package importer import ( "context" "crypto/sha256" "errors" "fmt" "io" "path" "strings" castorev1pb "code.tvl.fyi/tvix/castore-go" "github.com/nix-community/go-nix/pkg/nar" ) // An item on the directories stack type stackItem struct { path string directory *castorev1pb.Directory } // Import reads a NAR from a reader, and returns a the root node, // NAR size and NAR sha256 digest. func Import( // a context, to support cancellation ctx context.Context, // The reader the data is read from r io.Reader, // callback function called with each regular file content blobCb func(fileReader io.Reader) ([]byte, error), // callback function called with each finalized directory node directoryCb func(directory *castorev1pb.Directory) ([]byte, error), ) (*castorev1pb.Node, uint64, []byte, error) { // We need to wrap the underlying reader a bit. // - we want to keep track of the number of bytes read in total // - we calculate the sha256 digest over all data read // Express these two things in a MultiWriter, and give the NAR reader a // TeeReader that writes to it. narCountW := &CountingWriter{} sha256W := sha256.New() multiW := io.MultiWriter(narCountW, sha256W) narReader, err := nar.NewReader(io.TeeReader(r, multiW)) if err != nil { return nil, 0, nil, fmt.Errorf("failed to instantiate nar reader: %w", err) } defer narReader.Close() // If we store a symlink or regular file at the root, these are not nil. // If they are nil, we instead have a stackDirectory. var rootSymlink *castorev1pb.SymlinkNode var rootFile *castorev1pb.FileNode var stackDirectory *castorev1pb.Directory var stack = []stackItem{} // popFromStack is used when we transition to a different directory or // drain the stack when we reach the end of the NAR. // It adds the popped element to the element underneath if any, // and passes it to the directoryCb callback. // This function may only be called if the stack is not already empty. popFromStack := func() error { // Keep the top item, and "resize" the stack slice. // This will only make the last element unaccessible, but chances are high // we're re-using that space anyways. toPop := stack[len(stack)-1] stack = stack[:len(stack)-1] // call the directoryCb directoryDigest, err := directoryCb(toPop.directory) if err != nil { return fmt.Errorf("failed calling directoryCb: %w", err) } // if there's still a parent left on the stack, refer to it from there. if len(stack) > 0 { topOfStack := stack[len(stack)-1].directory topOfStack.Directories = append(topOfStack.Directories, &castorev1pb.DirectoryNode{ Name: []byte(path.Base(toPop.path)), Digest: directoryDigest, Size: toPop.directory.Size(), }) } // Keep track that we have encounter at least one directory stackDirectory = toPop.directory return nil } getBasename := func(p string) string { // extract the basename. In case of "/", replace with empty string. basename := path.Base(p) if basename == "/" { basename = "" } return basename } for { select { case <-ctx.Done(): return nil, 0, nil, ctx.Err() default: // call narReader.Next() to get the next element hdr, err := narReader.Next() // If this returns an error, it's either EOF (when we're done reading from the NAR), // or another error. if err != nil { // if this returns no EOF, bail out if !errors.Is(err, io.EOF) { return nil, 0, nil, fmt.Errorf("failed getting next nar element: %w", err) } // The NAR has been read all the way to the end… // Make sure we close the nar reader, which might read some final trailers. if err := narReader.Close(); err != nil { return nil, 0, nil, fmt.Errorf("unable to close nar reader: %w", err) } // Check the stack. While it's not empty, we need to pop things off the stack. for len(stack) > 0 { err := popFromStack() if err != nil { return nil, 0, nil, fmt.Errorf("unable to pop from stack: %w", err) } } // Stack is empty. // Now either root{File,Symlink,Directory} is not nil, // and we can return the root node. narSize := narCountW.BytesWritten() narSha256 := sha256W.Sum(nil) if rootFile != nil { return &castorev1pb.Node{ Node: &castorev1pb.Node_File{ File: rootFile, }, }, narSize, narSha256, nil } else if rootSymlink != nil { return &castorev1pb.Node{ Node: &castorev1pb.Node_Symlink{ Symlink: rootSymlink, }, }, narSize, narSha256, nil } else if stackDirectory != nil { // calculate directory digest (i.e. after we received all its contents) dgst, err := stackDirectory.Digest() if err != nil { return nil, 0, nil, fmt.Errorf("unable to calculate root directory digest: %w", err) } return &castorev1pb.Node{ Node: &castorev1pb.Node_Directory{ Directory: &castorev1pb.DirectoryNode{ Name: []byte{}, Digest: dgst, Size: stackDirectory.Size(), }, }, }, narSize, narSha256, nil } else { return nil, 0, nil, fmt.Errorf("no root set") } } // Check for valid path transitions, pop from stack if needed // The nar reader already gives us some guarantees about ordering and illegal transitions, // So we really only need to check if the top-of-stack path is a prefix of the path, // and if it's not, pop from the stack. We do this repeatedly until the top of the stack is // the subdirectory the new entry is in, or we hit the root directory. // We don't need to worry about the root node case, because we can only finish the root "/" // If we're at the end of the NAR reader (covered by the EOF check) for len(stack) > 1 && !strings.HasPrefix(hdr.Path, stack[len(stack)-1].path+"/") { err := popFromStack() if err != nil { return nil, 0, nil, fmt.Errorf("unable to pop from stack: %w", err) } } if hdr.Type == nar.TypeSymlink { symlinkNode := &castorev1pb.SymlinkNode{ Name: []byte(getBasename(hdr.Path)), Target: []byte(hdr.LinkTarget), } if len(stack) > 0 { topOfStack := stack[len(stack)-1].directory topOfStack.Symlinks = append(topOfStack.Symlinks, symlinkNode) } else { rootSymlink = symlinkNode } } if hdr.Type == nar.TypeRegular { // wrap reader with a reader counting the number of bytes read blobCountW := &CountingWriter{} blobReader := io.TeeReader(narReader, blobCountW) blobDigest, err := blobCb(blobReader) if err != nil { return nil, 0, nil, fmt.Errorf("failure from blobCb: %w", err) } // ensure blobCb did read all the way to the end. // If it didn't, the blobCb function is wrong and we should bail out. if blobCountW.BytesWritten() != uint64(hdr.Size) { panic("blobCB did not read to end") } fileNode := &castorev1pb.FileNode{ Name: []byte(getBasename(hdr.Path)), Digest: blobDigest, Size: uint32(hdr.Size), Executable: hdr.Executable, } if len(stack) > 0 { topOfStack := stack[len(stack)-1].directory topOfStack.Files = append(topOfStack.Files, fileNode) } else { rootFile = fileNode } } if hdr.Type == nar.TypeDirectory { directory := &castorev1pb.Directory{ Directories: []*castorev1pb.DirectoryNode{}, Files: []*castorev1pb.FileNode{}, Symlinks: []*castorev1pb.SymlinkNode{}, } stack = append(stack, stackItem{ directory: directory, path: hdr.Path, }) } } } }