【入门夯实】喇叭打码：汉字按字节截断出乱码

local function cutMsg(msg)
    return string.sub(msg, 1, 20)
end

local function safeCut(msg, maxBytes)
    if #msg <= maxBytes then
        return msg
    end
    local cut = string.sub(msg, 1, maxBytes)
    local n = #cut
    local cont = 0
    while n > 0 do
        local b = string.byte(cut, n)
        if b >= 128 and b < 192 then
            cont = cont + 1
            n = n - 1
        else
            break
        end
    end
    local lead = string.byte(cut, n) or 0
    local need = 0
    if lead >= 240 then need = 4
    elseif lead >= 224 then need = 3
    elseif lead >= 192 then need = 2 end
    if need > 0 and cont + 1 < need then
        cut = string.sub(cut, 1, n - 1)
    end
    return cut
end

local function hanCount(s)
    local n = 0
    for i = 1, #s do
        local b = string.byte(s, i)
        if b >= 224 and b < 240 then
            n = n + 1
        end
    end
    return n
end