feat: add constrained read-only diagnostics

internal/executor/diagnostic.go

@@ -0,0 +1,117 @@
+package executor
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"os/exec"
+	"strconv"
+	"strings"
+	"time"
+)
+
+// DiagnosticRequest is a structured, read-only diagnostic operation. It is deliberately
+// not a shell command: every action maps to a fixed executable/argument set.
+type DiagnosticRequest struct {
+	Action string `json:"action"`
+	Target string `json:"target,omitempty"`
+	Lines  int    `json:"lines,omitempty"`
+}
+
+type DiagnosticResult struct {
+	Action     string `json:"action"`
+	Target     string `json:"target,omitempty"`
+	ExitCode   int    `json:"exit_code"`
+	Stdout     string `json:"stdout"`
+	Stderr     string `json:"stderr"`
+	DurationMS int64  `json:"duration_ms"`
+}
+
+func Diagnostic(ctx context.Context, req DiagnosticRequest) (DiagnosticResult, error) {
+	args, err := diagnosticArgs(req)
+	if err != nil {
+		return DiagnosticResult{}, err
+	}
+	if req.Lines <= 0 {
+		req.Lines = 100
+	}
+	if req.Lines > 500 {
+		req.Lines = 500
+	}
+	// docker logs is the only operation where a caller-controlled numeric limit is useful.
+	if req.Action == "docker_logs" {
+		args = []string{"logs", "--tail", strconv.Itoa(req.Lines), req.Target}
+	}
+
+	start := time.Now()
+	c, cancel := context.WithTimeout(ctx, 15*time.Second)
+	defer cancel()
+	cmd := exec.CommandContext(c, args[0], args[1:]...)
+	out, runErr := cmd.CombinedOutput()
+	const maxOutput = 256 * 1024
+	if len(out) > maxOutput {
+		out = append(out[:maxOutput], []byte("\n[output truncated at 256 KiB]\n")...)
+	}
+	code := 0
+	if cmd.ProcessState != nil {
+		code = cmd.ProcessState.ExitCode()
+	}
+	result := DiagnosticResult{Action: req.Action, Target: req.Target, ExitCode: code, Stdout: string(out), DurationMS: time.Since(start).Milliseconds()}
+	if runErr != nil && code == -1 {
+		return result, fmt.Errorf("diagnostic failed: %w", runErr)
+	}
+	return result, nil
+}
+
+func diagnosticArgs(req DiagnosticRequest) ([]string, error) {
+	target := strings.TrimSpace(req.Target)
+	switch req.Action {
+	case "docker_ps":
+		if target != "" {
+			return nil, errors.New("docker_ps does not accept target")
+		}
+		return []string{"docker", "ps", "--no-trunc"}, nil
+	case "docker_logs":
+		if target == "" || strings.ContainsAny(target, " \t\r\n;|&<>$`") {
+			return nil, errors.New("invalid docker container target")
+		}
+		return []string{"docker", "logs", "--tail", "100", target}, nil
+	case "docker_inspect":
+		if target == "" || strings.ContainsAny(target, " \t\r\n;|&<>$`") {
+			return nil, errors.New("invalid docker target")
+		}
+		return []string{"docker", "inspect", target}, nil
+	case "systemctl_status":
+		if target == "" || strings.ContainsAny(target, " \t\r\n;|&<>$`") {
+			return nil, errors.New("invalid systemd unit")
+		}
+		return []string{"systemctl", "status", "--no-pager", "--full", target}, nil
+	case "journalctl":
+		if target == "" || strings.ContainsAny(target, " \t\r\n;|&<>$`") {
+			return nil, errors.New("invalid journal unit")
+		}
+		return []string{"journalctl", "--no-pager", "-u", target, "-n", "100"}, nil
+	case "ss_listen":
+		if target != "" {
+			return nil, errors.New("ss_listen does not accept target")
+		}
+		return []string{"ss", "-lntp"}, nil
+	case "df":
+		if target != "" {
+			return nil, errors.New("df does not accept target")
+		}
+		return []string{"df", "-h"}, nil
+	case "free":
+		if target != "" {
+			return nil, errors.New("free does not accept target")
+		}
+		return []string{"free", "-h"}, nil
+	case "uptime":
+		if target != "" {
+			return nil, errors.New("uptime does not accept target")
+		}
+		return []string{"uptime"}, nil
+	default:
+		return nil, fmt.Errorf("unsupported diagnostic action: %s", req.Action)
+	}
+}

internal/executor/diagnostic_test.go

@@ -0,0 +1,24 @@
+package executor
+
+import (
+	"context"
+	"strings"
+	"testing"
+)
+
+func TestDiagnosticRejectsShellInjection(t *testing.T) {
+	_, err := Diagnostic(context.Background(), DiagnosticRequest{Action: "docker_logs", Target: "edgeever;rm -rf /"})
+	if err == nil || !strings.Contains(err.Error(), "invalid docker") {
+		t.Fatalf("expected target rejection, got %v", err)
+	}
+}
+
+func TestDiagnosticAllowsReadOnlyUptime(t *testing.T) {
+	got, err := Diagnostic(context.Background(), DiagnosticRequest{Action: "uptime"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got.ExitCode != 0 || strings.TrimSpace(got.Stdout) == "" {
+		t.Fatalf("unexpected uptime result: %#v", got)
+	}
+}