werkdock/internal/instance/exec.go

package instance

import (
	"crypto/rand"
	"encoding/hex"
	"errors"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"strings"
	"time"

	"werkdock/internal/engine"
)

// An Exec is a second command in a running instance's sandbox, kept as
// a record of its own because docker's API creates it, starts it, and
// asks for its exit code in three separate calls (RFC 0005 milestone 3,
// docs/testcontainers-api.md). Records live in the instance's exec/
// directory and go with it.
type Exec struct {
	ID         string          `json:"id"`
	InstanceID string          `json:"instanceId"`
	Cmd        []string        `json:"cmd"`
	Env        []engine.EnvVar `json:"env,omitempty"`
	Workdir    string          `json:"workdir,omitempty"`
	User       string          `json:"user,omitempty"`
	Started    bool            `json:"started"`
	Running    bool            `json:"running"`
	ExitCode   int             `json:"exitCode"`
	StartedAt  time.Time       `json:"startedAt,omitempty"`
	FinishedAt time.Time       `json:"finishedAt,omitempty"`
	dir        string
}

func execDir(instanceDir string) string { return filepath.Join(instanceDir, "exec") }

// CreateExec records a command to be run in inst later.
func (m Manager) CreateExec(inst *Instance, e Exec) (*Exec, error) {
	if len(e.Cmd) == 0 {
		return nil, errors.New("exec needs a command")
	}
	raw := make([]byte, 32)
	if _, err := rand.Read(raw); err != nil {
		return nil, err
	}
	e.ID = hex.EncodeToString(raw)
	e.InstanceID = inst.Config.ID
	e.dir = execDir(inst.Dir)
	if err := os.MkdirAll(e.dir, 0o755); err != nil {
		return nil, err
	}
	return &e, e.save()
}

func (e *Exec) path() string { return filepath.Join(e.dir, e.ID+".json") }

func (e *Exec) save() error { return writeJSON(e.path(), e) }

// GetExec finds an exec record by id across all instances, together
// with the instance it belongs to.
func (m Manager) GetExec(id string) (*Exec, *Instance, error) {
	if !isHex(id) {
		return nil, nil, fmt.Errorf("%w: exec %s", ErrNotFound, id)
	}
	all, err := m.List()
	if err != nil {
		return nil, nil, err
	}
	for _, inst := range all {
		path := filepath.Join(execDir(inst.Dir), id+".json")
		var e Exec
		if err := readJSON(path, &e); err != nil {
			if os.IsNotExist(err) {
				continue
			}
			return nil, nil, err
		}
		e.dir = execDir(inst.Dir)
		return &e, inst, nil
	}
	return nil, nil, fmt.Errorf("%w: exec %s", ErrNotFound, id)
}

func isHex(s string) bool {
	if s == "" {
		return false
	}
	return strings.IndexFunc(s, func(r rune) bool {
		return !strings.ContainsRune("0123456789abcdefABCDEF", r)
	}) < 0
}

// RunExec executes the recorded command in the instance's sandbox and
// records the exit code. The sandbox is the instance's: same rootfs,
// mounts, uid and environment, with the exec's own overrides; not the
// same pid namespace.
func (m Manager) RunExec(e *Exec, inst *Instance, eng engine.Engine, stdout, stderr io.Writer) (int, error) {
	if e.Started {
		return 0, fmt.Errorf("exec %s has already been started", e.ID[:12])
	}
	spec, err := e.spec(inst)
	if err != nil {
		return 0, err
	}
	e.Started, e.Running, e.StartedAt = true, true, time.Now()
	if err := e.save(); err != nil {
		return 0, err
	}
	if b, ok := eng.(*engine.Bwrap); ok {
		b.Stdout, b.Stderr = stdout, stderr
	}
	code, runErr := eng.Run(spec)
	e.Running, e.FinishedAt, e.ExitCode = false, time.Now(), code
	if runErr != nil {
		e.ExitCode = ExitCodeLost
	}
	if err := e.save(); err != nil && runErr == nil {
		runErr = err
	}
	return code, runErr
}

// spec is the instance's RunSpec with the exec's command and overrides.
func (e *Exec) spec(inst *Instance) (engine.RunSpec, error) {
	spec := inst.Config.Spec
	spec.Command = e.Cmd
	spec.Mounts = append([]engine.Mount{}, inst.Config.Spec.Mounts...)
	spec.Env = append(append([]engine.EnvVar{}, inst.Config.Spec.Env...), e.Env...)
	if e.Workdir != "" {
		spec.Workdir = e.Workdir
	}
	if e.User != "" {
		u, err := engine.LookupUser(spec.RootFS, e.User)
		if err != nil {
			return engine.RunSpec{}, fmt.Errorf("user: %w", err)
		}
		spec.UID, spec.GID, spec.Home = u.UID, u.GID, u.Home
	}
	return spec, nil
}