internal/rosa: busybox binary artifact

This installs a statically linked busybox binary distribution for decompressing the gentoo stage3 tarball, since there is no native xz implementation.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/rosa/busybox.go

@@ -0,0 +1,99 @@
+package rosa
+
+import (
+	"fmt"
+	"io"
+	"net/http"
+	"os"
+	"time"
+
+	"hakurei.app/container/fhs"
+	"hakurei.app/internal/pkg"
+)
+
+// busyboxBin is a busybox binary distribution installed under bin/busybox.
+type busyboxBin struct {
+	// Underlying busybox binary.
+	bin pkg.File
+}
+
+// Kind returns the hardcoded [pkg.Kind] value.
+func (a busyboxBin) Kind() pkg.Kind { return kindBusyboxBin }
+
+// Params is a noop.
+func (a busyboxBin) Params(*pkg.IContext) {}
+
+// Dependencies returns the underlying busybox [pkg.File].
+func (a busyboxBin) Dependencies() []pkg.Artifact {
+	return []pkg.Artifact{a.bin}
+}
+
+// String returns the reporting name of the underlying file prefixed with expand.
+func (a busyboxBin) String() string {
+	return "expand-" + a.bin.(fmt.Stringer).String()
+}
+
+// Cure installs the underlying busybox [pkg.File] to bin/busybox.
+func (a busyboxBin) Cure(t *pkg.TContext) (err error) {
+	var r io.ReadCloser
+	if r, err = t.Open(a.bin); err != nil {
+		return
+	}
+	defer func() {
+		closeErr := r.Close()
+		if err == nil {
+			err = closeErr
+		}
+	}()
+
+	binDir := t.GetWorkDir().Append("bin")
+	if err = os.MkdirAll(binDir.String(), 0700); err != nil {
+		return
+	}
+
+	var w *os.File
+	if w, err = os.OpenFile(
+		binDir.Append("busybox").String(),
+		os.O_WRONLY|os.O_CREATE|os.O_EXCL,
+		0500,
+	); err != nil {
+		return
+	}
+	defer func() {
+		closeErr := w.Close()
+		if err == nil {
+			err = closeErr
+		}
+	}()
+
+	_, err = io.Copy(w, r)
+	return
+}
+
+// newBusyboxBin returns a [pkg.Artifact] containing a busybox installation from
+// the https://busybox.net/downloads/binaries/ binary release.
+func newBusyboxBin() pkg.Artifact {
+	const (
+		version  = "1.35.0"
+		checksum = "L7OBIsPu9enNHn7FqpBT1kOg_mCLNmetSeNMA3i4Y60Z5jTgnlX3qX3zcQtLx5AB"
+	)
+	return pkg.NewExec(
+		"busybox-bin-"+version, nil, pkg.ExecTimeoutMax, fhs.AbsRoot, []string{
+			"PATH=/system/bin",
+		},
+		AbsSystem.Append("bin", "busybox"),
+		[]string{"hush", "-c", "" +
+			"busybox mkdir -p /work/system/bin/ && " +
+			"busybox cp /system/bin/busybox /work/system/bin/ && " +
+			"busybox --install -s /work/system/bin/"},
+		pkg.Path(AbsSystem, true, busyboxBin{pkg.NewHTTPGet(
+			&http.Client{Transport: &http.Transport{
+				// busybox website is really slow to respond
+				TLSHandshakeTimeout: 2 * time.Minute,
+			}},
+			"https://busybox.net/downloads/binaries/"+
+				version+"-"+linuxArch()+"-linux-musl/busybox",
+			mustDecode(checksum),
+		)}),
+	)
+}

internal/rosa/rosa.go

@@ -2,10 +2,49 @@
 package rosa
 
 import (
+	"log"
+	"runtime"
+
+	"hakurei.app/container/fhs"
 	"hakurei.app/internal/pkg"
 )
 
 const (
 	// kindEtc is the kind of [pkg.Artifact] of cureEtc.
 	kindEtc = iota + pkg.KindCustomOffset
+
+	// kindBusyboxBin is the kind of [pkg.Artifact] of busyboxBin.
+	kindBusyboxBin
 )
+
+// mustDecode is like [pkg.MustDecode], but replaces the zero value and prints
+// a warning.
+func mustDecode(s string) pkg.Checksum {
+	var fallback = pkg.Checksum{}
+	if s == "" {
+		log.Println(
+			"falling back to",
+			pkg.Encode(fallback),
+			"for unpopulated checksum",
+		)
+		return fallback
+	}
+	return pkg.MustDecode(s)
+}
+
+var (
+	// AbsSystem is the Rosa OS installation prefix.
+	AbsSystem = fhs.AbsRoot.Append("system")
+)
+
+// linuxArch returns the architecture name used by linux corresponding to
+// [runtime.GOARCH].
+func linuxArch() string {
+	switch runtime.GOARCH {
+	case "amd64":
+		return "x86_64"
+
+	default:
+		panic("unsupported target " + runtime.GOARCH)
+	}
+}