httpError: write error string as body in 502 response

https.go

@@ -4,6 +4,7 @@ import (
 	"bufio"
 	"crypto/tls"
 	"errors"
+	"fmt"
 	"io"
 	"io/ioutil"
 	"net"
@@ -129,6 +130,7 @@ func (proxy *ProxyHttpServer) handleHttps(w http.ResponseWriter, r *http.Request
 		}
 		targetSiteCon, err := proxy.connectDial(ctx, "tcp", host)
 		if err != nil {
+			ctx.Warnf("Error dialing to %s: %s", host, err.Error())
 			httpError(proxyClient, ctx, err)
 			return
 		}
@@ -333,7 +335,8 @@ func (proxy *ProxyHttpServer) handleHttps(w http.ResponseWriter, r *http.Request
 }
 
 func httpError(w io.WriteCloser, ctx *ProxyCtx, err error) {
-	if _, err := io.WriteString(w, "HTTP/1.1 502 Bad Gateway\r\n\r\n"); err != nil {
+	errStr := fmt.Sprintf("HTTP/1.1 502 Bad Gateway\r\nContent-Type: text/plain\r\nContent-Length: %d\r\n\r\n%s", len(err.Error()), err.Error())
+	if _, err := io.WriteString(w, errStr); err != nil {
 		ctx.Warnf("Error responding to client: %s", err)
 	}
 	if err := w.Close(); err != nil {