ClickHouse/base/poco/Foundation/include/Poco/TextEncoding.h

//
// TextEncoding.h
//
// Library: Foundation
// Package: Text
// Module:  TextEncoding
//
// Definition of the abstract TextEncoding class.
//
// Copyright (c) 2004-2007, Applied Informatics Software Engineering GmbH.
// and Contributors.
//
// SPDX-License-Identifier:	BSL-1.0
//


#ifndef Foundation_TextEncoding_INCLUDED
#define Foundation_TextEncoding_INCLUDED


#include "Poco/Foundation.h"
#include "Poco/SharedPtr.h"


namespace Poco
{


class TextEncodingManager;


class Foundation_API TextEncoding
/// An abstract base class for implementing text encodings
/// like UTF-8 or ISO 8859-1.
///
/// Subclasses must override the canonicalName(), isA(),
/// characterMap() and convert() methods and need to be
/// thread safe and stateless.
///
/// TextEncoding also provides static member functions
/// for managing mappings from encoding names to
/// TextEncoding objects.
{
public:
    typedef SharedPtr<TextEncoding> Ptr;

    enum
    {
        MAX_SEQUENCE_LENGTH = 4 /// The maximum character byte sequence length supported.
    };

    typedef int CharacterMap[256];
    /// The map[b] member gives information about byte sequences
    /// whose first byte is b.
    /// If map[b] is c where c is >= 0, then b by itself encodes the Unicode scalar value c.
    /// If map[b] is -1, then the byte sequence is malformed.
    /// If map[b] is -n, where n >= 2, then b is the first byte of an n-byte
    /// sequence that encodes a single Unicode scalar value. Byte sequences up
    /// to 4 bytes in length are supported.

    virtual ~TextEncoding();
    /// Destroys the encoding.

    virtual const char * canonicalName() const = 0;
    /// Returns the canonical name of this encoding,
    /// e.g. "ISO-8859-1". Encoding name comparisons are case
    /// insensitive.

    virtual bool isA(const std::string & encodingName) const = 0;
    /// Returns true if the given name is one of the names of this encoding.
    /// For example, the "ISO-8859-1" encoding is also known as "Latin-1".
    ///
    /// Encoding name comparisons are case insensitive.

    virtual const CharacterMap & characterMap() const = 0;
    /// Returns the CharacterMap for the encoding.
    /// The CharacterMap should be kept in a static member. As
    /// characterMap() can be called frequently, it should be
    /// implemented in such a way that it just returns a static
    /// map. If the map is built at runtime, this should be
    /// done in the constructor.

    virtual int convert(const unsigned char * bytes) const;
    /// The convert function is used to convert multibyte sequences;
    /// bytes will point to a byte sequence of n bytes where
    /// sequenceLength(bytes, length) == -n, with length >= n.
    ///
    /// The convert function must return the Unicode scalar value
    /// represented by this byte sequence or -1 if the byte sequence is malformed.
    ///
    /// The default implementation returns (int) bytes[0].

    virtual int queryConvert(const unsigned char * bytes, int length) const;
    /// The queryConvert function is used to convert single byte characters
    /// or multibyte sequences;
    /// bytes will point to a byte sequence of length bytes.
    ///
    /// The queryConvert function must return the Unicode scalar value
    /// represented by this byte sequence or -1 if the byte sequence is malformed
    /// or -n where n is number of bytes requested for the sequence, if length is
    /// shorter than the sequence.
    /// The length of the sequence might not be determined by the first byte,
    /// in which case the conversion becomes an iterative process:
    /// First call with length == 1 might return -2,
    /// Then a second call with length == 2 might return -4
    /// Eventually, the third call with length == 4 should return either a
    /// Unicode scalar value, or -1 if the byte sequence is malformed.
    ///
    /// The default implementation returns (int) bytes[0].

    virtual int sequenceLength(const unsigned char * bytes, int length) const;
    /// The sequenceLength function is used to get the length of the sequence pointed
    /// by bytes. The length parameter should be greater or equal to the length of
    /// the sequence.
    ///
    /// The sequenceLength function must return the length of the sequence
    /// represented by this byte sequence or a negative value -n if length is
    /// shorter than the sequence, where n is the number of byte requested
    /// to determine the length of the sequence.
    /// The length of the sequence might not be determined by the first byte,
    /// in which case the conversion becomes an iterative process as long as the
    /// result is negative:
    /// First call with length == 1 might return -2,
    /// Then a second call with length == 2 might return -4
    /// Eventually, the third call with length == 4 should return 4.
    /// The default implementation returns 1.

    virtual int convert(int ch, unsigned char * bytes, int length) const;
    /// Transform the Unicode character ch into the encoding's
    /// byte sequence. The method returns the number of bytes
    /// used. The method must not use more than length characters.
    /// Bytes and length can also be null - in this case only the number
    /// of bytes required to represent ch is returned.
    /// If the character cannot be converted, 0 is returned and
    /// the byte sequence remains unchanged.
    /// The default implementation simply returns 0.

    static TextEncoding & byName(const std::string & encodingName);
    /// Returns the TextEncoding object for the given encoding name.
    ///
    /// Throws a NotFoundException if the encoding with given name is not available.

    static TextEncoding::Ptr find(const std::string & encodingName);
    /// Returns a pointer to the TextEncoding object for the given encodingName,
    /// or NULL if no such TextEncoding object exists.

    static void add(TextEncoding::Ptr encoding);
    /// Adds the given TextEncoding to the table of text encodings,
    /// under the encoding's canonical name.
    ///
    /// If an encoding with the given name is already registered,
    /// it is replaced.

    static void add(TextEncoding::Ptr encoding, const std::string & name);
    /// Adds the given TextEncoding to the table of text encodings,
    /// under the given name.
    ///
    /// If an encoding with the given name is already registered,
    /// it is replaced.

    static void remove(const std::string & encodingName);
    /// Removes the encoding with the given name from the table
    /// of text encodings.

    static TextEncoding::Ptr global(TextEncoding::Ptr encoding);
    /// Sets global TextEncoding object.
    ///
    /// This function sets the global encoding to the argument and returns a
    /// reference of the previous global encoding.

    static TextEncoding & global();
    /// Return the current global TextEncoding object

    static const std::string GLOBAL;
    /// Name of the global TextEncoding, which is the empty string.

protected:
    static TextEncodingManager & manager();
    /// Returns the TextEncodingManager.
};


} // namespace Poco


#endif // Foundation_TextEncoding_INCLUDED