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Tag: error-handling


Before we move on to parsing more of our raw packets, I want to take some time to improve our error handling strategy. Currently, the ersatz codebase contains a mix of Result<T, E>, and some methods that panic, like unwrap() and expect().

We also have a custom Error enum that lets us return rawsock errors, IO errors, or Win32 errors. First of all, I want to address something: When is it okay to panic?


A programming language’s solution to error handling significantly influences the robustness, brevity, readability and – to an extent – the runtime performance of your code. Consequently, the error handling story is an important part of PL design. So it should not come as a surprise that the Rust community constantly discusses this topic. Given some recent discussions and the emergence of more and more error handling crates, this article shares some of my thoughts (not solutions!) on this.


In our last adventure we looked at C++ exceptions in WebAssembly with the emscripten compiler. Now we’re taking a look at the main error handling system for another language targeting WebAssembly, Rust. Rust has a “panic”/”unwind” system similar to C++ exceptions, but it’s generally recommended against catching panics.

wasm error-handling

derive_more is a crate which has many proc macros, amongst which is a macro for deriving From for structs, enums, and newtypes. From is the basic mechanism for using ? ergonomically in a function which returns Result<T, Error>. Almost everything I write has the derive_more crate as a dependency, and the following pattern for handling errors.


I’m planning to release a 1.0.0 version of failure on March 15. Once this happens, I don’t plan to release any further breaking changes to the failure crate (though maybe someday in the distant future).
Breaking changes in 1.0 failure is in a somewhat unique position as being a significant part of the public API of other libraries that depend on it. Whether they use the Error struct or derive Fail for a custom error type, this becomes a part of the API they expose to other users.


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