package writer
import (
"fmt"
"io"
"path"
storev1pb "code.tvl.fyi/tvix/store/protos"
"github.com/nix-community/go-nix/pkg/nar"
)
type DirectoryLookupFn func([]byte) (*storev1pb.Directory, error)
type BlobLookupFn func([]byte) (io.ReadCloser, error)
// Export will traverse a given pathInfo structure, and write the contents
// in NAR format to the passed Writer.
// It uses directoryLookupFn and blobLookupFn to resolve references.
func Export(
w io.Writer,
pathInfo *storev1pb.PathInfo,
directoryLookupFn DirectoryLookupFn,
blobLookupFn BlobLookupFn,
) error {
// initialize a NAR writer
narWriter, err := nar.NewWriter(w)
if err != nil {
return fmt.Errorf("unable to initialize nar writer: %w", err)
}
defer narWriter.Close()
// populate rootHeader
rootHeader := &nar.Header{
Path: "/",
}
// populate a stack
// we will push paths and directories to it when entering a directory,
// and emit individual elements to the NAR writer, draining the Directory object.
// once it's empty, we can pop it off the stack.
var stackPaths = []string{}
var stackDirectories = []*storev1pb.Directory{}
// peek at the pathInfo root and assemble the root node and write to writer
// in the case of a regular file, we retrieve and write the contents, close and exit
// in the case of a symlink, we write the symlink, close and exit
switch v := (pathInfo.GetNode().GetNode()).(type) {
case *storev1pb.Node_File:
rootHeader.Type = nar.TypeRegular
rootHeader.Size = int64(v.File.GetSize())
rootHeader.Executable = v.File.GetExecutable()
err := narWriter.WriteHeader(rootHeader)
if err != nil {
return fmt.Errorf("unable to write root header: %w", err)
}
// if it's a regular file, retrieve and write the contents
blobReader, err := blobLookupFn(v.File.GetDigest())
if err != nil {
return fmt.Errorf("unable to lookup blob: %w", err)
}
defer blobReader.Close()
_, err = io.Copy(narWriter, blobReader)
if err != nil {
return fmt.Errorf("unable to read from blobReader: %w", err)
}
err = blobReader.Close()
if err != nil {
return fmt.Errorf("unable to close content reader: %w", err)
}
err = narWriter.Close()
if err != nil {
return fmt.Errorf("unable to close nar reader: %w", err)
}
return nil
case *storev1pb.Node_Symlink:
rootHeader.Type = nar.TypeSymlink
rootHeader.LinkTarget = string(v.Symlink.GetTarget())
err := narWriter.WriteHeader(rootHeader)
if err != nil {
return fmt.Errorf("unable to write root header: %w", err)
}
err = narWriter.Close()
if err != nil {
return fmt.Errorf("unable to close nar reader: %w", err)
}
return nil
case *storev1pb.Node_Directory:
// We have a directory at the root, look it up and put in on the stack.
directory, err := directoryLookupFn(v.Directory.Digest)
if err != nil {
return fmt.Errorf("unable to lookup directory: %w", err)
}
stackDirectories = append(stackDirectories, directory)
stackPaths = append(stackPaths, "/")
err = narWriter.WriteHeader(&nar.Header{
Path: "/",
Type: nar.TypeDirectory,
})
if err != nil {
return fmt.Errorf("error writing header: %w", err)
}
}
// as long as the stack is not empty, we keep running.
for {
if len(stackDirectories) == 0 {
return nil
}
// Peek at the current top of the stack.
topOfStack := stackDirectories[len(stackDirectories)-1]
topOfStackPath := stackPaths[len(stackPaths)-1]
// get the next element that's lexicographically smallest, and drain it from
// the current directory on top of the stack.
nextNode := drainNextNode(topOfStack)
// If nextNode returns nil, there's nothing left in the directory node, so we
// can emit it from the stack.
// Contrary to the import case, we don't emit the node popping from the stack, but when pushing.
if nextNode == nil {
// pop off stack
stackDirectories = stackDirectories[:len(stackDirectories)-1]
stackPaths = stackPaths[:len(stackPaths)-1]
continue
}
switch n := (nextNode).(type) {
case *storev1pb.DirectoryNode:
err := narWriter.WriteHeader(&nar.Header{
Path: path.Join(topOfStackPath, string(n.GetName())),
Type: nar.TypeDirectory,
})
if err != nil {
return fmt.Errorf("unable to write nar header: %w", err)
}
d, err := directoryLookupFn(n.GetDigest())
if err != nil {
return fmt.Errorf("unable to lookup directory: %w", err)
}
// add to stack
stackDirectories = append(stackDirectories, d)
stackPaths = append(stackPaths, path.Join(topOfStackPath, string(n.GetName())))
case *storev1pb.FileNode:
err := narWriter.WriteHeader(&nar.Header{
Path: path.Join(topOfStackPath, string(n.GetName())),
Type: nar.TypeRegular,
Size: int64(n.GetSize()),
Executable: n.GetExecutable(),
})
if err != nil {
return fmt.Errorf("unable to write nar header: %w", err)
}
// copy file contents
contentReader, err := blobLookupFn(n.GetDigest())
if err != nil {
return fmt.Errorf("unable to get blob: %w", err)
}
defer contentReader.Close()
_, err = io.Copy(narWriter, contentReader)
if err != nil {
return fmt.Errorf("unable to copy contents from contentReader: %w", err)
}
err = contentReader.Close()
if err != nil {
return fmt.Errorf("unable to close content reader: %w", err)
}
case *storev1pb.SymlinkNode:
err := narWriter.WriteHeader(&nar.Header{
Path: path.Join(topOfStackPath, string(n.GetName())),
Type: nar.TypeSymlink,
LinkTarget: string(n.GetTarget()),
})
if err != nil {
return fmt.Errorf("unable to write nar header: %w", err)
}
}
}
}
// TODO: add validation functions to Directory in both rust and golang, to
// validate the keys in directories, files and symlinks are sorted.
// drainNextNode will drain a directory message with one of its child nodes,
// whichever comes first alphabetically.
func drainNextNode(d *storev1pb.Directory) interface{} {
switch v := (smallestNode(d)).(type) {
case *storev1pb.DirectoryNode:
d.Directories = d.Directories[1:]
return v
case *storev1pb.FileNode:
d.Files = d.Files[1:]
return v
case *storev1pb.SymlinkNode:
d.Symlinks = d.Symlinks[1:]
return v
case nil:
return nil
default:
panic("invalid type encountered")
}
}
// smallestNode will return the node from a directory message,
// whichever comes first alphabetically.
func smallestNode(d *storev1pb.Directory) interface{} {
childDirectories := d.GetDirectories()
childFiles := d.GetFiles()
childSymlinks := d.GetSymlinks()
if len(childDirectories) > 0 {
if len(childFiles) > 0 {
if len(childSymlinks) > 0 {
// directories,files,symlinks
return smallerNode(smallerNode(childDirectories[0], childFiles[0]), childSymlinks[0])
} else {
// directories,files,!symlinks
return smallerNode(childDirectories[0], childFiles[0])
}
} else {
// directories,!files
if len(childSymlinks) > 0 {
// directories,!files,symlinks
return smallerNode(childDirectories[0], childSymlinks[0])
} else {
// directories,!files,!symlinks
return childDirectories[0]
}
}
} else {
// !directories
if len(childFiles) > 0 {
// !directories,files
if len(childSymlinks) > 0 {
// !directories,files,symlinks
return smallerNode(childFiles[0], childSymlinks[0])
} else {
// !directories,files,!symlinks
return childFiles[0]
}
} else {
//!directories,!files
if len(childSymlinks) > 0 {
//!directories,!files,symlinks
return childSymlinks[0]
} else {
//!directories,!files,!symlinks
return nil
}
}
}
}
// smallerNode compares two nodes by their name,
// and returns the one with the smaller name.
// both nodes may not be nil, we do check for these cases in smallestNode.
func smallerNode(a interface{ GetName() []byte }, b interface{ GetName() []byte }) interface{ GetName() []byte } {
if string(a.GetName()) < string(b.GetName()) {
return a
} else {
return b
}
}
