public ChecksumFileSystem(FileSystem fs) 
{
    super(fs);
}

 public  void completeLocalOutput(Path fsOutputFile,
    Path tmpLocalFile) throws IOException 
{
    moveFromLocalFile(tmpLocalFile, fsOutputFile);
}

 public  void copyFromLocalFile(boolean delSrc,
    Path src,
    Path dst) throws IOException 
{
    Configuration conf = getConf();
    FileUtil.copy(getLocal(conf), src, this, dst, delSrc, conf);
}

 public  void copyToLocalFile(boolean delSrc,
    Path src,
    Path dst) throws IOException 
{
    Configuration conf = getConf();
    FileUtil.copy(this, src, getLocal(conf), dst, delSrc, conf);
}

The src file is under FS, and the dst is on the local disk. Copy it from FS control to the local dst name.

 public  void copyToLocalFile(Path src,
    Path dst,
    boolean copyCrc) throws IOException 
{
    if (!fs.isDirectory(src)) { // source is a file
      fs.copyToLocalFile(src, dst);
      FileSystem localFs = getLocal(getConf());
      if (localFs instanceof ChecksumFileSystem) {
        localFs = ((ChecksumFileSystem) localFs).getRawFileSystem();
      }
      if (localFs.isDirectory(dst)) {
        dst = new Path(dst, src.getName());
      }
      dst = getChecksumFile(dst);
      if (localFs.exists(dst)) { //remove old local checksum file
        localFs.delete(dst);
      }
      Path checksumFile = getChecksumFile(src);
      if (copyCrc && fs.exists(checksumFile)) { //copy checksum file
        fs.copyToLocalFile(checksumFile, dst);
      }
    } else {
      Path[] srcs = listPaths(src);
      for (Path srcFile : srcs) {
        copyToLocalFile(srcFile, new Path(dst, srcFile.getName()), copyCrc);
      }
    }
}

The src file is under FS, and the dst is on the local disk. Copy it from FS control to the local dst name. If src and dst are directories, the copyCrc parameter determines whether to copy CRC files.

 public FSDataOutputStream create(Path f,
    boolean overwrite,
    int bufferSize,
    short replication,
    long blockSize,
    Progressable progress) throws IOException 
{
    Path parent = f.getParent();
    if (parent != null && !mkdirs(parent)) {
      throw new IOException("Mkdirs failed to create " + parent);
    }
    return new FSDataOutputStream(new ChecksumFSOutputSummer(
        this, f, overwrite, bufferSize, replication, blockSize, progress));
}

Opens an FSDataOutputStream at the indicated Path with write-progress reporting.

 public boolean delete(Path f) throws IOException 
{
    if (fs.isDirectory(f)) {
      return fs.delete(f);
    } else {
      Path checkFile = getChecksumFile(f);
      if (fs.exists(checkFile)) {
        fs.delete(checkFile);
      }
      return fs.delete(f);
    }
}

Get rid of Path f, whether a true file or dir.

 public static double getApproxChkSumLength(long size) 
{
       
    return ChecksumFSOutputSummer.CHKSUM_AS_FRACTION * size;
}

 public int getBytesPerSum() 
{
    return getConf().getInt("io.bytes.per.checksum", 512);
}

Return the bytes Per Checksum

 public Path getChecksumFile(Path file) 
{
    return new Path(file.getParent(), "." + file.getName() + ".crc");
}

Return the name of the checksum file associated with a file.

 public long getChecksumFileLength(Path file,
    long fileSize) 
{
    return ChecksumFSOutputSummer.getChecksumLength(fileSize, getBytesPerSum());
}

Return the length of the checksum file given the size of the actual file.

 public FileSystem getRawFileSystem() 
{
    return fs;
}

get the raw file system

 public static boolean isChecksumFile(Path file) 
{
    String name = file.getName();
    return name.startsWith(".") && name.endsWith(".crc");
}

Return true iff file is a checksum file name.

 public Path[] listPaths(Path[] files) throws IOException 
{
                                    
    return fs.listPaths(files, DEFAULT_FILTER);
}

Filter raw files in the given pathes using the default checksum filter.

 public Path[] listPaths(Path f) throws IOException 
{
    return fs.listPaths(f, DEFAULT_FILTER);
}

Filter raw files in the given path using the default checksum filter.

 public  void lock(Path f,
    boolean shared) throws IOException 
{
    if (fs.isDirectory(f)) {
      fs.lock(f, shared);
    } else {
      Path checkFile = getChecksumFile(f);
      if (fs.exists(checkFile)) {
        fs.lock(checkFile, shared);
      }
      fs.lock(f, shared);
    }
}

 public boolean mkdirs(Path f) throws IOException 
{
    return fs.mkdirs(f);
}

 public FSDataInputStream open(Path f,
    int bufferSize) throws IOException 
{
    return new FSDataInputStream(
        new ChecksumFSInputChecker(this, f, bufferSize) );
}

Opens an FSDataInputStream at the indicated Path.

 public  void release(Path f) throws IOException 
{
    if (fs.isDirectory(f)) {
      fs.release(f);
    } else {
      Path checkFile = getChecksumFile(f);
      if (fs.exists(checkFile)) {
        fs.release(getChecksumFile(f));
      }
      fs.release(f);
    }
}

 public boolean rename(Path src,
    Path dst) throws IOException 
{
    if (fs.isDirectory(src)) {
      return fs.rename(src, dst);
    } else {
      boolean value = fs.rename(src, dst);
      if (!value)
        return false;
      Path checkFile = getChecksumFile(src);
      if (fs.exists(checkFile)) { //try to rename checksum
        if (fs.isDirectory(dst)) {
          value = fs.rename(checkFile, dst);
        } else {
          value = fs.rename(checkFile, getChecksumFile(dst));
        }
      }
      return value;
    }
}

Rename files/dirs

 public boolean reportChecksumFailure(Path f,
    FSDataInputStream in,
    long inPos,
    FSDataInputStream sums,
    long sumsPos) 
{
    return false;
}

Report a checksum error to the file system.

 public boolean setReplication(Path src,
    short replication) throws IOException 
{
    boolean value = fs.setReplication(src, replication);
    if (!value)
      return false;
    Path checkFile = getChecksumFile(src);
    if (exists(checkFile))
      fs.setReplication(checkFile, replication);
    return true;
}

Set replication for an existing file. Implement the abstract setReplication of FileSystem

 public Path startLocalOutput(Path fsOutputFile,
    Path tmpLocalFile) throws IOException 
{
    return tmpLocalFile;
}