s3api: skip error response body when http forbids it (#11931)

WriteResponse wrote the payload even for HEAD requests and statuses
that disallow a body (1xx, 204, 304), which made net/http return
ErrBodyNotAllowed and logged 'write err: http: request method or
response status code does not allow body' for ordinary requests.

Generated with [Devin](https://devin.ai)

Co-authored-by: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

weed/s3api/s3err/error_handler.go

@@ -137,16 +137,30 @@ func setCommonHeaders(w http.ResponseWriter, r *http.Request) {
 	}
 }
 
+// bodyAllowedForStatus is a copy of http.bodyAllowedForStatus non-exported function.
+func bodyAllowedForStatus(status int) bool {
+	switch {
+	case status >= 100 && status <= 199:
+		return false
+	case status == http.StatusNoContent:
+		return false
+	case status == http.StatusNotModified:
+		return false
+	}
+	return true
+}
+
 func WriteResponse(w http.ResponseWriter, r *http.Request, statusCode int, response []byte, mType mimeType) {
 	setCommonHeaders(w, r)
-	if response != nil {
+	canHaveBody := bodyAllowedForStatus(statusCode)
+	if response != nil && canHaveBody {
 		w.Header().Set("Content-Length", strconv.Itoa(len(response)))
 	}
 	if mType != mimeNone {
 		w.Header().Set("Content-Type", string(mType))
 	}
 	w.WriteHeader(statusCode)
-	if response != nil {
+	if response != nil && canHaveBody && r.Method != http.MethodHead {
 		glog.V(4).Infof("status %d %s: %s", statusCode, mType, string(response))
 		_, err := w.Write(response)
 		if err != nil {

weed/s3api/s3err/error_handler_test.go

@@ -6,6 +6,7 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"regexp"
+	"strconv"
 	"testing"
 	"time"
 
@@ -54,6 +55,33 @@ func TestWriteErrorResponseDrainsRequestBodyBeforeWriting(t *testing.T) {
 	assert.True(t, rr.readDeadlines[1].IsZero())
 }
 
+func TestWriteResponseOmitsBodyWhenNotAllowed(t *testing.T) {
+	payload := []byte("<Error><Code>NoSuchKey</Code></Error>")
+	for _, tc := range []struct {
+		name              string
+		method            string
+		status            int
+		wantContentLength string
+	}{
+		{"head request", http.MethodHead, http.StatusNotFound, strconv.Itoa(len(payload))},
+		{"no content", http.MethodGet, http.StatusNoContent, ""},
+		{"not modified", http.MethodGet, http.StatusNotModified, ""},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			req := httptest.NewRequest(tc.method, "/bucket/object", nil)
+			rr := httptest.NewRecorder()
+			WriteResponse(rr, req, tc.status, payload, MimeXML)
+			assert.Empty(t, rr.Body.String())
+			assert.Equal(t, tc.wantContentLength, rr.Header().Get("Content-Length"))
+		})
+	}
+
+	req := httptest.NewRequest(http.MethodGet, "/bucket/object", nil)
+	rr := httptest.NewRecorder()
+	WriteResponse(rr, req, http.StatusOK, payload, MimeXML)
+	assert.Equal(t, string(payload), rr.Body.String())
+}
+
 func extractRequestIDFromBody(body string) string {
 	re := regexp.MustCompile(`<RequestId>([^<]+)</RequestId>`)
 	matches := re.FindStringSubmatch(body)