(libidn.info.gz) Punycode Functions

(libidn.info.gz) Stringprep Functions
 
 5 Punycode Functions
 ********************
 
 Punycode is a simple and efficient transfer encoding syntax designed
 for use with Internationalized Domain Names in Applications. It
 uniquely and reversibly transforms a Unicode string into an ASCII
 string. ASCII characters in the Unicode string are represented
 literally, and non-ASCII characters are represented by ASCII characters
 that are allowed in host name labels (letters, digits, and hyphens). A
 general algorithm called Bootstring allows a string of basic code
 points to uniquely represent any string of code points drawn from a
 larger set. Punycode is an instance of Bootstring that uses particular
 parameter values, appropriate for IDNA.
 
 5.1 Header file `punycode.h'
 ============================
 
 To use the functions explained in this chapter, you need to include the
 file `punycode.h' using:
 
      #include <punycode.h>
 
 5.2 Unicode Code Point Data Type
 ================================
 
 The punycode function uses a special type to denote Unicode code
 points.  It is guaranteed to always be a 32 bit unsigned integer.
 
  -- Punycode Unicode code point: uint32_t punycode_uint
      A unsigned integer that hold Unicode code points.
 
 5.3 Core Functions
 ==================
 
 Note that the current implementation will fail if the `input_length'
 exceed 4294967295 (the size of `punycode_uint').  This restriction may
 be removed in the future.  Meanwhile applications are encouraged to not
 depend on this problem, and use `sizeof' to initialize `input_length'
 and `output_length'.
 
    The functions provided are the following two entry points:
 
 punycode_encode
 ---------------
 
  -- Function: int punycode_encode (size_t INPUT_LENGTH, const
           punycode_uint [] INPUT, const unsigned char [] CASE_FLAGS,
           size_t * OUTPUT_LENGTH, char [] OUTPUT)
      INPUT_LENGTH: The number of code points in the `input' array and
      the number of flags in the `case_flags' array.
 
      INPUT: An array of code points.  They are presumed to be Unicode
      code points, but that is not strictly REQUIRED.  The array
      contains code points, not code units.  UTF-16 uses code units D800
      through DFFF to refer to code points 10000..10FFFF.  The code
      points D800..DFFF do not occur in any valid Unicode string.  The
      code points that can occur in Unicode strings (0..D7FF and
      E000..10FFFF) are also called Unicode scalar values.
 
      CASE_FLAGS: A `NULL' pointer or an array of boolean values parallel
      to the `input' array.  Nonzero (true, flagged) suggests that the
      corresponding Unicode character be forced to uppercase after being
      decoded (if possible), and zero (false, unflagged) suggests that
      it be forced to lowercase (if possible).  ASCII code points
      (0..7F) are encoded literally, except that ASCII letters are
      forced to uppercase or lowercase according to the corresponding
      case flags.  If `case_flags' is a `NULL' pointer then ASCII letters
      are left as they are, and other code points are treated as
      unflagged.
 
      OUTPUT_LENGTH: The caller passes in the maximum number of ASCII
      code points that it can receive.  On successful return it will
      contain the number of ASCII code points actually output.
 
      OUTPUT: An array of ASCII code points.  It is *not*
      null-terminated; it will contain zeros if and only if the `input'
      contains zeros.  (Of course the caller can leave room for a
      terminator and add one if needed.)
 
      Converts a sequence of code points (presumed to be Unicode code
      points) to Punycode.
 
      *Return value:* The return value can be any of the
      `Punycode_status' values defined above except
      `PUNYCODE_BAD_INPUT'.  If not `PUNYCODE_SUCCESS', then
      `output_size' and `output' might contain garbage.
 
 punycode_decode
 ---------------
 
  -- Function: int punycode_decode (size_t INPUT_LENGTH, const char []
           INPUT, size_t * OUTPUT_LENGTH, punycode_uint [] OUTPUT,
           unsigned char [] CASE_FLAGS)
      INPUT_LENGTH: The number of ASCII code points in the `input' array.
 
      INPUT: An array of ASCII code points (0..7F).
 
      OUTPUT_LENGTH: The caller passes in the maximum number of code
      points that it can receive into the `output' array (which is also
      the maximum number of flags that it can receive into the
      `case_flags' array, if `case_flags' is not a `NULL' pointer).  On
      successful return it will contain the number of code points
      actually output (which is also the number of flags actually
      output, if case_flags is not a null pointer).  The decoder will
      never need to output more code points than the number of ASCII
      code points in the input, because of the way the encoding is
      defined.  The number of code points output cannot exceed the
      maximum possible value of a punycode_uint, even if the supplied
      `output_length' is greater than that.
 
      OUTPUT: An array of code points like the input argument of
      `punycode_encode()' (see above).
 
      CASE_FLAGS: A `NULL' pointer (if the flags are not needed by the
      caller) or an array of boolean values parallel to the `output'
      array.  Nonzero (true, flagged) suggests that the corresponding
      Unicode character be forced to uppercase by the caller (if
      possible), and zero (false, unflagged) suggests that it be forced
      to lowercase (if possible).  ASCII code points (0..7F) are output
      already in the proper case, but their flags will be set
      appropriately so that applying the flags would be harmless.
 
      Converts Punycode to a sequence of code points (presumed to be
      Unicode code points).
 
      *Return value:* The return value can be any of the
      `Punycode_status' values defined above.  If not
      `PUNYCODE_SUCCESS', then `output_length', `output', and
      `case_flags' might contain garbage.
 
 5.4 Error Handling
 ==================
 
 punycode_strerror
 -----------------
 
  -- Function: const char * punycode_strerror (Punycode_status RC)
      RC: an `Punycode_status' return code.
 
      Convert a return code integer to a text string.  This string can be
      used to output a diagnostic message to the user.
 
      *PUNYCODE_SUCCESS:* Successful operation.  This value is guaranteed
      to always be zero, the remaining ones are only guaranteed to hold
      non-zero values, for logical comparison purposes.
 
      *PUNYCODE_BAD_INPUT:* Input is invalid.
 
      *PUNYCODE_BIG_OUTPUT:* Output would exceed the space provided.
 
      *PUNYCODE_OVERFLOW:* Input needs wider integers to process.
 
      *Return value:* Returns a pointer to a statically allocated string
      containing a description of the error with the return code `rc'.
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