[MM-63578] Fix support packet caching issue (#31133)

Fix support packet caching issue by adding no-cache headers

Added Cache-Control headers to prevent browser caching when downloading support packets.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

server/channels/api4/system.go

@@ -133,10 +133,13 @@ func generateSupportPacket(c *Context, w http.ResponseWriter, r *http.Request) {
 	}
 	fileBytesReader := bytes.NewReader(fileBytes)
 
-	// Send the zip file back to client
-	// We are able to pass 0 for content size due to the fact that Golang's serveContent (https://golang.org/src/net/http/fs.go)
-	// already sets that for us
-	web.WriteFileResponse(outputZipFilename, FileMime, 0, now, *c.App.Config().ServiceSettings.WebserverMode, fileBytesReader, true, w, r)
+	// Prevent caching so support packets are always fresh
+	w.Header().Set("Cache-Control", "no-cache, no-store, must-revalidate")
+
+	err = web.WriteStreamResponse(w, fileBytesReader, outputZipFilename, FileMime, true)
+	if err != nil {
+		c.Logger.Warn("Error while writing response", mlog.Err(err))
+	}
 }
 
 // supportPacketFileName returns the ZIP file name in the format mm_support_packet_$CUSTOMER_NAME_YYYY-MM-DDTHH-MM.zip.

server/channels/api4/system_test.go

@@ -236,7 +236,7 @@ func TestGenerateSupportPacket(t *testing.T) {
 		th.App.Srv().SetLicense(l)
 
 		th.TestForSystemAdminAndLocal(t, func(t *testing.T, c *model.Client4) {
-			file, filename, _, err := th.SystemAdminClient.GenerateSupportPacket(context.Background())
+			file, filename, resp, err := th.SystemAdminClient.GenerateSupportPacket(context.Background())
 			require.NoError(t, err)
 
 			assert.Contains(t, filename, "mm_support_packet_My_awesome_Company_")
@@ -244,6 +244,9 @@ func TestGenerateSupportPacket(t *testing.T) {
 			d, err := io.ReadAll(file)
 			require.NoError(t, err)
 			assert.NotZero(t, len(d))
+
+			// Verify that the Cache-Control header is set to prevent caching
+			assert.Equal(t, "no-cache, no-store, must-revalidate", resp.Header.Get("Cache-Control"))
 		})
 	})
 

server/platform/shared/web/files.go

@@ -54,20 +54,23 @@ func WriteFileResponse(filename string, contentType string, contentSize int64, l
 	http.ServeContent(w, r, filename, lastModification, fileReader)
 }
 
-// WriteStreamResponse copies the ReadCloser `r` to the ResponseWriter `w`. Use this when you need to stream a response
+// WriteStreamResponse copies the Reader `r` to the ResponseWriter `w`. Use this when you need to stream a response
 // to the client that will appear as a file `filename` of type `contentType`.
-func WriteStreamResponse(w http.ResponseWriter, r io.ReadCloser, filename string, contentType string, forceDownload bool) error {
+func WriteStreamResponse(w http.ResponseWriter, r io.Reader, filename string, contentType string, forceDownload bool) error {
 	setHeaders(w, contentType, forceDownload, filename)
 
 	if _, err := io.Copy(w, r); err != nil {
-		return errors.Wrap(err, "error streaming ReadCloser")
+		return errors.Wrap(err, "error streaming Reader")
 	}
 
 	return nil
 }
 
 func setHeaders(w http.ResponseWriter, contentType string, forceDownload bool, filename string) {
-	w.Header().Set("Cache-Control", "private, max-age=86400")
+	// Only set Cache-Control if it hasn't been set already
+	if w.Header().Get("Cache-Control") == "" {
+		w.Header().Set("Cache-Control", "private, max-age=86400")
+	}
 	w.Header().Set("X-Content-Type-Options", "nosniff")
 
 	if contentType == "" {