1 files changed, 212 insertions, 0 deletions
diff --git a/tvix/castore-go/castore.go b/tvix/castore-go/castore.go
new file mode 100644
index 000000000000..c9e3757885a0
--- /dev/null
+++ b/tvix/castore-go/castore.go
@@ -0,0 +1,212 @@
+package castorev1
+
+import (
+	"bytes"
+	"encoding/base64"
+	"fmt"
+
+	"google.golang.org/protobuf/proto"
+	"lukechampine.com/blake3"
+)
+
+// The size of a directory is calculated by summing up the numbers of
+// `directories`, `files` and `symlinks`, and for each directory, its size
+// field.
+func (d *Directory) Size() uint32 {
+	var size uint32
+	size = uint32(len(d.Files) + len(d.Symlinks))
+	for _, d := range d.Directories {
+		size += 1 + d.Size
+	}
+	return size
+}
+
+func (d *Directory) Digest() ([]byte, error) {
+	b, err := proto.MarshalOptions{
+		Deterministic: true,
+	}.Marshal(d)
+
+	if err != nil {
+		return nil, fmt.Errorf("error while marshalling directory: %w", err)
+	}
+
+	h := blake3.New(32, nil)
+
+	_, err = h.Write(b)
+	if err != nil {
+		return nil, fmt.Errorf("error writing to hasher: %w", err)
+	}
+
+	return h.Sum(nil), nil
+}
+
+// isValidName checks a name for validity.
+// We disallow slashes, null bytes, '.', '..' and the empty string.
+// Depending on the context, a *Node message with an empty string as name is
+// allowed, but they don't occur inside a Directory message.
+func isValidName(n []byte) bool {
+	if len(n) == 0 || bytes.Equal(n, []byte("..")) || bytes.Equal(n, []byte{'.'}) || bytes.Contains(n, []byte{'\x00'}) || bytes.Contains(n, []byte{'/'}) {
+		return false
+	}
+	return true
+}
+
+// Validate ensures a DirectoryNode has a valid name and correct digest len.
+func (n *DirectoryNode) Validate() error {
+	if len(n.Digest) != 32 {
+		return fmt.Errorf("invalid digest length for %s, expected %d, got %d", n.Name, 32, len(n.Digest))
+	}
+
+	if !isValidName(n.Name) {
+		return fmt.Errorf("invalid node name: %s", n.Name)
+	}
+
+	return nil
+}
+
+// Validate ensures a FileNode has a valid name and correct digest len.
+func (n *FileNode) Validate() error {
+	if len(n.Digest) != 32 {
+		return fmt.Errorf("invalid digest length for %s, expected %d, got %d", n.Name, 32, len(n.Digest))
+	}
+
+	if !isValidName(n.Name) {
+		return fmt.Errorf("invalid node name: %s", n.Name)
+	}
+
+	return nil
+}
+
+// Validate ensures a SymlinkNode has a valid name and target.
+func (n *SymlinkNode) Validate() error {
+	if len(n.Target) == 0 || bytes.Contains(n.Target, []byte{0}) {
+		return fmt.Errorf("invalid symlink target: %s", n.Target)
+	}
+
+	if !isValidName(n.Name) {
+		return fmt.Errorf("invalid node name: %s", n.Name)
+	}
+
+	return nil
+}
+
+// Validate ensures a node is valid, by dispatching to the per-type validation functions.
+func (n *Node) Validate() error {
+	if node := n.GetDirectory(); node != nil {
+		if err := node.Validate(); err != nil {
+			return fmt.Errorf("SymlinkNode failed validation: %w", err)
+		}
+	} else if node := n.GetFile(); node != nil {
+		if err := node.Validate(); err != nil {
+			return fmt.Errorf("FileNode failed validation: %w", err)
+		}
+	} else if node := n.GetSymlink(); node != nil {
+		if err := node.Validate(); err != nil {
+			return fmt.Errorf("SymlinkNode failed validation: %w", err)
+		}
+
+	} else {
+		// this would only happen if we introduced a new type
+		return fmt.Errorf("no specific node found")
+	}
+
+	return nil
+}
+
+// Validate thecks the Directory message for invalid data, such as:
+// - violations of name restrictions
+// - invalid digest lengths
+// - not properly sorted lists
+// - duplicate names in the three lists
+func (d *Directory) Validate() error {
+	// seenNames contains all seen names so far.
+	// We populate this to ensure node names are unique across all three lists.
+	seenNames := make(map[string]interface{})
+
+	// We also track the last seen name in each of the three lists,
+	// to ensure nodes are sorted by their names.
+	var lastDirectoryName, lastFileName, lastSymlinkName []byte
+
+	// helper function to only insert in sorted order.
+	// used with the three lists above.
+	// Note this consumes a *pointer to* a string,  as it mutates it.
+	insertIfGt := func(lastName *[]byte, name []byte) error {
+		// update if it's greater than the previous name
+		if bytes.Compare(name, *lastName) == 1 {
+			*lastName = name
+			return nil
+		} else {
+			return fmt.Errorf("%v is not in sorted order", name)
+		}
+	}
+
+	// insertOnce inserts into seenNames if the key doesn't exist yet.
+	insertOnce := func(name []byte) error {
+		encoded := base64.StdEncoding.EncodeToString(name)
+		if _, found := seenNames[encoded]; found {
+			return fmt.Errorf("duplicate name: %v", string(name))
+		}
+		seenNames[encoded] = nil
+		return nil
+	}
+
+	// Loop over all Directories, Files and Symlinks individually,
+	// check them for validity, then check for sorting in the current list, and
+	// uniqueness across all three lists.
+	for _, directoryNode := range d.Directories {
+		directoryName := directoryNode.GetName()
+
+		if err := directoryNode.Validate(); err != nil {
+			return fmt.Errorf("DirectoryNode %s failed validation: %w", directoryName, err)
+		}
+
+		// ensure names are sorted
+		if err := insertIfGt(&lastDirectoryName, directoryName); err != nil {
+			return err
+		}
+
+		// add to seenNames
+		if err := insertOnce(directoryName); err != nil {
+			return err
+		}
+
+	}
+
+	for _, fileNode := range d.Files {
+		fileName := fileNode.GetName()
+
+		if err := fileNode.Validate(); err != nil {
+			return fmt.Errorf("FileNode %s failed validation: %w", fileName, err)
+		}
+
+		// ensure names are sorted
+		if err := insertIfGt(&lastFileName, fileName); err != nil {
+			return err
+		}
+
+		// add to seenNames
+		if err := insertOnce(fileName); err != nil {
+			return err
+		}
+	}
+
+	for _, symlinkNode := range d.Symlinks {
+		symlinkName := symlinkNode.GetName()
+
+		if err := symlinkNode.Validate(); err != nil {
+			return fmt.Errorf("SymlinkNode %s failed validation: %w", symlinkName, err)
+		}
+
+		// ensure names are sorted
+		if err := insertIfGt(&lastSymlinkName, symlinkName); err != nil {
+			return err
+		}
+
+		// add to seenNames
+		if err := insertOnce(symlinkName); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}