# Crossref Fetcher (DOI → Research Packet)

This fetcher retrieves bibliographic metadata for a DOI from Crossref and emits a schema-conforming Research Packet.

## Security Constraints

- Only connects to: `https://api.crossref.org`
- Uses proxy env vars (`https_proxy`, `http_proxy`) via urllib
- Produces metadata-only packets (no full text)
- Output must pass `validate_research_packet.py` before CORE consumes it

## Usage

From repo root:

```sh
chmod +x fetch/crossref/fetch_by_doi.py
export PYTHONPATH="$(pwd)"

# Recommend setting CONTACT_EMAIL for Crossref etiquette
export CONTACT_EMAIL="you@example.org"

python3 fetch/crossref/fetch_by_doi.py \
  --doi 10.5555/12345678 \
  --out infra/volumes/handoff/inbound-to-core/RP-crossref-doi.md