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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.
punycode.hTo use the functions explained in this chapter, you need to include the file punycode.h using:
#include <punycode.h>
The punycode function uses a special type to denote Unicode code points. It is guaranteed to always be a 32 bit unsigned integer.
A unsigned integer that hold Unicode code points.
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:
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.
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.
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.
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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