Restore previous behaviour of no trailing newlines in HTTP error response bodies

CHANGELOG.md

@@ -52,6 +52,7 @@
 * [11195](https://github.com/grafana/loki/pull/11195) **canuteson** Generate tsdb_shipper storage_config even if using_boltdb_shipper is false
 * [11551](https://github.com/grafana/loki/pull/11551) **dannykopping** Do not reflect label names in request metrics' "route" label.
 * [11601](https://github.com/grafana/loki/pull/11601) **dannykopping** Ruler: Fixed a panic that can be caused by concurrent read-write access of tenant configs when there are a large amount of rules.
+* [11606](https://github.com/grafana/loki/pull/11606) **dannykopping** Fixed regression adding newlines to HTTP error response bodies which may break client integrations.
 
 ##### Changes
 

pkg/querier/http_test.go

@@ -45,7 +45,7 @@ func TestTailHandler(t *testing.T) {
 
 	handler.ServeHTTP(rr, req)
 	require.Equal(t, http.StatusBadRequest, rr.Code)
-	require.Equal(t, "multiple org IDs present\n", rr.Body.String())
+	require.Equal(t, "multiple org IDs present", rr.Body.String())
 }
 
 type slowConnectionSimulator struct {

pkg/querier/queryrange/serialize_test.go

@@ -104,7 +104,7 @@ func TestResponseFormat(t *testing.T) {
 			url:             "/loki/wrong/path",
 			response:        nil,
 			expectedCode:    http.StatusNotFound,
-			expectedRespone: "unknown request path: /loki/wrong/path\n",
+			expectedRespone: "unknown request path: /loki/wrong/path",
 		},
 	} {
 		t.Run(fmt.Sprintf("%s returns the expected format", tc.url), func(t *testing.T) {

pkg/util/server/error.go

@@ -3,6 +3,7 @@ package server
 import (
 	"context"
 	"errors"
+	"fmt"
 	"net/http"
 
 	"github.com/grafana/dskit/httpgrpc"
@@ -29,7 +30,10 @@ const (
 // WriteError write a go error with the correct status code.
 func WriteError(err error, w http.ResponseWriter) {
 	status, cerr := ClientHTTPStatusAndError(err)
-	http.Error(w, cerr.Error(), status)
+	w.Header().Set("Content-Type", "text/plain; charset=utf-8")
+	w.Header().Set("X-Content-Type-Options", "nosniff")
+	w.WriteHeader(status)
+	fmt.Fprint(w, cerr.Error())
 }
 
 // ClientHTTPStatusAndError returns error and http status that is "safe" to return to client without

pkg/util/server/error_test.go

@@ -56,7 +56,7 @@ func Test_writeError(t *testing.T) {
 			require.Equal(t, tt.expectedStatus, rec.Result().StatusCode)
 			b, err := io.ReadAll(rec.Result().Body)
 			require.NoError(t, err)
-			require.Equal(t, tt.msg, string(b[:len(b)-1]))
+			require.EqualValues(t, tt.msg, b)
 		})
 
 		t.Run(tt.name+"-roundtrip", func(t *testing.T) {
@@ -68,7 +68,7 @@ func Test_writeError(t *testing.T) {
 			require.Equal(t, tt.expectedStatus, rec.Result().StatusCode)
 			b, err := io.ReadAll(rec.Result().Body)
 			require.NoError(t, err)
-			require.Equal(t, tt.msg, string(b[:len(b)-1]))
+			require.EqualValues(t, tt.msg, b)
 		})
 	}
 }