fix: softap_tether_offload example replaces vendor offload HAL with system APIs

Replace android.hardware.tetheroffload.IOffload vendor HAL with
INetworkManagementService system service and /proc/net/dev traffic stats.
Shows network interfaces, tethering status, bandwidth control, and per-interface
traffic counters.

Author: xaionaro@dx.center

examples/softap_tether_offload/main.go

@@ -1,12 +1,14 @@
-// Query tethering offload statistics from the hardware offload HAL.
+// Query tethering and network interface status via INetworkManagementService.
 //
-// When SoftAP is active, the tethering offload HAL accelerates packet
-// forwarding in hardware. This example shows how to query forwarded
-// traffic statistics for each upstream interface.
+// Uses the "network_management" system service to list network interfaces,
+// check tethering status, and query interface configurations.
+// Replaces the previous vendor offload HAL approach with system-level APIs.
+//
+// Note: Some tethering methods were removed in Android API 36+.
 //
 // Build:
 //
-//	GOOS=linux GOARCH=amd64 CGO_ENABLED=0 go build -o build/softap_tether_offload ./examples/softap_tether_offload/
+//	GOOS=linux GOARCH=arm64 CGO_ENABLED=0 go build -o build/softap_tether_offload ./examples/softap_tether_offload/
 //	adb push softap_tether_offload /data/local/tmp/ && adb shell /data/local/tmp/softap_tether_offload
 package main
 
@@ -15,10 +17,9 @@ import (
 	"fmt"
 	"os"
 
+	genOs "github.com/xaionaro-go/binder/android/os"
 	"github.com/xaionaro-go/binder/binder"
 	"github.com/xaionaro-go/binder/binder/versionaware"
-	genOs "github.com/xaionaro-go/binder/android/os"
-	"github.com/xaionaro-go/binder/android/hardware/tetheroffload"
 	"github.com/xaionaro-go/binder/kernelbinder"
 	"github.com/xaionaro-go/binder/servicemanager"
 )
@@ -41,43 +42,123 @@ func main() {
 
 	sm := servicemanager.New(transport)
 
-	// First list network interfaces to know which upstreams exist.
-	netSvc, err := sm.GetService(ctx, servicemanager.NetworkmanagementService)
+	svc, err := sm.GetService(ctx, servicemanager.NetworkmanagementService)
 	if err != nil {
-		fmt.Fprintf(os.Stderr, "get network_management: %v\n", err)
-	} else {
-		netMgr := genOs.NewNetworkManagementServiceProxy(netSvc)
+		fmt.Fprintf(os.Stderr, "get network_management service: %v\n", err)
+		os.Exit(1)
+	}
+
+	netMgr := genOs.NewNetworkManagementServiceProxy(svc)
 
-		ifaces, err := netMgr.ListInterfaces(ctx)
-		if err != nil {
-			fmt.Fprintf(os.Stderr, "ListInterfaces: %v\n", err)
-		} else {
-			fmt.Printf("Network interfaces: %v\n\n", ifaces)
+	// List all network interfaces.
+	ifaces, err := netMgr.ListInterfaces(ctx)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "ListInterfaces: %v\n", err)
+	} else {
+		fmt.Printf("Network interfaces (%d):\n", len(ifaces))
+		for _, iface := range ifaces {
+			fmt.Printf("  %s\n", iface)
 		}
 	}
 
-	// Try to access the tethering offload HAL.
-	offloadSvc, err := sm.GetService(ctx, servicemanager.ServiceName("android.hardware.tetheroffload.IOffload/default"))
+	// Check tethering status (may be removed in API 36+).
+	fmt.Println()
+	tethering, err := netMgr.IsTetheringStarted(ctx)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "IsTetheringStarted: %v\n", err)
+		fmt.Fprintf(os.Stderr, "  (this method was removed in Android API 36)\n")
+	} else {
+		fmt.Printf("Tethering active: %v\n", tethering)
+	}
+
+	// List tethered interfaces (may be removed in API 36+).
+	tethered, err := netMgr.ListTetheredInterfaces(ctx)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "ListTetheredInterfaces: %v\n", err)
+		fmt.Fprintf(os.Stderr, "  (this method was removed in Android API 36)\n")
+	} else if len(tethered) == 0 {
+		fmt.Println("Tethered interfaces: (none)")
+	} else {
+		fmt.Printf("Tethered interfaces: %v\n", tethered)
+	}
+
+	// Check bandwidth control.
+	fmt.Println()
+	bwCtrl, err := netMgr.IsBandwidthControlEnabled(ctx)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "IsBandwidthControlEnabled: %v\n", err)
+	} else {
+		fmt.Printf("Bandwidth control enabled: %v\n", bwCtrl)
+	}
+
+	// Check IP forwarding (may be removed in API 36+).
+	fwd, err := netMgr.GetIpForwardingEnabled(ctx)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "GetIpForwardingEnabled: %v\n", err)
+	} else {
+		fmt.Printf("IP forwarding enabled: %v\n", fwd)
+	}
+
+	// Try to read network statistics from procfs as a complement.
+	fmt.Println()
+	printNetStats(ifaces)
+}
+
+// printNetStats reads basic traffic counters from /proc/net/dev for the
+// given interfaces.
+func printNetStats(ifaces []string) {
+	data, err := os.ReadFile("/proc/net/dev")
 	if err != nil {
-		fmt.Fprintf(os.Stderr, "get tether offload HAL: %v\n", err)
-		fmt.Fprintf(os.Stderr, "(offload HAL not available — no hardware offload support or SELinux denial)\n")
-		fmt.Fprintf(os.Stderr, "\nOn devices with offload support, this queries forwarded traffic stats:\n")
-		fmt.Fprintf(os.Stderr, "  offload.GetForwardedStats(ctx, \"wlan0\") → {RxBytes, TxBytes}\n")
-		os.Exit(0)
+		fmt.Fprintf(os.Stderr, "read /proc/net/dev: %v\n", err)
+		return
 	}
 
-	offload := tetheroffload.NewOffloadProxy(offloadSvc)
+	// Build a set of interfaces we care about.
+	ifaceSet := make(map[string]bool, len(ifaces))
+	for _, iface := range ifaces {
+		ifaceSet[iface] = true
+	}
 
-	// Query forwarded stats for common upstream interfaces.
-	upstreams := []string{"wlan0", "eth0", "rmnet0", "rmnet_data0"}
+	fmt.Println("Network traffic statistics:")
+	fmt.Printf("  %-15s %15s %15s\n", "Interface", "RX bytes", "TX bytes")
+	fmt.Printf("  %-15s %15s %15s\n", "---------", "--------", "--------")
 
-	fmt.Println("Tethering offload forwarded traffic:")
-	for _, iface := range upstreams {
-		stats, err := offload.GetForwardedStats(ctx, iface)
-		if err != nil {
+	lines := splitLines(string(data))
+	for _, line := range lines[2:] { // skip header lines
+		var iface string
+		var rxBytes, txBytes int64
+		var dummy int64
+		// Format: iface: rx_bytes rx_packets ... tx_bytes tx_packets ...
+		n, _ := fmt.Sscanf(line, " %s %d %d %d %d %d %d %d %d %d",
+			&iface, &rxBytes, &dummy, &dummy, &dummy, &dummy, &dummy, &dummy, &dummy, &txBytes)
+		if n < 10 {
 			continue
 		}
-		fmt.Printf("  %-15s RX: %d bytes  TX: %d bytes\n",
-			iface, stats.RxBytes, stats.TxBytes)
+		// Remove trailing colon from iface name.
+		if len(iface) > 0 && iface[len(iface)-1] == ':' {
+			iface = iface[:len(iface)-1]
+		}
+		if !ifaceSet[iface] {
+			continue
+		}
+		if rxBytes == 0 && txBytes == 0 {
+			continue
+		}
+		fmt.Printf("  %-15s %15d %15d\n", iface, rxBytes, txBytes)
+	}
+}
+
+func splitLines(s string) []string {
+	var lines []string
+	start := 0
+	for i := 0; i < len(s); i++ {
+		if s[i] == '\n' {
+			lines = append(lines, s[start:i])
+			start = i + 1
+		}
+	}
+	if start < len(s) {
+		lines = append(lines, s[start:])
 	}
+	return lines
 }