try: pdf = generate_pdf(data) return pdf except Exception as e: logger.error(f"PDF generation failed: str(e)") return jsonify( "success": False, "error": "code": "PDF_RENDER_ERROR", "message": "Report could not be assembled due to invalid data.", "recoverable": False, "userDataPreserved": True ), 200 # still 200 to avoid download interrupt If PDF fails, offer structured data export.
function logPDFFailure(error, context) navigator.sendBeacon('/api/log-pdf-error', JSON.stringify( errorCode: error.code, userAction: 'download_pdf', timestamp: Date.now(), page: window.location.pathname, dataSize: context.dataSize ));
function showGracefulFailureDialog(error) const dialog = <div class="pdf-error-card"> <h3>⚠️ PDF could not be generated</h3> <p>$error.message</p> $error.recoverable ? '<button onclick="retryPDF()">Try again</button>' : '' <button onclick="exportRawData()">Download data as CSV/JSON</button> <button onclick="contactSupport()">Report issue</button> <details> <summary>Technical details</summary> <pre>$error.code</pre> </details> </div> ; showModal(dialog); gracefully broken pdf download
Return a clean error message before ever calling the PDF engine. Never send an error inside a PDF binary. Use structured responses. Success (200 OK with PDF) Content-Type: application/pdf Content-Disposition: attachment; filename="report.pdf" Failure (200 OK with JSON) Even for errors, use 200 OK to avoid browser download interruption, then handle on frontend.
If the PDF library fails mid‑generation, catch and transform the error. try: pdf = generate_pdf(data) return pdf except Exception
# DON'T DO THIS output = BytesIO() pdf = canvas.Canvas(output) pdf.drawString(100, 750, "Report") # crash here – user gets zero-byte or partial PDF
Content-Type: application/json
// Normal PDF download const blob = await response.blob(); const url = URL.createObjectURL(blob); const a = document.createElement('a'); a.href = url; a.download = 'report.pdf'; a.click(); URL.revokeObjectURL(url);