您使用什么模块或库在 Erlang 中生成通用唯一标识符 (UUID)? [英] What module or library do you use to generate universally unique identifier (UUID) in Erlang?

问题描述

您使用什么模块或库来生成通用唯一标识符 (UUID)?

What module or library do you use to generate universally unique identifier (UUID)?

推荐答案

来自 couchdb 的 Uuid 生成器:http://svn.apache.org/viewvc/couchdb/主干/src/couchdb/couch_uuids.erl

Uuid generator from couchdb: http://svn.apache.org/viewvc/couchdb/trunk/src/couchdb/couch_uuids.erl

% Licensed under the Apache License, Version 2.0 (the "License"); you may not
% use this file except in compliance with the License. You may obtain a copy of
% the License at
%
%   http://www.apache.org/licenses/LICENSE-2.0
%
% Unless required by applicable law or agreed to in writing, software
% distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
% WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
% License for the specific language governing permissions and limitations under
% the License.
-module(couch_uuids).
-include("couch_db.hrl").

-behaviour(gen_server).

-export([start/0, stop/0]).
-export([new/0, random/0, utc_random/0]).

-export([init/1, terminate/2, code_change/3]).
-export([handle_call/3, handle_cast/2, handle_info/2]).

start() ->
    gen_server:start_link({local, ?MODULE}, ?MODULE, [], []).

stop() ->
    gen_server:cast(?MODULE, stop).

new() ->
    gen_server:call(?MODULE, create).

random() ->
    list_to_binary(couch_util:to_hex(crypto:rand_bytes(16))).

utc_random() ->
    Now = {_, _, Micro} = now(),
    Nowish = calendar:now_to_universal_time(Now),
    Nowsecs = calendar:datetime_to_gregorian_seconds(Nowish),
    Then = calendar:datetime_to_gregorian_seconds({{1970, 1, 1}, {0, 0, 0}}),
    Prefix = io_lib:format("~14.16.0b", [(Nowsecs - Then) * 1000000 + Micro]),
    list_to_binary(Prefix ++ couch_util:to_hex(crypto:rand_bytes(9))).

init([]) ->
    ok = couch_config:register(
        fun("uuids", _) -> gen_server:cast(?MODULE, change) end
    ),
    {ok, state()}.

terminate(_Reason, _State) ->
    ok.

handle_call(create, _From, random) ->
    {reply, random(), random};
handle_call(create, _From, utc_random) ->
    {reply, utc_random(), utc_random};
handle_call(create, _From, {sequential, Pref, Seq}) ->
    Result = ?l2b(Pref ++ io_lib:format("~6.16.0b", [Seq])),
    case Seq >= 16#fff000 of
        true ->
            {reply, Result, {sequential, new_prefix(), inc()}};
        _ ->
            {reply, Result, {sequential, Pref, Seq + inc()}}
    end.

handle_cast(change, _State) ->
    {noreply, state()};
handle_cast(stop, State) ->
    {stop, normal, State};
handle_cast(_Msg, State) ->
    {noreply, State}.

handle_info(_Info, State) ->
    {noreply, State}.

code_change(_OldVsn, State, _Extra) ->
    {ok, State}.

new_prefix() ->
    couch_util:to_hex((crypto:rand_bytes(13))).

inc() ->
    crypto:rand_uniform(1, 16#ffe).

state() ->
    AlgoStr = couch_config:get("uuids", "algorithm", "random"),
    case couch_util:to_existing_atom(AlgoStr) of
        random ->
            random;
        utc_random ->
            utc_random;
        sequential ->
            {sequential, new_prefix(), inc()};
        Unknown ->
            throw({unknown_uuid_algorithm, Unknown})
    end.

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