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# Pleroma: A lightweight social networking server
# Copyright © 2017-2019 Pleroma Authors <https://pleroma.social/>
# SPDX-License-Identifier: AGPL-3.0-only
defmodule Pleroma.FlakeId do
@moduledoc """
Flake is a decentralized, k-ordered id generation service.
Adapted from:
* [flaky](https://github.com/nirvana/flaky), released under the terms of the Truly Free License,
* [Flake](https://github.com/boundary/flake), Copyright 2012, Boundary, Apache License, Version 2.0
"""
@type t :: binary
@behaviour Ecto.Type
use GenServer
require Logger
alias __MODULE__
import Kernel, except: [to_string: 1]
defstruct node: nil, time: 0, sq: 0
@doc "Converts a binary Flake to a String"
def to_string(<<0::integer-size(64), id::integer-size(64)>>) do
Kernel.to_string(id)
end
def to_string(<<_::integer-size(64), _::integer-size(48), _::integer-size(16)>> = flake) do
encode_base62(flake)
end
def to_string(s), do: s
def from_string(int) when is_integer(int) do
from_string(Kernel.to_string(int))
end
for i <- [-1, 0] do
def from_string(unquote(i)), do: <<0::integer-size(128)>>
def from_string(unquote(Kernel.to_string(i))), do: <<0::integer-size(128)>>
end
def from_string(<<_::integer-size(128)>> = flake), do: flake
def from_string(string) when is_binary(string) and byte_size(string) < 18 do
case Integer.parse(string) do
{id, ""} -> <<0::integer-size(64), id::integer-size(64)>>
_ -> nil
end
end
def from_string(string) do
string |> decode_base62 |> from_integer
end
def to_integer(<<integer::integer-size(128)>>), do: integer
def from_integer(integer) do
<<_time::integer-size(64), _node::integer-size(48), _seq::integer-size(16)>> =
<<integer::integer-size(128)>>
end
@doc "Generates a Flake"
@spec get :: binary
def get, do: to_string(:gen_server.call(:flake, :get))
# -- Ecto.Type API
@impl Ecto.Type
def type, do: :uuid
@impl Ecto.Type
def cast(value) do
{:ok, FlakeId.to_string(value)}
end
@impl Ecto.Type
def load(value) do
{:ok, FlakeId.to_string(value)}
end
@impl Ecto.Type
def dump(value) do
{:ok, FlakeId.from_string(value)}
end
def autogenerate, do: get()
# -- GenServer API
def start_link do
:gen_server.start_link({:local, :flake}, __MODULE__, [], [])
end
@impl GenServer
def init([]) do
{:ok, %FlakeId{node: worker_id(), time: time()}}
end
@impl GenServer
def handle_call(:get, _from, state) do
{flake, new_state} = get(time(), state)
{:reply, flake, new_state}
end
# Matches when the calling time is the same as the state time. Incr. sq
defp get(time, %FlakeId{time: time, node: node, sq: seq}) do
new_state = %FlakeId{time: time, node: node, sq: seq + 1}
{gen_flake(new_state), new_state}
end
# Matches when the times are different, reset sq
defp get(newtime, %FlakeId{time: time, node: node}) when newtime > time do
new_state = %FlakeId{time: newtime, node: node, sq: 0}
{gen_flake(new_state), new_state}
end
# Error when clock is running backwards
defp get(newtime, %FlakeId{time: time}) when newtime < time do
{:error, :clock_running_backwards}
end
defp gen_flake(%FlakeId{time: time, node: node, sq: seq}) do
<<time::integer-size(64), node::integer-size(48), seq::integer-size(16)>>
end
defp nthchar_base62(n) when n <= 9, do: ?0 + n
defp nthchar_base62(n) when n <= 35, do: ?A + n - 10
defp nthchar_base62(n), do: ?a + n - 36
defp encode_base62(<<integer::integer-size(128)>>) do
integer
|> encode_base62([])
|> List.to_string()
end
defp encode_base62(int, acc) when int < 0, do: encode_base62(-int, acc)
defp encode_base62(int, []) when int == 0, do: '0'
defp encode_base62(int, acc) when int == 0, do: acc
defp encode_base62(int, acc) do
r = rem(int, 62)
id = div(int, 62)
acc = [nthchar_base62(r) | acc]
encode_base62(id, acc)
end
defp decode_base62(s) do
decode_base62(String.to_charlist(s), 0)
end
defp decode_base62([c | cs], acc) when c >= ?0 and c <= ?9,
do: decode_base62(cs, 62 * acc + (c - ?0))
defp decode_base62([c | cs], acc) when c >= ?A and c <= ?Z,
do: decode_base62(cs, 62 * acc + (c - ?A + 10))
defp decode_base62([c | cs], acc) when c >= ?a and c <= ?z,
do: decode_base62(cs, 62 * acc + (c - ?a + 36))
defp decode_base62([], acc), do: acc
defp time do
{mega_seconds, seconds, micro_seconds} = :erlang.timestamp()
1_000_000_000 * mega_seconds + seconds * 1000 + :erlang.trunc(micro_seconds / 1000)
end
defp worker_id do
<<worker::integer-size(48)>> = :crypto.strong_rand_bytes(6)
worker
end
end

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