Feature Request: Allow Custom Types for All Allocating Owned Types

[nu11ptr]

How It Works

• Define or create required trait or traits for every major allocating type category (Box, Vec, String, Bytes, etc.)
  • These would need to handle creation, mutation and usage (within Buffa)
• Implement only stdlib types (String, Vec, Box) and/or common 3rd party types (Bytes, etc.) in Buffa itself
• Default to these implementations, but allow override via build.rs via API or buf via string options

Why?

• Creates a universal mechanism for crate authors to implement Buffa support without Buffa authors constantly having to implement new feature requests for new types
  • Example: Removes need for buffa-codegen: configurable Box wrapping for message-type oneof variants #126 - SmallBox supports optional inline allocation without changing your existing boxing logic
• Removes need for Buffa to be aware of these types at all, as well as need to stay up to date on their interface versioning
  • Example: Removes need for Feature: configurable string field type (e.g. smol_str::SmolStr), mirroring use_bytes_type #127, and users can choose any string type that conforms to your trait definitions
• Applies to all allocated types, not just strings, since a user's allocation stress points and security needs are going to vary
• Allows users to create their own wrapper types for types where crate authors choose not to implement Buffa support
• Allows users to control things like allocation and security (Zeroize on Drop) based on their needs without involving Buffa authors
• Increases Buffa's theoretical top end performance by optionally removing many allocations from encode/decode path

Examples:

• FlexStr (String replacement) - not only supports ref counted and inline strings, but also zeroize on drop for security
  • Disclaimer: I am the author and maintainer of this crate
• SmallBox (Box replacement) - supports inline boxed values up to a certain size then falls back to heap
• SmallVec (Vec Replacement) - supports inline vec values up to a certain size then falls back to heap
• SmallBytes (Bytes replacement) - wrapper over Smallvec for Bytes-like support

Challenges:

• Naming the type - some of these types take multiple generic parameters, but only one of those needs dynamic replacement when used in a struct
  • Option: user supplies a type as a string with optional wildcard and Buffa parses the string into a full type: e.g. smallbox::SmallBox<*, S4> (where the * is replaced by whatever type you need in the box)