Rust APIs for performance & type safety
a case study
1. Why do rustaceans care? 🦀
2. FIX
3. Some ideas for fix-toy
4. Looking back 🤔
Doing some archeology
What is FIX?
Financial Information eXchange protocol
- A domain-specific data transfer protocol.
- Popularized in the '90s.
- Text-based, human-readable. Mostly.
-
Format: tag=value pairs, separated by SOH character.
8=FIX.4.4
9=148
35=D
34=1080
49=TESTBUY1
52=20180920-18:14:19.508
56=TESTSELL
111=636730640278898634
15=USD
21=2
38=7000
40=1
54=1
55=MSFT
60=20180920-18:14:19.492
10=092
TW: FIX is atrocious.
What we want out of fix-toy
A crate for FIX newcomers as well as demanding users.
1. Not standard-compliant: data and NumInGroup.
2. No streaming support!
3. DevX considerations.
4. N+1 allocations.
5. No choice of BuildHasher.
Introducing the FIX dictionary
A XML specification for FIX messages
The good...
- Type-safe
- Flexible querying
- Easily clonable
...and the ugly
- Expensive initialization
- Queries are expensive
- Huge memory consumption
Adding a dependency to the dictionary
- Parsing requires taking a
&. - DevX suggests
Arc<Dictionary>. 💡
Woeful restrictions for downstream users. 🐌
streaming support
FIX doesn't integrate any framing mechanism. 🖼️
Tokio to the rescue! 🚀
datagrams vs streams?
So, we're making the api more complete
But what did we lose?
Devs now have to think about dictionaries, Tokio, they can't directly use &[u8]. Every user seems to must care about every abstraction we introduce.
Soon enough: openssl & rustls, decimal, and others.
We can solve these problems with traits: the most comprehensive type abstraction tool we have in Rust.
💡
Much more we could do 👩🏼🔬
Huge dependencies like Dictionary are fertile grounds for trait-based abstractions.
RFC 1598 - GATs
RFC 3185 - async fn in traits
RFC 2532 - default associated types
feature(generic_const_exprs)
Traits enable late binding implementation details
We often introduce traits out of necessity, reacting to emerging requirements.
What if we were more proactive about this? ⚡
Does this type let me do that?
What is it exactly that I need here?
➡️
Public crate design differs greatly from private codebases.
- Traits allow us to be more agnostic towards downstream users' situations and use cases.
- This is only possible because of the added structure.
Don't be scared to populate your crates with many traits.
Your SemVer will be alright. Really.
Food for thought
- Abstracting
Dictionaryaway lets us explore truly zero-cost codegen solutions. 🏃🏻♂️ - Placing field getters into a trait would allow code reuse for JSON, Protobuf, and other FIX formats.
- Surrogate traits with associated would help to keep APIs slim and simple by introducing hierarchies.
Thank you!
Questions?
Rust APIs for performance & type safety: a case study
By filippoc
