[BUG] Set Host header to match target host in proxied requests

scope.go

@@ -396,6 +396,8 @@ func (s *scope) decorateRequest(req *http.Request) (*http.Request, url.Values) {
 	if req.RequestURI == pingEndpoint {
 		req.URL.Scheme = s.host.Scheme()
 		req.URL.Host = s.host.Host()
+		// Set the Host header to match the target URL host
+		req.Host = req.URL.Host
 		return req, req.URL.Query()
 	}
 
@@ -446,6 +448,9 @@ func (s *scope) decorateRequest(req *http.Request) (*http.Request, url.Values) {
 	req.URL.Scheme = s.host.Scheme()
 	req.URL.Host = s.host.Host()
 
+	// Set the Host header to match the target URL host
+	req.Host = req.URL.Host
+
 	// Extend ua with additional info, so it may be queried
 	// via system.query_log.http_user_agent.
 	ua := fmt.Sprintf("RemoteAddr: %s; LocalAddr: %s; CHProxy-User: %s; CHProxy-ClusterUser: %s; %s",

scope_test.go

@@ -523,3 +523,46 @@ func testGetScope(c *cluster, u *user, cu *clusterUser, sessionId string) *scope
 	}
 	return s
 }
+
+func TestDecorateRequestHostHeader(t *testing.T) {
+	testCases := []struct {
+		name       string
+		requestURI string
+		targetHost string
+	}{
+		{
+			name:       "ping endpoint",
+			requestURI: "/ping",
+			targetHost: "127.0.0.2:8123",
+		},
+		{
+			name:       "regular query",
+			requestURI: "/?query=SELECT%201",
+			targetHost: "127.0.0.3:9000",
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			req, err := http.NewRequest("GET", "http://127.0.0.1"+tc.requestURI, nil)
+			if err != nil {
+				t.Fatalf("unexpected error while creating request: %s", err)
+			}
+			s := &scope{
+				id:          newScopeID(),
+				clusterUser: &clusterUser{name: "default"},
+				user:        &user{},
+				host:        topology.NewNode(&url.URL{Host: tc.targetHost}, nil, "", ""),
+			}
+
+			req, _ = s.decorateRequest(req)
+
+			if req.Host != tc.targetHost {
+				t.Fatalf("expected Host header %q; got %q", tc.targetHost, req.Host)
+			}
+			if req.URL.Host != tc.targetHost {
+				t.Fatalf("expected URL.Host %q; got %q", tc.targetHost, req.URL.Host)
+			}
+		})
+	}
+}