62 lines
1.6 KiB
Lua
62 lines
1.6 KiB
Lua
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local _M = {}
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local function str_split(str, size)
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local result = {}
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for i=1, #str, size do
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table.insert(result, str:sub(i, i + size - 1))
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end
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return result
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end
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local function dec2bin(num)
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local result = ""
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repeat
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local halved = num / 2
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local int, frac = math.modf(halved)
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num = int
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result = math.ceil(frac) .. result
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until num == 0
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return result
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end
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local base32Alphabet = "0123456789ABCDEFGHIJKLMNOPQRSTUV"
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-- this is not a full implementation of base32 decoder, it doesn't
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-- cover all edge cases but it works good enough for decoding skylinks
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-- source: https://gist.github.com/linsonder6/3202fc06832f97905aab2a8a492a80de
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function decodeBase32Skylink(str)
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local binary = string.upper(str):gsub(".", function (char)
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if char == "=" then return "" end
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local pos = string.find(base32Alphabet, char)
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pos = pos - 1
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return string.format("%05u", dec2bin(pos))
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end)
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local bytes = str_split(binary, 8)
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local decoded = {}
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for _, byte in pairs(bytes) do
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table.insert(decoded, string.char(tonumber(byte, 2)))
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end
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local concatenated = table.concat(decoded)
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-- decoded skylink is always 34 bytes, anything
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-- else is leftover and should be discarded
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return string.sub(concatenated, 1, 34)
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end
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-- parse any skylink and return base64 version
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function _M.parse(skylink)
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if string.len(skylink) == 55 then
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local base64 = require("ngx.base64")
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local decoded = decodeBase32Skylink(skylink)
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return base64.encode_base64url(decoded)
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end
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return skylink
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end
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return _M
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