structured-asn1 — borrowed ASN.1 BER/DER parsing in Rust

A Rust ASN.1 reader for BER and DER that borrows encoded values and preserves their exact byte ranges. Useful for format parsers that must verify digital signatures over the bytes received. Nested readers share depth, element, length and work limits; resource exhaustion is distinct from malformed input.

no_std + alloc by default · Rust 1.92+ · No cryptographic backend or I/O

Install

[dependencies]
structured-asn1 = "0.1"

Enable the optional std feature for a standard-library integration, or name alloc explicitly for an alloc-only feature graph. See the API reference for parser limits and value types.

Quick start

use std::sync::Arc;
use structured_asn1::{Parser, Tag, universal};
use structured_asn1::memory::{Memory, MemoryAccount};

fn main() -> Result<(), structured_asn1::Error> {
    // SEQUENCE { INTEGER 1 }; shared limits: storage bytes and work units.
    let bytes = [0x30, 0x03, 0x02, 0x01, 0x01];
    let memory = Memory::new(Arc::new(MemoryAccount::new(1024, 1024)));
    let parser = Parser::der(memory);
    let mut reader = parser.read(&bytes, 0)?;
    let sequence = reader.expect(Tag::constructed(universal::SEQUENCE))?;
    let mut inside = reader.enter(&sequence)?;
    let integer = inside.expect(Tag::primitive(universal::INTEGER))?;

    assert_eq!(integer.contents(), &[1]);
    assert_eq!(integer.span().start, 2);
    assert_eq!(integer.span().length, 3);
    Ok(())
}

The value is a view into bytes. Choose Parser::ber for BER input, or use Parser::new to supply encoding and parser-local Limits explicitly. Borrowed values require the document to remain alive.

Explicit INTEGER recovery

Reader::integer and read_integer are strict: X.690 §8.3.2 requires minimal sign octets already under BER. The source version adds Reader::integer_reading(&Element) for schema readers that retain a uniquely readable value together with its nonminimal-encoding fault. This addition is not in crates.io 0.1.3.

IntegerReading::as_bytes() keeps the original contents; value() borrows a minimal suffix for bounded numeric conversion. fault() retains the original located IntegerNotMinimal, and into_parts() moves that diagnostic without an allocating clone. Recovery never repairs the received signed bytes or claims BER/DER conformance. Primitive implicit tags remain supported; empty and constructed contents remain errors. The producing Reader admits padding work through both local and current aggregate ceilings before scanning, and diagnostic storage remains charged until drop. Resource refusal never becomes a recovered value without its fault.

OIDs and retained memory

OID identity uses its encoded bytes. Oid::text(&Memory) and Arc::text(&Memory) materialize exact decimal text with fallible work and capacity admission. Returned text retains its storage charge until released; OID and arc values do not implement Display. Borrowed arc iteration leaves its traversal admission to the caller.

The source version also adds OwnedOid::parse(text, &Memory) for strict dotted-decimal identifiers with arbitrary-width arcs, and OwnedOid::from_oid(oid, &Memory) for fallible retained copies. Its validated immutable as_oid() view is constant-time and does not rescan the encoding. The independent result keeps its capacity charge; these additions are not available in the initial crates.io 0.1.0 release.

Owned vectors, maps and strings retain allocated capacity on their original resource account. Container construction, growth and copies operate in that declared domain. Map lookup/removal and try_iter(&Memory) may instead use a current execution account; iteration prepays control buckets, including sparse holes. Rebuilding a collection in another domain requires an explicit fallible copy; retained allocations are never silently rebound.

The source uses allocator-api2 0.4.0 for vectors and hashbrown 0.17.1 for maps. Hashbrown's published allocator interface still requires allocator-api2 0.2.21; that interface forwards to the same account allocator. Both container families share capacity, work, growth-peak and rollback rules. These dependency updates are not in registry version 0.1.2.

Raw byte views and ordinary formatting/equality traits leave application-owned traversal and output storage to the caller. An explicit budget bounds admitted mechanism work; it does not automatically account arbitrary caller code.

Related crate

For X.509 certificate parsing and provider-neutral path validation, use structured-pkix. This crate reads encoding structure; it does not decide certificate trust or signature validity.

License and source

Licensed under Apache-2.0. Source, issues and contribution instructions are in signature-primitives.