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187 lines
7.0 KiB
C++
187 lines
7.0 KiB
C++
//
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// TextEncoding.h
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//
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// Library: Foundation
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// Package: Text
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// Module: TextEncoding
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//
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// Definition of the abstract TextEncoding class.
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//
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// Copyright (c) 2004-2007, Applied Informatics Software Engineering GmbH.
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// and Contributors.
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//
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// SPDX-License-Identifier: BSL-1.0
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//
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#ifndef Foundation_TextEncoding_INCLUDED
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#define Foundation_TextEncoding_INCLUDED
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#include "Poco/Foundation.h"
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#include "Poco/SharedPtr.h"
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namespace Poco
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{
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class TextEncodingManager;
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class Foundation_API TextEncoding
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/// An abstract base class for implementing text encodings
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/// like UTF-8 or ISO 8859-1.
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///
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/// Subclasses must override the canonicalName(), isA(),
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/// characterMap() and convert() methods and need to be
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/// thread safe and stateless.
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///
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/// TextEncoding also provides static member functions
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/// for managing mappings from encoding names to
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/// TextEncoding objects.
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{
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public:
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typedef SharedPtr<TextEncoding> Ptr;
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enum
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{
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MAX_SEQUENCE_LENGTH = 4 /// The maximum character byte sequence length supported.
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};
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typedef int CharacterMap[256];
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/// The map[b] member gives information about byte sequences
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/// whose first byte is b.
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/// If map[b] is c where c is >= 0, then b by itself encodes the Unicode scalar value c.
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/// If map[b] is -1, then the byte sequence is malformed.
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/// If map[b] is -n, where n >= 2, then b is the first byte of an n-byte
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/// sequence that encodes a single Unicode scalar value. Byte sequences up
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/// to 4 bytes in length are supported.
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virtual ~TextEncoding();
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/// Destroys the encoding.
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virtual const char * canonicalName() const = 0;
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/// Returns the canonical name of this encoding,
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/// e.g. "ISO-8859-1". Encoding name comparisons are case
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/// insensitive.
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virtual bool isA(const std::string & encodingName) const = 0;
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/// Returns true if the given name is one of the names of this encoding.
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/// For example, the "ISO-8859-1" encoding is also known as "Latin-1".
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///
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/// Encoding name comparisons are case insensitive.
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virtual const CharacterMap & characterMap() const = 0;
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/// Returns the CharacterMap for the encoding.
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/// The CharacterMap should be kept in a static member. As
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/// characterMap() can be called frequently, it should be
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/// implemented in such a way that it just returns a static
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/// map. If the map is built at runtime, this should be
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/// done in the constructor.
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virtual int convert(const unsigned char * bytes) const;
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/// The convert function is used to convert multibyte sequences;
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/// bytes will point to a byte sequence of n bytes where
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/// sequenceLength(bytes, length) == -n, with length >= n.
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///
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/// The convert function must return the Unicode scalar value
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/// represented by this byte sequence or -1 if the byte sequence is malformed.
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///
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/// The default implementation returns (int) bytes[0].
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virtual int queryConvert(const unsigned char * bytes, int length) const;
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/// The queryConvert function is used to convert single byte characters
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/// or multibyte sequences;
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/// bytes will point to a byte sequence of length bytes.
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///
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/// The queryConvert function must return the Unicode scalar value
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/// represented by this byte sequence or -1 if the byte sequence is malformed
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/// or -n where n is number of bytes requested for the sequence, if length is
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/// shorter than the sequence.
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/// The length of the sequence might not be determined by the first byte,
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/// in which case the conversion becomes an iterative process:
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/// First call with length == 1 might return -2,
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/// Then a second call with length == 2 might return -4
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/// Eventually, the third call with length == 4 should return either a
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/// Unicode scalar value, or -1 if the byte sequence is malformed.
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///
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/// The default implementation returns (int) bytes[0].
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virtual int sequenceLength(const unsigned char * bytes, int length) const;
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/// The sequenceLength function is used to get the length of the sequence pointed
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/// by bytes. The length parameter should be greater or equal to the length of
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/// the sequence.
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///
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/// The sequenceLength function must return the length of the sequence
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/// represented by this byte sequence or a negative value -n if length is
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/// shorter than the sequence, where n is the number of byte requested
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/// to determine the length of the sequence.
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/// The length of the sequence might not be determined by the first byte,
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/// in which case the conversion becomes an iterative process as long as the
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/// result is negative:
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/// First call with length == 1 might return -2,
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/// Then a second call with length == 2 might return -4
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/// Eventually, the third call with length == 4 should return 4.
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/// The default implementation returns 1.
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virtual int convert(int ch, unsigned char * bytes, int length) const;
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/// Transform the Unicode character ch into the encoding's
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/// byte sequence. The method returns the number of bytes
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/// used. The method must not use more than length characters.
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/// Bytes and length can also be null - in this case only the number
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/// of bytes required to represent ch is returned.
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/// If the character cannot be converted, 0 is returned and
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/// the byte sequence remains unchanged.
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/// The default implementation simply returns 0.
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static TextEncoding & byName(const std::string & encodingName);
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/// Returns the TextEncoding object for the given encoding name.
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///
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/// Throws a NotFoundException if the encoding with given name is not available.
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static TextEncoding::Ptr find(const std::string & encodingName);
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/// Returns a pointer to the TextEncoding object for the given encodingName,
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/// or NULL if no such TextEncoding object exists.
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static void add(TextEncoding::Ptr encoding);
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/// Adds the given TextEncoding to the table of text encodings,
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/// under the encoding's canonical name.
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///
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/// If an encoding with the given name is already registered,
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/// it is replaced.
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static void add(TextEncoding::Ptr encoding, const std::string & name);
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/// Adds the given TextEncoding to the table of text encodings,
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/// under the given name.
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///
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/// If an encoding with the given name is already registered,
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/// it is replaced.
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static void remove(const std::string & encodingName);
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/// Removes the encoding with the given name from the table
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/// of text encodings.
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static TextEncoding::Ptr global(TextEncoding::Ptr encoding);
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/// Sets global TextEncoding object.
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///
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/// This function sets the global encoding to the argument and returns a
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/// reference of the previous global encoding.
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static TextEncoding & global();
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/// Return the current global TextEncoding object
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static const std::string GLOBAL;
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/// Name of the global TextEncoding, which is the empty string.
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protected:
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static TextEncodingManager & manager();
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/// Returns the TextEncodingManager.
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};
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} // namespace Poco
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#endif // Foundation_TextEncoding_INCLUDED
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