Package org.apache.lucene.codecs

Class CodecUtil

java.lang.Object
org.apache.lucene.codecs.CodecUtil
public final class CodecUtil extends Object
Utility class for reading and writing versioned headers.

Writing codec headers is useful to ensure that a file is in the format you think it is.

WARNING: This API is experimental and might change in incompatible ways in the next release.

  • Field Details

    • CODEC_MAGIC

      public static final int CODEC_MAGIC
      Constant to identify the start of a codec header.
      See Also:

  • Method Details

    • writeHeader

      public static void writeHeader(DataOutput out, String codec, int version) throws IOException
      Writes a codec header, which records both a string to identify the file and a version number. This header can be parsed and validated with checkHeader().

      CodecHeader --> Magic,CodecName,Version

      • Magic --> Uint32. This identifies the start of the header. It is always 1071082519.
      • CodecName --> String. This is a string to identify this file.
      • Version --> Uint32. Records the version of the file.

      Note that the length of a codec header depends only upon the name of the codec, so this length can be computed at any time with headerLength(String).

      Parameters:
      out - Output stream
      codec - String to identify this file. It should be simple ASCII, less than 128 characters in length.
      version - Version number
      Throws:
      IOException - If there is an I/O error writing to the underlying medium.
      IllegalArgumentException - If the codec name is not simple ASCII, or is more than 127 characters in length

    • writeIndexHeader

      public static void writeIndexHeader(DataOutput out, String codec, int version, byte[] id, String suffix) throws IOException
      Writes a codec header for an index file, which records both a string to identify the format of the file, a version number, and data to identify the file instance (ID and auxiliary suffix such as generation).

      This header can be parsed and validated with checkIndexHeader().

      IndexHeader --> CodecHeader,ObjectID,ObjectSuffix

      Note that the length of an index header depends only upon the name of the codec and suffix, so this length can be computed at any time with indexHeaderLength(String,String).

      Parameters:
      out - Output stream
      codec - String to identify the format of this file. It should be simple ASCII, less than 128 characters in length.
      id - Unique identifier for this particular file instance.
      suffix - auxiliary suffix information for the file. It should be simple ASCII, less than 256 characters in length.
      version - Version number
      Throws:
      IOException - If there is an I/O error writing to the underlying medium.
      IllegalArgumentException - If the codec name is not simple ASCII, or is more than 127 characters in length, or if id is invalid, or if the suffix is not simple ASCII, or more than 255 characters in length.

    • headerLength

      public static int headerLength(String codec)
      Computes the length of a codec header.
      Parameters:
      codec - Codec name.
      Returns:
      length of the entire codec header.
      See Also:

    • indexHeaderLength

      public static int indexHeaderLength(String codec, String suffix)
      Computes the length of an index header.
      Parameters:
      codec - Codec name.
      Returns:
      length of the entire index header.
      See Also:

    • checkHeader

      public static int checkHeader(DataInput in, String codec, int minVersion, int maxVersion) throws IOException
      Reads and validates a header previously written with writeHeader(DataOutput, String, int).

      When reading a file, supply the expected codec and an expected version range ( minVersion to maxVersion).

      Parameters:
      in - Input stream, positioned at the point where the header was previously written. Typically this is located at the beginning of the file.
      codec - The expected codec name.
      minVersion - The minimum supported expected version number.
      maxVersion - The maximum supported expected version number.
      Returns:
      The actual version found, when a valid header is found that matches codec, with an actual version where minVersion <= actual <= maxVersion. Otherwise an exception is thrown.
      Throws:
      CorruptIndexException - If the first four bytes are not CODEC_MAGIC, or if the actual codec found is not codec.
      IndexFormatTooOldException - If the actual version is less than minVersion.
      IndexFormatTooNewException - If the actual version is greater than maxVersion .
      IOException - If there is an I/O error reading from the underlying medium.
      See Also:

    • checkHeaderNoMagic

      public static int checkHeaderNoMagic(DataInput in, String codec, int minVersion, int maxVersion) throws IOException
      Like checkHeader(DataInput,String,int,int) except this version assumes the first int has already been read and validated from the input.
      Throws:
      IOException

    • checkIndexHeader

      public static int checkIndexHeader(DataInput in, String codec, int minVersion, int maxVersion, byte[] expectedID, String expectedSuffix) throws IOException
      Reads and validates a header previously written with writeIndexHeader(DataOutput, String, int, byte[], String).

      When reading a file, supply the expected codec, expected version range ( minVersion to maxVersion), and object ID and suffix.

      Parameters:
      in - Input stream, positioned at the point where the header was previously written. Typically this is located at the beginning of the file.
      codec - The expected codec name.
      minVersion - The minimum supported expected version number.
      maxVersion - The maximum supported expected version number.
      expectedID - The expected object identifier for this file.
      expectedSuffix - The expected auxiliary suffix for this file.
      Returns:
      The actual version found, when a valid header is found that matches codec, with an actual version where minVersion <= actual <= maxVersion, and matching expectedID and expectedSuffix Otherwise an exception is thrown.
      Throws:
      CorruptIndexException - If the first four bytes are not CODEC_MAGIC, or if the actual codec found is not codec, or if the expectedID or expectedSuffix do not match.
      IndexFormatTooOldException - If the actual version is less than minVersion.
      IndexFormatTooNewException - If the actual version is greater than maxVersion .
      IOException - If there is an I/O error reading from the underlying medium.
      See Also:

    • verifyAndCopyIndexHeader

      public static void verifyAndCopyIndexHeader(IndexInput in, DataOutput out, byte[] expectedID) throws IOException
      Expert: verifies the incoming IndexInput has an index header and that its segment ID matches the expected one, and then copies that index header into the provided DataOutput. This is useful when building compound files.
      Parameters:
      in - Input stream, positioned at the point where the index header was previously written. Typically this is located at the beginning of the file.
      out - Output stream, where the header will be copied to.
      expectedID - Expected segment ID
      Throws:
      CorruptIndexException - If the first four bytes are not CODEC_MAGIC, or if the expectedID does not match.
      IOException - If there is an I/O error reading from the underlying medium.
      NOTE: This API is for internal purposes only and might change in incompatible ways in the next release.

    • readIndexHeader

      public static byte[] readIndexHeader(IndexInput in) throws IOException
      Retrieves the full index header from the provided IndexInput. This throws CorruptIndexException if this file does not appear to be an index file.
      Throws:
      IOException

    • readFooter

      public static byte[] readFooter(IndexInput in) throws IOException
      Retrieves the full footer from the provided IndexInput. This throws CorruptIndexException if this file does not have a valid footer.
      Throws:
      IOException

    • checkIndexHeaderID

      public static byte[] checkIndexHeaderID(DataInput in, byte[] expectedID) throws IOException
      Expert: just reads and verifies the object ID of an index header
      Throws:
      IOException

    • checkIndexHeaderSuffix

      public static String checkIndexHeaderSuffix(DataInput in, String expectedSuffix) throws IOException
      Expert: just reads and verifies the suffix of an index header
      Throws:
      IOException

    • writeFooter

      public static void writeFooter(IndexOutput out) throws IOException
      Writes a codec footer, which records both a checksum algorithm ID and a checksum. This footer can be parsed and validated with checkFooter().

      CodecFooter --> Magic,AlgorithmID,Checksum

      • Magic --> Uint32. This identifies the start of the footer. It is always -1071082520.
      • AlgorithmID --> Uint32. This indicates the checksum algorithm used. Currently this is always 0, for zlib-crc32.
      • Checksum --> Uint64. The actual checksum value for all previous bytes in the stream, including the bytes from Magic and AlgorithmID.
      Parameters:
      out - Output stream
      Throws:
      IOException - If there is an I/O error writing to the underlying medium.

    • footerLength

      public static int footerLength()
      Computes the length of a codec footer.
      Returns:
      length of the entire codec footer.
      See Also:

    • checkFooter

      public static long checkFooter(ChecksumIndexInput in) throws IOException
      Validates the codec footer previously written by writeFooter(org.apache.lucene.store.IndexOutput).
      Returns:
      actual checksum value
      Throws:
      IOException - if the footer is invalid, if the checksum does not match, or if in is not properly positioned before the footer at the end of the stream.

    • checkFooter

      public static void checkFooter(ChecksumIndexInput in, Throwable priorException) throws IOException
      Validates the codec footer previously written by writeFooter(org.apache.lucene.store.IndexOutput), optionally passing an unexpected exception that has already occurred.

      When a priorException is provided, this method will add a suppressed exception indicating whether the checksum for the stream passes, fails, or cannot be computed, and rethrow it. Otherwise it behaves the same as checkFooter(ChecksumIndexInput).

      Example usage: 

       try (ChecksumIndexInput input = ...) {
   Throwable priorE = null;
   try {
     // ... read a bunch of stuff ...
   } catch (Throwable exception) {
     priorE = exception;
   } finally {
     CodecUtil.checkFooter(input, priorE);
   }
 }
      Throws:
      IOException

    • retrieveChecksum

      public static long retrieveChecksum(IndexInput in) throws IOException
      Returns (but does not validate) the checksum previously written by checkFooter(org.apache.lucene.store.ChecksumIndexInput).
      Returns:
      actual checksum value
      Throws:
      IOException - if the footer is invalid

    • retrieveChecksum

      public static long retrieveChecksum(IndexInput in, long expectedLength) throws IOException
      Returns (but does not validate) the checksum previously written by checkFooter(org.apache.lucene.store.ChecksumIndexInput).
      Returns:
      actual checksum value
      Throws:
      IOException - if the footer is invalid

    • checksumEntireFile

      public static long checksumEntireFile(IndexInput input) throws IOException
      Clones the provided input, reads all bytes from the file, and calls checkFooter(org.apache.lucene.store.ChecksumIndexInput)

      Note that this method may be slow, as it must process the entire file. If you just need to extract the checksum value, call retrieveChecksum(org.apache.lucene.store.IndexInput).

      Throws:
      IOException

    • writeBEInt

      public static void writeBEInt(DataOutput out, int i) throws IOException
      write int value on header / footer with big endian order
      Throws:
      IOException

    • writeBELong

      public static void writeBELong(DataOutput out, long l) throws IOException
      write long value on header / footer with big endian order
      Throws:
      IOException

    • readBEInt

      public static int readBEInt(DataInput in) throws IOException
      read int value from header / footer with big endian order
      Throws:
      IOException

    • readBELong

      public static long readBELong(DataInput in) throws IOException
      read long value from header / footer with big endian order
      Throws:
      IOException