From 450b5e741ed3e878e9b6cc0a9d468830d3c1ff6e Mon Sep 17 00:00:00 2001
From: Rajneesh Kumar <1109773+rajneesh2k10@users.noreply.github.com>
Date: Tue, 16 Jun 2026 17:26:46 +0000
Subject: [PATCH] api: return 400 instead of 500 on duplicate changefeed
 creation

ErrChangeFeedAlreadyExists was not in the httpBadRequestError
registry, so the v2 CreateChangefeed handler returned HTTP 500
when a client posted a changefeed ID that already existed. A
duplicate-create is a client-side condition and should be a 4xx.

Adds the error to the existing bad-request registry, mirroring
how ErrChangeFeedNotExists is already classified, and adds a
TestErrorHandleMiddleware regression test.

close #5427
---
 api/middleware/middleware_test.go | 52 +++++++++++++++++++++++++++++++
 pkg/api/util.go                   |  3 +-
 2 files changed, 54 insertions(+), 1 deletion(-)

diff --git a/api/middleware/middleware_test.go b/api/middleware/middleware_test.go
index f605bbe20d..48ecab88ff 100644
--- a/api/middleware/middleware_test.go
+++ b/api/middleware/middleware_test.go
@@ -24,6 +24,7 @@ import (
 
 	"github.com/gin-gonic/gin"
 	"github.com/pingcap/kvproto/pkg/keyspacepb"
+	cerrors "github.com/pingcap/ticdc/pkg/errors"
 	"github.com/pingcap/ticdc/pkg/node"
 	"github.com/pingcap/ticdc/pkg/pdutil"
 	"github.com/pingcap/ticdc/pkg/server"
@@ -205,6 +206,57 @@ func TestForwardToCoordinator(t *testing.T) {
 	}
 }
 
+func TestErrorHandleMiddleware(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+
+	cases := []struct {
+		name       string
+		err        error
+		wantStatus int
+	}{
+		{
+			name:       "no error returns 200",
+			err:        nil,
+			wantStatus: http.StatusOK,
+		},
+		{
+			name:       "registered bad-request error returns 400",
+			err:        cerrors.ErrAPIInvalidParam.GenWithStackByArgs("bad input"),
+			wantStatus: http.StatusBadRequest,
+		},
+		{
+			name:       "duplicate changefeed returns 400",
+			err:        cerrors.ErrChangeFeedAlreadyExists.GenWithStackByArgs("foo"),
+			wantStatus: http.StatusBadRequest,
+		},
+		{
+			name:       "unclassified error returns 500",
+			err:        errors.New("boom"),
+			wantStatus: http.StatusInternalServerError,
+		},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			router := gin.New()
+			router.Use(ErrorHandleMiddleware())
+			router.GET("/test", func(c *gin.Context) {
+				if tc.err != nil {
+					_ = c.Error(tc.err)
+					return
+				}
+				c.Status(http.StatusOK)
+			})
+
+			w := httptest.NewRecorder()
+			req := httptest.NewRequest(http.MethodGet, "/test", nil)
+			router.ServeHTTP(w, req)
+
+			require.Equal(t, tc.wantStatus, w.Code)
+		})
+	}
+}
+
 // mockServer implements server.Server interface for testing
 type mockServer struct {
 	server.Server
diff --git a/pkg/api/util.go b/pkg/api/util.go
index 465b8a279d..95342ce7ae 100644
--- a/pkg/api/util.go
+++ b/pkg/api/util.go
@@ -67,7 +67,8 @@ func NewHTTPError(err error) HTTPError {
 // httpBadRequestError is some errors that will cause a BadRequestError in http handler
 var httpBadRequestError = []*errors.Error{
 	cerror.ErrAPIInvalidParam, cerror.ErrSinkURIInvalid, cerror.ErrStartTsBeforeGC,
-	cerror.ErrChangeFeedNotExists, cerror.ErrTargetTsBeforeStartTs, cerror.ErrTableIneligible,
+	cerror.ErrChangeFeedNotExists, cerror.ErrChangeFeedAlreadyExists,
+	cerror.ErrTargetTsBeforeStartTs, cerror.ErrTableIneligible,
 	cerror.ErrFilterRuleInvalid, cerror.ErrChangefeedUpdateRefused, cerror.ErrMySQLConnectionError,
 	cerror.ErrMySQLInvalidConfig, cerror.ErrCaptureNotExist, cerror.ErrSchedulerRequestFailed,
 	cerror.ErrActiveActiveTSOIndexIncompatible,