path: root/internal/pkg/exec.go

package pkg

import (
	"bufio"
	"context"
	"errors"
	"fmt"
	"io"
	"os"
	"os/exec"
	"path"
	"slices"
	"strconv"
	"syscall"
	"time"

	"hakurei.app/container"
	"hakurei.app/container/check"
	"hakurei.app/container/fhs"
	"hakurei.app/container/std"
	"hakurei.app/message"
)

// AbsWork is the container pathname [CureContext.GetWorkDir] is mounted on.
var AbsWork = fhs.AbsRoot.Append("work/")

// ExecPath is a slice of [Artifact] and the [check.Absolute] pathname to make
// it available at under in the container.
type ExecPath struct {
	// Pathname in the container mount namespace.
	P *check.Absolute
	// Artifacts to mount on the pathname, must contain at least one [Artifact].
	// If there are multiple entries or W is true, P is set up as an overlay
	// mount, and entries of A must not implement [File].
	A []Artifact
	// Whether to make the mount point writable via the temp directory.
	W bool
}

// Path returns a populated [ExecPath].
func Path(pathname *check.Absolute, writable bool, a ...Artifact) ExecPath {
	return ExecPath{pathname, a, writable}
}

// MustPath is like [Path], but takes a string pathname via [check.MustAbs].
func MustPath(pathname string, writable bool, a ...Artifact) ExecPath {
	return ExecPath{check.MustAbs(pathname), a, writable}
}

const (
	// ExecTimeoutDefault replaces out of range [NewExec] timeout values.
	ExecTimeoutDefault = 15 * time.Minute
	// ExecTimeoutMax is the arbitrary upper bound of [NewExec] timeout.
	ExecTimeoutMax = 48 * time.Hour
)

// An execArtifact is an [Artifact] that produces output by running a program
// part of another [Artifact] in a [container] to produce its output.
//
// Methods of execArtifact does not modify any struct field or underlying arrays
// referred to by slices.
type execArtifact struct {
	// Caller-supplied user-facing reporting name, guaranteed to be nonzero
	// during initialisation.
	name string
	// Caller-supplied inner mount points.
	paths []ExecPath

	// Passed through to [container.Params].
	dir *check.Absolute
	// Passed through to [container.Params].
	env []string
	// Passed through to [container.Params].
	path *check.Absolute
	// Passed through to [container.Params].
	args []string

	// Duration the initial process is allowed to run. The zero value is
	// equivalent to execTimeoutDefault. This value is never encoded in Params
	// because it cannot affect outcome.
	timeout time.Duration
}

var _ fmt.Stringer = new(execArtifact)

// execNetArtifact is like execArtifact but implements [KnownChecksum] and has
// its resulting container keep the host net namespace.
type execNetArtifact struct {
	checksum Checksum

	execArtifact
}

var _ KnownChecksum = new(execNetArtifact)

// Checksum returns the caller-supplied checksum.
func (a *execNetArtifact) Checksum() Checksum { return a.checksum }

// Kind returns the hardcoded [Kind] constant.
func (a *execNetArtifact) Kind() Kind { return KindExecNet }

// Params is [Checksum] concatenated with [KindExec] params.
func (a *execNetArtifact) Params(ctx *IContext) {
	ctx.GetHash().Write(a.checksum[:])
	a.execArtifact.Params(ctx)
}

// Cure cures the [Artifact] in the container described by the caller. The
// container retains host networking.
func (a *execNetArtifact) Cure(f *FContext) error {
	return a.cure(f, true)
}

// NewExec returns a new [Artifact] that executes the program path in a
// container with specified paths bind mounted read-only in order. A private
// instance of /proc and /dev is made available to the container.
//
// The working and temporary directories are both created and mounted writable
// on [AbsWork] and [fhs.AbsTmp] respectively. If one or more paths target
// [AbsWork], the final entry is set up as a writable overlay mount on /work for
// which the upperdir is the host side work directory. In this configuration,
// the W field is ignored, and the program must avoid causing whiteout files to
// be created. Cure fails if upperdir ends up with entries other than directory,
// regular or symlink.
//
// If checksum is non-nil, the resulting [Artifact] implements [KnownChecksum]
// and its container runs in the host net namespace.
//
// The container is allowed to run for the specified duration before the initial
// process and all processes originating from it is terminated. A zero or
// negative timeout value is equivalent tp [ExecTimeoutDefault], a timeout value
// greater than [ExecTimeoutMax] is equivalent to [ExecTimeoutMax].
//
// The user-facing name is not accessible from the container and does not
// affect curing outcome. Because of this, it is omitted from parameter data
// for computing identifier.
func NewExec(
	name string,
	checksum *Checksum,
	timeout time.Duration,

	dir *check.Absolute,
	env []string,
	pathname *check.Absolute,
	args []string,

	paths ...ExecPath,
) Artifact {
	if name == "" {
		name = "exec-" + path.Base(pathname.String())
	}
	if timeout <= 0 {
		timeout = ExecTimeoutDefault
	}
	if timeout > ExecTimeoutMax {
		timeout = ExecTimeoutMax
	}
	a := execArtifact{name, paths, dir, env, pathname, args, timeout}
	if checksum == nil {
		return &a
	}
	return &execNetArtifact{*checksum, a}
}

// Kind returns the hardcoded [Kind] constant.
func (a *execArtifact) Kind() Kind { return KindExec }

// Params writes paths, executable pathname and args.
func (a *execArtifact) Params(ctx *IContext) {
	h := ctx.GetHash()

	_0, _1 := []byte{0}, []byte{1}
	for _, p := range a.paths {
		if p.W {
			h.Write(_1)
		} else {
			h.Write(_0)
		}
		if p.P != nil {
			h.Write([]byte(p.P.String()))
		} else {
			h.Write([]byte("invalid P\x00"))
		}
		h.Write(_0)
		for _, d := range p.A {
			ctx.WriteIdent(d)
		}
		h.Write(_0)
	}
	h.Write(_0)
	h.Write([]byte(a.dir.String()))
	h.Write(_0)
	for _, e := range a.env {
		h.Write([]byte(e))
	}
	h.Write(_0)
	h.Write([]byte(a.path.String()))
	h.Write(_0)
	for _, arg := range a.args {
		h.Write([]byte(arg))
	}
}

// Dependencies returns a slice of all artifacts collected from caller-supplied
// [ExecPath].
func (a *execArtifact) Dependencies() []Artifact {
	artifacts := make([][]Artifact, 0, len(a.paths))
	for _, p := range a.paths {
		artifacts = append(artifacts, p.A)
	}
	return slices.Concat(artifacts...)
}

// String returns the caller-supplied reporting name.
func (a *execArtifact) String() string { return a.name }

// Cure cures the [Artifact] in the container described by the caller.
func (a *execArtifact) Cure(f *FContext) (err error) {
	return a.cure(f, false)
}

const (
	// execWaitDelay is passed through to [container.Params].
	execWaitDelay = time.Nanosecond
)

// scanVerbose prefixes program output for a verbose [message.Msg].
func scanVerbose(
	msg message.Msg,
	done chan<- struct{},
	prefix string,
	r io.Reader,
) {
	defer close(done)
	s := bufio.NewScanner(r)
	for s.Scan() {
		msg.Verbose(prefix, s.Text())
	}
	if err := s.Err(); err != nil && !errors.Is(err, os.ErrClosed) {
		msg.Verbose("*"+prefix, err)
	}
}

// cure is like Cure but allows optional host net namespace. This is used for
// the [KnownChecksum] variant where networking is allowed.
func (a *execArtifact) cure(f *FContext, hostNet bool) (err error) {
	overlayWorkIndex := -1
	for i, p := range a.paths {
		if p.P == nil || len(p.A) == 0 {
			return os.ErrInvalid
		}
		if p.P.Is(AbsWork) {
			overlayWorkIndex = i
		}
	}

	var artifactCount int
	for _, p := range a.paths {
		artifactCount += len(p.A)
	}

	ctx, cancel := context.WithTimeout(f.Unwrap(), a.timeout)
	defer cancel()

	z := container.New(ctx, f.GetMessage())
	z.WaitDelay = execWaitDelay
	z.SeccompPresets |= std.PresetStrict
	z.ParentPerm = 0700
	z.HostNet = hostNet
	z.Hostname = "cure"
	if z.HostNet {
		z.Hostname = "cure-net"
	}
	z.Uid, z.Gid = (1<<10)-1, (1<<10)-1
	if msg := f.GetMessage(); msg.IsVerbose() {
		var stdout, stderr io.ReadCloser
		if stdout, err = z.StdoutPipe(); err != nil {
			return
		}
		if stderr, err = z.StderrPipe(); err != nil {
			_ = stdout.Close()
			return
		}
		defer func() {
			if err != nil && !errors.As(err, new(*exec.ExitError)) {
				_ = stdout.Close()
				_ = stderr.Close()
			}
		}()

		stdoutDone, stderrDone := make(chan struct{}), make(chan struct{})
		go scanVerbose(msg, stdoutDone, "("+a.name+":1)", stdout)
		go scanVerbose(msg, stderrDone, "("+a.name+":2)", stderr)
		defer func() { <-stdoutDone; <-stderrDone }()
	}

	z.Dir, z.Env, z.Path, z.Args = a.dir, a.env, a.path, a.args
	z.Grow(len(a.paths) + 4)

	temp, work := f.GetTempDir(), f.GetWorkDir()
	for i, b := range a.paths {
		layers := make([]*check.Absolute, len(b.A))
		for j, d := range b.A {
			layers[j] = f.Pathname(d)
		}

		if i == overlayWorkIndex {
			if err = os.MkdirAll(work.String(), 0700); err != nil {
				return
			}
			tempWork := temp.Append(".work")
			if err = os.MkdirAll(tempWork.String(), 0700); err != nil {
				return
			}
			z.Overlay(
				AbsWork,
				work,
				tempWork,
				layers...,
			)
			continue
		}

		if a.paths[i].W {
			tempUpper, tempWork := temp.Append(
				".upper", strconv.Itoa(i),
			), temp.Append(
				".work", strconv.Itoa(i),
			)
			if err = os.MkdirAll(tempUpper.String(), 0700); err != nil {
				return
			}
			if err = os.MkdirAll(tempWork.String(), 0700); err != nil {
				return
			}
			z.Overlay(b.P, tempUpper, tempWork, layers...)
		} else if len(layers) == 1 {
			z.Bind(layers[0], b.P, 0)
		} else {
			z.OverlayReadonly(b.P, layers...)
		}
	}
	if overlayWorkIndex < 0 {
		z.Bind(
			work,
			AbsWork,
			std.BindWritable|std.BindEnsure,
		)
	}
	z.Bind(
		f.GetTempDir(),
		fhs.AbsTmp,
		std.BindWritable|std.BindEnsure,
	)
	z.Proc(fhs.AbsProc).Dev(fhs.AbsDev, true)

	if err = z.Start(); err != nil {
		return
	}
	if err = z.Serve(); err != nil {
		return
	}
	if err = z.Wait(); err != nil {
		return
	}

	// do not allow empty directories to succeed
	for {
		err = syscall.Rmdir(work.String())
		if err != syscall.EINTR {
			break
		}
	}
	if err != nil && errors.Is(err, syscall.ENOTEMPTY) {
		err = nil
	}
	return
}