src/server/pfs/server/driver.go
func headerDirToPutFileRecords(tree hashtree.HashTree, path string, node *hashtree.NodeProto) (*pfs.PutFileRecords, error) {
	if node.DirNode == nil || node.DirNode.Shared == nil {
		return nil, fmt.Errorf("headerDirToPutFileRecords only works on header/footer dirs")
	}
	s := node.DirNode.Shared
	pfr := &pfs.PutFileRecords{
		Split: true,
	}
	if s.Header != nil {
		pfr.Header = &pfs.PutFileRecord{
			SizeBytes:  s.HeaderSize,
			ObjectHash: s.Header.Hash,
		}
	}
	if s.Footer != nil {
		pfr.Footer = &pfs.PutFileRecord{
			SizeBytes:  s.FooterSize,
			ObjectHash: s.Footer.Hash,
		}
	}
	if err := tree.List(path, func(child *hashtree.NodeProto) error {
		if child.FileNode == nil {
			return fmt.Errorf("header/footer dir contains child subdirectory, " +
				"which is invalid--header/footer dirs must be created by PutFileSplit")
		}
		for i, o := range child.FileNode.Objects {
			// same hack as copyFile--set size of first object to the size of the
			// whole subtree (and size of other objects to 0). I don't think
			// PutFileSplit files can have more than one object, but that invariant
			// isn't necessary to this code's correctness, so don't verify it.
			var size int64
			if i == 0 {
				size = child.SubtreeSize
			}
			pfr.Records = append(pfr.Records, &pfs.PutFileRecord{
				SizeBytes:  size,
				ObjectHash: o.Hash,
			})
		}
		return nil
	}); err != nil {
		return nil, err
	}
	return pfr, nil // TODO(msteffen) put something real here
}
func headerDirToPutFileRecords(tree hashtree.HashTree, path string, node *hashtree.NodeProto) (*pfs.PutFileRecords, error) {
	if node.DirNode == nil || node.DirNode.Shared == nil {
		return nil, fmt.Errorf("headerDirToPutFileRecords only works on header/footer dirs")
	}
	s := node.DirNode.Shared
	pfr := &pfs.PutFileRecords{
		Split: true,
	}
	if s.Header != nil {
		pfr.Header = &pfs.PutFileRecord{
			SizeBytes:  s.HeaderSize,
			ObjectHash: s.Header.Hash,
		}
	}
	if s.Footer != nil {
		pfr.Footer = &pfs.PutFileRecord{
			SizeBytes:  s.FooterSize,
			ObjectHash: s.Footer.Hash,
		}
	}
	if err := tree.List(path, func(child *hashtree.NodeProto) error {
		if child.FileNode == nil {
			return fmt.Errorf("header/footer dir contains child subdirectory, " +
				"which is invalid--header/footer dirs must be created by PutFileSplit")
		}
		for i, o := range child.FileNode.Objects {
			// same hack as copyFile--set size of first object to the size of the
			// whole subtree (and size of other objects to 0). I don't think
			// PutFileSplit files can have more than one object, but that invariant
			// isn't necessary to this code's correctness, so don't verify it.
			var size int64
			if i == 0 {
				size = child.SubtreeSize
			}
			pfr.Records = append(pfr.Records, &pfs.PutFileRecord{
				SizeBytes:  size,
				ObjectHash: o.Hash,
			})
		}
		return nil
	}); err != nil {
		return nil, err
	}
	return pfr, nil // TODO(msteffen) put something real here
}
// headerDirToPutFileRecords is a helper for copyFile that handles copying
// header/footer directories.
//
// Copy uses essentially the same codepath as putFile--it converts hashtree
// node(s) to PutFileRecords and then uses applyWrite to put the records back
// in the target hashtree. In putFile, the only way to create a headerDir is
// with PutFileSplit (PutFileRecord with Split==true). Rather than split the
// putFile codepath by adding a special case to applyWrite that was valid for
// copyFile but invalid for putFile, we use heaaderDirToPutFileRecords to
// convert a DirectoryNode to a PutFileRecord+Split==true, which applyWrite
// will correctly convert back to a header dir in the target hashtree via the
// regular putFile codepath.