mesh-sdk/go/forgekey/runner.go

package forgekey

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

// Ran is what a 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 installed, or says it was ended for taking too long.
	Err string
}

// Runner runs one command with extra environment words, so every tool can be tested without ssh.
type Runner func(ctx context.Context, env []string, name string, args ...string) Ran

// CallTimeout bounds one command of ExecRunner: below the runtime's thirty-second call limit. A variable so a
// test can lower it.
var CallTimeout = 20 * time.Second

// ExecRunner runs a command on this machine, with no terminal and nothing on its stdin, bounded by
// CallTimeout.
func ExecRunner(ctx context.Context, env []string, name string, args ...string) Ran {
	return ExecRunnerFor(CallTimeout)(ctx, env, name, args...)
}

// ExecRunnerFor is ExecRunner with its own bound (issue 1497): a build module's long step passes 0, so only the
// step's own context ends a command, and a fetch may outlast a tool call's thirty seconds.
func ExecRunnerFor(bound time.Duration) Runner {
	return func(ctx context.Context, env []string, name string, args ...string) Ran {
		return execRun(ctx, bound, false, env, name, args...)
	}
}

// ExecRunnerClean is ExecRunnerFor whose commands get exactly the env argument as their environment, and nothing of
// this process's (issue 1497; novox/hq ADR 0466 §4: no registry password in a fetch's environment). The caller
// gives PATH and HOME itself. A directory is the command's own business (`git -C`, `go -C`): it is started in the HOME
// it is given, or the machine's temporary directory, never in this process's (stableDir).
func ExecRunnerClean(bound time.Duration) Runner {
	return func(ctx context.Context, env []string, name string, args ...string) Ran {
		return execRun(ctx, bound, true, env, name, args...)
	}
}

func execRun(ctx context.Context, bound time.Duration, clean bool, env []string, name string, args ...string) Ran {
	if bound > 0 {
		var cancel context.CancelFunc
		ctx, cancel = context.WithTimeout(ctx, bound)
		defer cancel()
	}
	cmd := exec.CommandContext(ctx, name, args...)
	if clean {
		cmd.Env = append([]string{}, env...) // non-nil, so an empty list is an empty environment
	} else {
		cmd.Env = append(os.Environ(), env...)
	}
	cmd.Dir = stableDir(clean, env)
	var out, errb bytes.Buffer
	cmd.Stdout, cmd.Stderr = &out, &errb
	err := cmd.Run()
	r := Ran{Stdout: out.String(), Stderr: errb.String()}
	var exitErr *exec.ExitError
	switch {
	case errors.Is(ctx.Err(), context.DeadlineExceeded):
		r.Status, r.Err = 124, "ended by its step's deadline"
		if bound > 0 {
			r.Err = fmt.Sprintf("no answer within %d s", int(bound/time.Second))
		}
	case errors.Is(err, exec.ErrNotFound):
		r.Status, r.Err = 127, "ENOENT"
	case errors.As(err, &exitErr):
		r.Status = exitErr.ExitCode()
	case err != nil:
		r.Status, r.Err = 1, err.Error()
	}
	return r
}

// stableDir is the directory a command starts in when it names none (novox/hq issue 734). **Never one that may be
// deleted under it**: a module runs in the directory its build was unpacked in, which a new build replaces, and a
// command started there inherits it — `go version` then fails "getwd: no such file or directory" before it reads
// anything. A clean command starts in the HOME it is given, or the temporary directory; any other keeps this
// process's directory while it exists, and starts in the temporary directory once it is gone. "" is this process's.
func stableDir(clean bool, env []string) string {
	if !clean {
		if _, err := os.Getwd(); err == nil {
			return ""
		}
		return os.TempDir()
	}
	for i := len(env) - 1; i >= 0; i-- {
		if home, ok := strings.CutPrefix(env[i], "HOME="); ok {
			if info, err := os.Stat(home); err == nil && info.IsDir() {
				return home
			}
			break
		}
	}
	return os.TempDir()
}

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