wasm-snip

Important: As of this writing, there is a small bug in newly built Fuel indexer WASM modules that produces a WASM runtime error due an errant upstream dependency. For now, a quick workaround requires using wasm-snip to remove the errant symbols from the WASM module. More info can be found in the related script here.

About

wasm-snip replaces a WebAssembly function's body with an unreachable.

Maybe you know that some function will never be called at runtime, but the compiler can't prove that at compile time? Snip it! All the functions it transitively called — which weren't called by anything else and therefore could also never be called at runtime — will get removed too.

Very helpful when shrinking the size of WebAssembly binaries!

This functionality relies on the "name" section being present in the .wasm file, so build with debug symbols:

[profile.release]
debug = true

Executable

To install the wasm-snip executable, run

cargo install wasm-snip

You can use wasm-snip to remove the annoying_space_waster function from input.wasm and put the new binary in output.wasm like this:

wasm-snip input.wasm -o output.wasm annoying_space_waster

For information on using the wasm-snip executable, run

wasm-snip --help

And you'll get the most up-to-date help text, like:

Replace a wasm function with an `unreachable`.

USAGE:
wasm-snip [FLAGS] [OPTIONS] <input> [--] [function]...

FLAGS:
-h, --help                    Prints help information
--snip-rust-fmt-code          Snip Rust's `std::fmt` and `core::fmt` code.
--snip-rust-panicking-code    Snip Rust's `std::panicking` and `core::panicking` code.
-V, --version                 Prints version information

OPTIONS:
-o, --output <output>         The path to write the output wasm file to. Defaults to stdout.
-p, --pattern <pattern>...    Snip any function that matches the given regular expression.

ARGS:
<input>          The input wasm file containing the function(s) to snip.
<function>...    The specific function(s) to snip. These must match exactly. Use the -p flag for fuzzy matching.

Library

To use wasm-snip as a library, add this to your Cargo.toml:

[dependencies.wasm-snip]
# Do not build the executable.
default-features = false

See docs.rs/wasm-snip for API documentation.