feat(engine): orchestrate the sing-box service

internal/engine/engine.go

@@ -0,0 +1,143 @@
+// SPDX-License-Identifier: MIT
+
+// Package engine controls the proxy engine (sing-box) through systemd.
+package engine
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"os"
+	"strings"
+
+	"prx/internal/config"
+	"prx/internal/execx"
+)
+
+// IsActive reports whether the systemd unit is active.
+func IsActive(ctx context.Context, r execx.Runner, service string) (bool, error) {
+	res, err := r.Run(ctx, nil, "systemctl", "is-active", service)
+	state := strings.TrimSpace(string(res.Stdout))
+	if err != nil {
+		var ee *execx.ExitError
+		if errors.As(err, &ee) {
+			// inactive/failed units exit non-zero; that is not an error here.
+			return state == "active", nil
+		}
+		return false, err
+	}
+	return state == "active", nil
+}
+
+// Start starts the unit.
+func Start(ctx context.Context, r execx.Runner, service string) error {
+	_, err := r.Run(ctx, nil, "systemctl", "start", service)
+	if err != nil {
+		return fmt.Errorf("start %s: %w", service, err)
+	}
+	return nil
+}
+
+// Stop stops the unit.
+func Stop(ctx context.Context, r execx.Runner, service string) error {
+	_, err := r.Run(ctx, nil, "systemctl", "stop", service)
+	if err != nil {
+		return fmt.Errorf("stop %s: %w", service, err)
+	}
+	return nil
+}
+
+// Reload asks the unit to reload its configuration.
+func Reload(ctx context.Context, r execx.Runner, service string) error {
+	_, err := r.Run(ctx, nil, "systemctl", "reload", service)
+	if err != nil {
+		return fmt.Errorf("reload %s: %w", service, err)
+	}
+	return nil
+}
+
+// ValidateConfig inspects a sing-box configuration for the settings prx relies
+// on, returning human readable warnings (never fatal).
+func ValidateConfig(path string) ([]string, error) {
+	if path == "" {
+		return nil, nil
+	}
+	raw, err := os.ReadFile(path)
+	if err != nil {
+		return nil, err
+	}
+	var parsed struct {
+		Inbounds []struct {
+			Type string `json:"type"`
+		} `json:"inbounds"`
+		Route struct {
+			AutoRoute *bool `json:"auto_route"`
+		} `json:"route"`
+	}
+	if err := json.Unmarshal(raw, &parsed); err != nil {
+		return nil, fmt.Errorf("parse engine config %s: %w", path, err)
+	}
+	var warnings []string
+	hasTun := false
+	for _, in := range parsed.Inbounds {
+		if in.Type == "tun" {
+			hasTun = true
+		}
+	}
+	if !hasTun {
+		warnings = append(warnings, "engine config has no tun inbound; proxy routing expects TUN mode")
+	}
+	if parsed.Route.AutoRoute != nil && !*parsed.Route.AutoRoute {
+		warnings = append(warnings, "engine route.auto_route is false; the tunnel may not capture traffic")
+	}
+	return warnings, nil
+}
+
+// Template renders a baseline sing-box configuration derived from cfg.
+func Template(cfg *config.Config) ([]byte, error) {
+	directRule := map[string]any{
+		"action":   "route",
+		"outbound": "direct",
+	}
+	if len(cfg.Bypass.AlwaysCIDRs) > 0 || len(cfg.Bypass.ExtraCIDRs) > 0 {
+		directRule["ip_cidr"] = append(append([]string{}, cfg.Bypass.AlwaysCIDRs...), cfg.Bypass.ExtraCIDRs...)
+	}
+	if len(cfg.Bypass.Domains) > 0 {
+		directRule["domain"] = cfg.Bypass.Domains
+	}
+	if len(cfg.ProcessBypass.Names) > 0 {
+		directRule["process_name"] = cfg.ProcessBypass.Names
+	}
+
+	doc := map[string]any{
+		"log": map[string]any{"level": "info"},
+		"inbounds": []any{
+			map[string]any{
+				"type":           "tun",
+				"tag":            "tun-in",
+				"interface_name": "tun0",
+				"address":        []string{"172.19.0.1/30", "fdfe:dcba:9876::1/126"},
+				"mtu":            9000,
+				"auto_route":     true,
+				"strict_route":   true,
+				"stack":          "system",
+				"auto_redirect":  false,
+			},
+		},
+		"outbounds": []any{
+			// Replace "direct" with your proxy outbound (e.g. { "type": "shadowsocks", ... }).
+			map[string]any{"type": "direct", "tag": "direct"},
+		},
+		"route": map[string]any{
+			"auto_detect_interface": true,
+			"rules":                 []any{directRule},
+			"final":                 "direct",
+		},
+	}
+	out, err := json.MarshalIndent(doc, "", "  ")
+	if err != nil {
+		return nil, err
+	}
+	return append(out, '\n'), nil
+}