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44 lines
1.7 KiB
Markdown
44 lines
1.7 KiB
Markdown
# WASI plugin example
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In this example we extend the imports of Wasmer's WASI ABI to demonstrate how custom plugins work.
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See the `wasmer/examples/plugin.rs` file for the source code of the host system.
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## Compiling
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_Attention Windows users: WASI target only works with the `nightly-x86_64-pc-windows-gnu` toolchain._
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```
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# Install an up to date version of Rust nightly
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# Add the target
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rustup target add wasm32-unknown-wasi
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# build it
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cargo +nightly build --release --target=wasm32-unknown-wasi
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# copy it to examples folder
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cp ../../target/wasm32-unknown-wasi/release/plugin-for-example.wasm ../
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```
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## Running
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```
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# Go back to top level Wasmer dir
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cd ..
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# Run the example
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cargo run --example plugin
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```
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## Inspecting the plugin
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```
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# Install wabt via wapm; installed globally with the `g` flag
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wapm install -g wabt
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# Turn the binary WASM file in to a readable WAT text file
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wapm run wasm2wat examples/plugin-for-example.wasm
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```
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At the top of the file we can see which functions this plugin expects. Most are covered by WASI, but we handle the rest.
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## Explanation
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In this example, we instantiate a system with an extended (WASI)[wasi] ABI, allowing our program to rely on Wasmer's implementation of the syscalls defined by WASI as well as our own that we made. This allows us to use the full power of an existing ABI, like WASI, and give it super-powers for our specific use case.
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Because the Rust WASI doesn't support the crate type of `cdylib`, we have to include a main function which we don't use. This is being discussed [here](https://github.com/WebAssembly/WASI/issues/24).
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[wasi]: https://hacks.mozilla.org/2019/03/standardizing-wasi-a-webassembly-system-interface/
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