## idn2.h idn2.h — main library interfaces |

## Functions

#define | GCC_VERSION_AT_LEAST()
int | idn2_lookup_u8 ()
int | idn2_register_u8 ()
int | idn2_lookup_ul ()
int | idn2_register_ul ()
int | idn2_to_ascii_4i ()
int | idn2_to_ascii_4i2 ()
int | idn2_to_ascii_4z ()
int | idn2_to_ascii_8z ()
int | idn2_to_ascii_lz ()
int | idn2_to_unicode_8z4z ()
int | idn2_to_unicode_4z4z ()
int | idn2_to_unicode_44i ()
int | idn2_to_unicode_8z8z ()
int | idn2_to_unicode_8zlz ()
int | idn2_to_unicode_lzlz ()
int | idn2_punycode_encode ()
int | idn2_punycode_decode ()
const char * | idn2_strerror ()
const char * | idn2_strerror_name ()
const char * | idn2_check_version ()
void | idn2_free ()

## Types and Values

#define | G_GNUC_IDN2_ATTRIBUTE_PURE
#define | G_GNUC_IDN2_ATTRIBUTE_CONST
#define | G_GNUC_UNUSED
#define | IDN2_VERSION
#define | IDN2_VERSION_NUMBER
#define | IDN2_VERSION_MAJOR
#define | IDN2_VERSION_MINOR
#define | IDN2_VERSION_PATCH
#define | IDN2_LABEL_MAX_LENGTH
#define | IDN2_DOMAIN_MAX_LENGTH
enum | idn2_flags
enum | idn2_rc

## Description

The main library interfaces are declared in idn2.h.

## Functions

### GCC_VERSION_AT_LEAST()

    #  define GCC_VERSION_AT_LEAST(major, minor) ((__GNUC__ > (major)) || (__GNUC__ == (major) && __GNUC_MINOR__ >= (minor)))

Pre-processor symbol to check the gcc version.

#### Parameters

major | gcc major version number to compare with |
minor | gcc minor version number to compare with |

### idn2_lookup_u8 ()

    int
    idn2_lookup_u8 (const uint8_t *src,
                    uint8_t **lookupname,
                    int flags);

Perform IDNA2008 lookup string conversion on domain name `src` , as described in section 5 of RFC 5891. Note that the input string must be encoded in UTF-8 and be in Unicode NFC form.

Pass `IDN2_NFC_INPUT` in `flags` to convert input to NFC form before further processing. `IDN2_TRANSITIONAL` and `IDN2_NONTRANSITIONAL` do already imply `IDN2_NFC_INPUT`.

Pass `IDN2_ALABEL_ROUNDTRIP` in `flags` to convert any input A-labels to U-labels and perform additional testing. This is default since version 2.2. To switch this behavior off, pass IDN2_NO_ALABEL_ROUNDTRIP

Pass `IDN2_TRANSITIONAL` to enable Unicode TR46 transitional processing, and `IDN2_NONTRANSITIONAL` to enable Unicode TR46 non-transitional processing.

Multiple flags may be specified by binary or:ing them together.

After version 2.0.3: `IDN2_USE_STD3_ASCII_RULES` disabled by default. Previously we were eliminating non-STD3 characters from domain strings such as _443._tcp.example.com, or IPs 1.2.3.4/24 provided to libidn2 functions. That was an unexpected regression for applications switching from libidn and thus it is no longer applied by default. Use `IDN2_USE_STD3_ASCII_RULES` to enable that behavior again.

After version 0.11: `lookupname` may be NULL to test lookup of `src` without allocating memory.

#### Parameters

src | input zero-terminated UTF-8 string in Unicode NFC normalized form. |
lookupname | newly allocated output variable with name to lookup in DNS. |
flags | optional idn2_flags to modify behaviour. |

#### Returns

On successful conversion `IDN2_OK` is returned, if the output domain or any label would have been too long `IDN2_TOO_BIG_DOMAIN` or `IDN2_TOO_BIG_LABEL` is returned, or another error code is returned.

Since: 0.1

### idn2_register_u8 ()

    int
    idn2_register_u8 (const uint8_t *ulabel,
                      const uint8_t *alabel,
                      uint8_t **insertname,
                      int flags);

Perform IDNA2008 register string conversion on domain label `ulabel` and `alabel` , as described in section 4 of RFC 5891. Note that the input `ulabel` must be encoded in UTF-8 and be in Unicode NFC form.

Pass `IDN2_NFC_INPUT` in `flags` to convert input `ulabel` to NFC form before further processing.

It is recommended to supply both `ulabel` and `alabel` for better error checking, but supplying just one of them will work. Passing in only `alabel` is better than only `ulabel` . See RFC 5891 section 4 for more information.

After version 0.11: `insertname` may be NULL to test conversion of `src` without allocating memory.

#### Parameters

ulabel | input zero-terminated UTF-8 and Unicode NFC string, or NULL. |
alabel | input zero-terminated ACE encoded string (xn--), or NULL. |
insertname | newly allocated output variable with name to register in DNS. |
flags | optional idn2_flags to modify behaviour. |

#### Returns

On successful conversion `IDN2_OK` is returned, when the given `ulabel` and `alabel` does not match each other `IDN2_UALABEL_MISMATCH` is returned, when either of the input labels are too long `IDN2_TOO_BIG_LABEL` is returned, when `alabel` does does not appear to be a proper A-label `IDN2_INVALID_ALABEL` is returned, or another error code is returned.

### idn2_lookup_ul ()

    int
    idn2_lookup_ul (const char *src,
                    char **lookupname,
                    int flags);

Perform IDNA2008 lookup string conversion on domain name `src` , as described in section 5 of RFC 5891. Note that the input is assumed to be encoded in the locale's default coding system, and will be transcoded to UTF-8 and NFC normalized by this function.

Pass `IDN2_ALABEL_ROUNDTRIP` in `flags` to convert any input A-labels to U-labels and perform additional testing. This is default since version 2.2. To switch this behavior off, pass IDN2_NO_ALABEL_ROUNDTRIP

Pass `IDN2_TRANSITIONAL` to enable Unicode TR46 transitional processing, and `IDN2_NONTRANSITIONAL` to enable Unicode TR46 non-transitional processing.

Multiple flags may be specified by binary or:ing them together, for example `IDN2_ALABEL_ROUNDTRIP` | `IDN2_NONTRANSITIONAL`.

The `IDN2_NFC_INPUT` in `flags` is always enabled in this function.

After version 0.11: `lookupname` may be NULL to test lookup of `src` without allocating memory.

#### Parameters

src | input zero-terminated locale encoded string. |
lookupname | newly allocated output variable with name to lookup in DNS. |
flags | optional idn2_flags to modify behaviour. |

#### Returns

On successful conversion `IDN2_OK` is returned, if conversion from locale to UTF-8 fails then `IDN2_ICONV_FAIL` is returned, if the output domain or any label would have been too long `IDN2_TOO_BIG_DOMAIN` or `IDN2_TOO_BIG_LABEL` is returned, or another error code is returned.

Since: 0.1

### idn2_register_ul ()

    int
    idn2_register_ul (const char *ulabel,
                      const char *alabel,
                      char **insertname,
                      int flags);

Perform IDNA2008 register string conversion on domain label `ulabel` and `alabel` , as described in section 4 of RFC 5891. Note that the input `ulabel` is assumed to be encoded in the locale's default coding system, and will be transcoded to UTF-8 and NFC normalized by this function.

It is recommended to supply both `ulabel` and `alabel` for better error checking, but supplying just one of them will work. Passing in only `alabel` is better than only `ulabel` . See RFC 5891 section 4 for more information.

After version 0.11: `insertname` may be NULL to test conversion of `src` without allocating memory.

#### Parameters

ulabel | input zero-terminated locale encoded string, or NULL. |
alabel | input zero-terminated ACE encoded string (xn--), or NULL. |
insertname | newly allocated output variable with name to register in DNS. |
flags | optional idn2_flags to modify behaviour. |

#### Returns

On successful conversion `IDN2_OK` is returned, when the given `ulabel` and `alabel` does not match each other `IDN2_UALABEL_MISMATCH` is returned, when either of the input labels are too long `IDN2_TOO_BIG_LABEL` is returned, when `alabel` does does not appear to be a proper A-label `IDN2_INVALID_ALABEL` is returned, when `ulabel` locale to UTF-8 conversion failed `IDN2_ICONV_FAIL` is returned, or another error code is returned.

### idn2_to_ascii_4i ()

    int
    idn2_to_ascii_4i (const uint32_t *input,
                      size_t inlen,
                      char *output,
                      int flags);

The ToASCII operation takes a sequence of Unicode code points that make up one domain label and transforms it into a sequence of code points in the ASCII range (0..7F). If ToASCII succeeds, the original sequence and the resulting sequence are equivalent labels.

It is important to note that the ToASCII operation can fail. ToASCII fails if any step of it fails. If any step of the ToASCII operation fails on any label in a domain name, that domain name MUST NOT be used as an internationalized domain name. The method for dealing with this failure is application-specific.

The inputs to ToASCII are a sequence of code points.

ToASCII never alters a sequence of code points that are all in the ASCII range to begin with (although it could fail). Applying the ToASCII operation multiple effect as applying it just once.

The default behavior of this function (when flags are zero) is to apply the IDNA2008 rules without the TR46 amendments. As the TR46 non-transitional processing is nowadays ubiquitous, when unsure, it is recommended to call this function with the `IDN2_NONTRANSITIONAL` and the `IDN2_NFC_INPUT` flags for compatibility with other software.

Warning: With version 2.1.1 until before version 2.3.5 this function was deprecated in favor `idn2_to_ascii_4i2()`. We still encourage you to use `idn2_to_ascii_4i2()` when appropriate.

#### Parameters

input | zero terminated input Unicode (UCS-4) string. |
inlen | number of elements in `input` . |
output | output zero terminated string that must have room for at least 63 characters plus the terminating zero. |
flags | optional idn2_flags to modify behaviour. |

#### Returns

On successful conversion `IDN2_OK` is returned; if the output label would have been too long `IDN2_TOO_BIG_LABEL` is returned, or another error code is returned.

Since: 2.0.0

### idn2_to_ascii_4i2 ()

    int
    idn2_to_ascii_4i2 (const uint32_t *input,
                       size_t inlen,
                       char **output,
                       int flags);

The ToASCII operation takes a sequence of Unicode code points that make up one domain label and transforms it into a sequence of code points in the ASCII range (0..7F). If ToASCII succeeds, the original sequence and the resulting sequence are equivalent labels.

It is important to note that the ToASCII operation can fail. ToASCII fails if any step of it fails. If any step of the ToASCII operation fails on any label in a domain name, that domain name MUST NOT be used as an internationalized domain name. The method for dealing with this failure is application-specific.

The inputs to ToASCII are a sequence of code points.

ToASCII never alters a sequence of code points that are all in the ASCII range to begin with (although it could fail). Applying the ToASCII operation multiple effect as applying it just once.

The default behavior of this function (when flags are zero) is to apply the IDNA2008 rules without the TR46 amendments. As the TR46 non-transitional processing is nowadays ubiquitous, when unsure, it is recommended to call this function with the `IDN2_NONTRANSITIONAL` and the `IDN2_NFC_INPUT` flags for compatibility with other software.

#### Parameters

input | zero terminated input Unicode (UCS-4) string. |
inlen | number of elements in `input` . |
output | pointer to newly allocated zero-terminated output string. |
flags | optional idn2_flags to modify behaviour. |

#### Returns

On successful conversion `IDN2_OK` is returned; if the output label would have been too long `IDN2_TOO_BIG_LABEL` is returned, or another error code is returned.

Since: 2.1.1

### idn2_to_ascii_4z ()

    int
    idn2_to_ascii_4z (const uint32_t *input,
                      char **output,
                      int flags);

Convert UCS-4 domain name to ASCII string using the IDNA2008 rules. The domain name may contain several labels, separated by dots. The output buffer must be deallocated by the caller.

The default behavior of this function (when flags are zero) is to apply the IDNA2008 rules without the TR46 amendments. As the TR46 non-transitional processing is nowadays ubiquitous, when unsure, it is recommended to call this function with the `IDN2_NONTRANSITIONAL` and the `IDN2_NFC_INPUT` flags for compatibility with other software.

#### Parameters

input | zero terminated input Unicode (UCS-4) string. |
output | pointer to newly allocated zero-terminated output string. |
flags | optional idn2_flags to modify behaviour. |

#### Returns

Returns `IDN2_OK` on success, or error code.

Since: 2.0.0

### idn2_to_ascii_8z ()

    int
    idn2_to_ascii_8z (const char *input,
                      char **output,
                      int flags);

Convert UTF-8 domain name to ASCII string using the IDNA2008 rules. The domain name may contain several labels, separated by dots. The output buffer must be deallocated by the caller.

The default behavior of this function (when flags are zero) is to apply the IDNA2008 rules without the TR46 amendments. As the TR46 non-transitional processing is nowadays ubiquitous, when unsure, it is recommended to call this function with the `IDN2_NONTRANSITIONAL` and the `IDN2_NFC_INPUT` flags for compatibility with other software.

#### Parameters

input | zero terminated input UTF-8 string. |
output | pointer to newly allocated output string. |
flags | optional idn2_flags to modify behaviour. |

#### Returns

Returns `IDN2_OK` on success, or error code.

Since: 2.0.0

### idn2_to_ascii_lz ()

    int
    idn2_to_ascii_lz (const char *input,
                      char **output,
                      int flags);

Convert a domain name in locale's encoding to ASCII string using the IDNA2008 rules. The domain name may contain several labels, separated by dots. The output buffer must be deallocated by the caller.

The default behavior of this function (when flags are zero) is to apply the IDNA2008 rules without the TR46 amendments. As the TR46 non-transitional processing is nowadays ubiquitous, when unsure, it is recommended to call this function with the `IDN2_NONTRANSITIONAL` and the `IDN2_NFC_INPUT` flags for compatibility with other software.

#### Parameters

input | zero terminated input UTF-8 string. |
output | pointer to newly allocated output string. |
flags | optional idn2_flags to modify behaviour. |

#### Returns

`IDN2_OK` on success, or error code. Same as described in `idn2_lookup_ul()` documentation.

Since: 2.0.0

### idn2_to_unicode_8z4z ()

    int
    idn2_to_unicode_8z4z (const char *input,
                          uint32_t **output,
                          int flags);

Converts a possibly ACE encoded domain name in UTF-8 format into a UTF-32 string (punycode decoding). The output buffer will be zero-terminated and must be deallocated by the caller.

`output` may be NULL to test lookup of `input` without allocating memory.

#### Parameters

input | Input zero-terminated UTF-8 string. |
output | Newly allocated UTF-32/UCS-4 output string. |
flags | Currently unused. |

#### Returns

`IDN2_OK`: The conversion was successful. `IDN2_TOO_BIG_DOMAIN`: The domain is too long. `IDN2_TOO_BIG_LABEL`: A label is would have been too long. `IDN2_ENCODING_ERROR`: Character conversion failed. `IDN2_MALLOC`: Memory allocation failed.

Since: 2.0.0

### idn2_to_unicode_4z4z ()

    int
    idn2_to_unicode_4z4z (const uint32_t *input,
                          uint32_t **output,
                          int flags);

Converts a possibly ACE encoded domain name in UTF-32 format into a UTF-32 string (punycode decoding). The output buffer will be zero-terminated and must be deallocated by the caller.

`output` may be NULL to test lookup of `input` without allocating memory.

#### Parameters

input | Input zero-terminated UTF-32 string. |
output | Newly allocated UTF-32 output string. |
flags | Currently unused. |

#### Returns

`IDN2_OK`: The conversion was successful. `IDN2_TOO_BIG_DOMAIN`: The domain is too long. `IDN2_TOO_BIG_LABEL`: A label is would have been too long. `IDN2_ENCODING_ERROR`: Character conversion failed. `IDN2_MALLOC`: Memory allocation failed.

Since: 2.0.0

### idn2_to_unicode_44i ()

    int
    idn2_to_unicode_44i (const uint32_t *in,
                         size_t inlen,
                         uint32_t *out,
                         size_t *outlen,
                         int flags);

The ToUnicode operation takes a sequence of UTF-32 code points that make up one domain label and returns a sequence of UTF-32 code points. If the input sequence is a label in ACE form, then the result is an equivalent internationalized label that is not in ACE form, otherwise the original sequence is returned unaltered.

`output` may be NULL to test lookup of `input` without allocating memory.

#### Parameters

in | Input array with UTF-32 code points. |
inlen | number of code points of input array |
out | output array with UTF-32 code points. |
outlen | on input, maximum size of output array with UTF-32 code points, on exit, actual size of output array with UTF-32 code points. |
flags | Currently unused. |

#### Returns

`IDN2_OK`: The conversion was successful. `IDN2_TOO_BIG_DOMAIN`: The domain is too long. `IDN2_TOO_BIG_LABEL`: A label is would have been too long. `IDN2_ENCODING_ERROR`: Character conversion failed. `IDN2_MALLOC`: Memory allocation failed.

Since: 2.0.0

### idn2_to_unicode_8z8z ()

    int
    idn2_to_unicode_8z8z (const char *input,
                          char **output,
                          int flags);

Converts a possibly ACE encoded domain name in UTF-8 format into a UTF-8 string (punycode decoding). The output buffer will be zero-terminated and must be deallocated by the caller.

`output` may be NULL to test lookup of `input` without allocating memory.

#### Parameters

input | Input zero-terminated UTF-8 string. |
output | Newly allocated UTF-8 output string. |
flags | Currently unused. |

#### Returns

`IDN2_OK`: The conversion was successful. `IDN2_TOO_BIG_DOMAIN`: The domain is too long. `IDN2_TOO_BIG_LABEL`: A label is would have been too long. `IDN2_ENCODING_ERROR`: Character conversion failed. `IDN2_MALLOC`: Memory allocation failed.

Since: 2.0.0

### idn2_to_unicode_8zlz ()

    int
    idn2_to_unicode_8zlz (const char *input,
                          char **output,
                          int flags);

Converts a possibly ACE encoded domain name in UTF-8 format into a string encoded in the current locale's character set (punycode decoding). The output buffer will be zero-terminated and must be deallocated by the caller.

`output` may be NULL to test lookup of `input` without allocating memory.

#### Parameters

input | Input zero-terminated UTF-8 string. |
output | Newly allocated output string in current locale's character set. |
flags | Currently unused. |

#### Returns

`IDN2_OK`: The conversion was successful. `IDN2_TOO_BIG_DOMAIN`: The domain is too long. `IDN2_TOO_BIG_LABEL`: A label is would have been too long. `IDN2_ENCODING_ERROR`: Character conversion failed. `IDN2_MALLOC`: Memory allocation failed.

Since: 2.0.0

### idn2_to_unicode_lzlz ()

    int
    idn2_to_unicode_lzlz (const char *input,
                          char **output,
                          int flags);

Converts a possibly ACE encoded domain name in the locale's character set into a string encoded in the current locale's character set (punycode decoding). The output buffer will be zero-terminated and must be deallocated by the caller.

`output` may be NULL to test lookup of `input` without allocating memory.

#### Parameters

input | Input zero-terminated string encoded in the current locale's character set. |
output | Newly allocated output string in current locale's character set. |
flags | Currently unused. |

#### Returns

`IDN2_OK`: The conversion was successful. `IDN2_TOO_BIG_DOMAIN`: The domain is too long. `IDN2_TOO_BIG_LABEL`: A label is would have been too long. `IDN2_ENCODING_ERROR`: Output character conversion failed. `IDN2_ICONV_FAIL`: Input character conversion failed. `IDN2_MALLOC`: Memory allocation failed.

Since: 2.0.0

### idn2_punycode_encode ()

    int
    idn2_punycode_encode (const uint32_t *input,
                          size_t input_length,
                          char *output,
                          size_t *output_length);

Converts a sequence of code points to Punycode.

Warning: Be aware that is rare for applications to need to perform Punycode operations, and you should consider `idn2_to_ascii_8z()`, `idn2_to_ascii_lz()`, `idn2_to_ascii_4z()` etc.

#### Parameters

input | array of input Unicode (UCS-4) code points |
input_length | number of code points in the `input` array. |
output | output character array with ASCII code points. |
output_length | size of `output` array |

#### Returns

On successful encoding `IDN2_OK` is returned, or an error codes like `IDN2_PUNYCODE_BAD_INPUT`, `IDN2_PUNYCODE_BIG_OUTPUT`, or `IDN2_PUNYCODE_OVERFLOW`.

Since: 2.3.5

### idn2_punycode_decode ()

    int
    idn2_punycode_decode (const char *input,
                          size_t input_length,
                          uint32_t *output,
                          size_t *output_length);

Converts Punycode to a sequence of code points.

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 uint32_t, even if the supplied `output_length` is greater than that.

Warning: Be aware that is rare for applications to need to perform Punycode operations, and you should consider `idn2_to_unicode_8z8z()`, `idn2_to_unicode_lzlz()` etc.

#### Parameters

input | array of ASCII characters (0..7F) |
input_length | Number of ASCII characters in the `input` array. |
output | output character array with ASCII code points. |
output_length | on input, guarantee that `output` has room for this many code points; on output, *`output_length` holds number of code points in `output` . |

#### Returns

On successful encoding `IDN2_OK` is returned, or an error codes like `IDN2_PUNYCODE_BAD_INPUT`, `IDN2_PUNYCODE_BIG_OUTPUT`, or `IDN2_PUNYCODE_OVERFLOW`.

Since: 2.3.5

### idn2_strerror ()

    const char *
    idn2_strerror (int rc);

Convert internal libidn2 error code to a humanly readable string. The returned pointer must not be de-allocated by the caller.

#### Parameters

rc | return code from another libidn2 function. |

#### Returns

A humanly readable string describing error.

### idn2_strerror_name ()

    const char *
    idn2_strerror_name (int rc);

Convert internal libidn2 error code to a string corresponding to internal header file symbols. For example, idn2_strerror_name(IDN2_MALLOC) will return the string "IDN2_MALLOC".

The caller must not attempt to de-allocate the returned string.

#### Parameters

rc | return code from another libidn2 function. |

#### Returns

A string corresponding to error code symbol.

### idn2_check_version ()

    const char *
    idn2_check_version (const char *req_version);

Check IDN2 library version. This function can also be used to read out the version of the library code used. See `IDN2_VERSION` for a suitable `req_version` string, it corresponds to the idn2.h header file version. Normally these two version numbers match, but if you are using an application built against an older libidn2 with a newer libidn2 shared library they will be different.

#### Parameters

req_version | version string to compare with, or NULL. |

#### Returns

Check that the version of the library is at minimum the one given as a string in `req_version` and return the actual version string of the library; return NULL if the condition is not met. If NULL is passed to this function no check is done and only the version string is returned.

### idn2_free ()

    void
    idn2_free (void *ptr);

Call free(3) on the given pointer.

This function is typically only useful on systems where the library malloc heap is different from the library caller malloc heap, which happens on Windows when the library is a separate DLL.

#### Parameters

ptr | pointer to deallocate |

## Types and Values

### G_GNUC_IDN2_ATTRIBUTE_PURE

    #  define G_GNUC_IDN2_ATTRIBUTE_PURE __attribute__ ((pure))

Function attribute: Function is a pure function.

### G_GNUC_IDN2_ATTRIBUTE_CONST

    #  define G_GNUC_IDN2_ATTRIBUTE_CONST __attribute__ ((const))

Function attribute: Function is a const function.

### G_GNUC_UNUSED

    #  define G_GNUC_UNUSED __attribute__ ((__unused__))

Parameter attribute: Parameter is not used.

### IDN2_VERSION

    # define IDN2_VERSION "2.3.7"

Pre-processor symbol with a string that describe the header file version number. Used together with `idn2_check_version()` to verify header file and run-time library consistency.

### IDN2_VERSION_NUMBER

    # define IDN2_VERSION_NUMBER 0x02030007

Pre-processor symbol with a hexadecimal value describing the header file version number. For example, when the header version is 1.2.4711 this symbol will have the value 0x01021267. The last four digits are used to enumerate development snapshots, but for all public releases they will be 0000.

### IDN2_VERSION_MAJOR

    # define IDN2_VERSION_MAJOR 2

Pre-processor symbol for the major version number (decimal). The version scheme is major.minor.patchlevel.

### IDN2_VERSION_MINOR

    # define IDN2_VERSION_MINOR 3

Pre-processor symbol for the minor version number (decimal). The version scheme is major.minor.patchlevel.

### IDN2_VERSION_PATCH

    # define IDN2_VERSION_PATCH 7

Pre-processor symbol for the patch level number (decimal). The version scheme is major.minor.patchlevel.

### IDN2_LABEL_MAX_LENGTH

    # define IDN2_LABEL_MAX_LENGTH 63

Constant specifying the maximum length of a DNS label to 63 characters, as specified in RFC 1034.

### IDN2_DOMAIN_MAX_LENGTH

    # define IDN2_DOMAIN_MAX_LENGTH 255

Constant specifying the maximum size of the wire encoding of a DNS domain to 255 characters, as specified in RFC 1034. Note that the usual printed representation of a domain name is limited to 253 characters if it does not end with a period, or 254 characters if it ends with a period.

### enum idn2_flags

Flags to IDNA2008 functions, to be binary or:ed together. Specify only 0 if you want the default behaviour.

#### Members

IDN2_NFC_INPUT | Normalize input string using normalization form C. |
IDN2_ALABEL_ROUNDTRIP | Perform optional IDNA2008 lookup roundtrip check (default). |
IDN2_TRANSITIONAL | Perform Unicode TR46 transitional processing. |
IDN2_NONTRANSITIONAL | Perform Unicode TR46 non-transitional processing (default). |
IDN2_ALLOW_UNASSIGNED | Libidn compatibility flag, unused. |
IDN2_USE_STD3_ASCII_RULES | Use STD3 ASCII rules. This is a Unicode TR46 only flag, and will be ignored when set without either `IDN2_TRANSITIONAL` or `IDN2_NONTRANSITIONAL` . |
IDN2_NO_TR46 | Disable Unicode TR46 processing. |
IDN2_NO_ALABEL_ROUNDTRIP | Disable ALabel lookup roundtrip check. |

### enum idn2_rc

Return codes for IDN2 functions. All return codes are negative except for the successful code IDN2_OK which are guaranteed to be

1. Positive values are reserved for non-error return codes.

Note that the idn2_rc enumeration may be extended at a later date to include new return codes.

#### Members

IDN2_OK | Successful return. |
IDN2_MALLOC | Memory allocation error. |
IDN2_NO_CODESET | Could not determine locale string encoding format. |
IDN2_ICONV_FAIL | Could not transcode locale string to UTF-8. |
IDN2_ENCODING_ERROR | Unicode data encoding error. |
IDN2_NFC | Error normalizing string. |
IDN2_PUNYCODE_BAD_INPUT | Punycode invalid input. |
IDN2_PUNYCODE_BIG_OUTPUT | Punycode output buffer too small. |
IDN2_PUNYCODE_OVERFLOW | Punycode conversion would overflow. |
IDN2_TOO_BIG_DOMAIN | Domain name longer than 255 characters. |
IDN2_TOO_BIG_LABEL | Domain label longer than 63 characters. |
IDN2_INVALID_ALABEL | Input A-label is not valid. |
IDN2_UALABEL_MISMATCH | Input A-label and U-label does not match. |
IDN2_INVALID_FLAGS | Invalid combination of flags. |
IDN2_NOT_NFC | String is not NFC. |
IDN2_2HYPHEN | String has forbidden two hyphens. |
IDN2_HYPHEN_STARTEND | String has forbidden starting/ending hyphen. |
IDN2_LEADING_COMBINING | String has forbidden leading combining character. |
IDN2_DISALLOWED | String has disallowed character. |
IDN2_CONTEXTJ | String has forbidden context-j character. |
IDN2_CONTEXTJ_NO_RULE | String has context-j character with no rull. |
IDN2_CONTEXTO | String has forbidden context-o character. |
IDN2_CONTEXTO_NO_RULE | String has context-o character with no rull. |
IDN2_UNASSIGNED | String has forbidden unassigned character. |
IDN2_BIDI | String has forbidden bi-directional properties. |
IDN2_DOT_IN_LABEL | Label has forbidden dot (TR46). |
IDN2_INVALID_TRANSITIONAL | Label has character forbidden in transitional mode (TR46). |
IDN2_INVALID_NONTRANSITIONAL | Label has character forbidden in non-transitional mode (TR46). |
IDN2_ALABEL_ROUNDTRIP_FAILED | ALabel -> Ulabel -> ALabel result differs from input. |