How to proxy a preflight request with status OK using Go?

huangapple
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英文:

How to proxy a preflight request with status OK using Go?

问题

给定一个发出HTTP请求的客户端：

  1. <!DOCTYPE html>
  2. <html>
  3.     <body>
  4.         <script>
  5.             fetch('http://localhost:3000/messages', {
  6.                 method: 'POST',
  7.                 headers: { 'content-type': 'application/json' },
  8.                 body: JSON.stringify({ data: 'foo' })
  9.             })
  10.             .then(async response => {
  11.                 console.log(await response.json());
  12.             });
  13.         </script>
  14.     </body>
  15. </html>

API服务器无法处理该请求，请求处理程序应充当代理并将请求发送到另一个服务器：

  1. import (
  2. 	"net/http"
  3. 	"net/http/httputil"
  4. 	"net/url"
  5. )
  7. func main() {
  8. 	mux := http.NewServeMux()
  10. 	mux.HandleFunc("/messages", handleRequest)
  12. 	http.ListenAndServe(":3000", mux)
  13. }
  15. func handleRequest(w http.ResponseWriter, r *http.Request) {
  16. 	w.Header().Set("Access-Control-Allow-Origin", "*")
  17. 	w.Header().Set("Access-Control-Allow-Headers", "*")
  18. 	w.Header().Set("Access-Control-Allow-Methods", "*")
  20. 	targetUrl, _ := url.Parse("http://localhost:3001/messages")
  22. 	proxy := httputil.NewSingleHostReverseProxy(targetUrl)
  23. 	proxy.ServeHTTP(w, r)
  24. }

目标服务器应处理该请求并发送响应：

  1. import (
  2. 	"encoding/json"
  3. 	"net/http"
  4. )
  6. func main() {
  7. 	mux := http.NewServeMux()
  9. 	mux.HandleFunc("/messages", handleRequest)
  11. 	http.ListenAndServe(":3001", mux)
  12. }
  14. func handleRequest(w http.ResponseWriter, r *http.Request) {
  15. 	w.Header().Set("Access-Control-Allow-Origin", "*")
  16. 	w.Header().Set("Access-Control-Allow-Headers", "*")
  17. 	w.Header().Set("Access-Control-Allow-Methods", "*")
  19. 	w.WriteHeader(http.StatusOK)
  21. 	json.NewEncoder(w).Encode("bar")
  22. }

我启动了两个服务器并运行了.html文件，我期望在控制台中看到：

bar

但不幸的是，我收到了错误信息：

Access to fetch at 'http://localhost:3000/messages' from origin 'null' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: It does not have HTTP ok status.

有人知道如何解决这个问题吗？

英文:

Given a client making a HTTP request

  1. &lt;!DOCTYPE html&gt;
  2. &lt;html&gt;
  3.     &lt;body&gt;
  4.         &lt;script&gt;
  5.             fetch(&#39;http://localhost:3000/messages&#39;, {
  6.                 method: &#39;POST&#39;,
  7.                 headers: { &#39;content-type&#39;: &#39;application/json&#39; },
  8.                 body: JSON.stringify({ data: &#39;foo&#39; })
  9.             })
  10.             .then(async response =&gt; {
  11.                 console.log(await response.json());
  12.             });
  13.         &lt;/script&gt;
  14.     &lt;/body&gt;
  15. &lt;/html&gt;

The API server does not handle the request, the request handler should act as a proxy and send the request to another server

  1. import (
  2. 	&quot;net/http&quot;
  3. 	&quot;net/http/httputil&quot;
  4. 	&quot;net/url&quot;
  5. )
  7. func main() {
  8. 	mux := http.NewServeMux()
  10. 	mux.HandleFunc(&quot;/messages&quot;, handleRequest)
  12. 	http.ListenAndServe(&quot;:3000&quot;, mux)
  13. }
  15. func handleRequest(w http.ResponseWriter, r *http.Request) {
  16. 	w.Header().Set(&quot;Access-Control-Allow-Origin&quot;, &quot;*&quot;)
  17. 	w.Header().Set(&quot;Access-Control-Allow-Headers&quot;, &quot;*&quot;)
  18. 	w.Header().Set(&quot;Access-Control-Allow-Methods&quot;, &quot;*&quot;)
  20. 	targetUrl, _ := url.Parse(&quot;http://localhost:3001/messages&quot;)
  22. 	proxy := httputil.NewSingleHostReverseProxy(targetUrl)
  23. 	proxy.ServeHTTP(w, r)
  24. }

The target server should handle the request and send back the response

  1. import (
  2. 	&quot;encoding/json&quot;
  3. 	&quot;net/http&quot;
  4. )
  6. func main() {
  7. 	mux := http.NewServeMux()
  9. 	mux.HandleFunc(&quot;/messages&quot;, handleRequest)
  11. 	http.ListenAndServe(&quot;:3001&quot;, mux)
  12. }
  14. func handleRequest(w http.ResponseWriter, r *http.Request) {
  15. 	w.Header().Set(&quot;Access-Control-Allow-Origin&quot;, &quot;*&quot;)
  16. 	w.Header().Set(&quot;Access-Control-Allow-Headers&quot;, &quot;*&quot;)
  17. 	w.Header().Set(&quot;Access-Control-Allow-Methods&quot;, &quot;*&quot;)
  19. 	w.WriteHeader(http.StatusOK)
  21. 	json.NewEncoder(w).Encode(&quot;bar&quot;)
  22. }

I start both servers and run the .html file, I would expect a

> bar

in the console. But unfortunately I get the error

> Access to fetch at 'http://localhost:3000/messages' from origin 'null' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: It does not have HTTP ok status.

How to proxy a preflight request with status OK using Go?

Does someone know how to fix this?

答案1

得分: 5

你需要为代理添加一个处理预检请求的不同路径。
以下是你的代理应该如何看起来的示例代码：

  1. func handleRequest(w http.ResponseWriter, r *http.Request) {
  2. 	w.Header().Set("Access-Control-Allow-Origin", "*")
  3. 	w.Header().Set("Access-Control-Allow-Headers", "*")
  4. 	w.Header().Set("Access-Control-Allow-Methods", "*")
  6. 	if r.Method == "OPTIONS" {
  7. 		w.WriteHeader(http.StatusOK)
  8. 		return
  9. 	}
  10. 	targetUrl, _ := url.Parse("http://localhost:3001")
  12. 	proxy := httputil.NewSingleHostReverseProxy(targetUrl)
  13. 	proxy.ServeHTTP(w, r)
  14. }

注意以下更改：

  1. OPTIONS 请求（预检请求）不会传递给服务器，你只需通过发送 OK 状态来接受它们。

2.（与 CORS 问题无关）目标 URL 不应包含 /message 部分。路径部分已经包含在你的请求中，不需要重复。

此外，你需要更改服务器代码并删除这些头部信息：

  1. // w.Header().Set("Access-Control-Allow-Origin", "*")
  2. // w.Header().Set("Access-Control-Allow-Headers", "*")
  3. // w.Header().Set("Access-Control-Allow-Methods", "*")

这些头部信息已经由代理设置。服务器不再响应 web 浏览器。

英文:

You need to add a different path for handling preflight requests in your proxy.
this is how your proxy should look like:

  1. func handleRequest(w http.ResponseWriter, r *http.Request) {
  2. 	w.Header().Set(&quot;Access-Control-Allow-Origin&quot;, &quot;*&quot;)
  3. 	w.Header().Set(&quot;Access-Control-Allow-Headers&quot;, &quot;*&quot;)
  4. 	w.Header().Set(&quot;Access-Control-Allow-Methods&quot;, &quot;*&quot;)
  6. 	if r.Method == &quot;OPTIONS&quot; {
  7. 		w.WriteHeader(http.StatusOK)
  8. 		return
  9. 	}
  10. 	targetUrl, _ := url.Parse(&quot;http://localhost:3001&quot;)
  12. 	proxy := httputil.NewSingleHostReverseProxy(targetUrl)
  13. 	proxy.ServeHTTP(w, r)
  14. }

Notice the changes:

  1. OPTION requests(preflights) are not passed to server, you just accept them by sending a OK status.

  2. (irrelevant to CORS problem) target url should not have /message part. path part is already present in your request, you should not repeat it.

Also you need to change the server code and remove these headers:

  1. // w.Header().Set(&quot;Access-Control-Allow-Origin&quot;, &quot;*&quot;)
  2. // w.Header().Set(&quot;Access-Control-Allow-Headers&quot;, &quot;*&quot;)
  3. // w.Header().Set(&quot;Access-Control-Allow-Methods&quot;, &quot;*&quot;)

They are already set by the proxy. Server doesn't respond to the web-browser anymore.

huangapple
  • 本文由 发表于 2022年12月30日 17:02:06
  • 转载请务必保留本文链接：https://go.coder-hub.com/74959810.html
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