#25504: Find more generic ways to handle smartlist_t/Vec<T> between C and Rust ------------------------------+---------------------------------- Reporter: isis | Owner: (none) Type: enhancement | Status: new Priority: Medium | Milestone: Tor: 0.3.5.x-final Component: Core Tor/Tor | Version: Severity: Normal | Keywords: rust, datatypes, ffi Actual Points: | Parent ID: Points: 3 | Reviewer: Sponsor: Sponsor8-can | ------------------------------+---------------------------------- From #25368, we discussed having a possibly more generic and/or more rusty way to handle our `smartlist_t`s in C (and whatever underlying types the smartlist contains). Right now we have a `Stringlist` type in `src/rust/smartlist/smartlist.rs`, which is a Rust representation of `smartlist_t` using C types, and then we have a conversion between that and a `Vec<String>`:
{{{#!rust pub trait Smartlist<T> { fn get_list(&self) -> Vec<T>; } #[repr(C)] pub struct Stringlist { pub list: *const *const c_char, pub num_used: c_int, pub capacity: c_int, } impl Smartlist<String> for Stringlist { fn get_list(&self) -> Vec<String> { // [...] } } }}} I have not thought about this nearly as much as komlo has, but maybe one way to do it is to have direct conversion between a `smartlist_t` and a `Vec<T>`, where `T` is probably an opaque pointer to whatever type in C, ''or'' `T` is only allowed to be a `String` which we've copied from a non- NULL `char*` (e.g. `impl From<Stringlist> for Vec<String>`, or something, and then keep `Stringlist` private since internally it's a bunch of C types that we don't want propagating into our more Rusty code). Another idea might be to only handle `Vec<T>`-like things in Rust (if/when we move to the Rust-is-required phase), since we already have a nice datatype there, and then provide safe interfaces for C code to do all the things with/to the vectors that it currently does. (This sounds easier and more maintainable to me.) We should probably brainstorm other ideas of how we're going to do this generically moving forward, because our C code uses smartlists everywhere. -- Ticket URL: <https://trac.torproject.org/projects/tor/ticket/25504> Tor Bug Tracker & Wiki <https://trac.torproject.org/> The Tor Project: anonymity online
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