zip: add support for symlink extraction (#39)

Signed-off-by: Jakub Wójtowicz <jakub.wojtowic@gmail.com>

Author: sephriot

testdata/symlinks.zip

@@ -8,6 +8,7 @@ import (
 	"io"
 	"io/fs"
 	"log"
+	"os"
 	"path"
 	"strings"
 
@@ -215,10 +216,16 @@ func (z Zip) Extract(ctx context.Context, sourceArchive io.Reader, handleFile Fi
 		}
 
 		info := f.FileInfo()
+		linkTarget, err := z.getLinkTarget(f)
+		if err != nil {
+			return fmt.Errorf("getting link target for file %d: %s: %w", i, f.Name, err)
+		}
+
 		file := FileInfo{
 			FileInfo:      info,
 			Header:        f.FileHeader,
 			NameInArchive: f.Name,
+			LinkTarget:    linkTarget,
 			Open: func() (fs.File, error) {
 				openedFile, err := f.Open()
 				if err != nil {
@@ -228,7 +235,7 @@ func (z Zip) Extract(ctx context.Context, sourceArchive io.Reader, handleFile Fi
 			},
 		}
 
-		err := handleFile(ctx, file)
+		err = handleFile(ctx, file)
 		if errors.Is(err, fs.SkipAll) {
 			break
 		} else if errors.Is(err, fs.SkipDir) && file.IsDir() {
@@ -264,6 +271,33 @@ func (z Zip) decodeText(hdr *zip.FileHeader) {
 	}
 }
 
+func (z Zip) getLinkTarget(f *zip.File) (string, error) {
+	info := f.FileInfo()
+	// Exit early if not a symlink
+	if info.Mode()&os.ModeSymlink == 0 {
+		return "", nil
+	}
+
+	// Open the file and read the link target
+	file, err := f.Open()
+	if err != nil {
+		return "", err
+	}
+	defer file.Close()
+
+	const maxLinkTargetSize = 32768
+	linkTargetBytes, err := io.ReadAll(io.LimitReader(file, maxLinkTargetSize))
+	if err != nil {
+		return "", err
+	}
+
+	if len(linkTargetBytes) == maxLinkTargetSize {
+		return "", fmt.Errorf("link target is too large: %d bytes", len(linkTargetBytes))
+	}
+
+	return string(linkTargetBytes), nil
+}
+
 // Insert appends the listed files into the provided Zip archive stream.
 // If the filename already exists in the archive, it will be replaced.
 func (z Zip) Insert(ctx context.Context, into io.ReadWriteSeeker, files []FileInfo) error {

zip.go

@@ -0,0 +1,38 @@
+package archives
+
+import (
+	"context"
+	"os"
+	"reflect"
+	"sort"
+	"testing"
+)
+
+func TestZip_ExtractZipWithSymlinks(t *testing.T) {
+	zipFile, err := os.Open("testdata/symlinks.zip")
+	if err != nil {
+		t.Errorf("failed to open zip file: %v", err)
+	}
+	defer zipFile.Close()
+
+	zip := Zip{}
+	extractedFiles := []string{}
+	zip.Extract(context.Background(), zipFile, func(ctx context.Context, file FileInfo) error {
+		extractedFiles = append(extractedFiles, file.Name())
+		if file.Name() == "symlinked" {
+			if file.LinkTarget != "../a/hello" {
+				t.Errorf("expected symlink target to be '../a/hello', got %s", file.LinkTarget)
+			}
+		}
+		return nil
+	})
+
+	if len(extractedFiles) != 5 {
+		t.Errorf("expected 5 files to be extracted, got %d", len(extractedFiles))
+	}
+	sort.Strings(extractedFiles)
+	expectedFiles := []string{"a", "b", "hello", "symlinked", "zip_test"}
+	if !reflect.DeepEqual(extractedFiles, expectedFiles) {
+		t.Errorf("expected files to be %v, got %v", expectedFiles, extractedFiles)
+	}
+}