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4 Stringprep Functions

Stringprep describes a framework for preparing Unicode text strings in order to increase the likelihood that string input and string comparison work in ways that make sense for typical users throughout the world. The stringprep protocol is useful for protocol identifier values, company and personal names, internationalized domain names, and other text strings.

4.1 Header file stringprep.h

To use the functions explained in this chapter, you need to include the file stringprep.h using: 

     #include <stringprep.h>

4.2 Defining A Stringprep Profile

Further types and structures are defined for applications that want to specify their own stringprep profile. As these are fairly obscure, and by necessity tied to the implementation, we do not document them here. Look into the stringprep.h header file, and the profiles.c source code for the details.

4.3 Control Flags

— Stringprep flags: Stringprep_profile_flags STRINGPREP_NO_NFKC

Disable the NFKC normalization, as well as selecting the non-NFKC case folding tables. Usually the profile specifies BIDI and NFKC settings, and applications should not override it unless in special situations.

— Stringprep flags: Stringprep_profile_flags STRINGPREP_NO_BIDI

Disable the BIDI step. Usually the profile specifies BIDI and NFKC settings, and applications should not override it unless in special situations.

— Stringprep flags: Stringprep_profile_flags STRINGPREP_NO_UNASSIGNED

Make the library return with an error if string contains unassigned characters according to profile.

4.4 Core Functions

stringprep_4i

— Function: int stringprep_4i (uint32_t * ucs4, size_t * len, size_t maxucs4len, Stringprep_profile_flags flags, const Stringprep_profile * profile)

ucs4: input/output array with string to prepare.

len: on input, length of input array with Unicode code points, on exit, length of output array with Unicode code points.

maxucs4len: maximum length of input/output array.

flags: a Stringprep_profile_flags value, or 0.

profile: pointer to Stringprep_profile to use.

Prepare the input UCS-4 string according to the stringprep profile, and write back the result to the input string.

The input is not required to be zero terminated (ucs4[len] = 0). The output will not be zero terminated unless ucs4[len] = 0. Instead, see stringprep_4zi() if your input is zero terminated or if you want the output to be.

Since the stringprep operation can expand the string, maxucs4len indicate how large the buffer holding the string is. This function will not read or write to code points outside that size.

The flags are one of Stringprep_profile_flags values, or 0.

The profile contain the Stringprep_profile instructions to perform. Your application can define new profiles, possibly re-using the generic stringprep tables that always will be part of the library, or use one of the currently supported profiles.

Return value: Returns STRINGPREP_OK iff successful, or an Stringprep_rc error code.

stringprep_4zi

— Function: int stringprep_4zi (uint32_t * ucs4, size_t maxucs4len, Stringprep_profile_flags flags, const Stringprep_profile * profile)

ucs4: input/output array with zero terminated string to prepare.

maxucs4len: maximum length of input/output array.

flags: a Stringprep_profile_flags value, or 0.

profile: pointer to Stringprep_profile to use.

Prepare the input zero terminated UCS-4 string according to the stringprep profile, and write back the result to the input string.

Since the stringprep operation can expand the string, maxucs4len indicate how large the buffer holding the string is. This function will not read or write to code points outside that size.

The flags are one of Stringprep_profile_flags values, or 0.

The profile contain the Stringprep_profile instructions to perform. Your application can define new profiles, possibly re-using the generic stringprep tables that always will be part of the library, or use one of the currently supported profiles.

Return value: Returns STRINGPREP_OK iff successful, or an Stringprep_rc error code.

stringprep

— Function: int stringprep (char * in, size_t maxlen, Stringprep_profile_flags flags, const Stringprep_profile * profile)

in: input/ouput array with string to prepare.

maxlen: maximum length of input/output array.

flags: a Stringprep_profile_flags value, or 0.

profile: pointer to Stringprep_profile to use.

Prepare the input zero terminated UTF-8 string according to the stringprep profile, and write back the result to the input string.

Note that you must convert strings entered in the systems locale into UTF-8 before using this function, see stringprep_locale_to_utf8().

Since the stringprep operation can expand the string, maxlen indicate how large the buffer holding the string is. This function will not read or write to characters outside that size.

The flags are one of Stringprep_profile_flags values, or 0.

The profile contain the Stringprep_profile instructions to perform. Your application can define new profiles, possibly re-using the generic stringprep tables that always will be part of the library, or use one of the currently supported profiles.

Return value: Returns STRINGPREP_OK iff successful, or an error code.

stringprep_profile

— Function: int stringprep_profile (const char * in, char ** out, const char * profile, Stringprep_profile_flags flags)

in: input array with UTF-8 string to prepare.

out: output variable with pointer to newly allocate string.

profile: name of stringprep profile to use.

flags: a Stringprep_profile_flags value, or 0.

Prepare the input zero terminated UTF-8 string according to the stringprep profile, and return the result in a newly allocated variable.

Note that you must convert strings entered in the systems locale into UTF-8 before using this function, see stringprep_locale_to_utf8().

The output out variable must be deallocated by the caller.

The flags are one of Stringprep_profile_flags values, or 0.

The profile specifies the name of the stringprep profile to use. It must be one of the internally supported stringprep profiles.

Return value: Returns STRINGPREP_OK iff successful, or an error code.

4.5 Error Handling

stringprep_strerror

— Function: const char * stringprep_strerror (Stringprep_rc rc)

rc: a Stringprep_rc return code.

Convert a return code integer to a text string. This string can be used to output a diagnostic message to the user.

STRINGPREP_OK: 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.

STRINGPREP_CONTAINS_UNASSIGNED: String contain unassigned Unicode code points, which is forbidden by the profile.

STRINGPREP_CONTAINS_PROHIBITED: String contain code points prohibited by the profile.

STRINGPREP_BIDI_BOTH_L_AND_RAL: String contain code points with conflicting bidirection category.

STRINGPREP_BIDI_LEADTRAIL_NOT_RAL: Leading and trailing character in string not of proper bidirectional category.

STRINGPREP_BIDI_CONTAINS_PROHIBITED: Contains prohibited code points detected by bidirectional code.

STRINGPREP_TOO_SMALL_BUFFER: Buffer handed to function was too small. This usually indicate a problem in the calling application.

STRINGPREP_PROFILE_ERROR: The stringprep profile was inconsistent. This usually indicate an internal error in the library.

STRINGPREP_FLAG_ERROR: The supplied flag conflicted with profile. This usually indicate a problem in the calling application.

STRINGPREP_UNKNOWN_PROFILE: The supplied profile name was not known to the library.

STRINGPREP_NFKC_FAILED: The Unicode NFKC operation failed. This usually indicate an internal error in the library.

STRINGPREP_MALLOC_ERROR: The malloc() was out of memory. This is usually a fatal error.

Return value: Returns a pointer to a statically allocated string containing a description of the error with the return code rc.

4.6 Stringprep Profile Macros

— Function: int stringprep_nameprep_no_unassigned (char * in, int maxlen)

in: input/ouput array with string to prepare.

maxlen: maximum length of input/output array.

Prepare the input UTF-8 string according to the nameprep profile. The AllowUnassigned flag is false, use stringprep_nameprep for true AllowUnassigned. Returns 0 iff successful, or an error code.

— Function: int stringprep_iscsi (char * in, int maxlen)

in: input/ouput array with string to prepare.

maxlen: maximum length of input/output array.

Prepare the input UTF-8 string according to the draft iSCSI stringprep profile. Returns 0 iff successful, or an error code.

— Function: int stringprep_plain (char * in, int maxlen)

in: input/ouput array with string to prepare.

maxlen: maximum length of input/output array.

Prepare the input UTF-8 string according to the draft SASL ANONYMOUS profile. Returns 0 iff successful, or an error code.

— Function: int stringprep_xmpp_nodeprep (char * in, int maxlen)

in: input/ouput array with string to prepare.

maxlen: maximum length of input/output array.

Prepare the input UTF-8 string according to the draft XMPP node identifier profile. Returns 0 iff successful, or an error code.

— Function: int stringprep_xmpp_resourceprep (char * in, int maxlen)

in: input/ouput array with string to prepare.

maxlen: maximum length of input/output array.

Prepare the input UTF-8 string according to the draft XMPP resource identifier profile. Returns 0 iff successful, or an error code.