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diff --git a/doc/devel/utfconv.txt b/doc/devel/utfconv.txt new file mode 100644 index 0000000..88dfb1d --- /dev/null +++ b/doc/devel/utfconv.txt @@ -0,0 +1,291 @@ + Dec 5, 2000 + Dave Steck + Novell, Inc. + + UTF-8 Conversion Functions + + +1. Strings in the LDAP C SDK should be encoded in UTF-8 format. + However, most platforms do not provide APIs for converting to + this format. If they do, they are platform-specific. + + As a result, most applications (knowingly or not) use local strings + with LDAP functions. This works fine for 7-bit ASCII characters, + but will fail with 8-bit European characters, Asian characters, etc. + + We propose adding the following platform-independent conversion functions + to the OpenLDAP SDK. There are 4 functions for converting between UTF-8 + and wide characters, and 4 functions for converting between UTF-8 and + multibyte characters. + + For multibyte to UTF-8 conversions, charset translation is necessary. + While a full charset translator is not practical or appropriate for the + LDAP SDK, we can pass the translator function in as an argument. + A NULL for this argument will use the ANSI C functions mbtowc, mbstowcs, + wctomb, and wcstombs. + +2. UTF-8 <--> Wide Character conversions + +The following new conversion routines will be added, following the pattern of +the ANSI C conversion routines (mbtowc, mbstowcs, etc). These routines use +the wchar_t type. wchar_t is 2 bytes on some systems and 4 bytes on others. +However the advantage of using wchar_t is that all the standard wide character +string functions may be used on these strings: wcslen, wcscpy, etc. + + int ldap_x_utf8_to_wc - Convert a single UTF-8 encoded character to a wide character. + int ldap_x_utf8s_to_wcs - Convert a UTF-8 string to a wide character string. + int ldap_x_wc_to_utf8 - Convert a single wide character to a UTF-8 sequence. + int ldap_x_wcs_to_utf8s - Convert a wide character string to a UTF-8 string. + + +2.1 ldap_x_utf8_to_wc - Convert a single UTF-8 encoded character to a wide character. + +int ldap_x_utf8_to_wc ( wchar_t *wchar, const char *utf8char ) + + wchar (OUT) Points to a wide character code to receive the + converted character. + + utf8char (IN) Address of the UTF8 sequence of bytes. + +Return Value: + If successful, the function returns the length in + bytes of the UTF-8 input character. + + If utf8char is NULL or points to an empty string, the + function returns 1 and a NULL is written to wchar. + + If utf8char contains an invalid UTF-8 sequence -1 is returned. + + +2.2 ldap_x_utf8s_to_wcs - Convert a UTF-8 string to a wide character string. + +int ldap_x_utf8s_to_wcs (wchar_t *wcstr, const char *utf8str, size_t count) + + wcstr (OUT) Points to a wide char buffer to receive the + converted wide char string. The output string will be + null terminated if there is space for it in the + buffer. + + utf8str (IN) Address of the null-terminated UTF-8 string to convert. + + count (IN) The number of UTF-8 characters to convert, or + equivalently, the size of the output buffer in wide + characters. + +Return Value: + If successful, the function returns the number of wide + characters written to wcstr, excluding the null termination + character, if any. + + If wcstr is NULL, the function returns the number of wide + characters required to contain the converted string, + excluding the null termination character. + + If an invalid UTF-8 sequence is encountered, the + function returns -1. + + If the return value equals count, there was not enough space to fit the + string and the null terminator in the buffer. + + +2.3 ldap_x_wc_to_utf8 - Convert a single wide character to a UTF-8 sequence. + +int ldap_x_wc_to_utf8 ( char *utf8char, wchar_t wchar, count ) + + utf8char (OUT) Points to a byte array to receive the converted UTF-8 + string. + + wchar (IN) The wide character to convert. + + count (IN) The maximum number of bytes to write to the output + buffer. Normally set this to LDAP_MAX_UTF8_LEN, which + is defined as 3 or 6 depending on the size of wchar_t. + A partial character will not be written. + +Return Value: + If successful, the function returns the length in bytes of + the converted UTF-8 output character. + + If wchar is NULL, the function returns 1 and a NULL is + written to utf8char. + + If wchar cannot be converted to a UTF-8 character, the + function returns -1. + + +2.4 int ldap_x_wcs_to_utf8s - Convert a wide character string to a UTF-8 string. + +int ldap_x_wcs_to_utf8s (char *utf8str, const wchar_t *wcstr, size_t count) + + utf8str (OUT) Points to a byte array to receive the converted + UTF-8 string. The output string will be null + terminated if there is space for it in the + buffer. + + + wcstr (IN) Address of the null-terminated wide char string to convert. + + count (IN) The size of the output buffer in bytes. + +Return Value: + If successful, the function returns the number of bytes + written to utf8str, excluding the null termination + character, if any. + + If utf8str is NULL, the function returns the number of + bytes required to contain the converted string, excluding + the null termination character. The 'count' parameter is ignored. + + If the function encounters a wide character that cannot + be mapped to a UTF-8 sequence, the function returns -1. + + If the return value equals count, there was not enough space to fit + the string and the null terminator in the buffer. + + + +3. Multi-byte <--> UTF-8 Conversions + +These functions convert the string in a two-step process, from multibyte +to Wide, then from Wide to UTF8, or vice versa. This conversion requires a +charset translation routine, which is passed in as an argument. + + ldap_x_mb_to_utf8 - Convert a multi-byte character to a UTF-8 character. + ldap_x_mbs_to_utf8s - Convert a multi-byte string to a UTF-8 string. + ldap_x_utf8_to_mb - Convert a UTF-8 character to a multi-byte character. + ldap_x_utf8s_to_mbs - Convert a UTF-8 string to a multi-byte string. + +3.1 ldap_x_mb_to_utf8 - Convert a multi-byte character to a UTF-8 character. + +int ldap_x_mb_to_utf8 ( char *utf8char, const char *mbchar, size_t mbsize, int (*f_mbtowc)(wchar_t *wchar, const char *mbchar, size_t count) ) + + utf8char (OUT) Points to a byte buffer to receive the converted + UTF-8 character. May be NULL. The output is not + null-terminated. + + mbchar (IN) Address of a sequence of bytes forming a multibyte character. + + mbsize (IN) The maximum number of bytes of the mbchar argument to + check. This should normally be MB_CUR_MAX. + + f_mbtowc (IN) The function to use for converting a multibyte + character to a wide character. If NULL, the local + ANSI C routine mbtowc is used. + +Return Value: + If successful, the function returns the length in bytes of + the UTF-8 output character. + + If utf8char is NULL, count is ignored and the funtion + returns the number of bytes that would be written to the + output char. + + If count is zero, 0 is returned and nothing is written to + utf8char. + + If mbchar is NULL or points to an empty string, the + function returns 1 and a null byte is written to utf8char. + + If mbchar contains an invalid multi-byte character, -1 is returned. + + +3.2 ldap_x_mbs_to_utf8s - Convert a multi-byte string to a UTF-8 string. + +int ldap_x_mbs_to_utf8s (char *utf8str, const char *mbstr, size_t count, + size_t (*f_mbstowcs)(wchar_t *wcstr, const char *mbstr, size_t count)) + +utf8str (OUT) Points to a buffer to receive the converted UTF-8 string. + May be NULL. + + mbchar (IN) Address of the null-terminated multi-byte input string. + + count (IN) The size of the output buffer in bytes. + + f_mbstowcs (IN) The function to use for converting a multibyte string + to a wide character string. If NULL, the local ANSI + C routine mbstowcs is used. + +Return Value: + If successful, the function returns the length in + bytes of the UTF-8 output string, excluding the null + terminator, if present. + + If utf8str is NULL, count is ignored and the function + returns the number of bytes required for the output string, + excluding the NULL. + + If count is zero, 0 is returned and nothing is written to utf8str. + + If mbstr is NULL or points to an empty string, the + function returns 1 and a null byte is written to utf8str. + + If mbstr contains an invalid multi-byte character, -1 is returned. + + If the returned value is equal to count, the entire null-terminated + string would not fit in the output buffer. + + +3.3 ldap_x_utf8_to_mb - Convert a UTF-8 character to a multi-byte character. + +int ldap_x_utf8_to_mb ( char *mbchar, const char *utf8char, + int (*f_wctomb)(char *mbchar, wchar_t wchar) ) + +mbchar (OUT) Points to a byte buffer to receive the converted multi-byte + character. May be NULL. + + utf8char (IN) Address of the UTF-8 character sequence. + + f_wctomb (IN) The function to use for converting a wide character + to a multibyte character. If NULL, the local + ANSI C routine wctomb is used. + + +Return Value: + If successful, the function returns the length in + bytes of the multi-byte output character. + + If utf8char is NULL or points to an empty string, the + function returns 1 and a null byte is written to mbchar. + + If utf8char contains an invalid UTF-8 sequence, -1 is returned. + + +3.4 int ldap_x_utf8s_to_mbs - Convert a UTF-8 string to a multi-byte string. + + +int ldap_x_utf8s_to_mbs ( char *mbstr, const char *utf8str, size_t count, + size_t (*f_wcstombs)(char *mbstr, const wchar_t *wcstr, size_t count) ) + + mbstr (OUT) Points to a byte buffer to receive the converted + multi-byte string. May be NULL. + + utf8str (IN) Address of the null-terminated UTF-8 string to convert. + + count (IN) The size of the output buffer in bytes. + + f_wcstombs (IN) The function to use for converting a wide character + string to a multibyte string. If NULL, the local + ANSI C routine wcstombs is used. + +Return Value: + If successful, the function returns the number of bytes + written to mbstr, excluding the null termination + character, if any. + + If mbstr is NULL, count is ignored and the funtion + returns the number of bytes required for the output string, + excluding the NULL. + + If count is zero, 0 is returned and nothing is written to + mbstr. + + If utf8str is NULL or points to an empty string, the + function returns 1 and a null byte is written to mbstr. + + If an invalid UTF-8 character is encountered, the + function returns -1. + +The output string will be null terminated if there is space for it in +the output buffer. + + |