Set up Rust toolchain

In the following chapters, we will show how to build and compile Rust programs into WASM bytecode and then run them in WasmEdge.

Before we start, let's set up the software we need.

Install WasmEdge

Use the following command line to install WasmEdge on your machine. If you use Windows or other non-Unix-like platforms, please refer to the WasmEdge installation.

curl -sSf https://raw.githubusercontent.com/WasmEdge/WasmEdge/master/utils/install.sh | bash

Install Rust

Use the following command line to install Rust on your machine. If you use Windows or other non-Unix-like platforms, please refer to the Rust installation instruction.

curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh

Set up the Rust compiler's target

To build a WASM file running in server-side WebAssembly like WasmEdge, we need to add the wasm32-wasi target for the Rust compiler after Rust is installed.

rustup target add wasm32-wasi

Special notes for networking apps

Tokio support

WasmEdge supports async networking APIs provided by Tokio and related crates. If you have tokio in your Cargo.toml, you need to add a few config flags to help the Rust compiler choose the correct feature branches in the library source code. Here is an example of cargo build command for compiling a tokio app to Wasm.

RUSTFLAGS="--cfg wasmedge --cfg tokio_unstable" cargo build --target wasm32-wasi --release

Alternatively, you could add these lines to the .cargo/config.toml file.

[build]
target = "wasm32-wasi"
rustflags = ["--cfg", "wasmedge", "--cfg", "tokio_unstable"]

Once you have these lines in .cargo/config.toml, you can simply use the regular cargo command.

cargo build --target wasm32-wasi --release

TLS on MacOS

The standard cargo toolchain can support the Rust TLS library on Linux. However, on MacOS, you need a special version of the Clang tool, released from the official wasi-sdk, in order to support TLS libraries.

When you compile Rust TLS source code to Wasm on Linux, the result Wasm file is cross-platform and can run correctly on any platform with WasmEdge installed. This section is only applicable when you need to compile Rust TLS source code on MacOS.

Download the latest wasi-sdk release for your platform and expand it into a directory. Point the WASI_SDK_PATH variable to this directory and export a CC variable for the default Clang.

export WASI_SDK_PATH /path/to/wasi-sdk-22.0
export CC="${WASI_SDK_PATH}/bin/clang --sysroot=${WASI_SDK_PATH}/share/wasi-sysroot"

That's it. Now you can use the cargo tools on MacOS to compile tokio libraries with rust-tls feature turned on.