bot-bottle/docs/prds/0041-git-http-request-bounds.md

PRD 0041: Git HTTP Request Bounds

• Status: Draft
• Author: didericis-codex
• Created: 2026-06-02
• Issue: #138

Summary

Add Content-Length validation and a body-size cap to git_http_backend.py so malformed or oversized smart-HTTP requests fail cleanly rather than crashing the handler or exhausting memory.

Problem

bot_bottle/git_http_backend.py calls int(self.headers.get("Content-Length", 0)) without catching ValueError. A request with a non-numeric Content-Length raises an unhandled exception in the request handler.

The handler reads the full declared length into memory before passing the body to git http-backend with no upper bound. A local or compromised client can force arbitrarily high memory use. For comparison, supervise_server.py caps request bodies at 1 MiB.

Goals / Success Criteria

• A missing or non-numeric Content-Length returns HTTP 400.
• A negative Content-Length returns HTTP 400.
• A body larger than the cap (1 MiB, matching supervise_server.py) returns HTTP 413.
• Valid Git smart-HTTP pushes and fetches continue to work.
• Unit tests cover: missing length, non-numeric length, negative length, over-cap length, and a valid push/fetch passthrough.

Non-goals

• No changes to git-gate authentication or route logic.
• No changes to supervise_server.py.
• No streaming / chunked-transfer-encoding support.
• No TLS changes.

Scope

In scope:

• bot_bottle/git_http_backend.py request parsing and body reading.
• Unit tests in tests/unit/test_git_http_backend.py.

Out of scope:

• Integration tests that drive a real Git client through the handler.

Design

Wrap the Content-Length parse in a try/except and return 400 on ValueError. Add an explicit check for negative values. After parsing, compare the declared length against a module-level _MAX_BODY_BYTES constant (default 1 MiB) and return 413 if exceeded. Read exactly min(content_length, _MAX_BODY_BYTES) bytes.

Testing Strategy

• Unit tests using unittest.mock to drive the handler with crafted headers.
• Test cases: no Content-Length header, Content-Length: abc, Content-Length: -1, Content-Length: 2097152 (over cap), and a normal small POST body.

Run:

• python3 -m unittest tests.unit.test_git_http_backend
• python3 -m unittest discover -s tests/unit

Open Questions

None.