util.dbuffer: Add efficient shortcuts for discard() in certain cases
If the buffer is already empty, nothing to do. If we're throwing away the
whole buffer, we can just empty it and avoid read_chunk() (which in turn
may collapse()). These shortcuts are much more efficient.
-- Prosody IM
-- Copyright (C) 2008-2010 Matthew Wild
-- Copyright (C) 2008-2010 Waqas Hussain
--
-- This project is MIT/X11 licensed. Please see the
-- COPYING file in the source package for more information.
--
local random = require "util.random";
local random_bytes = random.bytes;
local hex = require "util.hex".encode;
local m_ceil = math.ceil;
local function get_nibbles(n)
return hex(random_bytes(m_ceil(n/2))):sub(1, n);
end
local function get_twobits()
return ("%x"):format(random_bytes(1):byte() % 4 + 8);
end
local function generate()
-- generate RFC 4122 complaint UUIDs (version 4 - random)
return get_nibbles(8).."-"..get_nibbles(4).."-4"..get_nibbles(3).."-"..(get_twobits())..get_nibbles(3).."-"..get_nibbles(12);
end
return {
get_nibbles=get_nibbles;
generate = generate ;
-- COMPAT
seed = random.seed;
};