martian: when handling 101 response panic on response read after ucon…

…n extraction

The std http package returns the underlying connection in body of 101 response. The response body needs to be removed form the response.
Make reads from the replaced body panic to ensure that it's always handled correctly.

internal/martian/proxy.go

@@ -18,6 +18,7 @@ import (
 	"context"
 	"crypto/tls"
 	"errors"
+	"io"
 	"net"
 	"net/http"
 	"net/url"
@@ -388,3 +389,11 @@ func upgradeType(h http.Header) string {
 	}
 	return h.Get("Upgrade")
 }
+
+type panicReader struct{}
+
+func (panicReader) Read(p []byte) (int, error) {
+	panic("unexpected read")
+}
+
+var panicBody = io.NopCloser(panicReader{})

internal/martian/proxy_conn.go

@@ -259,8 +259,7 @@ func (p *proxyConn) handleUpgradeResponse(res *http.Response) error {
 		log.Errorf(res.Request.Context(), "internal error: switching protocols response with non-writable body")
 		return errClose
 	}
-
-	res.Body = nil
+	res.Body = panicBody
 
 	if err := p.tunnel(resUpType, res, uconn); err != nil {
 		log.Errorf(res.Request.Context(), "%s tunnel: %v", resUpType, err)

internal/martian/proxy_handler.go

@@ -149,8 +149,7 @@ func (p proxyHandler) handleUpgradeResponse(rw http.ResponseWriter, req *http.Re
 		log.Errorf(ctx, "%s tunnel: internal error: switching protocols response with non-ReadWriteCloser body", resUpType)
 		panic(http.ErrAbortHandler)
 	}
-
-	res.Body = nil
+	res.Body = panicBody
 
 	if err := p.tunnel(resUpType, rw, req, res, uconn); err != nil {
 		log.Errorf(ctx, "%s tunnel: %v", resUpType, err)