NOW-proto PDU encoding/decoding library

This crate provides a Rust implementation of the NOW protocol encoding/decoding library.

Library architecture details

• The library only provides encoding/decoding functions for the NOW protocol, transport layer and session processing logic should be implemented by the client/server.
• #[no_std] compatible. Requires alloc.
• PDUs could contain borrowed data by default to avoid unnecessary string/vec allocations when parsing. The only exception is error types which are 'static and may allocate if optional message is set.
• PDUs are immutable by default. PDU constructors take only required fields, optional fields are set using implicit builder pattern (consuming .with_* and .set_* methods).
• User-facing bitfield types should be avoied in the public API if incorrect usage could lead to invalid PDUs. E.g. ExecData's stdio stream flags are represented as a bitfield, but exactly one of the flags should be set at a time. The public API should provide a safe way to set and retrieve these flags. Channel capabilities flags on the other hand could all be set independently, therefore it is safe to expose them in the public API.
• Primitive protocol types e.g NOW_STRING should not be exposed in the public API.
• Message validition should be always checked in the PDU constructor(s). If the message have variable fields, it should be ensured that it could fit into the message body (u32).
• PDUs should NOT fail on deserialization if message body have more data to ensure backwards compatibility with future protocol versions (e.g. new fields added to the end of the message in the new protocol version).

Versioning

Crate version is not tied to the protocol version (e.g. Introduction of breaking changes in the crate API does not necessarily mean a protocol version bump and vice versa). The currently implemented protocol version is stored in [NowProtoVersion::CURRENT] and should be updated accordingly when the protocol is updated.