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In the example below:
package main
import (
"fmt"
"log"
"net/http"
"net/http/httputil"
"net/url"
)
func main() {
p := new(Proxy)
//host := "www.google.com" // WORKS AS EXPECTED
host := "www.apple.com" // GIVES AN ERROR
u, err := url.Parse(fmt.Sprintf("http://%v/", host))
if err != nil {
log.Printf("Error parsing URL")
}
p.proxy = httputil.NewSingleHostReverseProxy(u)
http.Handle("/", p)
log.Fatal(http.ListenAndServe("localhost:8000", nil))
}
type Proxy struct {
proxy *httputil.ReverseProxy
}
func (p *Proxy) ServeHTTP(w http.ResponseWriter, r *http.Request) {
p.proxy.ServeHTTP(w, r)
}
swapping 'www.google.com' with 'www.apple.com' results in this error when pointing Chrome to 'localhost:8000':
Invalid URL
The requested URL "/", is invalid. Reference #9.a61a32b8.1438231668.41733295
Doing a little bit more digging, for www.apple.com, I am getting:
➜ ~ curl --ipv4 -v localhost:8000
< HTTP/1.1 400 Bad Request
< Content-Length: 194
< Content-Type: text/html
< Date: Thu, 30 Jul 2015 05:20:38 GMT
< Expires: Thu, 30 Jul 2015 05:20:38 GMT
< Mime-Version: 1.0
* Server AkamaiGHost is not blacklisted
< Server: AkamaiGHost
<
<HTML><HEAD>
<TITLE>Invalid URL</TITLE>
</HEAD><BODY>
<H1>Invalid URL</H1>
The requested URL "/", is invalid.<p>
Reference #9.65b454b8.1438233638.1f1b8a40
</BODY></HTML>
* Connection #0 to host localhost left intact
and for www.google.com:
➜ ~ curl --ipv4 -v localhost:8000
< HTTP/1.1 302 Found
< Alternate-Protocol: 80:quic,p=0
< Cache-Control: private
< Content-Length: 219
< Content-Type: text/html; charset=UTF-8
< Date: Thu, 30 Jul 2015 05:03:16 GMT
< Location: http://www.google.com/
* Server sffe is not blacklisted
< Server: sffe
< X-Content-Type-Options: nosniff
< X-Xss-Protection: 1; mode=block
<
<HTML><HEAD><meta http-equiv="content-type" content="text/html;charset=utf-8">
<TITLE>302 Moved</TITLE></HEAD><BODY>
<H1>302 Moved</H1>
The document has moved
<A HREF="http://www.google.com/">here</A>.
</BODY></HTML>
* Connection #0 to host localhost left intact
Now when I use 'apple.com' instead of 'www.apple.com', things work fine:
➜ ~ curl --ipv4 -v localhost:8000
< HTTP/1.1 301 Moved Permanently
< Content-Type: text/html
< Date:
< Location: http://www.apple.com/
< Referer:
* Server is not blacklisted
< Server:
< Content-Length: 0
<
* Connection #0 to host localhost left intact
What's going on?
332
The problem here is virtual servers; some of the web sites that you are connecting to don't know what domain you are requesting (i.e. the Host HTTP header field is set to localhost:8000, not, for example, www.apple.com). To fix this, the reverse proxy must rewrite the Host header.
Unfortunately, httputil.NewSingleHostReverseProxy doesn't provide an easy way to do the rewriting, so most of what I have added below has been copied from the net/http/httputil source code:
package main
import (
"fmt"
"log"
"net/http"
"net/http/httputil"
"net/url"
"strings"
)
func main() {
host := "www.apple.com"
u, err := url.Parse(fmt.Sprintf("http://%v/", host))
if err != nil {
log.Printf("Error parsing URL")
}
targetQuery := u.RawQuery
p := &httputil.ReverseProxy{
Director: func(req *http.Request) {
req.Host = host
req.URL.Scheme = u.Scheme
req.URL.Host = u.Host
req.URL.Path = singleJoiningSlash(u.Path, req.URL.Path)
if targetQuery == "" || req.URL.RawQuery == "" {
req.URL.RawQuery = targetQuery + req.URL.RawQuery
} else {
req.URL.RawQuery = targetQuery + "&" + req.URL.RawQuery
}
},
}
http.Handle("/", p)
log.Fatal(http.ListenAndServe("localhost:8000", nil))
}
func singleJoiningSlash(a, b string) string {
aslash := strings.HasSuffix(a, "/")
bslash := strings.HasPrefix(b, "/")
switch {
case aslash && bslash:
return a + b[1:]
case !aslash && !bslash:
return a + "/" + b
}
return a + b
}
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