ClickHouse/contrib/libpoco/Foundation/include/Poco/TextEncoding.h

186 lines
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C++

//
// TextEncoding.h
//
// $Id: //poco/1.4/Foundation/include/Poco/TextEncoding.h#1 $
//
// 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 = 6 /// 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 6 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 comparision are be 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 lenght 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 lenght == 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 lenth of the sequence pointed
/// by bytes. The length paramater should be greater or equal to the length of
/// the sequence.
///
/// The sequenceLength function must return the lenght 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 lenght == 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