From 3f4223879b1a89836879f6416f7ac1405dbc4fa6 Mon Sep 17 00:00:00 2001
From: MDietermann <mdietermann253@gmail.com>
Date: Tue, 14 Apr 2026 08:29:42 +0200
Subject: [PATCH] feat(platform): add tar.gz and zip extract helpers with
 traversal guard

---
 internal/platform/extract.go      | 114 ++++++++++++++++++++++++++++++
 internal/platform/extract_test.go |  80 +++++++++++++++++++++
 2 files changed, 194 insertions(+)
 create mode 100644 internal/platform/extract.go
 create mode 100644 internal/platform/extract_test.go

diff --git a/internal/platform/extract.go b/internal/platform/extract.go
new file mode 100644
index 0000000..d205530
--- /dev/null
+++ b/internal/platform/extract.go
@@ -0,0 +1,114 @@
+package platform
+
+import (
+	"archive/tar"
+	"archive/zip"
+	"compress/gzip"
+	"context"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+func safeJoin(dest, name string) (string, error) {
+	p := filepath.Join(dest, name)
+	cleanDest := filepath.Clean(dest) + string(os.PathSeparator)
+	if !strings.HasPrefix(filepath.Clean(p)+string(os.PathSeparator), cleanDest) {
+		return "", fmt.Errorf("unsafe path %q escapes %q", name, dest)
+	}
+	return p, nil
+}
+
+func ExtractTarGz(ctx context.Context, archivePath, destDir string) error {
+	f, err := os.Open(archivePath)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+	gz, err := gzip.NewReader(f)
+	if err != nil {
+		return err
+	}
+	defer gz.Close()
+	tr := tar.NewReader(gz)
+	for {
+		if err := ctx.Err(); err != nil {
+			return err
+		}
+		h, err := tr.Next()
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			return err
+		}
+		target, err := safeJoin(destDir, h.Name)
+		if err != nil {
+			return err
+		}
+		switch h.Typeflag {
+		case tar.TypeDir:
+			if err := os.MkdirAll(target, os.FileMode(h.Mode)); err != nil {
+				return err
+			}
+		case tar.TypeReg:
+			if err := os.MkdirAll(filepath.Dir(target), 0o755); err != nil {
+				return err
+			}
+			w, err := os.OpenFile(target, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, os.FileMode(h.Mode))
+			if err != nil {
+				return err
+			}
+			if _, err := io.Copy(w, tr); err != nil {
+				w.Close()
+				return err
+			}
+			w.Close()
+		}
+	}
+	return nil
+}
+
+func ExtractZip(ctx context.Context, archivePath, destDir string) error {
+	zr, err := zip.OpenReader(archivePath)
+	if err != nil {
+		return err
+	}
+	defer zr.Close()
+	for _, zf := range zr.File {
+		if err := ctx.Err(); err != nil {
+			return err
+		}
+		target, err := safeJoin(destDir, zf.Name)
+		if err != nil {
+			return err
+		}
+		if zf.FileInfo().IsDir() {
+			if err := os.MkdirAll(target, zf.Mode()); err != nil {
+				return err
+			}
+			continue
+		}
+		if err := os.MkdirAll(filepath.Dir(target), 0o755); err != nil {
+			return err
+		}
+		rc, err := zf.Open()
+		if err != nil {
+			return err
+		}
+		w, err := os.OpenFile(target, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, zf.Mode())
+		if err != nil {
+			rc.Close()
+			return err
+		}
+		_, err = io.Copy(w, rc)
+		rc.Close()
+		w.Close()
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
diff --git a/internal/platform/extract_test.go b/internal/platform/extract_test.go
new file mode 100644
index 0000000..7a652a1
--- /dev/null
+++ b/internal/platform/extract_test.go
@@ -0,0 +1,80 @@
+package platform
+
+import (
+	"archive/tar"
+	"archive/zip"
+	"compress/gzip"
+	"context"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func makeTarGz(t *testing.T, entries map[string]string) string {
+	t.Helper()
+	p := filepath.Join(t.TempDir(), "a.tar.gz")
+	f, err := os.Create(p)
+	if err != nil {
+		t.Fatal(err)
+	}
+	gz := gzip.NewWriter(f)
+	tw := tar.NewWriter(gz)
+	for name, body := range entries {
+		tw.WriteHeader(&tar.Header{Name: name, Mode: 0o644, Size: int64(len(body))})
+		tw.Write([]byte(body))
+	}
+	tw.Close()
+	gz.Close()
+	f.Close()
+	return p
+}
+
+func makeZip(t *testing.T, entries map[string]string) string {
+	t.Helper()
+	p := filepath.Join(t.TempDir(), "a.zip")
+	f, _ := os.Create(p)
+	zw := zip.NewWriter(f)
+	for name, body := range entries {
+		w, _ := zw.Create(name)
+		w.Write([]byte(body))
+	}
+	zw.Close()
+	f.Close()
+	return p
+}
+
+func TestExtractTarGz(t *testing.T) {
+	src := makeTarGz(t, map[string]string{"hello.txt": "world", "sub/x.txt": "y"})
+	dest := t.TempDir()
+	if err := ExtractTarGz(context.Background(), src, dest); err != nil {
+		t.Fatal(err)
+	}
+	got, _ := os.ReadFile(filepath.Join(dest, "hello.txt"))
+	if string(got) != "world" {
+		t.Fatalf("got %q", got)
+	}
+	got, _ = os.ReadFile(filepath.Join(dest, "sub", "x.txt"))
+	if string(got) != "y" {
+		t.Fatalf("got %q", got)
+	}
+}
+
+func TestExtractZip(t *testing.T) {
+	src := makeZip(t, map[string]string{"a.txt": "A"})
+	dest := t.TempDir()
+	if err := ExtractZip(context.Background(), src, dest); err != nil {
+		t.Fatal(err)
+	}
+	got, _ := os.ReadFile(filepath.Join(dest, "a.txt"))
+	if string(got) != "A" {
+		t.Fatalf("got %q", got)
+	}
+}
+
+func TestExtractRejectsPathTraversal(t *testing.T) {
+	src := makeTarGz(t, map[string]string{"../evil.txt": "x"})
+	dest := t.TempDir()
+	if err := ExtractTarGz(context.Background(), src, dest); err == nil {
+		t.Fatal("want error on path traversal")
+	}
+}