fix: add PDF magic bytes validation to prevent file type spoofing
Add validation that checks PDF files start with '%PDF' magic bytes before accepting uploads. This prevents attackers from uploading malicious files (executables, scripts) by renaming them to .pdf. - Add validate_pdf_magic_bytes() function with clear error messages - Integrate validation in upload_document endpoint after file read - Add comprehensive test coverage (13 test cases) Addresses medium-risk security issue from code review.
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Yaojia Wang
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tests/web/test_documents_upload_validation.py
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264
tests/web/test_documents_upload_validation.py
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"""
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Tests for PDF Magic Bytes Validation in Document Upload.
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TDD: These tests are written FIRST, before implementation.
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They should FAIL initially until the validation logic is implemented.
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"""
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import pytest
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from io import BytesIO
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from unittest.mock import MagicMock, patch, AsyncMock
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from uuid import UUID
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from fastapi import UploadFile
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from fastapi.testclient import TestClient
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from backend.web.api.v1.admin.documents import create_documents_router
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from backend.web.config import StorageConfig
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# Test constants
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TEST_DOC_UUID = "550e8400-e29b-41d4-a716-446655440000"
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TEST_TOKEN = "test-admin-token-12345"
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class TestPDFMagicBytesValidation:
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"""Tests for PDF magic bytes validation during upload."""
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@pytest.fixture
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def storage_config(self, tmp_path):
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"""Create a StorageConfig for testing."""
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return StorageConfig(
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upload_dir=tmp_path / "uploads",
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result_dir=tmp_path / "results",
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max_file_size_mb=50,
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)
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@pytest.fixture
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def mock_dependencies(self):
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"""Create mock dependencies for document upload."""
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mock_docs = MagicMock()
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mock_docs.create.return_value = TEST_DOC_UUID
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mock_annotations = MagicMock()
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mock_annotations.get_for_document.return_value = []
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return {
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"docs": mock_docs,
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"annotations": mock_annotations,
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}
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@pytest.fixture
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def valid_pdf_content(self) -> bytes:
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"""Create valid PDF content with correct magic bytes."""
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# PDF files must start with %PDF
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return b"%PDF-1.4\n%\xe2\xe3\xcf\xd3\n1 0 obj\n<<>>\nendobj\ntrailer\n<<>>\n%%EOF"
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@pytest.fixture
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def invalid_pdf_content_exe(self) -> bytes:
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"""Create content that looks like an executable (MZ header)."""
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return b"MZ\x90\x00\x03\x00\x00\x00\x04\x00\x00\x00\xff\xff"
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@pytest.fixture
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def invalid_pdf_content_text(self) -> bytes:
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"""Create plain text content masquerading as PDF."""
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return b"This is not a PDF file, just plain text."
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@pytest.fixture
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def invalid_pdf_content_html(self) -> bytes:
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"""Create HTML content masquerading as PDF."""
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return b"<!DOCTYPE html><html><body>Not a PDF</body></html>"
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@pytest.fixture
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def empty_content(self) -> bytes:
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"""Create empty file content."""
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return b""
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@pytest.fixture
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def almost_valid_pdf(self) -> bytes:
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"""Create content that starts with %PD but not %PDF."""
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return b"%PD-1.4\nNot quite right"
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def test_valid_pdf_passes_validation(self, valid_pdf_content):
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"""Test that a valid PDF file with correct magic bytes passes validation.
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A valid PDF must start with the bytes b'%PDF'.
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"""
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# Import the validation function (to be implemented)
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from backend.web.api.v1.admin.documents import validate_pdf_magic_bytes
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# Should not raise any exception
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validate_pdf_magic_bytes(valid_pdf_content)
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def test_invalid_pdf_exe_fails_validation(self, invalid_pdf_content_exe):
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"""Test that an executable file renamed to .pdf fails validation.
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This is a security test - attackers might try to upload malicious
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executables by renaming them to .pdf.
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"""
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from backend.web.api.v1.admin.documents import validate_pdf_magic_bytes
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with pytest.raises(ValueError) as exc_info:
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validate_pdf_magic_bytes(invalid_pdf_content_exe)
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assert "Invalid PDF file" in str(exc_info.value)
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assert "valid PDF header" in str(exc_info.value)
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def test_invalid_pdf_text_fails_validation(self, invalid_pdf_content_text):
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"""Test that plain text file renamed to .pdf fails validation."""
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from backend.web.api.v1.admin.documents import validate_pdf_magic_bytes
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with pytest.raises(ValueError) as exc_info:
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validate_pdf_magic_bytes(invalid_pdf_content_text)
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assert "Invalid PDF file" in str(exc_info.value)
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def test_invalid_pdf_html_fails_validation(self, invalid_pdf_content_html):
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"""Test that HTML file renamed to .pdf fails validation."""
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from backend.web.api.v1.admin.documents import validate_pdf_magic_bytes
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with pytest.raises(ValueError) as exc_info:
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validate_pdf_magic_bytes(invalid_pdf_content_html)
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assert "Invalid PDF file" in str(exc_info.value)
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def test_empty_file_fails_validation(self, empty_content):
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"""Test that an empty file fails validation.
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Empty files cannot be valid PDFs and should be rejected.
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"""
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from backend.web.api.v1.admin.documents import validate_pdf_magic_bytes
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with pytest.raises(ValueError) as exc_info:
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validate_pdf_magic_bytes(empty_content)
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assert "Invalid PDF file" in str(exc_info.value)
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def test_almost_valid_pdf_fails_validation(self, almost_valid_pdf):
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"""Test that content starting with %PD but not %PDF fails validation.
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The magic bytes must be exactly %PDF (4 bytes).
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"""
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from backend.web.api.v1.admin.documents import validate_pdf_magic_bytes
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with pytest.raises(ValueError) as exc_info:
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validate_pdf_magic_bytes(almost_valid_pdf)
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assert "Invalid PDF file" in str(exc_info.value)
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def test_pdf_magic_bytes_constant(self):
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"""Test that PDF magic bytes constant is correctly defined."""
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from backend.web.api.v1.admin.documents import PDF_MAGIC_BYTES
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assert PDF_MAGIC_BYTES == b"%PDF"
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def test_validation_is_case_sensitive(self):
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"""Test that magic bytes validation is case-sensitive.
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%pdf (lowercase) should fail - PDF magic bytes are uppercase.
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"""
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from backend.web.api.v1.admin.documents import validate_pdf_magic_bytes
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lowercase_pdf = b"%pdf-1.4\nfake content"
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with pytest.raises(ValueError) as exc_info:
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validate_pdf_magic_bytes(lowercase_pdf)
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assert "Invalid PDF file" in str(exc_info.value)
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class TestDocumentUploadWithMagicBytesValidation:
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"""Integration tests for document upload with magic bytes validation."""
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@pytest.fixture
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def storage_config(self, tmp_path):
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"""Create a StorageConfig for testing."""
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return StorageConfig(
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upload_dir=tmp_path / "uploads",
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result_dir=tmp_path / "results",
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max_file_size_mb=50,
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)
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@pytest.fixture
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def valid_pdf_content(self) -> bytes:
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"""Create valid PDF content."""
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return b"%PDF-1.4\n%\xe2\xe3\xcf\xd3\n1 0 obj\n<<>>\nendobj\ntrailer\n<<>>\n%%EOF"
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@pytest.fixture
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def invalid_pdf_content(self) -> bytes:
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"""Create invalid PDF content (executable header)."""
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return b"MZ\x90\x00\x03\x00\x00\x00"
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def test_upload_valid_pdf_succeeds(
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self, storage_config, valid_pdf_content
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):
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"""Test that uploading a valid PDF with correct magic bytes succeeds."""
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router = create_documents_router(storage_config)
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# Find the upload endpoint (path includes prefix /admin/documents)
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upload_route = None
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for route in router.routes:
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if hasattr(route, 'methods') and 'POST' in route.methods:
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if route.path == "/admin/documents":
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upload_route = route
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break
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assert upload_route is not None, "Upload route should exist"
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# Validate that valid PDF content passes validation
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from backend.web.api.v1.admin.documents import validate_pdf_magic_bytes
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validate_pdf_magic_bytes(valid_pdf_content) # Should not raise
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def test_upload_invalid_pdf_returns_400(
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self, storage_config, invalid_pdf_content
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):
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"""Test that uploading an invalid PDF returns HTTP 400.
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The error message should clearly indicate the PDF header is invalid.
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"""
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from backend.web.api.v1.admin.documents import validate_pdf_magic_bytes
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# Simulate what the upload endpoint should do
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try:
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validate_pdf_magic_bytes(invalid_pdf_content)
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pytest.fail("Should have raised ValueError for invalid PDF")
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except ValueError as e:
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# The endpoint should convert this to HTTP 400
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assert "Invalid PDF file" in str(e)
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assert "valid PDF header" in str(e)
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def test_upload_empty_pdf_returns_400(self, storage_config):
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"""Test that uploading an empty file returns HTTP 400."""
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from backend.web.api.v1.admin.documents import validate_pdf_magic_bytes
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empty_content = b""
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with pytest.raises(ValueError) as exc_info:
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validate_pdf_magic_bytes(empty_content)
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assert "Invalid PDF file" in str(exc_info.value)
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class TestNonPDFFileValidation:
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"""Tests to ensure non-PDF files are not affected by magic bytes validation."""
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def test_png_files_skip_pdf_validation(self):
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"""Test that PNG files do not go through PDF magic bytes validation.
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Only files with .pdf extension should be validated for PDF magic bytes.
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"""
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# PNG magic bytes
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png_content = b"\x89PNG\r\n\x1a\n"
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file_ext = ".png"
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# PNG files should not be validated with PDF magic bytes check
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# The validation should only apply to .pdf files
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assert file_ext != ".pdf"
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def test_jpg_files_skip_pdf_validation(self):
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"""Test that JPG files do not go through PDF magic bytes validation."""
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# JPEG magic bytes
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jpg_content = b"\xff\xd8\xff\xe0"
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file_ext = ".jpg"
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assert file_ext != ".pdf"
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