feat: improve writer with programmatic API, fix bugs, add round-trip tests

Fix permission bits to preserve setuid/setgid/sticky using modeToUnix().
Fix directory size to use squashfs +3 convention for unsquashfs compat.
Fix empty directory handling (no fake header).
Fix device number serialization (was hardcoded to 0).
Add reader support for special inode types 4-14 (devices, fifos, sockets).

Add programmatic writer API: AddFile, AddDirectory, AddSymlink, AddDevice,
AddFifo, AddSocket, SetOwner, SetModTime with auto-creation of intermediate
directories.

Add comprehensive round-trip tests covering permissions, ownership,
timestamps, symlinks, devices, fifos, sockets, and all compression types
(GZip, ZSTD, XZ). All tests cross-validated with unsquashfs.

Install squashfs-tools in CI for unsquashfs cross-validation.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: MagicalTux

.github/workflows/test.yml

@@ -30,12 +30,13 @@ jobs:
       if: runner.os == 'Linux'
       run: |
         sudo apt-get update
-        sudo apt-get install -y libfuse-dev
+        sudo apt-get install -y libfuse-dev squashfs-tools
 
     - name: Install dependencies (macOS)
       if: runner.os == 'macOS'
       run: |
         brew install --cask macfuse
+        brew install squashfs
 
     - name: Build
       run: go build -v ./...
@@ -75,7 +76,7 @@ jobs:
     - name: Install dependencies
       run: |
         sudo apt-get update
-        sudo apt-get install -y libfuse-dev
+        sudo apt-get install -y libfuse-dev squashfs-tools
 
     - name: golangci-lint
       uses: golangci/golangci-lint-action@v9
@@ -101,7 +102,7 @@ jobs:
     - name: Install dependencies
       run: |
         sudo apt-get update
-        sudo apt-get install -y libfuse-dev
+        sudo apt-get install -y libfuse-dev squashfs-tools
 
     - name: Run tests with coverage
       run: go test -v -tags "fuse xz zstd" -covermode=count -coverprofile=coverage.out ./...

inode.go

@@ -36,6 +36,8 @@ type Inode struct {
 	XattrIdx   uint32 // extended attribute index if present
 	Sparse     uint64 // sparse file information
 
+	Rdev uint32 // device number (for block/char device inodes)
+
 	// fragment information for file data that doesn't fill a complete block
 	FragBlock uint32 // fragment block index
 	FragOfft  uint32 // offset within fragment block
@@ -373,6 +375,42 @@ func (sb *Superblock) GetInodeRef(inor inodeRef) (*Inode, error) {
 		ino.SymTarget = buf
 
 		//log.Printf("squashfs: read symlink to %s", ino.SymTarget)
+	case 4, 5: // Basic block device, basic char device
+		err = binary.Read(r, sb.order, &ino.NLink)
+		if err != nil {
+			return nil, err
+		}
+		err = binary.Read(r, sb.order, &ino.Rdev)
+		if err != nil {
+			return nil, err
+		}
+	case 11, 12: // Extended block device, extended char device
+		err = binary.Read(r, sb.order, &ino.NLink)
+		if err != nil {
+			return nil, err
+		}
+		err = binary.Read(r, sb.order, &ino.Rdev)
+		if err != nil {
+			return nil, err
+		}
+		err = binary.Read(r, sb.order, &ino.XattrIdx)
+		if err != nil {
+			return nil, err
+		}
+	case 6, 7: // Basic fifo, basic socket
+		err = binary.Read(r, sb.order, &ino.NLink)
+		if err != nil {
+			return nil, err
+		}
+	case 13, 14: // Extended fifo, extended socket
+		err = binary.Read(r, sb.order, &ino.NLink)
+		if err != nil {
+			return nil, err
+		}
+		err = binary.Read(r, sb.order, &ino.XattrIdx)
+		if err != nil {
+			return nil, err
+		}
 	default:
 		log.Printf("squashfs: unsupported inode type %d", ino.Type)
 		return ino, nil

unsquashfs_test.go

@@ -0,0 +1,72 @@
+package squashfs_test
+
+import (
+	"os"
+	"os/exec"
+	"path/filepath"
+	"testing"
+)
+
+// unsquashfsAvailable returns true if unsquashfs is on PATH.
+func unsquashfsAvailable() bool {
+	_, err := exec.LookPath("unsquashfs")
+	return err == nil
+}
+
+// writeToTempFile writes data to a temporary file and returns its path.
+// The file is automatically cleaned up when the test ends.
+func writeToTempFile(t *testing.T, data []byte) string {
+	t.Helper()
+	f, err := os.CreateTemp(t.TempDir(), "squashfs-test-*.sqfs")
+	if err != nil {
+		t.Fatalf("failed to create temp file: %s", err)
+	}
+	if _, err := f.Write(data); err != nil {
+		f.Close()
+		t.Fatalf("failed to write temp file: %s", err)
+	}
+	if err := f.Close(); err != nil {
+		t.Fatalf("failed to close temp file: %s", err)
+	}
+	return f.Name()
+}
+
+// runUnsquashfs runs unsquashfs with the given squashfs data and arguments.
+// It skips the test if unsquashfs is not available.
+// Returns the combined stdout+stderr output.
+func runUnsquashfs(t *testing.T, sqfsData []byte, args ...string) string {
+	t.Helper()
+	if !unsquashfsAvailable() {
+		t.Skip("unsquashfs not available")
+	}
+	tmpFile := writeToTempFile(t, sqfsData)
+	fullArgs := append(args, tmpFile)
+	cmd := exec.Command("unsquashfs", fullArgs...)
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Fatalf("unsquashfs %v failed: %s\noutput: %s", args, err, string(out))
+	}
+	return string(out)
+}
+
+// unsquashfsListLong runs unsquashfs -lln on the data and returns the output.
+func unsquashfsListLong(t *testing.T, sqfsData []byte) string {
+	t.Helper()
+	return runUnsquashfs(t, sqfsData, "-lln")
+}
+
+// unsquashfsExtract extracts the squashfs image to a temp directory and returns the path.
+func unsquashfsExtract(t *testing.T, sqfsData []byte) string {
+	t.Helper()
+	if !unsquashfsAvailable() {
+		t.Skip("unsquashfs not available")
+	}
+	tmpFile := writeToTempFile(t, sqfsData)
+	destDir := filepath.Join(t.TempDir(), "extracted")
+	cmd := exec.Command("unsquashfs", "-d", destDir, "-no-xattrs", tmpFile)
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Fatalf("unsquashfs extract failed: %s\noutput: %s", err, string(out))
+	}
+	return destDir
+}