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Overview

The Document Download Frontend uses Flask’s Blueprint system to organize routes. All routes are defined in the main Blueprint within app/main/views/index.py.

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Health Check Routes

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Status Endpoint

Route: GET /_status Function: status() (index.py:23) Purpose: Health check endpoint for monitoring Response: 
{
  "status": "ok"
}
Status Code: 200

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Legacy API Redirect Routes

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Services Endpoints

Routes:
  • GET /services/_status
  • GET /services/<uuid:service_id>/documents/<uuid:document_id>
  • GET /services/<uuid:service_id>/documents/<uuid:document_id>.<extension>
  • GET /services/<uuid:service_id>/documents/<uuid:document_id>/check
Function: services() (index.py:30) Purpose: Legacy endpoints that redirect to the Document Download API Parameters:
  • service_id (UUID, optional): Service identifier
  • document_id (UUID, optional): Document identifier
  • extension (string, optional): File extension
Behavior: 
api_host = current_app.config["DOCUMENT_DOWNLOAD_API_HOST_NAME"]
path = request.path
query_string = request.query_string.decode("utf-8")
if len(query_string) > 1:
    return redirect(f"{api_host}{path}?{query_string}", 301)
else:
    return redirect(f"{api_host}{path}", 301)
Status Code: 301 (Permanent Redirect)

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Security Policy Routes

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Security.txt

Routes:
  • GET /.well-known/security.txt
  • GET /security.txt
Function: security_policy() (index.py:44) Purpose: Implements GDS Way security vulnerability disclosure policy Reference: GDS Way Security Standards Behavior: Redirects to Cabinet Office VDP security.txt

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Document Download Routes

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Landing Page

Route: GET /d/<base64_uuid:service_id>/<base64_uuid:document_id> Function: landing() (index.py:52) Purpose: Initial landing page when user clicks document link Parameters:
  • service_id (base64-encoded UUID): Service that sent the document
  • document_id (base64-encoded UUID): Document identifier
  • key (query parameter, required): Decryption key for the document
Behavior:
  1. Validates key query parameter exists (404 if missing)
  2. Fetches service information via ServiceApiClient
  3. Retrieves document metadata from Document Download API
  4. Checks if email confirmation is required via confirm_email metadata field
  5. Routes to appropriate next step:
    • If confirm_email is True: redirects to email confirmation
    • Otherwise: redirects to download page
Error Handling:
  • Returns file-unavailable.html template for 404/410 errors
  • Aborts with 404 if key parameter missing
Template: views/landing.html Example: 
/d/c2VydmljZS1pZA==/ZG9jLWlk?key=encryption-key-here

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Email Confirmation

Route: GET|POST /d/<base64_uuid:service_id>/<base64_uuid:document_id>/confirm-email-address Function: confirm_email_address() (index.py:102) Purpose: Verify user’s email address before allowing download Parameters:
  • service_id (base64-encoded UUID): Service identifier
  • document_id (base64-encoded UUID): Document identifier
  • key (query parameter, required): Decryption key
GET Behavior:
  1. Validates key exists (404 if missing)
  2. Fetches service information
  3. Retrieves document metadata
  4. If confirm_email is False, redirects to download page
  5. Displays email confirmation form
POST Behavior:
  1. Validates email address using EmailAddressForm
  2. Authenticates email via Document Download API
  3. On success:
    • Sets document_access_signed_data cookie with authentication token
    • Cookie configured with proper domain, path, and security flags
    • Redirects to download page
  4. On failure:
    • Returns error message:
    This is not the email address the file was sent to.

To confirm the file was meant for you, enter the email address
{service_name} sent the file to.
Rate Limiting:
  • Returns 429 error if too many authentication attempts
Cookie Configuration: 
set_cookie_values = {
    "key": "document_access_signed_data",
    "value": authentication_data["signed_data"],
    "path": authentication_data["cookie_path"],
    "secure": current_app.config["HTTP_PROTOCOL"] == "https",
    "httponly": True,
    "domain": cookie_domain  # Allows subdomain access
}
Template: views/confirm-email-address.html Status Codes:
  • 200: Form displayed successfully
  • 400: Form validation errors
  • 429: Too many requests

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Download Page

Route: GET /d/<base64_uuid:service_id>/<base64_uuid:document_id>/download Function: download_document() (index.py:185) Purpose: Display download page with file information and download link Parameters:
  • service_id (base64-encoded UUID): Service identifier
  • document_id (base64-encoded UUID): Document identifier
  • key (query parameter, required): Decryption key
Behavior:
  1. Validates key parameter (404 if missing)
  2. Fetches service information
  3. Retrieves document metadata including:
    • direct_file_url: Pre-signed download URL
    • size_in_bytes: File size
    • file_extension: File type
    • available_until: Expiry timestamp
  4. Formats display information:
    • File size: via format_file_size()
    • File type: via format_file_type()
    • Expiry date: via _format_file_expiry_date()
Template Variables:
  • download_link: Direct URL to download file
  • file_size: Human-readable file size (e.g., “2.5 MB”)
  • file_type: Human-readable file type (e.g., “PDF”)
  • service_name: Name of sending service
  • service_contact_info: Support contact
  • contact_info_type: Type of contact (link, email, phone)
  • file_expiry_date: Formatted expiry date
Template: views/download.html

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Helper Functions

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Format File Expiry Date

Function: _format_file_expiry_date() (index.py:221) Purpose: Format ISO timestamp into user-friendly date Parameters:
  • available_until (str): ISO 8601 timestamp
Returns: Formatted date string Logic: 
file_expiry_date = parser.parse(available_until).date()
formatted_date = file_expiry_date.strftime("%d %B %Y").lstrip("0")
day_of_week = file_expiry_date.strftime("%A")

# Show day of week if within 30 days
if file_expiry_date - date.today() <= timedelta(days=30):
    return f"{day_of_week} {formatted_date}"

return formatted_date
Examples:
  • Within 30 days: "Monday 15 March 2026"
  • After 30 days: "15 March 2026"

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Get Service

Function: _get_service_or_raise_error() (index.py:234) Purpose: Fetch service details from Notify API Parameters:
  • service_id: Service UUID
Returns: Service data dictionary Error Handling: Aborts with API error status code on failure

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Get Document Metadata

Function: _get_document_metadata() (index.py:241) Purpose: Retrieve document metadata from Document Download API Parameters:
  • service_id: Service UUID
  • document_id: Document UUID
  • key: Decryption key
API Endpoint: 
GET {DOCUMENT_DOWNLOAD_API_HOST_NAME_INTERNAL}/services/{service_id}/documents/{document_id}/check?key={key}
Response Structure: 
{
  "document": {
    "direct_file_url": "https://...",
    "size_in_bytes": 1024000,
    "file_extension": "pdf",
    "available_until": "2026-03-31T23:59:59Z",
    "confirm_email": true
  }
}
Error Handling:
  • 400 with “decryption key” or “Forbidden” in error message → 404
  • 403 or 404 → 404
  • 410 → 410 (Gone)
  • Missing available_until or expired document → 410

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Authenticate Document Access

Function: _authenticate_access_to_document() (index.py:276) Purpose: Verify email address with Document Download API Parameters:
  • service_id: Service UUID
  • document_id: Document UUID
  • key: Decryption key
  • email_address: Email to verify
Returns: Dictionary with signed_data and cookie_path, or None on auth failure API Endpoint: 
POST {DOCUMENT_DOWNLOAD_API_HOST_NAME_INTERNAL}/services/{service_id}/documents/{document_id}/authenticate
Request Body: 
{
  "key": "decryption-key",
  "email_address": "user@example.com"
}
Error Handling:
  • 429 → Raises TooManyRequests exception
  • 400 or 403 → Returns None (authentication failed)
  • Other errors → Raises for 500 handler

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URL Converters

The application uses custom URL converters for base64-encoded UUIDs: Converter: base64_uuid Purpose: Decode base64-encoded UUIDs from URL paths Usage: 
@main.route("/d/<base64_uuid:service_id>/<base64_uuid:document_id>")
This allows URLs to use URL-safe base64 encoding instead of hyphenated UUIDs, making links shorter and cleaner.

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