Function decode_from_transport

atomic-canonical/src/delegation.rs:303–317

Decode a certificate presented in a request header. Checks the size cap first, then base64, then JSON. Does **not** verify — [`verify`] against the delegator's registered key is a separate, mandatory step, and keeping them apart means no call site can accidentally treat a well-formed certificate as a trusted one.

(encoded: &str)

/// step, and keeping them apart means no call site can accidentally treat a
/// well-formed certificate as a trusted one.
pub fn decode_from_transport(encoded: &str) -> Result<Value> {
    if encoded.len() > MAX_ENCODED_DELEGATION {
        return Err(CanonicalError::Proof(format!(
            "delegation is {} bytes, over the {MAX_ENCODED_DELEGATION}-byte limit",
            encoded.len()
        )));
    }

    let bytes = data_encoding::BASE64URL_NOPAD
        .decode(encoded.trim().as_bytes())
        .map_err(|e| CanonicalError::Proof(format!("delegation is not valid base64url: {e}")))?;

    serde_json::from_slice(&bytes)
        .map_err(|e| CanonicalError::Proof(format!("delegation is not valid JSON: {e}")))
}

/// A stable fingerprint of an encoded certificate, for caching a verified
/// result without re-running the Ed25519 check on every request.