2.0.50727
  18. Access-Control-Allow-Origin: http://www.meng_xian_hui.com:801
  19. Access-Control-Allow-Methods: POST, GET, OPTIONS
  20. Access-Control-Allow-Headers: POWERED-BY-MENGXIANHUI
  21. Access-Control-Max-Age: 30
  22. Set-Cookie: ASP.NET_SessionId=5npqri55dl1k1zvij1tlw3re; path=/; HttpOnly
  23. Cache-Control: private
  24. Content-Length: 0
  25. POST /PreflightedRequests.aspx HTTP/1.1
  26. Host: dotnet.aspx.cc
  27. User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.2; zh-CN; rv:1.9.1.7) Gecko/20091221 Firefox/3.5.7 (.NET CLR 3.5.30729)
  28. Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
  29. Accept-Language: zh-cn,zh;q=0.5
  30. Accept-Encoding: gzip,deflate
  31. Accept-Charset: GB2312,utf-8;q=0.7,*;q=0.7
  32. Keep-Alive: 300
  33. Connection: keep-alive
  34. POWERED-BY-MENGXIANHUI: Approve
  35. Content-Type: application/xml; charset=UTF-8
  36. Referer: http://www.meng_xian_hui.com:801/CrossDomainAjax/PreflightedRequests.html
  37. Content-Length: 19
  38. Origin: http://www.meng_xian_hui.com:801
  39. Pragma: no-cache
  40. Cache-Control: no-cache
  41. <root>测试</root>
  42. HTTP/1.x 200 OK
  43. Date: Sun, 10 Jan 2010 14:00:34 GMT
  44. Server: Microsoft-IIS/6.0
  45. X-Powered-By: ASP.NET
  46. X-AspNet-Version: 2.0.50727
  47. Access-Control-Allow-Origin: http://www.meng_xian_hui.com:801
  48. Set-Cookie: ASP.NET_SessionId=byvose45zmtbqy45d2a1jf2i; path=/; HttpOnly
  49. Cache-Control: private
  50. Content-Type: text/html; charset=utf-8
  51. Content-Length: 65

以上的代码反映了预检请求的执行过程：首先发送 OPTIONS 请求头，用来向服务器咨询服务器的更多信息，以便为后续的真实请求做准备。比如是否支持 POST 方法等。值得注意的是：

浏览器还发送 Access-Control-Request-Method: POST 和 Access-Control-Request-Headers: powered-by-mengxianhui 请求头。

注意：以上过程是第一次请求的时候的过程，如果在 30 秒内重复点击按钮，你可以看不到 OPTIONS 这一过程。则执行过程是这样的：

  1. POST /PreflightedRequests.aspx HTTP/1.1
  2. Host: dotnet.aspx.cc
  3. User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.2; zh-CN; rv:1.9.1.7) Gecko/20091221 Firefox/3.5.7 (.NET CLR 3.5.30729)
  4. Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
  5. Accept-Language: zh-cn,zh;q=0.5
  6. Accept-Encoding: gzip,deflate
  7. Accept-Charset: GB2312,utf-8;q=0.7,*;q=0.7
  8. Keep-Alive: 300
  9. Connection: keep-alive
  10. POWERED-BY-MENGXIANHUI: Approve
  11. Content-Type: application/xml; charset=UTF-8
  12. Referer: http://www.meng_xian_hui.com:801/CrossDomainAjax/PreflightedRequests.html
  13. Content-Length: 19
  14. Origin: http://www.meng_xian_hui.com:801
  15. Pragma: no-cache
  16. Cache-Control: no-cache
  17. <root>测试</root>
  18. HTTP/1.x 200 OK
  19. Date: Sun, 10 Jan 2010 14:06:32 GMT
  20. Server: Microsoft-IIS/6.0
  21. X-Powered-By: ASP.NET
  22. X-AspNet-Version: 2.0.50727
  23. Access-Control-Allow-Origin: http://www.meng_xian_hui.com:801
  24. Set-Cookie: ASP.NET_SessionId=qs1c4urxywdbdx55u04pvual;path=/; HttpOnly
  25. Cache-Control: private
  26. Content-Type: text/html; charset=utf-8
  27. Content-Length: 65
  1. POST /PreflightedRequests.aspx HTTP/1.1
  2. Host: dotnet.aspx.cc
  3. User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.2; zh-CN; rv:1.9.1.7) Gecko/20091221 Firefox/3.5.7 (.NET CLR 3.5.30729)
  4. Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
  5. Accept-Language: zh-cn,zh;q=0.5
  6. Accept-Encoding: gzip,deflate
  7. Accept-Charset: GB2312,utf-8;q=0.7,*;q=0.7
  8. Keep-Alive: 300
  9. Connection: keep-alive
  10. POWERED-BY-MENGXIANHUI: Approve
  11. Content-Type: application/xml; charset=UTF-8
  12. Referer: http://www.meng_xian_hui.com:801/CrossDomainAjax/PreflightedRequests.html
  13. Content-Length: 19
  14. Origin: http://www.meng_xian_hui.com:801
  15. Pragma: no-cache
  16. Cache-Control: no-cache
  17. <root>测试</root>
  18. HTTP/1.x 200 OK
  19. Date: Sun, 10 Jan 2010 14:06:32 GMT
  20. Server: Microsoft-IIS/6.0
  21. X-Powered-By: ASP.NET
  22. X-AspNet-Version: 2.0.50727
  23. Access-Control-Allow-Origin: http://www.meng_xian_hui.com:801
  24. Set-Cookie: ASP.NET_SessionId=qs1c4urxywdbdx55u04pvual; path=/; HttpOnly
  25. Cache-Control: private
  26. Content-Type: text/html; charset=utf-8
  27. Content-Length: 65

为什么会这样？细心的童鞋可能注意到了，在服务器端有一行代码 Response.AddHeader("Access-Control-Max-Age", "30"); 它是用来设置预检的有效时间的，单位是秒。这一点要特别注意。

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