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workers-rs

workers-rs is Cloudflare's Rust SDK for writing Cloudflare Workers. Rust source is compiled to WebAssembly (wasm32-unknown-unknown target), marshalled across the Rust↔JS boundary by wasm-bindgen, and executed inside a V8 isolate on workerd.

Role on this wiki

Canonical system for Rust-on-Workers reliability work disclosed in Cloudflare's 2026-04-22 post. Two inflection points:

• workers-rs 0.6 — first fix: a platform-side custom wrapper combining a Rust panic handler that tracks failure state per Worker, JS Proxy encapsulation of every Rust↔JS call, and targeted patches to wasm-bindgen's generated bindings to reinitialize the Wasm module after failure. Solved the sandbox-poisoning symptom for workers-rs users but lived outside wasm-bindgen.
• workers-rs 0.8.0 — second fix: the upstreamed panic=unwind + abort-recovery machinery, gated behind a --panic-unwind build flag. "Highly recommend upgrading and trying it out for a more stable Rust Workers experience, and plan to make panic=unwind the default in a subsequent release." Users staying on panic=abort still get the 0.6.0 wrapper.

Failure-mode substrate

Rust on wasm32-unknown-unknown defaults to panic=abort: a panic traps with unreachable, exits Wasm back to JS with WebAssembly.RuntimeError, and — in stock wasm-bindgen — leaves the instance in an undefined state. Before workers-rs 0.6, "panics were historically fatal, poisoning the instance and possibly even bricking the Worker for a period of time." Workers holding in-memory state (e.g. Durable Objects) were particularly exposed because reinitialisation would destroy that state.

Emscripten-target examples: native Rust + Tokio (2026-09-28)

workers-rs today compiles to the wasm32-unknown-unknown target. The 2026-09-28 experimental preview adds a second path via the Emscripten wasm32-unknown-emscripten target in wasm-bindgen, enabling native Rust — including Tokio-based apps — on Workers, with "significantly improved library compatibility." The Rust Workers Emscripten examples require the Tokio patchsets directly (JSPI + LocalEventLoop; socket support via -sNODERAWSOCKETS) pending further upstream integration into Tokio. This is a distinct target/experience from the panic-recovery-hardened wasm32-unknown-unknown path above — a preview of the second Rust-on-Workers sub-tier rather than a change to the existing one. (Source: sources/2026-09-28-cloudflare-supporting-native-rust-in-workers-with-the-new-emscripten-target)

Seen in

• sources/2026-09-28-cloudflare-supporting-native-rust-in-workers-with-the-new-emscripten-target — the experimental wasm32-unknown-emscripten examples for running native Rust + Tokio on Workers, shipped in the workers-rs examples/emscripten tree.
• sources/2026-04-22-cloudflare-making-rust-workers-reliable-panic-and-abort-recovery-in-wasm-bindgen — canonical wiki instance. Disclosure of the two-step reliability arc (0.6 platform wrapper → 0.8 upstreamed exception-handling recovery) and the Rust-Wasm-error-class taxonomy workers-rs now handles.

Related

• systems/cloudflare-workers — host platform.
• systems/wasm-bindgen — binding generator workers-rs consumes; now co-maintained by Cloudflare.
• systems/webassembly — runtime substrate.
• systems/workerd — the V8 isolate runtime executing the compiled Wasm module.
• systems/emscripten — the wasm32-unknown-emscripten target enabling native-Rust/Tokio Workers examples.
• systems/tokio — the async runtime the Emscripten examples run.
• panic-unwind — the recovery primitive 0.8.0 unlocks.
• abort-recovery — last-resort reinit for the non-unwindable class.
• sandbox-poisoning — the failure class workers-rs 0.6 addressed platform-side and 0.8 addresses upstream.
• reinitialize-on-unrecoverable-error / proxy-based-entrypoint-encapsulation — the 0.6 pre-upstream recipes.
• companies/cloudflare — author.