WasmEdge Reqwest Demo

In this project, we demonstrate how to use reqwest and tokio to build async http client in WebAssembly and execute it using WasmEdge.

Why tokio in WasmEdge?

There are growing demands to perform network requests in WASM and cloud computing. But it would be inefficient to perform network requests synchronously so we need async in WASM.

As tokio is widely accepted, we can bring many projects that depend on tokio to WASM if we can port tokio into WASM. After that, the developers can have async functions in WASM as well as efficient programs.

With the help of tokio support of WasmEdge, the developers can compile the projects that use tokio into WASM and execute it using WasmEdge.

Prequsites

We need install rust and wasm target first.

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

# install wasm target 
rustup target add wasm32-wasi

Then install the WasmEdge.

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

Add dependencies in Cargo.toml

In this project, we add tokio and reqwest as dependencies. You will need to add wasi specific patches to make those crates compile to Wasm.

[patch.crates-io]
tokio = { git = "https://github.com/second-state/wasi_tokio.git", branch = "v1.36.x" }
socket2 = { git = "https://github.com/second-state/socket2.git", branch = "v0.5.x" }
hyper = { git = "https://github.com/second-state/wasi_hyper.git", branch = "v0.14.x" }
reqwest = { git = "https://github.com/second-state/wasi_reqwest.git", branch = "0.11.x" }

[dependencies]
reqwest = { version = "0.11", default-features = false, features = ["rustls-tls"] }
tokio = { version = "1", features = ["rt", "macros", "net", "time"] }

Write the code

We need to add some code into src/main.rs.

Build and run it

Note on Mac

ring v0.17 can't build on Mac with default clang. So, you need install wasi-sdk.

Download wasi-sdk

export WASI_VERSION=22
export WASI_VERSION_FULL=${WASI_VERSION}.0
wget https://github.com/WebAssembly/wasi-sdk/releases/download/wasi-sdk-${WASI_VERSION}/wasi-sdk-${WASI_VERSION_FULL}-macos.tar.gz
tar xvf wasi-sdk-${WASI_VERSION_FULL}-macos.tar.gz

Use the clang included in wasi-sdk for compilation.

export WASI_SDK_PATH=`pwd`/wasi-sdk-${WASI_VERSION_FULL}
export CC="${WASI_SDK_PATH}/bin/clang --sysroot=${WASI_SDK_PATH}/share/wasi-sysroot"

First we need to compile the code. You will need to pass some flags to make sure that the Rust compiler knows to use the correct patches for the wasmedge target.

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

Then we can run it using WasmEdge.

wasmedge target/wasm32-wasi/release/wasmedge_reqwest_demo.wasm

For simpilicity, we can add the following configs to .cargo/config.toml.

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

[target.wasm32-wasi]
runner = "wasmedge"

And then we can use cargo build and cargo run.

FAQ

use of unstable library feature 'wasi_ext'

If you are using rustc 1.64, you may encounter this error. There are two options:

1. Update rustc to newer version. Validated versions are 1.65 and 1.59.
2. Add #![feature(wasi_ext)] to the top of mio/src/lib.rs.