FSInputChecker (Hadoop 1.2.1 API)
Date: 2013-07-22

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## org.apache.hadoop.fs
Class FSInputChecker

    java.lang.Object
      java.io.InputStream
          org.apache.hadoop.fs.FSInputStream
              org.apache.hadoop.fs.FSInputChecker

All Implemented Interfaces:
  Closeable, PositionedReadable, Seekable

    public abstract class FSInputChecker

extends FSInputStream

This is a generic input stream for verifying checksums for data before it is read by a user.

Field Summary
`protected Path` | `file` The file name from which data is read from
`static org.apache.commons.logging.Log` | `LOG`

Constructor Summary
`protected` | `FSInputChecker(Path file, int numOfRetries)` Constructor
`protected` | `FSInputChecker(Path file, int numOfRetries, boolean verifyChecksum, Checksum sum, int chunkSize, int checksumSize)` Constructor

Method Summary
`int` | `available()`
`static long` | `checksum2long(byte[] checksum)` Convert a checksum byte array to a long
`protected abstract long` | `getChunkPosition(long pos)` Return position of beginning of chunk containing pos.
`long` | `getPos()` Return the current offset from the start of the file
`void` | `mark(int readlimit)`
`boolean` | `markSupported()`
`protected boolean` | `needChecksum()` Return true if there is a need for checksum verification
`int` | `read()` Read one checksum-verified byte
`int` | `read(byte[] b, int off, int len)` Read checksum verified bytes from this byte-input stream into the specified byte array, starting at the given offset.
`protected abstract int` | `readChunk(long pos, byte[] buf, int offset, int len, byte[] checksum)` Reads in next checksum chunk data into `buf` at `offset` and checksum into `checksum`.
`protected static int` | `readFully(InputStream stm, byte[] buf, int offset, int len)` A utility function that tries to read up to `len` bytes from `stm`
`void` | `reset()`
`void` | `seek(long pos)` Seek to the given position in the stream.
`protected void` | `set(boolean verifyChecksum, Checksum sum, int maxChunkSize, int checksumSize)` Set the checksum related parameters
`long` | `skip(long n)` Skips over and discards `n` bytes of data from the input stream.

Methods inherited from class org.apache.hadoop.fs.FSInputStream
`read, readFully, readFully, seekToNewSource`

Methods inherited from class java.io.InputStream
`close, read`

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Field Detail

### LOG

    public static final org.apache.commons.logging.Log LOG

### file

    protected Path file

  The file name from which data is read from

Constructor Detail

### FSInputChecker

    protected FSInputChecker(Path file,
                             int numOfRetries)

  Constructor

  Parameters:
    `file` - The name of the file to be read
    `numOfRetries` - Number of read retries when ChecksumError occurs

### FSInputChecker

    protected FSInputChecker(Path file,
                             int numOfRetries,
                             boolean verifyChecksum,
                             Checksum sum,
                             int chunkSize,
                             int checksumSize)

  Constructor

  Parameters:
    `file` - The name of the file to be read
    `numOfRetries` - Number of read retries when ChecksumError occurs
    `sum` - the type of Checksum engine
    `chunkSize` - maximun chunk size
    `checksumSize` - the number byte of each checksum

Method Detail

### readChunk

    protected abstract int readChunk(long pos,
                                     byte[] buf,
                                     int offset,
                                     int len,
                                     byte[] checksum)
                              throws IOException

  Reads in next checksum chunk data into `buf` at `offset` and checksum into `checksum`. The method is used for implementing read, therefore, it should be optimized for sequential reading

  Parameters:
    `pos` - chunkPos
    `buf` - desitination buffer
    `offset` - offset in buf at which to store data
    `len` - maximun number of bytes to read
  Returns:
    number of bytes read
  Throws:
    `IOException`

### getChunkPosition

    protected abstract long getChunkPosition(long pos)

  Return position of beginning of chunk containing pos.

  Parameters:
    `pos` - a postion in the file
  Returns:
    the starting position of the chunk which contains the byte

### needChecksum

    protected boolean needChecksum()

  Return true if there is a need for checksum verification

### read

    public int read()
             throws IOException

  Read one checksum-verified byte

  Specified by:
    `read` in class `InputStream`
  Returns:
    the next byte of data, or `-1` if the end of the stream is reached.
  Throws:
    `IOException` - if an I/O error occurs.

### read

    public int read(byte[] b,
                    int off,
                    int len)
             throws IOException

  Read checksum verified bytes from this byte-input stream into the specified byte array, starting at the given offset.

  This method implements the general contract of the corresponding ``read`` method of the ``InputStream`` class. As an additional convenience, it attempts to read as many bytes as possible by repeatedly invoking the `read` method of the underlying stream. This iterated `read` continues until one of the following conditions becomes true:

  - The specified number of bytes have been read,
  - The `read` method of the underlying stream returns `-1`, indicating end-of-file.
  If the first `read` on the underlying stream returns `-1` to indicate end-of-file then this method returns `-1`. Otherwise this method returns the number of bytes actually read.

  Overrides:
    `read` in class `InputStream`
  Parameters:
    `b` - destination buffer.
    `off` - offset at which to start storing bytes.
    `len` - maximum number of bytes to read.
  Returns:
    the number of bytes read, or `-1` if the end of the stream has been reached.
  Throws:
    `IOException` - if an I/O error occurs. ChecksumException if any checksum error occurs

### checksum2long

    public static long checksum2long(byte[] checksum)

  Convert a checksum byte array to a long

### getPos

    public long getPos()
                throws IOException

  Description copied from class: `FSInputStream`
  Return the current offset from the start of the file

  Specified by:
    `getPos` in interface `Seekable`
  Specified by:
    `getPos` in class `FSInputStream`
  Throws:
    `IOException`

### available

    public int available()
                  throws IOException

  Overrides:
    `available` in class `InputStream`
  Throws:
    `IOException`

### skip

    public long skip(long n)
              throws IOException

  Skips over and discards `n` bytes of data from the input stream.

  This method may skip more bytes than are remaining in the backing file. This produces no exception and the number of bytes skipped may include some number of bytes that were beyond the EOF of the backing file. Attempting to read from the stream after skipping past the end will result in -1 indicating the end of the file.

  If `n` is negative, no bytes are skipped.

  Overrides:
    `skip` in class `InputStream`
  Parameters:
    `n` - the number of bytes to be skipped.
  Returns:
    the actual number of bytes skipped.
  Throws:
    `IOException` - if an I/O error occurs. ChecksumException if the chunk to skip to is corrupted

### seek

    public void seek(long pos)
              throws IOException

  Seek to the given position in the stream. The next read() will be from that position.

  This method may seek past the end of the file. This produces no exception and an attempt to read from the stream will result in -1 indicating the end of the file.

  Specified by:
    `seek` in interface `Seekable`
  Specified by:
    `seek` in class `FSInputStream`
  Parameters:
    `pos` - the postion to seek to.
  Throws:
    `IOException` - if an I/O error occurs. ChecksumException if the chunk to seek to is corrupted

### readFully

    protected static int readFully(InputStream stm,
                                   byte[] buf,
                                   int offset,
                                   int len)
                            throws IOException

  A utility function that tries to read up to `len` bytes from `stm`

  Parameters:
    `stm` - an input stream
    `buf` - destiniation buffer
    `offset` - offset at which to store data
    `len` - number of bytes to read
  Returns:
    actual number of bytes read
  Throws:
    `IOException` - if there is any IO error

### set

    protected final void set(boolean verifyChecksum,
                             Checksum sum,
                             int maxChunkSize,
                             int checksumSize)

  Set the checksum related parameters

  Parameters:
    `verifyChecksum` - whether to verify checksum
    `sum` - which type of checksum to use
    `maxChunkSize` - maximun chunk size
    `checksumSize` - checksum size

### markSupported

    public final boolean markSupported()

  Overrides:
    `markSupported` in class `InputStream`

### mark

    public final void mark(int readlimit)

  Overrides:
    `mark` in class `InputStream`

### reset

    public final void reset()
                     throws IOException

  Overrides:
    `reset` in class `InputStream`
  Throws:
    `IOException`

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