openresty string hmac implementation

hmac.lua

local ffi = require "ffi"
local sha512 = require "resty.sha512"
local aes = require "resty.aes"

local ffi_new = ffi.new
local ffi_str = ffi.string
local C = ffi.C
local setmetatable = setmetatable
local error = error


module(...)

_VERSION = '0.01'

local mt = { __index = _M }


ffi.cdef[[

typedef struct HMACstate_st
        {
        SHA512_CTX shactx;
        unsigned char k_opad[128];
        } HMAC_CTX;

void HMAC_CTX_init(HMAC_CTX *ctx);
int HMAC_Init_ex(HMAC_CTX *ctx, const void* key, int key_len, const EVP_MD *md, ENGINE *imple);
int HMAC_Update(HMAC_CTX *ctx, const unsigned char *data, int len);
int HMAC_Final(HMAC_CTX *ct, unsigned char *md, unsigned int *len);
void HMAC_CTX_cleanup(HMAC_CTX *ctx);
]]

--[[
    Support openssl version >= 1.0.0
    HMAC_Init_ex(), HMAC_Update() and HMAC_Final() did not return values in versions of OpenSSL before 1.0.0. You may change ffi hmac definition if your version is below 1.0.0.
--]]

local ctx_ptr_type = ffi.typeof("HMAC_CTX[1]")

hash = {
    md5 = C.EVP_md5(),
    sha1 = C.EVP_sha1(),
    sha224 = C.EVP_sha224(),
    sha256 = C.EVP_sha256(),
    sha384 = C.EVP_sha384(),
    sha512 = C.EVP_sha512()
}

local buf = ffi_new("unsigned char[64]")


function new(self, key, _hash)
    local ctx = ffi_new(ctx_ptr_type)
    
    C.HMAC_CTX_init(ctx)
    
    local md = _hash or hash.md5

    if C.HMAC_Init_ex(ctx, key, #key, md, nil) == 0 then
        return nil
    end

    return setmetatable({ _ctx = ctx }, mt)
end

function update(self, s)
    return C.HMAC_Update(self._ctx, s, #s) == 1
end


function final(self)
    local out_len = ffi_new("unsigned int[1]")

    if C.HMAC_Final(self._ctx, buf, out_len) == 1 then
        return ffi_str(buf, out_len[0])
    end
    
    return nil
end


function reset(self)
    C.HMAC_Init_ex(self._ctx, nil, 0, nil, nil)
end

function cleanup(self)
    C.HMAC_CTX_cleanup(self._ctx)
end

local class_mt = {
    -- to prevent use of casual module global variables
    __newindex = function (table, key, val)
        error('attempt to write to undeclared variable "' .. key .. '"')
    end
}

setmetatable(_M, class_mt)

Very Useful!