Part 2 – Serving a File (Download Route)

Add a controlled download endpoint for payload delivery; discuss headers and error handling.

Learning Objectives

• Implement a GET route that returns a file with explicit error handling.

• Explain the effects of Content-Disposition and Content-Type in payload delivery.

• Compare Flask send_file vs manual streaming approaches.

Goals

• Implement a /download (later randomized) route that returns a file.

• Understand Content-Disposition, Content-Type, and explicit 404 handling.

Key Terms

• Content-Disposition: HTTP header indicating inline vs attachment; controls filename.

• Content-Type (MIME): Declares media type (e.g., application/octet-stream).

• 404 Not Found: Explicit error when the payload file doesn’t exist.

What You’ll Build

• A download handler using send_file, plus a brief alt-path using manual streaming.

Sections

• Route Contract: Validate existence → return file → explicit errors.

• Headers: Attachment vs inline; mimetype defaults; size and range handling.

• Operational Notes: Deterministic filenames for reproducibility.

• Milestone: File download succeeds; 404 when missing.

• Troubleshooting: Permissions, relative vs absolute paths, large files.

Exercises

• Change filename and observe Content-Disposition.

• Force mimetype="application/octet-stream" and compare behavior.

What’s Next

• Introduce uploads via multipart/form-data.