tomatosliu/java-dfs

Implement a DFS in Java from scratch

Java DFS

First Milestone

NamingServer

As long as one client want to create or delete file, it must interact with NamingServer. It means NamingServer maintains a complete structure of directory tree. DirectoryTree usually accepts a Path as input and outputs DirectoryNode or other information. Most of methods in Service need to utilize DirectoryTree to store and retrieve information of directories and files.

At the same time, DirectoryTree makes the distributed file system hided from the view from clients, however, NamingServer handles the schedule of StorageServer. Therefore, I implement a module of Scheduler. Scheduler has two kinds of function. First, it maintain a list of StorageServer. When a file creation is requested from client, NamingServer will call Scheduler to get a proper StorageServer to actually create the file. Second, it provides a algorithm module for choosing a StorageServer from a list of them. When a client asks for a file, we choose a specific StorageServer to return to the client, which allows the client to read and write.

Directory Tree

There are a list of APIs which can be used to modify directory tree.

The following is the set of methods I think which may be used in later locking and replication:

/** Get a directory node in the tree by Path p.
    @return a directory node, if there is a node of Path p, otherwise, return <code>null</code>.
      */
public DirectoryNode getNode(Path p)

/** Create a directory.
     */
private boolean createDir(Path directory)

/** Delete the node of Path p.
    <p>
    If the Path is not reachable, throw FileNotFoundException.
    @return <code>true</code>, if successiful;
            <code>false</code>, if the Path is root, return false.
*/
public boolean deleteNode(Path p)

/** Insert a file node into the tree, if it does not exist.
    This will success when the directory already exists. If not, please call creatDir first to
    create parent directory.
    <p>
    This only takes charge of creating a node without path components.
    @return <code>true</code>, if success.
            <code>false</code>, if the file path already exists or file is root.
    @throws FileNotFoundException If the parent directory does not exist or
 */
public boolean insertNode(Path file, boolean isDirectory)
  
/** Insert path component into a Path.
    This will success when the directory already exists. If not, please call creatDir first to
    create parent directory.
    Also, this method usually follows insertNode.
    <p>
    Take charge of insert path component into the Path, the caller need to call scheduler to
    get a storage server for operating.
    @throws FileNotFoundException If the path does not exist or the path is a directory.
 */
public void insertPathComp(Path p, PathComponents pathComp)

Service Interface

String[] list(Path directory)

1. You need to make sure that directory exists and corresponds to a actually directory, not a file.

boolean createFile(Path file)

You need to do two things related to DirectoryTree and Scheduler.

1. Find a available StorageServer from Scheduler to actually create the file.
2. Insert a file node into DirectoryTree

boolean createDirectory(Path directory)

You do not need to inform StorageServer to create a directory, because when creating files, the StorageServer will automatically create needed directories.

Storage getStorage(Path file)

It needs to make sure file is a file, not a directory.

Registration Interface

Path[] register(Storage client_stub, Command command_stub, Path[] files)

You need to do two things related to DirectoryTree and Scheduler.

1. Insert the stubs into Scheduler.
2. Insert files into DirectoryTree.