X-Git-Url: http://git.tdb.fi/?a=blobdiff_plain;ds=sidebyside;f=source%2Fstringcodec%2Fcodec.h;fp=source%2Fstringcodec%2Fcodec.h;h=e04e909fb7a1fc5c4750db7e13f33f2d44a96f92;hb=b42ed73a1b241c0e93ee03c43c4584b41c549bac;hp=0000000000000000000000000000000000000000;hpb=5b1368cb791cab043f0435628cacbaff36e39b7b;p=libs%2Fcore.git diff --git a/source/stringcodec/codec.h b/source/stringcodec/codec.h new file mode 100644 index 0000000..e04e909 --- /dev/null +++ b/source/stringcodec/codec.h @@ -0,0 +1,205 @@ +/* $Id$ + +This file is part of libmspstrings +Copyright © 2006-2007 Mikko Rasa +Distributed under the LGPL +*/ + +#ifndef MSP_STRINGS_CODEC_H_ +#define MSP_STRINGS_CODEC_H_ + +#include +#include + +namespace Msp { +namespace Codecs { + +typedef int UnicodeChar; + +typedef std::basic_string ustring; + +enum ErrorMode +{ + THROW_ON_ERROR, + IGNORE_ERRORS, + TRANSLITERATE +}; + +/** +An exception thrown for all kinds of problems encountered while encoding or +decoding strings. +*/ +class CodecError: public Exception +{ +public: + CodecError(const std::string &w_): Exception(w_) { } +}; + +/** +Base class for string codecs. Use one of the derived classes or the function +create_codec to create a specific codec. + +Unicode strings are represented as ustrings. An std::string is considered to +be an encoded sequence of bytes. A codec is able to determine if an encoded +string could be decoded with it. +*/ +class Codec +{ +public: + /** + Base class for string encoder. + + Each codec class should contain an Encoder class derived from this. The + encode_char and transliterate functions must be overloaded. Some encoders + may find it useful or necessary to implement some other functions too + (particularly sync and reset for stateful codecs). + */ + class Encoder + { + protected: + ErrorMode err_mode; + + Encoder(ErrorMode em): err_mode(em) { } + public: + virtual ~Encoder() { } + + /** Encodes a single unicode character. If the character can't be + represented in this encoding, error() should be called. */ + virtual void encode_char(UnicodeChar ch, std::string &buf) = 0; + + /** Encodes a unicode string. This is equivalent to calling encode_char + for each character in the string with the same buffer. */ + virtual void encode(const ustring &str, std::string &buf); + + std::string encode(const ustring &); + + /** Procuces a sequence of bytes that will bring the encoder back to the + initial state. */ + virtual void sync(std::string &buf) { (void)buf; } + + /** Resets the encoder to the initial state without producing output. */ + virtual void reset() { } + + protected: + /** Handles an error depending on the error mode. + + THROW_ON_ERROR: throws CodecError(msg) + IGNORE_ERRORS: does nothing + TRANSLITERATE: calls transliterate(ch, buf) */ + void error(UnicodeChar ch, std::string &buf, const std::string &msg); + + /** Attempts to produce an alternative encoding for a unicode character. + Typically this includes dropping accent marks or romanizing letters. */ + virtual void transliterate(UnicodeChar ch, std::string &buf) = 0; + }; + + /** + Base class for string decoder. + + Each codec class should contain an Decoder class derived from this. + */ + class Decoder + { + protected: + ErrorMode err_mode; + + Decoder(ErrorMode em): err_mode(em) { } + public: + virtual ~Decoder() { } + + /** Decodes a single character from a string. The iterator is advanced + to the next character. For stateful codecs, -1 may be returned if a + state change sequence was decoded but no character followed it. If + invalid input is encountered, the error() function should be called and + the iterator advanced only if it doesn't throw. */ + virtual UnicodeChar decode_char(const std::string &str, std::string::const_iterator &i) = 0; + + /** Decodes a string. */ + virtual void decode(const std::string &str, ustring &buf); + + ustring decode(const std::string &); + + /** Resets the decoder to the initial state. */ + virtual void reset() { } + + protected: + /** Handles an error depending on the error mode. The return value is + suitable for returning from decode_char. + + THROW_ON_ERROR: throws CodecError(msg) + IGNORE_ERRORS: returns -1 + TRANSLITERATE: return 0xFFFE */ + UnicodeChar error(const std::string &msg); + }; + +protected: + Codec() { } +public: + virtual ~Codec() { } + + /** Returns the name of the encoding handled by this codec. */ + virtual const char *get_name() const = 0; + + /** Creates an encoder for this codec. */ + virtual Encoder *create_encoder(ErrorMode err_mode = THROW_ON_ERROR) const = 0; + + /** Creates a decoder for this codec. */ + virtual Decoder *create_decoder(ErrorMode err_mode = THROW_ON_ERROR) const = 0; + + /** Determines whether the given string can be successfully decoded with + this codec. Note that this function returning true does not guarantee that + the string was actually encoded with this codec. In particular, many 8-bit + encodings are indistinguishable. */ + virtual bool detect(const std::string &) const; +}; + +typedef Codec::Encoder Encoder; +typedef Codec::Decoder Decoder; + +/** Convenience function that decodes a string. */ +template +ustring decode(const std::string &s) +{ + typename C::Decoder dec; + ustring result; + dec.decode(s, result); + return result; +} + +/** Convenience function that encodes a string. */ +template +std::string encode(const ustring &s) +{ + typename C::Encoder enc; + std::string result; + enc.encode(s, result); + enc.sync(result); + return result; +} + +/** Convenience function that transcodes a string from one codec to another. */ +template +std::string transcode(const std::string &s) +{ + typename F::Decoder from; + typename T::Encoder to; + ustring temp; + from.decode(s, temp); + std::string result; + to.encode(temp, result); + to.sync(result); + return result; +} + +/** Creates a codec for an encoding by name. The caller is responsible for +deleting the codec when it's no longer needed. */ +Codec *create_codec(const std::string &); + +/** Automatically detects the encoding of a string and creates a codec for it. +The codec must be deleted when it's no longer needed. */ +Codec *detect_codec(const std::string &); + +} // namespace Codecs +} // namespace Msp + +#endif