UTF-8 module for Lua 5.x

This module adds UTF-8 support to Lua.

It use data extracted from Unicode Character Database, and tested on Lua 5.2.3, Lua 5.3.0 and LuaJIT.

parseucd.lua is a pure Lua script generate unidata.h, to support convert characters and check characters' category.

It mainly used to compatible with Lua's own string module, it passed all string and pattern matching test in lua test suite2.

It also adds some useful routines against UTF-8 features, such as:

• a convenient interface to escape Unicode sequence in string.
• string insert/remove, since UTF-8 substring extract may expensive.
• calculate Unicode width, useful when implement e.g. console emulator.
• a useful interface to translate Unicode offset and byte offset.
• checking UTF-8 strings for validity and removing invalid byte sequences.

Note that to avoid conflict with the Lua5.3's buitin library 'utf8', this library produce a file like lua-utf8.dll or lua-utf8.so. so use it like this:

local utf8 = require 'lua-utf8'

in your codes :-(

LuaRocks Installation

luarocks install luautf8

It's now full-compatible with Lua5.3's utf8 library, so replace this file (and headers) with lua5.3 source's lutf8lib.c is also okay.

Usage

Many routines are same as Lua's string module:

• utf8.byte
• utf8.char
• utf8.find
• utf8.gmatch
• utf8.gsub
• utf8.len
• utf8.lower
• utf8.match
• utf8.reverse
• utf8.sub
• utf8.upper

The document of these functions can be find in Lua manual3.

Some routines in string module needn't support Unicode:

• string.dump
• string.format
• string.rep

They are NOT in utf8 module.

Some routines are the compatible for Lua 5.3's basic UTF-8 support library:

• utf8.offset
• utf8.codepoint
• utf8.codes

See Lua5.3's manual to get usage.

Some routines are new, with some Unicode-spec functions:

utf8.escape(str) -> utf8 string

escape a str to UTF-8 format string. It support several escape format:

• %ddd - which ddd is a decimal number at any length: change Unicode code point to UTF-8 format.
• %{ddd} - same as %nnn but has bracket around.
• %uddd - same as %ddd, u stands Unicode
• %u{ddd} - same as %{ddd}
• %xhhh - hexadigit version of %ddd
• %x{hhh} same as %xhhh.
• %? - '?' stands for any other character: escape this character.

Examples:

local u = utf8.escape
print(u"%123%u123%{123}%u{123}%xABC%x{ABC}")
print(u"%%123%?%d%%u")

utf8.charpos(s[[, charpos], index]) -> charpos, code point

convert UTF-8 position to byte offset. if only index is given, return byte offset of this UTF-8 char index. if both charpos and index is given, a new charpos will be calculated, by add/subtract UTF-8 char index to current charpos. in all cases, it returns a new char position, and code point (a number) at this position.

utf8.next(s[, charpos[, index]]) -> charpos, code point

iterate though the UTF-8 string s. If only s is given, it can used as a iterator:

for pos, code in utf8.next, "utf8-string" do
   -- ...
end

if only charpos is given, return the next byte offset of in string. if charpos and index is given, a new charpos will be calculated, by add/subtract UTF-8 char offset to current charpos. in all case, it return a new char position (in bytes), and code point (a number) at this position.

utf8.insert(s[, idx], substring) -> new_string

insert a substring to s. If idx is given, insert substring before char at this index, otherwise substring will concat to s. idx can be negative.

utf8.remove(s[, start[, stop]]) -> new_string

delete a substring in s. If neither start nor stop is given, delete the last UTF-8 char in s, otherwise delete char from start to end of s. if stop is given, delete char from start to stop (include start and stop). start and stop can be negative.

utf8.width(s[, ambi_is_double[, default_width]]) -> width

calculate the width of UTF-8 string s. if ambi_is_double is given, the ambiguous width character's width is 2, otherwise it's 1. fullwidth/doublewidth character's width is 2, and other character's width is 1. if default_width is given, it will be the width of unprintable character, used display a non-character mark for these characters. if s is a code point, return the width of this code point.

utf8.widthindex(s, location[, ambi_is_double[, default_width]]) -> idx, offset, width

return the character index at given location in string s. this is a reverse operation of utf8.width(). this function return a index of location, and a offset in in UTF-8 encoding. e.g. if cursor is at the second column (middle) of the wide char, offset will be 2. the width of character at idx is returned, also.

utf8.title(s) -> new_string

utf8.fold(s) -> new_string

convert UTF-8 string s to title-case, or folded case used to compare by ignore case. if s is a number, it's treat as a code point and return a convert code point (number). utf8.lower/utf8.upper has the same extension.

utf8.ncasecmp(a, b) -> [-1,0,1]

compare a and b without case, -1 means a < b, 0 means a == b and 1 means a > b.

utf8.isvalid(s) -> boolean

check whether s is a valid UTF-8 string or not.

utf8.clean(s[, replacement_string]) -> cleaned_string, was_valid

replace any invalid UTF-8 byte sequences in s with the replacement string. if no replacement string is provided, the default is "�" (REPLACEMENT CHARACTER U+FFFD). note that any number of consecutive invalid bytes will be replaced by a single copy of the replacement string. the 2nd return value is true if the original string was already valid (meaning no replacements were made).

utf8.invalidoffset(s[, init]) -> offset

return the byte offset within s of the first invalid UTF-8 byte sequence. (1 is the first byte of the string.) if s is a valid UTF-8 string, return nil. the optional numeric argument init specifies where to start the search; its default value is 1 and can be negative.

utf8.isnfc(s) -> boolean

check whether s is in Normal Form C or not. "Normal Form C" means that whenever possible, combining marks are combined with a preceding codepoint. For example, instead of U+0041 (LATIN CAPITAL LETTER A) U+00B4 (ACUTE ACCENT), an NFC string will use U+00C1 (LATIN CAPITAL LETTER A WITH ACUTE). Also, some deprecated codepoints are converted to the recommended replacements. since the same sequence of characters can be represented in more than one way in Unicode, it is better to ensure strings are in Normal Form before comparing them. an error may be raised if s is not a valid UTF-8 string.

utf8.normalize_nfc(s) -> normal_string, was_nfc

convert s to Normal Form C. the 2nd return value is true if the original string was already in NFC (meaning no modifications were made). an error will be raised if s is not a valid UTF-8 string.

utf8.grapheme_indices(s[, start[, stop]]) -> iterator

return an iterator which yields the starting and ending byte index of each successive grapheme cluster in s. This range of bytes is inclusive of the endpoints, so the yielded values can be passed to string.sub to extract the grapheme cluster. if you provide start and stop byte indices, then the iterator will only cover the requested byte range. start and stop should fall on character boundaries, since an error will be raised if the requested byte range is not a valid UTF-8 string.

local i = 1
for from,to in utf8.grapheme_indices(s) do
  print("grapheme cluster "..i.." is from byte "..from.." to byte "..to)
  i = i + 1
end

Improvement needed

• add Lua 5.3 spec test-suite.
• more test case.
• grapheme-compose support, and affect in utf8.reverse and utf8.width

License

It use same license with Lua: http://www.lua.org/license.html