feat(cmd): add prx and prx-helper entrypoints

cmd/prx-helper/main.go

@@ -0,0 +1,52 @@
+// SPDX-License-Identifier: MIT
+
+// Command prx-helper is the privileged core of prx.
+//
+// It reads a single JSON Plan from stdin, executes it and writes a JSON Result
+// to stdout. It refuses to run without root privileges and is intended to be
+// launched by the prx CLI through pkexec or sudo.
+package main
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"os"
+	"os/signal"
+	"syscall"
+
+	"prx/internal/execx"
+	"prx/internal/helper"
+	"prx/internal/proto"
+)
+
+func main() {
+	if os.Geteuid() != 0 {
+		fmt.Fprintln(os.Stderr, "prx-helper: must run as root (use pkexec or sudo)")
+		os.Exit(1)
+	}
+
+	// Cancelling on SIGINT/SIGTERM lets an in-flight transaction roll back
+	// instead of being killed part-way through.
+	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
+	defer stop()
+
+	var plan proto.Plan
+	dec := json.NewDecoder(os.Stdin)
+	if err := dec.Decode(&plan); err != nil {
+		fmt.Fprintln(os.Stderr, "prx-helper: invalid plan on stdin: "+err.Error())
+		os.Exit(2)
+	}
+
+	res := helper.Execute(ctx, execx.OSRunner{}, plan)
+
+	enc := json.NewEncoder(os.Stdout)
+	enc.SetIndent("", "  ")
+	if err := enc.Encode(res); err != nil {
+		fmt.Fprintln(os.Stderr, "prx-helper: encode result: "+err.Error())
+		os.Exit(2)
+	}
+	if !res.OK {
+		os.Exit(1)
+	}
+}