content-addressable

Data carries its own proof of integrity, intrinsically.

IPLD-native content addressing for Rust and Python. A content address is derived from the data itself, not assigned by an authority — give someone the bytes and the address, and they can recompute the address and know, with no trusted third party, that the bytes are exactly what the address names. The proof travels with the data.

This crate is deliberately small and honest: it is the instrument, not the sky.

It speaks the multiformats / IPLD stack, so its artifacts interoperate with the wider content-addressed world (IPFS, IPLD, libp2p). Every id is a CIDv1 with a fixed profile:

Field	Value
CID version	v1
Codec	DAG-CBOR (0x71)
Multihash	BLAKE3 (0x1e)
Digest	32 bytes
Encoding	canonical DAG-CBOR (strict key order, definite lengths, tag-42 links)

Rust is the core implementation; the Python package is a PyO3 binding over that same Rust core, so an id computed in Python is byte-identical to the one Rust computes for the same canonical IPLD value.

Status & stability

The package is 0.1.0 — the first release that freezes the core contract. The core byte/wire and API contracts are locked for the whole 0.1.x line (changing any is a breaking release outside 0.1.x), while the optional unstable-merkle / unstable-store features are explicitly still moving and are named to say so.

Surface	Default	Stability
ContentId, canonical encoding, core errors, presentation, MSRV	Yes	Frozen for 0.1.x — changing any is a breaking release outside 0.1.x
Python core parity	Separate package	Same core byte profile
unstable-merkle feature	No	Experimental — serialized node bytes NOT frozen
unstable-store feature	No	Experimental — trait/API surface NOT frozen (no new wire format of its own)

Details and rationale: docs/STABILITY.md.

Installation

Rust:

[dependencies]
content-addressable = "0.1.0"

With the optional (default-off) features:

content-addressable = { version = "0.1.0", features = ["unstable-merkle"] }
content-addressable = { version = "0.1.0", features = ["unstable-store"] }
content-addressable = { version = "0.1.0", features = ["unstable-merkle", "unstable-store"] }

Python:

pip install content-addressable

The PyPI distribution is content-addressable (hyphen); the import name is content_addressable (underscore):

import content_addressable

Rust quick start

Implement ContentAddressable by providing canonical_form; content_id, verify, and ensure_content_id come for free:

use content_addressable::{canonical, ContentAddressable, ContentError};
use serde::Serialize;

#[derive(Serialize)]
struct Record {
    name: String,
}

impl ContentAddressable for Record {
    fn canonical_form(&self) -> Result<Vec<u8>, ContentError> {
        canonical::to_canonical_dagcbor(self)
    }
}

let record = Record { name: "alpha".into() };

let id = record.content_id()?;          // a CIDv1 (DAG-CBOR + BLAKE3)
assert!(record.verify(&id)?);           // self-certifying: re-derive and compare
println!("{id}");                       // "bafyr4i…" — the canonical text form
# Ok::<(), ContentError>(())

verify returns Ok(false) on a mismatch; its strict sibling ensure_content_id returns Err(ContentError::VerificationFailed) instead. The secondary digest and binary presentation forms are in Presentation forms.

Python quick start

The Python face exposes the same byte profile, but not the Rust ContentAddressable trait or verify — you canonicalize a native Python value and take its content_id directly. This block is mirrored by tests/test_readme.py (every call identical), so CI's python job proves it still works:

from content_addressable import (
    ContentId, content_id,
    to_canonical_dagcbor, from_canonical_dagcbor,
)

# A value's content id (CIDv1, DAG-CBOR + BLAKE3). Key order is irrelevant.
record = {"name": "alpha", "attrs": {}}
cid = content_id(record)

assert str(cid).startswith("b")                # base32-lower multibase text
assert len(cid.digest_hex()) == 64             # 64-char bare-digest-hex
assert isinstance(to_canonical_dagcbor(record), bytes)

# Canonical bytes round-trip; equal values -> equal bytes -> equal ids.
raw = to_canonical_dagcbor(record)
assert content_id(record) == ContentId.from_canonical_bytes(raw)
assert from_canonical_dagcbor(raw) == record
assert content_id({"attrs": {}, "name": "alpha"}) == cid  # order-independent

# Parse an id back from its text / binary forms.
assert ContentId.parse(str(cid)) == cid
assert ContentId.from_bytes(cid.to_bytes()) == cid

# Wrap an already-computed 32-byte BLAKE3 digest with NO re-hash.
assert ContentId.from_blake3_content_digest(cid.digest_bytes()) == cid
assert len(cid.digest_bytes()) == 32           # the raw BLAKE3 hash

ContentId implements __eq__ / __hash__, so an id is usable as a dict key or set member.

Choosing a construction path

Prefer the safe path. from_canonical_bytes is fast but carries a real precondition — it is not universally safe.

Use case	API (Rust / Python)	Contract
Hash a normal value	value.content_id() / content_id(value)	Preferred safe path
Encode a value to bytes	canonical::to_canonical_dagcbor(v) / to_canonical_dagcbor(v)	Produces canonical DAG-CBOR
Accept foreign / untrusted bytes	Rust: ContentId::from_canonical_bytes_checked(b) · Python: no single checked constructor yet	Validates DAG-CBOR canonicality; errors on non-canonical
Hash already-trusted canonical bytes	ContentId::from_canonical_bytes(b)	Unchecked precondition: caller asserts b is canonical DAG-CBOR
Wrap an existing BLAKE3 digest	ContentId::from_blake3_content_digest(d)	No rehash; caller asserts the digest is BLAKE3 over canonical DAG-CBOR

Presentation forms

A ContentId names four distinct presentation forms so callers can't confuse them; each is frozen (changing any is a breaking release outside 0.1.x):

Form	Rust	Python	What it is
Canonical text	Display / to_string()	str(id)	multibase base32-lower (b…) — the IPLD-canonical CID string
Binary envelope	to_bytes() / from_bytes()	to_bytes() / from_bytes()	the full CID binary form (version + codec + multihash + digest)
Bare digest	digest_bytes() -> [u8; 32]	digest_bytes() -> bytes	the raw 32-byte BLAKE3 hash, no envelope
Bare-digest-hex	digest_hex() -> String	digest_hex() -> str	lower-hex of the 32-byte digest (64 chars, no prefix)

Display is the inverse of FromStr for base32-lower, and that round-trip is frozen and tested. Full CID bytes can be hex-encoded by a caller directly (hex::encode(id.to_bytes())) — the crate deliberately does not bless a second "hex" method; see docs/STABILITY.md for why.

Experimental features

Both features are default-off and exercised in CI via --all-features. Do not depend on the unstable-merkle node bytes yet.

merkle — content-addressed DAG nodes

MerkleNode<T> is a payload: T plus parents: BTreeSet<ContentId>; its id is derived from both the payload and the parent links, so a root id plus the node bytes determines the whole DAG. Because parents are a BTreeSet, they are deduplicated and ordered by content-derived Ord — equal parent sets always produce equal bytes regardless of insertion order, and each parent serializes as a real DAG-CBOR tag-42 link.

use content_addressable::merkle::MerkleNode; // feature = "unstable-merkle"

let root = MerkleNode::genesis("hello");
let root_id = root.id()?;
let child = MerkleNode::new("world", [root_id]);
assert!(child.parents().contains(&root_id));
# Ok::<(), content_addressable::ContentError>(())

The serialized node layout is experimental and NOT frozen — pinning it (Merkle conformance vectors) is post-0.1.0 work.

store — the CID-addressed node store seam

A narrow, backend-agnostic seam: get/put by ContentId, with a verified read path the extension-trait implementation establishes. The pieces:

• NodeStore — the raw backend seam (two dumb ops: get_unverified, insert). Backends implement only this.
• NodeStoreExt — blanket-implemented, sealed-by-coherence verified operations (get, get_node, put, put_checked, …). A backend cannot re-implement them.
• VerifiedStore<B> — the recommended capability-safe facade: it exposes only the verified operations (dispatched via UFCS), so a backend's own inherent method cannot intercept a call made through it. Use this unless you have a reason to drop to raw ops.
• MemoryStore — the grow-only in-memory reference backend.
• AddressedBytes — an unforgeable, address-consistent (id, bytes) pair; it is the only thing insert accepts, so a backend can't be handed a mismatched pair.

Typed writes/reads are the strict doors:

use content_addressable::store::{MemoryStore, VerifiedStore};
use content_addressable::{canonical, ContentAddressable, ContentError};
use serde::{Deserialize, Serialize};

#[derive(Debug, PartialEq, Serialize, Deserialize)]
struct Record {
    name: String,
}

impl ContentAddressable for Record {
    fn canonical_form(&self) -> Result<Vec<u8>, ContentError> {
        canonical::to_canonical_dagcbor(self)
    }
}

let mut store = VerifiedStore::new(MemoryStore::new());
let record = Record { name: "alpha".into() };

let id = store.put_node(&record)?;               // strict: rejects non-canonical
let recovered: Record = store.get_node(&id)?;    // identity-preserving typed read
assert_eq!(record, recovered);
# Ok::<(), content_addressable::store::StoreError>(())

• put_node strictly validates canonical DAG-CBOR before insertion; put is unchecked with respect to canonicality (put_checked / put_node are the strict doors).
• get_node performs an identity-preserving typed read (decode, re-encode, and require the value to be the one named by the id). Raw get proves only that the returned bytes hash to the requested CID — not that they are canonical.

Trust boundary. The seam derives addresses on write and verifies them on read (seam theorems). Successful persistence, durability, no-rebind, and grow-only behavior are backend obligations (backend refinement laws), not seam theorems — MemoryStore discharges its documented in-memory obligations. The formal Lean/TLA+ artifacts are deferred proof targets (tracked in #71); the store module docs in src/store.rs carry the full proof-obligation catalog. The store trait/API is experimental and NOT frozen.

Stability details

The frozen 0.1.x contracts — CID profile, presentation, serde representation, error policy, verify/ensure_content_id, crate-root exports, MSRV/edition, the no-rehash digest bridge, and the experimental-feature exclusions — are recorded in docs/STABILITY.md, with issue provenance. Treat the frozen surfaces as durable.

Development

just check            # the local gate: fmt + clippy + test + docs + leaf-deps

A pre-push hook runs the same checks; the individual cargo fmt / cargo clippy / cargo test --all-features steps work directly too.

Releasing

Tag-driven; see RELEASING.md for the wheel matrix, PyPI Trusted Publishing, and crates.io steps.

License

Apache-2.0.