tinygo-org · acouvreur · Apr 10, 2026 · Apr 19, 2026 · Apr 19, 2026
diff --git a/adapter_js.go b/adapter_js.go
@@ -0,0 +1,44 @@
+package bluetooth
+
+import (
+	"errors"
+	"syscall/js"
+)
+
+var _ BLEAdapter = (*Adapter)(nil)
+
+// Adapter represents the WebBluetooth adapter accessed via navigator.bluetooth.
+type Adapter struct {
+	bluetooth      js.Value
+	connectHandler func(device Device, connected bool)
+
+	// RequestedServices is the list of service UUIDs that will be passed as
+	// optionalServices to navigator.bluetooth.requestDevice(). WebBluetooth
+	// requires services to be declared upfront — you cannot discover or
+	// access services that are not listed here or matched by a filter.
+	//
+	// Set this before calling Scan().
+	RequestedServices []UUID
+}
+
+// DefaultAdapter is the default adapter using the navigator.bluetooth API.
+//
+// Make sure to call Enable() before using it to initialize the adapter.
+var DefaultAdapter = &Adapter{
+	connectHandler: func(device Device, connected bool) {},
+}
+
+// Enable configures the BLE stack. It must be called before any
+// Bluetooth-related calls (unless otherwise indicated).
+func (a *Adapter) Enable() error {
+	navigator := js.Global().Get("navigator")
+	if navigator.IsUndefined() {
+		return errors.New("bluetooth: navigator is not available")
+	}
+	bt := navigator.Get("bluetooth")
+	if bt.IsUndefined() {
+		return errors.New("bluetooth: WebBluetooth is not supported in this browser")
+	}
+	a.bluetooth = bt
+	return nil
+}
diff --git a/examples/webbluetooth/html/.gitignore b/examples/webbluetooth/html/.gitignore
@@ -0,0 +1,2 @@
+wasm_exec.js
+wasm.wasm
diff --git a/examples/webbluetooth/html/index.html b/examples/webbluetooth/html/index.html
@@ -0,0 +1,38 @@
+<!DOCTYPE html>
+<html lang="en">
+<head>
+    <meta charset="UTF-8">
+    <meta name="viewport" content="width=device-width, initial-scale=1.0">
+    <title>WebBluetooth - TinyGo Device Information</title>
+    <style>
+        body { font-family: system-ui, sans-serif; max-width: 720px; margin: 2rem auto; padding: 0 1rem; }
+        button { font-size: 1.1rem; padding: 0.5rem 1.5rem; cursor: pointer; }
+        #log { background: #f5f5f5; border: 1px solid #ddd; border-radius: 4px; padding: 1rem; margin-top: 1rem; min-height: 120px; }
+        #log p { margin: 0.25rem 0; font-family: monospace; font-size: 0.9rem; }
+    </style>
+</head>
+<body>
+    <h1>WebBluetooth - TinyGo Device Information</h1>
+    <p>Click the button below to connect to a BLE device and read its Device Information service (manufacturer, model, firmware).</p>
+    <button id="connectBtn" disabled>Loading WASM…</button>
+    <div id="log"></div>
+
+    <script src="wasm_exec.js"></script>
+    <script>
+        const go = new Go();
+        WebAssembly.instantiateStreaming(fetch("wasm.wasm"), go.importObject).then((result) => {
+            go.run(result.instance);
+            const btn = document.getElementById("connectBtn");
+            btn.textContent = "Connect";
+            btn.disabled = false;
+            btn.addEventListener("click", () => {
+                if (typeof btConnect === "function") {
+                    btConnect();
+                } else {
+                    alert("WASM not ready yet");
+                }
+            });
+        });
+    </script>
+</body>
+</html>
diff --git a/examples/webbluetooth/main.go b/examples/webbluetooth/main.go
@@ -0,0 +1,152 @@
+// This example demonstrates using the Web Bluetooth API via TinyGo WASM.
+// It opens the browser's Bluetooth device picker, connects to any BLE
+// peripheral, and reads the Device Information service (manufacturer name,
+// model number, firmware revision).
+//
+// To build:
+//
+//	tinygo build -o ./examples/webbluetooth/html/wasm.wasm -target wasm ./examples/webbluetooth/
+//
+// Then serve the html directory over HTTPS (or localhost). A minimal server is
+// included:
+//
+//	go run ./examples/webbluetooth/server/
+//
+// Open http://localhost:8080 in Chrome/Edge, click the "Connect" button and
+// pick a Bluetooth device from the browser dialog.
+package main
+
+import (
+	"syscall/js"
+
+	"tinygo.org/x/bluetooth"
+)
+
+var adapter = bluetooth.DefaultAdapter
+
+var (
+	deviceInfoServiceUUID = bluetooth.ServiceUUIDDeviceInformation
+
+	manufacturerNameUUID  = bluetooth.CharacteristicUUIDManufacturerNameString
+	modelNumberUUID       = bluetooth.CharacteristicUUIDModelNumberString
+	firmwareRevisionUUID  = bluetooth.CharacteristicUUIDFirmwareRevisionString
+)
+
+func main() {
+	// Export a function that the HTML page calls when the user clicks Connect.
+	js.Global().Set("btConnect", js.FuncOf(func(this js.Value, args []js.Value) any {
+		go run()
+		return nil
+	}))
+
+	logMsg("WebBluetooth example loaded. Click 'Connect' to start.")
+
+	// Keep the Go program alive.
+	select {}
+}
+
+func run() {
+	logMsg("Enabling BLE adapter...")
+	must("enable BLE stack", adapter.Enable())
+
+	// WebBluetooth requires listing the services you want to access upfront.
+	adapter.RequestedServices = []bluetooth.UUID{
+		deviceInfoServiceUUID,
+	}
+
+	logMsg("Opening device picker...")
+
+	var result bluetooth.ScanResult
+	err := adapter.Scan(func(a *bluetooth.Adapter, r bluetooth.ScanResult) {
+		result = r
+		a.StopScan()
+	})
+	must("scan", err)
+
+	logMsg("Selected device: " + result.LocalName() + " (" + result.Address.String() + ")")
+
+	// Connection can fail if the device is asleep or out of range. Retry a
+	// few times before giving up.
+	var device bluetooth.Device
+	const maxRetries = 3
+	for attempt := 1; attempt <= maxRetries; attempt++ {
+		logMsg("Connecting (attempt " + itoa(attempt) + "/" + itoa(maxRetries) + ")...")
+		device, err = adapter.Connect(result.Address, bluetooth.ConnectionParams{})
+		if err == nil {
+			break
+		}
+		logMsg("Connection failed: " + err.Error())
+		if attempt == maxRetries {
+			logMsg("Could not connect after " + itoa(maxRetries) + " attempts. Make sure the device is awake and in range, then click Connect again.")
+			return
+		}
+	}
+	logMsg("Connected!")
+
+	logMsg("Discovering Device Information service...")
+	srvcs, err := device.DiscoverServices([]bluetooth.UUID{deviceInfoServiceUUID})
+	must("discover services", err)
+
+	srvc := srvcs[0]
+	logMsg("Found service: " + srvc.UUID().String())
+
+	// Read each Device Information characteristic. Not all devices expose
+	// every characteristic, so we read them individually and tolerate errors.
+	buf := make([]byte, 128)
+
+	for _, item := range []struct {
+		name string
+		uuid bluetooth.UUID
+	}{
+		{"Manufacturer Name", manufacturerNameUUID},
+		{"Model Number", modelNumberUUID},
+		{"Firmware Revision", firmwareRevisionUUID},
+	} {
+		chars, err := srvc.DiscoverCharacteristics([]bluetooth.UUID{item.uuid})
+		if err != nil {
+			logMsg("  " + item.name + ": not available")
+			continue
+		}
+		n, err := chars[0].Read(buf)
+		if err != nil {
+			logMsg("  " + item.name + ": read error: " + err.Error())
+			continue
+		}
+		logMsg("  " + item.name + ": " + string(buf[:n]))
+	}
+
+	logMsg("Disconnecting...")
+	device.Disconnect()
+	logMsg("Done.")
+}
+
+// logMsg writes a message to the browser console and appends it to the #log element.
+func logMsg(msg string) {
+	js.Global().Get("console").Call("log", msg)
+	doc := js.Global().Get("document")
+	logEl := doc.Call("getElementById", "log")
+	if !logEl.IsNull() {
+		p := doc.Call("createElement", "p")
+		p.Set("textContent", msg)
+		logEl.Call("appendChild", p)
+	}
+}
+
+func must(action string, err error) {
+	if err != nil {
+		logMsg("FATAL: failed to " + action + ": " + err.Error())
+		panic("failed to " + action + ": " + err.Error())
+	}
+}
+
+func itoa(n int) string {
+	if n == 0 {
+		return "0"
+	}
+	s := ""
+	for n > 0 {
+		s = string(rune('0'+n%10)) + s
+		n /= 10
+	}
+	return s
+}
diff --git a/examples/webbluetooth/server/main.go b/examples/webbluetooth/server/main.go
@@ -0,0 +1,111 @@
+// A minimal HTTP server for the WebBluetooth example.
+//
+// Usage:
+//
+//	go run ./examples/webbluetooth/server/
+//
+// Then open http://localhost:8080 in Chrome or Edge.
+// WebBluetooth works on localhost without HTTPS.
+package main
+
+import (
+	"fmt"
+	"log"
+	"net/http"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"runtime"
+	"strings"
+)
+
+func main() {
+	dir := findHTMLDir()
+
+	ensureWASMExecJS(dir)
+	ensureWASM(dir)
+
+	addr := ":8080"
+	fmt.Printf("Serving %s on http://localhost%s\n", dir, addr)
+	log.Fatal(http.ListenAndServe(addr, http.FileServer(http.Dir(dir))))
+}
+
+// findHTMLDir locates the html/ directory relative to this file or cwd.
+func findHTMLDir() string {
+	// Try relative to the working directory first.
+	candidates := []string{
+		"examples/webbluetooth/html",
+		"html",
+	}
+	for _, c := range candidates {
+		if info, err := os.Stat(c); err == nil && info.IsDir() {
+			return c
+		}
+	}
+	fmt.Fprintln(os.Stderr, "Could not find html/ directory. Run from the repo root or the example directory.")
+	os.Exit(1)
+	return ""
+}
+
+// ensureWASMExecJS copies the TinyGo wasm_exec.js support file into the html directory.
+func ensureWASMExecJS(dir string) {
+	dst := filepath.Join(dir, "wasm_exec.js")
+	if _, err := os.Stat(dst); err == nil {
+		return // already exists
+	}
+
+	// Try TinyGo's wasm_exec.js first (targets/wasm_exec.js).
+	if tinygoRoot := os.Getenv("TINYGOROOT"); tinygoRoot != "" {
+		src := filepath.Join(tinygoRoot, "targets", "wasm_exec.js")
+		if copyFile(src, dst) == nil {
+			fmt.Println("Copied wasm_exec.js from TINYGOROOT")
+			return
+		}
+	}
+
+	// Try to find tinygo in PATH.
+	if tinygo, err := exec.LookPath("tinygo"); err == nil {
+		// tinygo env TINYGOROOT
+		out, err := exec.Command(tinygo, "env", "TINYGOROOT").Output()
+		if err == nil {
+			root := strings.TrimSpace(string(out))
+			src := filepath.Join(root, "targets", "wasm_exec.js")
+			if copyFile(src, dst) == nil {
+				fmt.Println("Copied wasm_exec.js from tinygo in PATH")
+				return
+			}
+		}
+	}
+
+	// Last resort: standard Go's wasm_exec.js. Note: this will NOT work
+	// with TinyGo-built WASM because it lacks WASI shims.
+	goroot := runtime.GOROOT()
+	src := filepath.Join(goroot, "lib", "wasm", "wasm_exec.js")
+	if copyFile(src, dst) == nil {
+		fmt.Println("WARNING: copied wasm_exec.js from GOROOT — this will NOT work with TinyGo WASM.")
+		fmt.Println("Install TinyGo or set TINYGOROOT to get the correct wasm_exec.js.")
+		return
+	}
+
+	fmt.Fprintln(os.Stderr, "Warning: could not find wasm_exec.js. Copy it manually into", dir)
+	fmt.Fprintln(os.Stderr, "  cp $(tinygo env TINYGOROOT)/targets/wasm_exec.js", dst)
+}
+
+// ensureWASM checks that wasm.wasm exists, and prints a hint if not.
+func ensureWASM(dir string) {
+	dst := filepath.Join(dir, "wasm.wasm")
+	if _, err := os.Stat(dst); err == nil {
+		return
+	}
+	fmt.Fprintln(os.Stderr, "Warning: wasm.wasm not found in", dir)
+	fmt.Fprintln(os.Stderr, "Build it with:")
+	fmt.Fprintln(os.Stderr, "  tinygo build -o "+dst+" -target wasm ./examples/webbluetooth/")
+}
+
+func copyFile(src, dst string) error {
+	data, err := os.ReadFile(src)
+	if err != nil {
+		return err
+	}
+	return os.WriteFile(dst, data, 0o644)
+}