Move proxy logic into proxy package

proxy/proxy.go

@@ -0,0 +1,115 @@
+package proxy
+
+import (
+	"context"
+	"crypto"
+	"crypto/tls"
+	"crypto/x509"
+	"fmt"
+	"log"
+	"net"
+	"net/http"
+	"net/http/httputil"
+)
+
+var httpHandler = &httputil.ReverseProxy{
+	Director:     func(r *http.Request) {},
+	ErrorHandler: errorHandler,
+}
+
+var httpsHandler = &httputil.ReverseProxy{
+	Director: func(r *http.Request) {
+		r.URL.Host = r.Host
+		r.URL.Scheme = "https"
+	},
+	ErrorHandler: errorHandler,
+}
+
+func errorHandler(w http.ResponseWriter, r *http.Request, err error) {
+	if err == context.Canceled {
+		return
+	}
+	log.Printf("[ERROR]: Proxy error: %v", err)
+	w.WriteHeader(http.StatusBadGateway)
+}
+
+// Proxy implements http.Handler and offers MITM behaviour for modifying
+// HTTP requests and responses.
+type Proxy struct {
+	certConfig *CertConfig
+}
+
+// NewProxy returns a new Proxy.
+func NewProxy(ca *x509.Certificate, key crypto.PrivateKey) (*Proxy, error) {
+	certConfig, err := NewCertConfig(ca, key)
+	if err != nil {
+		return nil, err
+	}
+
+	return &Proxy{
+		certConfig: certConfig,
+	}, nil
+}
+
+func (p *Proxy) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	if r.Method == http.MethodConnect {
+		p.handleConnect(w, r)
+		return
+	}
+
+	httpHandler.ServeHTTP(w, r)
+}
+
+// handleConnect hijacks the incoming HTTP request and sets up an HTTP tunnel.
+// During the TLS handshake with the client, we use the proxy's CA config to
+// create a certificate on-the-fly.
+func (p *Proxy) handleConnect(w http.ResponseWriter, r *http.Request) {
+	hj, ok := w.(http.Hijacker)
+	if !ok {
+		log.Printf("[ERROR] handleConnect: ResponseWriter is not a http.Hijacker (type: %T)", w)
+		writeError(w, r, http.StatusServiceUnavailable)
+		return
+	}
+
+	w.WriteHeader(http.StatusOK)
+
+	clientConn, _, err := hj.Hijack()
+	if err != nil {
+		log.Printf("[ERROR] Hijacking client connection failed: %v", err)
+		writeError(w, r, http.StatusServiceUnavailable)
+		return
+	}
+	defer clientConn.Close()
+
+	// Secure connection to client.
+	clientConn, err = p.clientTLSConn(clientConn)
+	if err != nil {
+		log.Printf("[ERROR] Securing client connection failed: %v", err)
+		return
+	}
+	clientConnNotify := ConnNotify{clientConn, make(chan struct{})}
+
+	l := &OnceAcceptListener{clientConnNotify.Conn}
+
+	err = http.Serve(l, httpsHandler)
+	if err != nil && err != ErrAlreadyAccepted {
+		log.Printf("[ERROR] Serving HTTP request failed: %v", err)
+	}
+	<-clientConnNotify.closed
+}
+
+func (p *Proxy) clientTLSConn(conn net.Conn) (*tls.Conn, error) {
+	tlsConfig := p.certConfig.TLSConfig()
+
+	tlsConn := tls.Server(conn, tlsConfig)
+	if err := tlsConn.Handshake(); err != nil {
+		tlsConn.Close()
+		return nil, fmt.Errorf("handshake error: %v", err)
+	}
+
+	return tlsConn, nil
+}
+
+func writeError(w http.ResponseWriter, r *http.Request, code int) {
+	http.Error(w, http.StatusText(code), code)
+}