前端程序使用extjs寫，在本地測試，發送請求到服務器時，發現存在跨域的問題，cookie也沒有set成功，於是乎在這里整理一下解決過程
由於篇幅較長，不想看解決過程的可以翻到最后看總結
1.跨域允許
2.客戶端無法攜帶跨域cookie
3.因為加了withCredentials報文頭，可是客戶端不知道服務器允不允許報的錯
4.由於客戶端不知道服務端是否允許POST請求而報的錯
假設我的服務器IP是120.111.111.123
# 本地的html
# index.html
<html> <head> <meta charset="utf8"> </head> <body> <input type="button" onclick="request()" value="請求"> </body> <script type="text/javascript" src="./ext-all.js"></script> <script type="text/javascript"> function request(){ Ext.Ajax.request({ url: 'http://120.111.111.123/setcookie.php', method: 'POST', params: { 'text': 'hello world' }, success: function(transport){ // do something }, failure: function(transport){ alert("Error: " - transport.responseText); } }); } </script> </html> #服務器的php文件
#path setcookie.php
<?php session_start(); ?> 點擊“請求”按鈕，發送請求后發現js報錯
XMLHttpRequest cannot load http://120.111.111.123/setcookie.php. Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'null' is therefore not allowed access. 報這個錯就說明我們跨域了，不在允許的訪問源，於是乎我在服務的setcookie.php加入header('Access-Control-Allow-Origin:*');允許所有源
<?php session_start(); header('Access-Control-Allow-Origin:*'); // 功能... // ... 然后又報錯
XMLHttpRequest cannot load http://120.111.111.123/setcookie.php. Request header field X-Requested-With is not allowed by Access-Control-Allow-Headers in preflight response. 這次的報錯是因為，在跨域的時候，extjs不會直接發post請求，而是先發送一個option請求，看看服務器允許什么訪問頭（比如是不是允許post請求），驗證成功后才會發送真正的請求
#用谷歌的開發者工具抓的option報文 OPTIONS /setcookie.php HTTP/1.1 Host: 120.111.111.123 Connection: keep-alive Pragma: no-cache Cache-Control: no-cache Access-Control-Request-Method: POST Origin: null User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/52.0.2743.116 Safari/537.36 Access-Control-Request-Headers: x-requested-with Accept: */* Accept-Encoding: gzip, deflate, sdch Accept-Language: zh-CN,zh;q=0.8 接下來，我們只要發送我們允許什么請求頭就行了
#path /setcookie.php session_start(); header('Access-Control-Allow-Origin:*'); header('Access-Control-Allow-Methods:OPTIONS, GET, POST'); // 允許option，get，post請求 header('Access-Control-Allow-Headers:x-requested-with'); // 允許x-requested-with請求頭 header('Access-Control-Max-Age:86400'); // 允許訪問的有效期 // 功能... // ... 繼續測試我們的新功能，成功的解決了跨域問題
but，cookie沒有“設置成功”。而之所以沒有“設置成功”，是因為cookie存在本地，但是每個cookie都有一個domain，當你本地的cookie中存在你當前訪問的域時，才會被帶過去，而我的index.html文件是本地訪問的，即http://localhost/index.html，而cookie的域是120.111.111.123的，所以不行了。於是乎繼續改
#path index.html <html> <head> <meta charset="utf8"> </head> <body> <input type="button" onclick="request()" value="請求"> </body> <script type="text/javascript" src="./ext-all.js"></script> <script type="text/javascript"> function request(){ Ext.Ajax.request({ url: 'http://120.111.111.123/setcookie.php', method: 'POST', params: { 'text': 'hello world' }, withCredentials: true, # 加了這個 success: function(transport){ // do something }, failure: function(transport){ alert("Error: " - transport.responseText); } }); } </script> </html> 繼續訪問，報錯
XMLHttpRequest cannot load http://120.111.111.123/setcookie.php. Response to preflight request doesn't pass access control check: A wildcard '*' cannot be used in the 'Access-Control-Allow-Origin' header when the credentials flag is true. Origin 'null' is therefore not allowed access. The credentials mode of an XMLHttpRequest is controlled by the withCredentials attribute. 現在這個錯誤產生的原因就是
1.因為加入了withCredentials之后，Access-Control-Allow-Origin就不能用“*”了，既然不允許訪問這個源，那我就讓你發個報文頭讓你允許訪問唄！
<?php #path setcookie.php session_start(); // 是否存在請求源 if(isset($_SERVER["HTTP_ORIGIN"])) { header('Access-Control-Allow-Origin:'.$_SERVER["HTTP_ORIGIN"]); } header('Access-Control-Allow-Methods:OPTIONS, GET, POST'); header('Access-Control-Allow-Headers:x-requested-with'); header('Access-Control-Max-Age:86400'); // 功能... // ... ?> 好了，上傳完代碼，繼續測試。發送請求之后，又報錯了（這錯中錯，一個個坑搞的大家都看得不耐煩了吧，我保證，這是最后一個報錯了）
XMLHttpRequest cannot load http://120.111.111.123/setcookie.php. Response to preflight request doesn't pass access control check: Credentials flag is 'true', but the 'Access-Control-Allow-Credentials' header is ''. It must be 'true' to allow credentials. Origin 'null' is therefore not allowed access. 大概的意思就是說我給你發了withCredentials報文頭，但是你服務器沒有跟我說允許我帶這個報文頭，那么解決方法就是加上允許發這個報文頭的報文頭
# path setcookie.php
<?php session_start(); // 是否存在請求源 if(isset($_SERVER["HTTP_ORIGIN"])) { header('Access-Control-Allow-Origin:'.$_SERVER["HTTP_ORIGIN"]); } header('Access-Control-Allow-Origin:null'); header('Access-Control-Allow-Methods:OPTIONS, GET, POST'); header('Access-Control-Allow-Headers:x-requested-with'); header('Access-Control-Max-Age:86400'); header('Access-Control-Allow-Credentials:true'); // 功能... // ... ?> 接下來進行最終的測試，biu~成功了，終於成功了！！！（0.0自己嗨起來了）
接下來總結一下，之所以跨域會引起那么多問題，都是因為耿直的客戶端，發什么類型的請求都要服務器允許，而且要明文允許，允許的內容包括如下
1.跨域允許
解決方法：服務器發送允許客戶端發送源的報文頭
header('Access-Control-Allow-Origin:'.$_SERVER["HTTP_ORIGIN"]);
2.客戶端無法攜帶跨域cookie
這個時候就可以在extjs中加入withCredentials
Ext.Ajax.request({ url: 'http://120.111.111.123/setcookie.php', method: 'POST', params: { 'text': 'hello world' }, withCredentials: true, success: function(transport){ // do something }, failure: function(transport){ alert("Error: " - transport.responseText); } }); 3.因為加了withCredentials報文頭，可是客戶端不知道服務器允不允許報的錯（耿直的客戶端）
這個時候就在服務器發送Access-Control-Allow-Credentials
header('Access-Control-Allow-Credentials:true');
4.由於客戶端不知道服務端是否允許POST請求而報的錯
這個時候要在服務器端加入
header('Access-Control-Allow-Methods:OPTIONS, GET, POST');
header('Access-Control-Allow-Headers:x-requested-with');
header('Access-Control-Max-Age:86400');
以上匯總起來就是
header('Access-Control-Allow-Methods:OPTIONS, GET, POST');
header('Access-Control-Allow-Headers:x-requested-with');
header('Access-Control-Max-Age:86400');
header('Access-Control-Allow-Origin:'.$_SERVER['HTTP_ORIGIN']);
header('Access-Control-Allow-Credentials:true');
header('Access-Control-Allow-Methods:GET, POST, PUT, DELETE, OPTIONS');
header('Access-Control-Allow-Headers:x-requested-with,content-type');
header('Access-Control-Allow-Headers:Origin, No-Cache, X-Requested-With, If-Modified-Since, Pragma, Last-Modified, Cache-Control, Expires, Content-Type, X-E4M-With');