Repository Guidelines

Project Structure & Module Organization

src/main.rs: Entry point; wires CLI to parser.
src/cli.rs: Clap-based argument parsing (flags like --file, --input-format).
src/color.rs: Minimal ANSI color helpers.
src/parser/: Parser submodule containing all DER decoding and pretty-printing logic.
- mod.rs: Public API surface for the parser (re-exports types and pretty_print_der, parse_and_print).
- asn1_types.rs: TLV parsing, OID decode, helpers.
- encoding_utils.rs: Hex/bits formatting utilities and truncation logic.
- pretty_printer.rs: Recursive DER walker and structure rendering.
- value_printer.rs: Leaf value formatting (strings, times, OIDs, bit/octet strings).
- certificate_utils.rs: X.509-specific helpers and detection.
- time_utils.rs: UTCTime/GeneralizedTime humanization.
- oid_registry.rs: Friendly OID names.
tests/data/: Sample keys/certs used by integration tests or manual runs.
Cargo.toml: Rust 2021 package config and dependencies.

Build: cargo build (use --release for optimized binary).
Run help: cargo run -- --help.
Parse DER file: cargo run -- --file tests/data/test.cert.der --input-format der.
Parse hex string: cargo run -- 3082... (whitespace allowed; auto-detected).
Lint: cargo clippy --all-targets -- -D warnings.
Format: cargo fmt.
Tests: cargo test.

Clippy: configured via clippy.toml; we keep warnings at deny to avoid regressions.
BIT STRINGs: truncated by default for readability (bits: 128, hex bytes: 16). Override with --bits-truncate or --bits-truncate-bytes.

Rust 2021; 4-space indent; rustfmt defaults (cargo fmt).
Naming: modules snake_case; types/enums CamelCase; functions snake_case; constants SCREAMING_SNAKE_CASE.
Avoid unsafe; prefer clear, small functions. Keep CLI parsing in cli.rs, decoding/formatting in src/parser/.
Run cargo clippy locally and fix lints before PRs.

Framework: built-in Rust tests (cargo test).
Unit tests: add #[cfg(test)] mod tests { ... } near code in the relevant file under src/parser/.
Integration tests: create Rust files under tests/ (e.g., tests/parse_certificate.rs) and use fixtures in tests/data/.
Naming: prefer descriptive test names (e.g., it_parses_bit_string_flags).
If output formats change, update or add tests that assert on rendered lines.

Commits: write imperative, concise subjects (e.g., "parse: handle BIT STRING hex mode"). Conventional Commit prefixes are welcome.
PRs: include a clear description, reproduction or sample command, and before/after output when changing formatting.
Link related issues; add tests or fixtures when fixing bugs or adding options.
CI expectations: code compiles, cargo fmt has no diff, and cargo clippy shows no warnings.

Binary DER from stdin isn’t supported in text mode; use --file with --input-format der.
Colors auto-detect TTY; force with --color always.