Lua URL parser/cleaner

-- (C) Tommy aka 16Tomatons
-- MIT license

local url = {}
url.cleaning = {
    {rx = '%s.*',   rp = ''},    -- clear all after space character
    {rx = '&+',     rp = '&'},
    {rx = '=+',     rp = '='},
    {rx = '@+',     rp = '@'},
    {rx = ':+',     rp = ':'},
    {rx = '#+',     rp = '#'},
    {rx = '/+',     rp = '/'},   -- remove all '/'-duplicates
    {rx = '%?+',    rp = '?'},
    {rx = '^%w+:/', rp = '%1/'}, -- restore '/', if scheme is here
}

function url.clear(u)
    local sub, subs = 0, 0
    for i, v in pairs(url.cleaning) do
        u, sub = u:gsub(v.rx, v.rp)
        subs = subs + sub
    end
    return u, subs
end

-- specific string function, like table.remove returning an erased item
-- a, b = url.extract('qwerty', 'w(er)') --> er, qty
function url.extract(str, regex)
    local a, b, matched = str:find(regex)
    if not a then
        return nil, str
    end
    local head, mid, tail = str:sub(1, a - 1), str:sub(a, b), str:sub(b + 1)
    return matched, head .. tail
end

-- average string-split
function url.split(str, delm)
    delm = delm or ' '
    local res = {}
    for line in (str..delm):gmatch('(.-)'..delm) do
        res[#res + 1] = line
    end
    return res
end

function url.parse_query(query)
    local res = {}
    for i, line in ipairs(url.split(query, '&')) do
        local k, v = line:match('(.-)=(.*)')
        if k then -- key-value
            res[k] = v
        else      -- flag, like /page?flag1&flag2
            res[line] = true
        end
    end
    return res
end

function url.parse(u)
    local res = {}

    -- foo://username:password@www.example.com.net:8080/hello/world.html/?arg1=val1&arg2=val2#frag
    u = url.clear(u)

    -- (foo):// | username:password@www.example.com.net:8080/hello/world.html/?arg1=val1&arg2=val2#frag
    local scheme, u = url.extract(u, '^(%w+)://')
    res.scheme = scheme

    -- (username:password)@ | www.example.com.net:8080/hello/world.html/?arg1=val1&arg2=val2#frag
    local userdata, u = url.extract(u, '^([^/]+)@')

    if userdata then
        res.authority = {}
        -- (username):(password) -- first priority
        local user, pass = userdata:match('([^:]*):?(.*)')
        res.authority.username = user
        res.authority.password = pass
    end

    -- (www.example.com.net:8080) | /hello/world.html/?arg1=val1&arg2=val2#frag
    local hostname, u = url.extract(u, '^([^/]+)')
    if hostname then
        res.authority = res.authority or {}
        -- (www.example.com.net):(8080) -- first priority
        local host, port = hostname:match('([^:]*):?(.*)')
        res.authority.hostname = host
        res.authority.port     = port
    end

    -- /(hello/world.html/) | ?arg1=val1&arg2=val2#frag
    local path, u = url.extract(u, '^(/[^?]+)')
    res.path  = (path or '//'):gsub('/$', '') -- remove endslash, '/' - is default path
    res.ppath = url.split(res.path:sub(2), '/')

    -- ?(arg1=val1&arg2=val2) | #frag
    local query, u = url.extract(u, '^?([^#]+)')
    if query then
        res.query  = query
        res.pquery = url.parse_query(query)
    end

    -- #(frag)
    local fragment, u = url.extract(u, '^#(.+)')

    res.fragment = fragment

    return res
end

if ... then return url end

local URL = 'foo:::///////username:::password@@@www.example.com.net::8080///hello//world.html/???arg1====val1&&&arg2=val2#frag qwe'

print('URL: ['..URL..']')                           -- bad, bad, dirty url!
print('Parsed: '..require'inspect'(url.parse(URL))) -- mmm.. pretty clear parsed url!