Merge pull request #2479 from keboola/JakubK-AJDA-1935

Data Apps - Inactivity Timeout

Author: natocTo

internal/pkg/service/appsproxy/proxy/pagewriter/pagewriter.go

@@ -62,6 +62,19 @@ func (pw *Writer) MountAssets(mux *http.ServeMux) {
 }
 
 func (pw *Writer) writePage(w http.ResponseWriter, req *http.Request, page string, status int, data any) {
+	// WORKAROUND for AJDA-1935: Return plain text for Streamlit health checks.
+	// Streamlit displays error responses in a modal that doesn't properly render HTML,
+	// resulting in broken/escaped HTML being shown to users. This returns plain text
+	// for known Streamlit internal endpoints to provide a better user experience.
+	// See IsStreamlitHealthCheck() for full documentation and limitations.
+	if IsStreamlitHealthCheck(req.URL.Path) {
+		plainText := renderPlainText(page, status)
+		w.Header().Set("Content-Type", "text/plain; charset=utf-8")
+		w.WriteHeader(status)
+		_, _ = w.Write([]byte(plainText))
+		return
+	}
+
 	var buf bytes.Buffer
 
 	// Render template

internal/pkg/service/appsproxy/proxy/pagewriter/pathutil.go

@@ -0,0 +1,21 @@
+package pagewriter
+
+import "strings"
+
+// IsStreamlitHealthCheck detects Streamlit health check endpoints.
+//
+// WORKAROUND: This is a temporary solution for AJDA-1935 to prevent broken HTML
+// from being displayed in Streamlit's error modal when the app is starting or unavailable.
+// Streamlit makes health check requests to these endpoints and renders the response
+// in an error dialog, which doesn't properly handle HTML responses.
+//
+// Limitations:
+//   - This approach is Streamlit-specific and does not scale to other frameworks
+//   - Only covers /_stcore/health and /_stcore/host-config endpoints
+//   - Other Streamlit internal endpoints (e.g., /_stcore/stream) are not covered
+//
+// Long-term solution: Modify Streamlit to properly handle HTML error responses
+// or provide a query parameter for clients to request plain text format.
+func IsStreamlitHealthCheck(path string) bool {
+	return strings.HasSuffix(path, "/_stcore/health") || strings.HasSuffix(path, "/_stcore/host-config")
+}

internal/pkg/service/appsproxy/proxy/pagewriter/renderer.go

@@ -0,0 +1,21 @@
+package pagewriter
+
+import (
+	"fmt"
+)
+
+func renderPlainText(page string, status int) string {
+	switch page {
+	case "spinner.gohtml":
+		return `The application is re-starting. Please wait...`
+
+	case "restart_disabled.gohtml":
+		return `The application has been stopped and cannot be restarted automatically.`
+
+	case "error.gohtml":
+		return fmt.Sprintf("An error occurred (status code: %d). Please try again later.", status)
+
+	default:
+		return `No additional information is available.`
+	}
+}