package reader import ( "context" "crypto/sha256" "errors" "fmt" "io" "path" "strings" castorev1pb "code.tvl.fyi/tvix/castore/protos" storev1pb "code.tvl.fyi/tvix/store/protos" "github.com/nix-community/go-nix/pkg/nar" "lukechampine.com/blake3" ) type Reader struct { hrSha256 *Hasher } // An item on the directories stack type item struct { path string directory *castorev1pb.Directory } func New(r io.Reader) *Reader { // Instead of using the underlying reader itself, wrap the reader // with a hasher calculating sha256 and one calculating sha512, // and feed that one into the NAR reader. hrSha256 := NewHasher(r, sha256.New()) return &Reader{ hrSha256: hrSha256, } } // Import reads from the internally-wrapped reader, // and calls the callback functions whenever regular file contents are // encountered, or a Directory node is about to be finished. func (r *Reader) Import( ctx context.Context, // callback function called with each regular file content blobCb func(fileReader io.Reader) error, // callback function called with each finalized directory node directoryCb func(directory *castorev1pb.Directory) error, ) (*storev1pb.PathInfo, error) { // construct a NAR reader, by reading through hrSha256 narReader, err := nar.NewReader(r.hrSha256) if err != nil { return 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 = []item{} // 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] // if there's still a parent left on the stack, refer to it from there. if len(stack) > 0 { dgst, err := toPop.directory.Digest() if err != nil { return fmt.Errorf("unable to calculate directory digest: %w", err) } topOfStack := stack[len(stack)-1].directory topOfStack.Directories = append(topOfStack.Directories, &castorev1pb.DirectoryNode{ Name: []byte(path.Base(toPop.path)), Digest: dgst, Size: toPop.directory.Size(), }) } // call the directoryCb if err := directoryCb(toPop.directory); err != nil { return fmt.Errorf("failed calling directoryCb: %w", err) } // Keep track that we have encounter at least one directory stackDirectory = toPop.directory return nil } // Assemble a PathInfo struct, the Node is populated later. assemblePathInfo := func() *storev1pb.PathInfo { return &storev1pb.PathInfo{ Node: nil, References: [][]byte{}, Narinfo: &storev1pb.NARInfo{ NarSize: uint64(r.hrSha256.BytesWritten()), NarSha256: r.hrSha256.Sum(nil), Signatures: []*storev1pb.NARInfo_Signature{}, ReferenceNames: []string{}, }, } } 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, 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, 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, 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, fmt.Errorf("unable to pop from stack: %w", err) } } // Stack is empty. We now either have a regular or symlink root node, or we encountered at least one directory. // assemble pathInfo with these and return. pi := assemblePathInfo() if rootFile != nil { pi.Node = &castorev1pb.Node{ Node: &castorev1pb.Node_File{ File: rootFile, }, } } if rootSymlink != nil { pi.Node = &castorev1pb.Node{ Node: &castorev1pb.Node_Symlink{ Symlink: rootSymlink, }, } } if stackDirectory != nil { // calculate directory digest (i.e. after we received all its contents) dgst, err := stackDirectory.Digest() if err != nil { return nil, fmt.Errorf("unable to calculate root directory digest: %w", err) } pi.Node = &castorev1pb.Node{ Node: &castorev1pb.Node_Directory{ Directory: &castorev1pb.DirectoryNode{ Name: []byte{}, Digest: dgst, Size: stackDirectory.Size(), }, }, } } return pi, nil } // 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, 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 calculating the blake3 hash fileReader := NewHasher(narReader, blake3.New(32, nil)) err := blobCb(fileReader) if err != nil { return nil, fmt.Errorf("failure from blobCb: %w", err) } // drive the file reader to the end, in case the CB function doesn't read // all the way to the end on its own if fileReader.BytesWritten() != uint32(hdr.Size) { _, err := io.ReadAll(fileReader) if err != nil { return nil, fmt.Errorf("unable to read until the end of the file content: %w", err) } } // read the blake3 hash dgst := fileReader.Sum(nil) fileNode := &castorev1pb.FileNode{ Name: []byte(getBasename(hdr.Path)), Digest: dgst, 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, item{ directory: directory, path: hdr.Path, }) } } } }