WASI - WebAssembly System Interface

WASI (WebAssembly System Interface) is a modular system interface for WebAssembly. It enables WASM modules to run safely outside the browser and access operating system resources.

What is WASI?

flowchart LR
    subgraph WASM["WASM Module"]
        F[Functions]
    end
    subgraph WASI["WASI API"]
        FS[File System]
        N[Network]
        C[Clock]
        R[Random]
        E[Environment Variables]
    end
    subgraph OS["Operating System"]
        K[Kernel]
    end
    F --> WASI
    WASI --> OS

Core Components

WASI SDK

# Download WASI SDK
curl -LO https://github.com/WebAssembly/wasi-sdk/releases/download/wasi-sdk-20/wasi-sdk-20.0-linux-x86_64.tar.gz
tar -xzf wasi-sdk-20.0-linux-x86_64.tar.gz

# Set environment
export WASI_SDK_PATH=$PWD/wasi-sdk-20.0

Compile with WASI

# C/C++ with WASI
$WASI_SDK_PATH/bin/clang \
  --target=wasm32-wasi \
  --sysroot=$WASI_SDK_PATH/share/wasi-sysroot \
  source.c -o output.wasm

# Rust with WASI
cargo build --target wasm32-wasi --release

Common Use Cases

Use Case	Example	Benefits
Serverless functions	AWS Lambda Edge	Cold start performance
CLI tools	wapm packages	Cross-platform binaries
Plugin systems	Secure sandbox	Isolation + capability
Edge computing	CDN functions	Fast execution

Security Model

WASI uses a capability-based security model:

• No ambient authority
• Resources explicitly passed
• Least privilege

Tool Ecosystem

Tool	Purpose
Wasmtime	Runtime (CLI + library)
WasmEdge	High-performance runtime
wasmer	General-purpose runtime
wapm	Package registry
cargo-wasi	Rust WASI support

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