libdd-capabilities

Portable capability traits for cross-platform libdatadog.

Overview

libdd-capabilities defines abstract traits that decouple core libdatadog crates from platform-specific I/O. Core crates are generic over a capability parameter C that implements these traits, allowing native and wasm targets to provide different backends without changing shared logic.

This crate has zero platform dependencies: it compiles on any target including wasm32-unknown-unknown.

Traits

• HttpClientCapability: Async HTTP request/response using http::Request<Bytes> / http::Response<Bytes>.
• MaybeSend: Conditional Send bound: equivalent to Send on native, auto-implemented for all types on wasm. This bridges the gap between tokio's multi-threaded runtime (requires Send futures) and wasm's single-threaded model (where JS interop types are !Send).

Architecture

Three-layer design:

1. Trait definitions (this crate): Pure traits, no platform deps.
2. Core crates (libdd-trace-utils, libdd-data-pipeline): Generic over C: HttpClientCapability. Depend only on this crate for trait bounds.
3. Leaf crates (FFI, wasm bindings): Pin a concrete type, NativeCapabilities from libdd-capabilities-impl on native, WasmCapabilities from the Node.js binding crate on wasm.

Usage

use libdd_capabilities::{HttpClientCapability, MaybeSend};

async fn fetch<C: HttpClientCapability>(client: &C, req: http::Request<bytes::Bytes>) {
    let response = client.request(req).await.unwrap();
    println!("status: {}", response.status());
}

Critical rule: never use + Send directly in trait bounds for async functions in wasm-compatible code. Always use + MaybeSend instead.