CSV parser in Lua

Readme.md

The make_csv_parser{ separator="char", delimiter="char", escape=true or "char", trim=true } function builds a CSV line parser. The make_csv_parser() function returns a new function that takes a string (e.g. one line from a CSV file) as an argument and returns an array of field values. The returned function splits the string into components according to the provided special CSV charaters. By default, the setting separator is a comma, the string delimiter is a double-quote, no escape character is used (i.e., string delimiters must be stuttered within a string) and extra spaces around the separators are not trimmed. Setting escape to true uses the backslash character as the escape. Setting trim to true enables the trimming of whitespace around the separator characters.

For example:

> parse = make_csv_parser()
> T = parse [[a b,"a,b"," a,""b""c", hello "world"!,]]
> for i, v in ipairs(T) do print(i, v) end
1	a b
2	a,b
3	 a,"b"c
4	 hello "world"!
5	
>
> parse = make_csv_parser{ separator = ";", delimiter = "'", escape = true, trim = true }
> T = parse [[a b;a\;b;'a;b';' a,\'b\'c'; hello 'world'!;]]
> for i, v in ipairs(T) do print(i, v) end
1	a b
2	a;b
3	a;b
4	 a,'b'c
5	hello 'world'!
6	
> 

csv.lua

function make_csv_parser(args)
	args = args or {}
	local separator = args.separator or  ','
	local delimiter = args.delimiter or '"'
	local escape = args.escape or false
	local trim = args.trim or false

	if escape then
		local e_escape
		if escape == true then
			escape = "\\"
			e_escape = "\\"
		elseif escape == "\\"  then
			e_escape = escape
		elseif escape:find("%w") then
			e_escape = escape
		else
			e_escape = "%" .. escape
		end
		return function (s)
			s = (s or "") .. separator  -- ending separator
			local t = {}  -- table to collect fields
			local fieldstart = 1
			repeat
				if trim then
					local s, e = s:find("^%s+", fieldstart)
					if e then
						fieldstart =  e + 1
					end
				end
				if s:find('^' .. delimiter, fieldstart) then
					-- field is quoted (starts with delimiter)
					local a, c
					local i = fieldstart
					repeat  -- find closing delimiter
						a, i, c = s:find('(' .. e_escape .. '?)' .. delimiter, i + 1)
					until c ~= escape  -- delimiter not preceeded by escape?
					if not i then
						return nil, 'unmatched delimiter (' .. delimiter .. ')'
					end
					local f = s:sub(fieldstart + 1, i - 1)
					if trim then
						t[#t + 1] = rtrim(f:gsub(e_escape .. '(.)', '%1'))
					else
						t[#t + 1] = (f:gsub(e_escape .. '(.)', '%1'))
					end
					fieldstart = s:find(separator, i) + 1
				else
					local a, c
					local i = fieldstart - 1
					repeat  -- find next separator
						a, i, c = s:find('(' .. e_escape .. '?)' .. separator, i + 1)
					until c ~= escape  -- separator not preceeded by escape?
					if not i then
						return nil, 'missing separator (' .. separator .. ')'
					end
					local f = s:sub(fieldstart, i - 1)
					if trim then
						t[#t + 1] = rtrim(f:gsub(e_escape .. '(.)', '%1'))
					else
						t[#t + 1] = (f:gsub(e_escape .. '(.)', '%1'))
					end
					fieldstart = i + 1
				end
			until fieldstart > #s
			return t
		end
	else -- stutter
		return function (s)
			s = (s or "") .. separator  -- ending separator
			local t = {}  -- table to collect fields
			local fieldstart = 1
			repeat
				if trim then
					local s, e = s:find("^%s+", fieldstart)
					if e then
						fieldstart =  e + 1
					end
				end
				if s:find('^' .. delimiter, fieldstart) then
					-- field is quoted (starts with delimiter)
					local a, c
					local i = fieldstart
					repeat  -- find closing delimiter
						a, i, c = s:find(delimiter .. '(' .. delimiter .. '?)', i + 1)
					until c ~= delimiter  -- delimiter not followed by delimiter?
					if not i then
						return nil, 'unmatched delimiter (' .. delimiter .. ')'
					end
					local f = s:sub(fieldstart + 1, i - 1)
					if trim then
						t[#t + 1] = rtrim(f:gsub(delimiter .. delimiter, delimiter))
					else
						t[#t + 1] = (f:gsub(delimiter .. delimiter, delimiter))
					end
					fieldstart = s:find(separator, i) + 1
				else
					local i = s:find(separator, fieldstart)
					if trim then
						t[#t + 1] = rtrim(s:sub(fieldstart, i - 1))
					else
						t[#t + 1] = s:sub(fieldstart, i - 1)
					end
					fieldstart = i + 1
				end
			until fieldstart > #s
			return t
		end
	end
end

function rtrim(s)
	s = s or ""
	local first, last = s:find"%s+$"
	if first then
		return s:sub(1, first-1)
	else
		return s
	end
end