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proxy.go
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proxy.go
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package proxy
import (
"crypto/tls"
"encoding/base64"
"fmt"
"log"
"net"
"net/http"
"net/http/httputil"
"net/url"
"strings"
"sync"
"time"
"github.com/gorilla/websocket"
)
var websocketPingInterval = 30 * time.Second
var websocketTimeout = 30 * time.Second
type Config struct {
HeaderBlacklist []string
Endpoint *url.URL
TLSClientConfig *tls.Config
Origin string
}
type Proxy struct {
reverseProxy *httputil.ReverseProxy
config *Config
}
func filterHeaders(r *http.Response) error {
badHeaders := []string{"Connection", "Keep-Alive", "Proxy-Connection", "Transfer-Encoding", "Upgrade"}
for _, h := range badHeaders {
r.Header.Del(h)
}
return nil
}
func NewProxy(cfg *Config) *Proxy {
// Copy of http.DefaultTransport with TLSClientConfig added
transport := &http.Transport{
Proxy: http.ProxyFromEnvironment,
Dial: (&net.Dialer{
Timeout: 30 * time.Second,
KeepAlive: 30 * time.Second,
}).Dial,
TLSClientConfig: cfg.TLSClientConfig,
TLSHandshakeTimeout: 10 * time.Second,
}
reverseProxy := httputil.NewSingleHostReverseProxy(cfg.Endpoint)
reverseProxy.FlushInterval = time.Millisecond * 100
reverseProxy.Transport = transport
reverseProxy.ModifyResponse = filterHeaders
proxy := &Proxy{
reverseProxy: reverseProxy,
config: cfg,
}
return proxy
}
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
}
// decodeSubprotocol decodes the impersonation "headers" on a websocket.
// Subprotocols don't allow '=' or '/'
func decodeSubprotocol(encodedProtocol string) (string, error) {
encodedProtocol = strings.Replace(encodedProtocol, "_", "=", -1)
encodedProtocol = strings.Replace(encodedProtocol, "-", "/", -1)
decodedProtocol, err := base64.StdEncoding.DecodeString(encodedProtocol)
return string(decodedProtocol), err
}
var headerBlacklist = []string{"Cookie", "X-CSRFToken"}
func (p *Proxy) ServeHTTP(w http.ResponseWriter, r *http.Request) {
// Block scripts from running in proxied content for browsers that support Content-Security-Policy.
w.Header().Set("Content-Security-Policy", "default-src 'none';")
isWebsocket := false
upgrades := r.Header["Upgrade"]
for _, upgrade := range upgrades {
if strings.ToLower(upgrade) == "websocket" {
isWebsocket = true
break
}
}
for _, h := range headerBlacklist {
r.Header.Del(h)
}
if !isWebsocket {
p.reverseProxy.ServeHTTP(w, r)
return
}
r.Host = p.config.Endpoint.Host
r.URL.Host = p.config.Endpoint.Host
r.URL.Path = SingleJoiningSlash(p.config.Endpoint.Path, r.URL.Path)
r.URL.Scheme = p.config.Endpoint.Scheme
if r.URL.Scheme == "https" {
r.URL.Scheme = "wss"
} else {
r.URL.Scheme = "ws"
}
subProtocol := ""
proxiedHeader := make(http.Header, len(r.Header))
for key, value := range r.Header {
if key != "Sec-Websocket-Protocol" {
// Do not proxy the subprotocol to the API server because k8s does not understand what we're sending
proxiedHeader.Set(key, r.Header.Get(key))
continue
}
for _, protocols := range value {
for _, protocol := range strings.Split(protocols, ",") {
protocol = strings.TrimSpace(protocol)
// TODO: secure by stripping newlines & other invalid stuff
// "Impersonate-User" and "Impersonate-Group" and bridge specific (not a k8s thing)
if strings.HasPrefix(protocol, "Impersonate-User.") {
encodedProtocol := strings.TrimPrefix(protocol, "Impersonate-User.")
decodedProtocol, err := decodeSubprotocol(encodedProtocol)
if err != nil {
errMsg := fmt.Sprintf("Error decoding Impersonate-User subprotocol: %v", err)
http.Error(w, errMsg, http.StatusBadRequest)
return
}
proxiedHeader.Set("Impersonate-User", decodedProtocol)
subProtocol = protocol
} else if strings.HasPrefix(protocol, "Impersonate-Group.") {
encodedProtocol := strings.TrimPrefix(protocol, "Impersonate-Group.")
decodedProtocol, err := decodeSubprotocol(encodedProtocol)
if err != nil {
errMsg := fmt.Sprintf("Error decoding Impersonate-Group subprotocol: %v", err)
http.Error(w, errMsg, http.StatusBadRequest)
return
}
proxiedHeader.Set("Impersonate-User", string(decodedProtocol))
proxiedHeader.Set("Impersonate-Group", string(decodedProtocol))
subProtocol = protocol
} else {
proxiedHeader.Set("Sec-Websocket-Protocol", protocol)
subProtocol = protocol
}
}
}
}
// Filter websocket headers.
websocketHeaders := []string{
"Connection",
"Sec-Websocket-Extensions",
"Sec-Websocket-Key",
// NOTE: kans - Sec-Websocket-Protocol must be proxied in the headers
"Sec-Websocket-Version",
"Upgrade",
}
for _, header := range websocketHeaders {
proxiedHeader.Del(header)
}
// NOTE (ericchiang): K8s might not enforce this but websockets requests are
// required to supply an origin.
proxiedHeader.Add("Origin", "http://localhost")
dialer := &websocket.Dialer{
TLSClientConfig: p.config.TLSClientConfig,
}
backend, resp, err := dialer.Dial(r.URL.String(), proxiedHeader)
if err != nil {
errMsg := fmt.Sprintf("Failed to dial backend: '%v'", err)
statusCode := http.StatusBadGateway
if resp == nil || resp.StatusCode == 0 {
log.Println(errMsg)
} else {
statusCode = resp.StatusCode
if resp.Request == nil {
log.Printf("%s Status: '%v' (no request object)", errMsg, resp.Status)
} else {
log.Printf("%s Status: '%v' URL: '%v'", errMsg, resp.Status, resp.Request.URL)
}
}
http.Error(w, errMsg, statusCode)
return
}
defer backend.Close()
upgrader := &websocket.Upgrader{
Subprotocols: []string{subProtocol},
CheckOrigin: func(r *http.Request) bool {
origin := r.Header["Origin"]
if p.config.Origin == "" {
log.Printf("CheckOrigin: Proxy has no configured Origin. Allowing origin %v to %v", origin, r.URL)
return true
}
if len(origin) == 0 {
log.Printf("CheckOrigin: No origin header. Denying request to %v", r.URL)
return false
}
if p.config.Origin == origin[0] {
return true
}
log.Printf("CheckOrigin '%v' != '%v'", p.config.Origin, origin[0])
return false
},
}
frontend, err := upgrader.Upgrade(w, r, nil)
if err != nil {
log.Printf("Failed to upgrade websocket to client: '%v'", err)
return
}
ticker := time.NewTicker(websocketPingInterval)
var writeMutex sync.Mutex // Needed because ticker & copy are writing to frontend in separate goroutines
defer func() {
ticker.Stop()
frontend.Close()
}()
errc := make(chan error, 2)
// Can't just use io.Copy here since browsers care about frame headers.
go func() { errc <- copyMsgs(nil, frontend, backend) }()
go func() { errc <- copyMsgs(&writeMutex, backend, frontend) }()
for {
select {
case <-errc:
// Only wait for a single error and let the defers close both connections.
return
case <-ticker.C:
writeMutex.Lock()
// Send pings to client to prevent load balancers and other middlemen from closing the connection early
err := frontend.WriteControl(websocket.PingMessage, []byte{}, time.Now().Add(websocketTimeout))
writeMutex.Unlock()
if err != nil {
return
}
}
}
}
func copyMsgs(writeMutex *sync.Mutex, dest, src *websocket.Conn) error {
for {
messageType, msg, err := src.ReadMessage()
if err != nil {
return err
}
if writeMutex == nil {
err = dest.WriteMessage(messageType, msg)
} else {
writeMutex.Lock()
err = dest.WriteMessage(messageType, msg)
writeMutex.Unlock()
}
if err != nil {
return err
}
}
}