mesh-catalog/modules/avahi/cmd/avahi-tools/machine.go

package main

// The commands this bundle runs on its machine, and who runs them.
//
// Who asks. The node's tool runtime runs as the operator account, not root (novox/hq ADR 0175 §4),
// and launches this binary as a process of its own (ADR 0188, ADR 0193) with the runtime's words —
// HOME, a PATH, MESH_OPERATOR_ACCOUNT — and no session words. Reading needs nothing more; what only
// root may do goes through `sudo -n`, as the packet filter's, the service manager's and the
// intrusion prevention's tools do (to-be 38 WP4), and the `sudo` module is what declares that the
// account may (to-be 42, research 027). A refusal is named by how it failed, never read as an
// empty answer.
//
// The runner is injected, so every tool is tested over a fake one without the machine.

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"io/fs"
	"os"
	"os/exec"
	"strings"
	"time"
)

// Ran is what one command did: its output, its exit status, and why it never ran to an answer.
type Ran struct {
	Stdout string
	Stderr string
	Status int
	// Err is "ENOENT" when the program is not there, or that it was ended for taking too long.
	Err string
}

// Runner runs one command, so the tools can be tested without the machine.
type Runner func(ctx context.Context, name string, args ...string) Ran

// CallTimeout is how long one command may take: below the runtime's thirty-second call limit, so a
// command that hangs is answered as such rather than as a call the runtime gave up on.
const CallTimeout = 20 * time.Second

// outputLimit bounds what one command may hand back, so a runaway listing cannot exhaust the
// process; well above anything a tool answers.
const outputLimit = 16 << 20

type bounded struct {
	bytes.Buffer
	cut bool
}

func (b *bounded) Write(p []byte) (int, error) {
	if room := outputLimit - b.Len(); room < len(p) {
		if room > 0 {
			b.Buffer.Write(p[:room])
		}
		b.cut = true
		return len(p), nil
	}
	return b.Buffer.Write(p)
}

// ExecRunner runs a command on this machine, in the C locale so what is parsed is one language.
func ExecRunner(ctx context.Context, name string, args ...string) Ran {
	ctx, cancel := context.WithTimeout(ctx, CallTimeout)
	defer cancel()
	cmd := exec.CommandContext(ctx, name, args...)
	cmd.Env = append(os.Environ(), "LC_ALL=C")
	var out, errb bounded
	cmd.Stdout, cmd.Stderr = &out, &errb
	err := cmd.Run()
	r := Ran{Stdout: out.String(), Stderr: errb.String()}
	if ctx.Err() == context.DeadlineExceeded {
		r.Status, r.Err = 124, fmt.Sprintf("no answer within %d s", int(CallTimeout.Seconds()))
		return r
	}
	var exit *exec.ExitError
	switch {
	case err == nil:
	case errors.As(err, &exit):
		r.Status = exit.ExitCode()
	case errors.Is(err, exec.ErrNotFound) || errors.Is(err, fs.ErrNotExist):
		r.Status, r.Err = 127, "ENOENT"
	default:
		r.Status, r.Err = 126, err.Error()
	}
	return r
}

// Escalated is the command as it is run: as given when this process is root, else through sudo
// without a prompt.
func Escalated(uid int, name string, args ...string) (string, []string) {
	if uid == 0 {
		return name, args
	}
	return "sudo", append([]string{"-n", name}, args...)
}

// Machine is this machine as the tools see it: a runner, who this process is, and its files.
type Machine struct {
	Run      Runner
	UID      int
	User     string
	Account  string
	ReadFile func(path string) ([]byte, error)
	Now      func() time.Time
	Sleep    func(time.Duration)
}

// ThisMachine is the machine the runtime launched this bundle on.
func ThisMachine() *Machine {
	user := os.Getenv("USER")
	if user == "" {
		user = os.Getenv("LOGNAME")
	}
	account := strings.TrimSpace(os.Getenv("MESH_OPERATOR_ACCOUNT"))
	if account == "" {
		account = user
	}
	return &Machine{Run: ExecRunner, UID: os.Getuid(), User: user, Account: account, ReadFile: os.ReadFile, Now: time.Now, Sleep: time.Sleep}
}

// Out runs a command that only reads, and fails with what went wrong named.
func (m *Machine) Out(name string, args ...string) (string, error) {
	r := m.Run(context.Background(), name, args...)
	if r.Status == 0 && r.Err == "" {
		return r.Stdout, nil
	}
	return r.Stdout, failure(name, name, r)
}

// Root runs a command that needs root, escalated when this process is not.
func (m *Machine) Root(name string, args ...string) (string, error) {
	program, argv := Escalated(m.UID, name, args...)
	r := m.Run(context.Background(), program, argv...)
	if r.Status == 0 && r.Err == "" {
		return r.Stdout, nil
	}
	return r.Stdout, failure(name, program, r)
}

// RootRan is Root's raw answer, for a command whose non-zero status is itself an answer.
func (m *Machine) RootRan(name string, args ...string) (Ran, error) {
	program, argv := Escalated(m.UID, name, args...)
	r := m.Run(context.Background(), program, argv...)
	if r.Err != "" || (program == "sudo" && sudoRefused(r)) {
		return r, failure(name, program, r)
	}
	return r, nil
}

func sudoRefused(r Ran) bool {
	return strings.HasPrefix(strings.TrimSpace(r.Stderr), "sudo:")
}

// failure names what failed by how it failed: the program missing is a spawn error, sudo missing
// or refusing speaks for itself, and the rest is the command's own first line.
func failure(cmd, program string, r Ran) error {
	said := strings.TrimSpace(r.Stderr + "\n" + r.Stdout)
	if r.Err == "ENOENT" {
		if program == "sudo" {
			return fmt.Errorf("%s needs root for this, and sudo is not installed here for the runtime's account to escalate with", cmd)
		}
		return fmt.Errorf("%s is not installed on this machine", cmd)
	}
	if r.Err != "" {
		return fmt.Errorf("%s did not answer: %s", cmd, r.Err)
	}
	if program == "sudo" && sudoRefused(r) {
		if strings.Contains(said, "command not found") {
			return fmt.Errorf("%s is not installed on this machine", cmd)
		}
		return fmt.Errorf("%s needs root for this and the runtime's account may not run it without a prompt: %s", cmd, firstLine(said))
	}
	if line := firstLine(said); line != "" {
		return fmt.Errorf("%s failed (%d): %s", cmd, r.Status, line)
	}
	return fmt.Errorf("%s failed with status %d", cmd, r.Status)
}

func firstLine(text string) string {
	for _, l := range strings.Split(text, "\n") {
		if l = strings.TrimSpace(l); l != "" {
			return l
		}
	}
	return ""
}

func lines(text string) []string {
	var out []string
	for _, l := range strings.Split(text, "\n") {
		if l = strings.TrimRight(l, "\r"); strings.TrimSpace(l) != "" {
			out = append(out, l)
		}
	}
	return out
}

// text is a string argument; required says whether it may be absent. It is never something a
// command would read as an option, which under sudo would be root's option.
func text(args map[string]any, key string, required bool) (string, error) {
	raw, present := args[key]
	if !present || raw == nil {
		if required {
			return "", fmt.Errorf("%s is required", key)
		}
		return "", nil
	}
	s, ok := raw.(string)
	if !ok {
		return "", fmt.Errorf("%s must be a string", key)
	}
	s = strings.TrimSpace(s)
	if required && s == "" {
		return "", fmt.Errorf("%s is required", key)
	}
	if strings.HasPrefix(s, "-") || strings.ContainsRune(s, 0) || strings.ContainsAny(s, "\n\r") {
		return "", fmt.Errorf("%s %q is not a value this tool passes on", key, s)
	}
	return s, nil
}

// whole is a whole-number argument with a default, kept within bounds.
func whole(args map[string]any, key string, def, least, most int) (int, error) {
	raw, present := args[key]
	if !present || raw == nil {
		return def, nil
	}
	f, ok := raw.(float64)
	if !ok || f != float64(int(f)) {
		return 0, fmt.Errorf("%s must be a whole number", key)
	}
	n := int(f)
	if n < least {
		return 0, fmt.Errorf("%s must be at least %d", key, least)
	}
	if n > most {
		n = most
	}
	return n, nil
}

// flag is a boolean argument, false when absent.
func flag(args map[string]any, key string) (bool, error) {
	raw, present := args[key]
	if !present || raw == nil {
		return false, nil
	}
	b, ok := raw.(bool)
	if !ok {
		return false, fmt.Errorf("%s must be true or false", key)
	}
	return b, nil
}

// schema is a tool's input: its properties and the ones it requires.
func schema(properties map[string]any, required ...string) map[string]any {
	s := map[string]any{"type": "object", "properties": properties}
	if len(required) > 0 {
		s["required"] = required
	}
	return s
}

// unitProps reads a unit's properties as systemctl shows them.
func (m *Machine) unitProps(unit string, props ...string) (map[string]string, error) {
	args := []string{"show", unit, "--no-pager"}
	for _, p := range props {
		args = append(args, "--property="+p)
	}
	out, err := m.Out("systemctl", args...)
	if err != nil {
		return nil, err
	}
	return keyValues(out, "="), nil
}

// keyValues reads `key<sep>value` lines; a line without the separator is skipped.
func keyValues(out, sep string) map[string]string {
	kv := map[string]string{}
	for _, l := range strings.Split(out, "\n") {
		k, v, ok := strings.Cut(l, sep)
		if ok {
			kv[strings.TrimSpace(k)] = strings.TrimSpace(v)
		}
	}
	return kv
}