hello world in wat
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102
pkg/wasm/README.md
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102
pkg/wasm/README.md
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# WebAssembly Test Server
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Simple Go web server for serving WebAssembly files with correct MIME types.
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## Quick Start
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```bash
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# Build and run the server
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go run server.go
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# Or with custom port
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go run server.go -port 3000
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# Or serve from a different directory
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go run server.go -dir /path/to/wasm/files
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```
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## Build and Install
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```bash
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# Build binary
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go build -o wasm-server server.go
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# Run
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./wasm-server
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# Install to PATH
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go install
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```
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## Usage
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Once the server is running, open your browser to:
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- http://localhost:8080/
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The server will serve:
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- `index.html` - Main HTML page
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- `hello.js` - JavaScript loader for WASM
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- `hello.wasm` - WebAssembly binary module
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- `hello.wat` - WebAssembly text format (for reference)
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## Files
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- **server.go** - Go web server with WASM MIME type support
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- **index.html** - HTML page that loads the WASM module
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- **hello.js** - JavaScript glue code to instantiate and run WASM
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- **hello.wasm** - Compiled WebAssembly binary
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- **hello.wat** - WebAssembly text format source
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## Building WASM Files
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### From WAT (WebAssembly Text Format)
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```bash
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# Install wabt tools
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sudo apt install wabt
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# Compile WAT to WASM
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wat2wasm hello.wat -o hello.wasm
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# Disassemble WASM back to WAT
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wasm2wat hello.wasm -o hello.wat
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```
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### From Go (using TinyGo)
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```bash
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# Install TinyGo
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wget https://github.com/tinygo-org/tinygo/releases/download/v0.31.0/tinygo_0.31.0_amd64.deb
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sudo dpkg -i tinygo_0.31.0_amd64.deb
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# Create Go program
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cat > main.go << 'EOF'
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package main
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import "fmt"
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func main() {
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fmt.Println("Hello from Go WASM!")
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}
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EOF
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# Compile to WASM
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tinygo build -o main.wasm -target=wasm main.go
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# Get the WASM runtime helper
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cp $(tinygo env TINYGOROOT)/targets/wasm_exec.js .
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```
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## Browser Console
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Open your browser's developer console (F12) to see the output from the WASM module.
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The `hello.wasm` module should print "Hello, World!" to the console.
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## CORS Headers
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The server includes CORS headers to allow:
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- Cross-origin requests during development
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- Loading WASM modules from different origins
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This is useful when developing and testing WASM modules.
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18
pkg/wasm/hello.js
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pkg/wasm/hello.js
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const memory = new WebAssembly.Memory({ initial: 1 });
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const log = (offset, length) => {
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const bytes = new Uint8Array(memory.buffer, offset, length);
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const string = new TextDecoder('utf8').decode(bytes);
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console.log(string);
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};
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(async () => {
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const response = await fetch('./hello.wasm');
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const bytes = await response.arrayBuffer();
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const { instance } = await WebAssembly.instantiate(bytes, {
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env: { log, memory }
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});
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instance.exports.hello();
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})();
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10
pkg/wasm/index.html
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pkg/wasm/index.html
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<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta charset="UTF-8">
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<title>Hello, World! in WebAssembly</title>
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</head>
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<body>
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<script src="hello.js" type="module"></script>
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</body>
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</html>
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48
pkg/wasm/server.go
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48
pkg/wasm/server.go
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package main
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import (
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"flag"
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"fmt"
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"log"
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"net/http"
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"path/filepath"
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)
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func main() {
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port := flag.Int("port", 8080, "Port to serve on")
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dir := flag.String("dir", ".", "Directory to serve files from")
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flag.Parse()
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// Create file server
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fs := http.FileServer(http.Dir(*dir))
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// Wrap with MIME type handler for WASM files
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http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
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// Set correct MIME type for WebAssembly files
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if filepath.Ext(r.URL.Path) == ".wasm" {
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w.Header().Set("Content-Type", "application/wasm")
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}
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// Set CORS headers to allow cross-origin requests (useful for development)
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w.Header().Set("Access-Control-Allow-Origin", "*")
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w.Header().Set("Access-Control-Allow-Methods", "GET, OPTIONS")
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w.Header().Set("Access-Control-Allow-Headers", "Content-Type")
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// Handle OPTIONS preflight requests
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if r.Method == "OPTIONS" {
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w.WriteHeader(http.StatusOK)
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return
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}
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fs.ServeHTTP(w, r)
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})
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addr := fmt.Sprintf(":%d", *port)
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log.Printf("Starting WASM server on http://localhost%s", addr)
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log.Printf("Serving files from: %s", *dir)
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log.Printf("\nOpen http://localhost%s/ in your browser", addr)
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if err := http.ListenAndServe(addr, nil); err != nil {
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log.Fatal(err)
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}
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}
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