fix: Clean up temporary PDF file after FileResponse using BackgroundTask

[Devguru-codes]

The download_pdf endpoint creates a temp PDF with delete=False but never cleans it up. Each request leaks a temp file. This fix attaches a BackgroundTask to the FileResponse that calls os.unlink(tmp_path) after the response is fully sent.

Fix

• Added from starlette.background import BackgroundTask import
• Attached background=BackgroundTask(os.unlink, tmp_path) to the FileResponse

File Changed

apps/backend/app/routers/reports.py

+from starlette.background import BackgroundTask

     with tempfile.NamedTemporaryFile(delete=False, suffix=".pdf") as tmp:
         HTML(string=html_content).write_pdf(tmp.name)
         tmp_path = tmp.name
-    return FileResponse(tmp_path, media_type="application/pdf", filename="report.pdf")
+    return FileResponse(
+        tmp_path,
+        media_type="application/pdf",
+        filename="report.pdf",
+        background=BackgroundTask(os.unlink, tmp_path)
+    )

Note: delete=False is intentionally kept because the file must persist until FileResponse finishes streaming it. The BackgroundTask runs after the response is fully sent.

---

API Endpoint Validation (POST /api/report/report-pdf)

Request

{
    "report_data": {
        "asl_parameters": [["Magnetic Field Strength", "3T"], ["Manufacturer", "Siemens"]],
        "basic_report": "Test report content",
        "extended_report": "Extended test report",
        "missing_parameters": ["EchoTime"]
    }
}

Response (after fix)

Status Code: 200
Content-Type: application/pdf
Content-Disposition: attachment; filename="report.pdf"
Content-Length: 37 bytes
Leftover temp PDFs: 0

API Endpoint Test Results

#	Test	Status	Detail
1	POST /api/report/report-pdf returns 200	PASS
2	Response content-type is application/pdf	PASS
3	Response body is non-empty	PASS
4	Content-Disposition includes report.pdf	PASS
5	No leftover temp PDF files after response	PASS	BackgroundTask cleaned up

API Summary: PASSED=5 FAILED=0

---

Before/After Comparison

main branch (before fix)

#	Test	Status	Detail
1	Temp PDF created with delete=False	FAIL	File persists after response
2	Temp PDF is cleaned up after response	FAIL	No cleanup found
3	FileResponse uses BackgroundTask	FAIL	No BackgroundTask attached

Summary: PASSED=0 FAILED=3

Temporary_PDF branch (after fix)

#	Test	Status	Detail
1	delete=False paired with BackgroundTask cleanup	PASS	File persists for streaming, then cleaned up
2	Temp PDF is cleaned up after response	PASS	os.unlink via BackgroundTask
3	FileResponse uses BackgroundTask	PASS	BackgroundTask attached

Summary: PASSED=3 FAILED=0
Resolves #17