en Copyright 2015 Java http://172.16.0.5:8080/history/wasmtime-44.0.1/crates/fuzzing/src/oracles/component_async.rs#da093747 Relax panics in async/futures to traps/errors (#12688)* Relax panics in async/futures to traps/errorsThis commit is an admittance that I don't believe we're going to getto a point where we are confident enough in the fuzzing ofcomponent-model-async such that we could confidently say we'reexercising the vast majority of possible panics. Development ofcomponent-model-async has shown a steady trickle of panics over thecourse of the development of the feature, and this trend has beenpersistent over time as well.An attempt was made in #12119 to add a fuzzer dedicated to async eventsbut that didn't actually find anything in development and it has misseda number of panics present before and discovered after its introduction.Overall I do not know how to improve the fuzzer to the point that itwould find pretty much all of the existing async-related panics overtime.To help address this concern of the `concurrent.rs` implementation thiscommit goes through and replaces things like `unwrap()`, `assert!`,`panic!`, and `unreachable!` with an error-producing form. The benefitof this is that a bug in the implementation is less likely to result ina panic and instead just results in a non-spec-compliant trap. Thedownside of doing this though is that it can become unclear what errorsare "first class traps", or expected to be guest reachable, and whichare expected to be bugs in Wasmtime. To help address this I've performeda few refactorings here as well.* Some traps previously present as error strings are now promoted to using `Trap::Foo` instead. This has some refactoring of the Rust/C side as well to make it easier to define new variants. Tests were additionally added for any trap messages that weren't previously tested as being reachable.* A new `bail_bug!` macro was added (internally) for Wasmtime. This is coupled with a concrete `WasmtimeBug` error type (exported as `wasmtime::WasmtimeBug`). The intention is that `bail!` continues to be "here's a string and I'm a bit too lazy to make a concrete error" while `bail_bug!` indicates "this is a bug in wasmtime please report this if you see it".The rough vision is that if an error condition is reached, and the systemis not broken in such a way that panicking is required, then `bail_bug!`can be used to indicate a bug in Wasmtime as opposed to panicking. Thisreduces the real-world impact of hitting these scenarios by downgrading aCVE-worthy `panic!` into a bug-worthy non-spec-compliant trap. Not allpanics are able to be transitioned to this as some are load bearing froma safety perspective or similar (or indicate something equally broken),but the vast majority of cases are suitable for "return a trap, lockdown the store, and let destructors take care of everything else".This change additionally has resulted in API changes for `FutureReader`and `StreamReader`. For example creation of these types now returns a`Result` for when the `ResourceTable` is full, for example, instead ofpanicking.* Fix CI build* Translate `WasmtimeBug` to panics in debug mode* Review comments* Refactor some stream methods for fewer panics List of files: /wasmtime-44.0.1/crates/fuzzing/src/oracles/component_async.rs Mon, 02 Mar 2026 21:26:40 +0000 Alex Crichton <alex@alexcrichton.com> http://172.16.0.5:8080/history/wasmtime-44.0.1/crates/fuzzing/src/oracles/component_async.rs#e472f50c Fix component-async fuzzer on OSS-Fuzz (#12400)On OSS-Fuzz the fuzzers are built in one place and run in another, so`include_bytes!` is needed to get the wasm into the final binary. Thisis done with a layer of macros to avoid an `include_bytes!` for all wasmprograms which would make the generated Rust metadata a bit... large. List of files: /wasmtime-44.0.1/crates/fuzzing/src/oracles/component_async.rs Fri, 23 Jan 2026 16:54:39 +0000 Alex Crichton <alex@alexcrichton.com> http://172.16.0.5:8080/history/wasmtime-44.0.1/crates/fuzzing/src/oracles/component_async.rs#cc8d04f4 Remove need for explicit `Config::async_support` knob (#12371)* Refactor component model host function definitionsPush the `async`-ness down one layer.* Remove need for explicit `Config::async_support` knobThis commit is an attempt to step towards reconciling "old async" and"new async" in Wasmtime. The old async style is the original asyncsupport in Wasmtime with `call_async`, `func_wrap_async`, etc, where themain property is that the store is "locked" during an async operation.Put another way, a store can only execute at most one async operation ata time. This is in contrast to "new async" support in Wasmtime with thecomponent-model-async (WASIp3) support, where stores can have more thanone async operation in flight at once.This commit does not fully reconcile these differences, but it doesremove one hurdle along the way: `Config::async_support`. Since thebeginning of Wasmtime this configuration knob has existed to explicitlydemarcate a config/engine/store as "this thing requires `async` stuffinternally." This has started to make less and less sense over timewhere the line between sync and async has become more murky with WASIp3where the two worlds comingle. The goal of this commit is to deprecate`Config::async_support` and make the function not actually do anything.In isolation this can't simply be done, however, because there are manyload-bearing aspects of Wasmtime that rely on this `async_support` knob.For example once epochs + yielding are enabled it's required that allWasm is executed on a fiber lest it hit an epoch and not know how toyield. That means that this commit is not a simple removal of`async_support` but instead a refactoring/rearchitecting of how async isused internally within Wasmtime. The high-level ideas within Wasmtimenow are:* A `Store` has a "requires async" boolean stored within it.* All configuration options which end up requiring async, such as yielding with epochs, turn this boolean on.* Creation of host functions which use async (e.g. `func_wrap_{async,concurrent}`) will also turn this option on.* Synchronous API entrypoints into Wasmtime ensure that this boolean is disabled.* Asynchronous APIs are usable at any time.This means that the concept of an async store vs a sync store is nowgone. All stores are equally capable of executing sync/async, and thechange now is that dynamically some stores will require that async isused with certain configuration. Additionally all panicking conditionsaround `async_support` have been converted to errors instead. Allrelevant APIs already returned an error and things are murky enough nowthat it's not necessarily trivial to get this right at the embedderlevel. In the interest of avoiding panics all detected async mismatchesare now first-class `wasmtime::Error` values.The end result of this commit is that `Config::async_support` is adeprecated `#[doc(hidden)]` function that does nothing. While manyinternal changes happened as well as having new tests for all this sortof behavior this is not expected to have a great impact on externalconsumers. In general a deletion of `async_support(true)` is in theoryall that's required. This is intended to make it easier to think aboutasync/sync/etc in the future with WASIp3 and eventually reconcile`func_wrap_async` and `func_wrap_concurrent` for example. That's leftfor future refactorings however.prtest:full* Review comments* Fix CI failures List of files: /wasmtime-44.0.1/crates/fuzzing/src/oracles/component_async.rs Fri, 23 Jan 2026 02:46:45 +0000 Alex Crichton <alex@alexcrichton.com> http://172.16.0.5:8080/history/wasmtime-44.0.1/crates/fuzzing/src/oracles/component_async.rs#fee9be21 Add a new fuzzer focused on component-model-async events (#12119)* Add a new fuzzer focused on component-model-async eventsThis commit adds a new fuzzer mode to the `misc` fuzzer of Wasmtimewhich is focused on async events and interleavings of components usingthe component-model-async proposal. This fuzzer works by having aprecompiled guest program which serves as the component to run. Thisprecompiled component has a custom `fuzz.wit` which is used to interfacewith the fuzzer itself. The fuzzer is then a fuzz-generated sequence ofcommands to send to the component which verifies that everythingexecutes correctly, has no panics, etc.This fuzzer intends to stress async communication and taskinfrastructure with component-model-async. Notably this does not stresslifting/lowering or arbitrary type signatures. This does, however,permute all of the following:* Guest/host interactions (also guest/guest, host/host, etc).* Async functions, both ready and pending.* Future operations: reads, writes, cancellation, transfers, etc.* Stream operations: reads, writes, cancellation, transfers, etc.This is all throwing into a large "soup" and then asserted to workcorrectly. There's a few gotchas here and there for how this fuzzer isdesigned, such as some events requiring "yield N times to await thisevent happening". This is required because Wasmtime is allowed tonon-deterministically select between a number of "ready events" and whatto dispatch.This is not intended to be a one-size-fits-all fuzzer forcomponent-model-async. The recent enhancements to the `component_api`fuzzer are intended to complement this fuzzer in terms of what'sstressed where internally.* Review comments List of files: /wasmtime-44.0.1/crates/fuzzing/src/oracles/component_async.rs Tue, 09 Dec 2025 19:32:20 +0000 Alex Crichton <alex@alexcrichton.com>