// Package httpproxy contains a censoring HTTP proxy. This proxy will
// vet all the traffic and reply with 451 responses for a configurable
// set of offending Host headers in incoming requests.
package httpproxy
import (
"net"
"net/http"
"net/http/httputil"
"net/url"
"strings"
"github.com/ooni/probe-cli/v3/internal/engine/netx"
)
const product = "jafar/0.1.0"
// CensoringProxy is a censoring HTTP proxy
type CensoringProxy struct {
keywords []string
transport http.RoundTripper
}
// NewCensoringProxy creates a new CensoringProxy instance using
// the specified list of keywords to censor. keywords is the list
// of keywords that trigger censorship if any of them appears in
// the Host header of a request. dnsNetwork and dnsAddress are
// settings to configure the upstream, non censored DNS.
func NewCensoringProxy(
keywords []string, uncensored netx.HTTPRoundTripper,
) *CensoringProxy {
return &CensoringProxy{keywords: keywords, transport: uncensored}
}
var blockpage = []byte(`<html><head>
<title>451 Unavailable For Legal Reasons</title>
</head><body>
<center><h1>451 Unavailable For Legal Reasons</h1></center>
<p>This content is not available in your jurisdiction.</p>
</body></html>
`)
// ServeHTTP serves HTTP requests
func (p *CensoringProxy) ServeHTTP(w http.ResponseWriter, r *http.Request) {
// Implementation note: use Via header to detect in a loose way
// requests originated by us and directed to us
if r.Header.Get("Via") != "" || r.Host == "" {
w.WriteHeader(http.StatusBadRequest)
return
}
for _, pattern := range p.keywords {
if strings.Contains(r.Host, pattern) {
w.WriteHeader(http.StatusUnavailableForLegalReasons)
w.Write(blockpage)
return
}
}
r.Header.Add("Via", product) // see above
proxy := httputil.NewSingleHostReverseProxy(&url.URL{
Host: r.Host,
Scheme: "http",
})
proxy.ModifyResponse = func(resp *http.Response) error {
resp.Header.Add("Via", product) // see above
return nil
}
proxy.Transport = p.transport
proxy.ServeHTTP(w, r)
}
// Start starts the censoring proxy.
func (p *CensoringProxy) Start(address string) (*http.Server, net.Addr, error) {
server := &http.Server{Handler: p}
listener, err := net.Listen("tcp", address)
if err != nil {
return nil, nil, err
}
go server.Serve(listener)
return server, listener.Addr(), nil
}