logstash-input-redis源码解析

首先是程序的自定义，这里设置了redis插件需要的参数，默认值，以及校验等。

然后注册Redis实例需要的信息，比如key的名字或者url等，可以看到默认的data_type是list模式。

程序运行的主要入口，根据不同的data_type，传递不同的实现方法，然后调用listener_loop执行循环监听

Listner_loop方法传递了两个参数，一个是监听器实现的方法，一个是处理的数据队列。循环是每秒钟执行一次，如果循环标识被设置，则退出。

上面的循环方法可以看到，是通过一个参数shutdown_requested来判断是否继续循环。该参数通过tear_down方法设置为true，然后根据不同的模式，指定不同的退出方式。
如果是list模式，则直接退出；如果是channel模式，则发送redis的unsubsribe命令退出；如果是pattern_channel,则发送punsubscribe退出。

在循环内部，判断是否已经创建了redis实例，如果没有创建，则调用connect方法创建；否则直接执行。

这里前一段是调用Redis的new方法，初始化一个redis实例。紧接着判断batch_count是否大于1，如果等于1，就什么也不做，然后返回redis。
如果batch_count大于1，那么就调用load_batch_script方法，加载Lua脚本，存储到redis中的lua脚本字典中，供后面使用。代码如下：

上面的代码应该是这个插件最难理解的部分了。为了弄清楚这段代码的工作，需要了解下面几个知识点：

lua脚本基本概念
Redis中的EVAL命令如何使用
理解上面脚本的工作

首先，要想运行上面的脚本，必须是Redis2.6+的版本，才支持EVAL，否则会报错！EVAL命令与js中的差不多，就是可以把某一个字符串当做命令解析，其中字符串就包括lua脚本。这样有什么好处呢？

说白了，就是能一次性进行多个操作。比如我们可以在脚本中写入一连串的操作，这些操作会以原子模式，一次性在服务器执行完，在返回回来。

Lua脚本

关于lua脚本，其实没有详细研究的必要，但是一定要知道一个local和table的概念。local是创建本地的变量，这样就不会污染redis的数据。table是lua的一种数据结构，有点类似于json，可以存储数据。

EVAL命令

另外还要知道EVAL命令的使用方法，看下面这个命令，就好理解了！
EVAL "return KEYS[1] KEYS[2] ARGV[1] ARGV[2];" 2 name:xing age:13
就会返回：

name
age
xing
13

这段代码没有经过真正的操作，但是有助于理解就好！也就是说，EVAL后面跟着一段脚本，脚本后面跟着的就是参数，可以通过KEYS和ARGV数组获得，但是下标从1开始。

再来说说EVAL命令，它的执行过程如下：

解析字符串脚本，根据校验和生成lua的方法
把校验和和函数放入一个lua_script字典里面，之后就可以通过EVALSHA命令直接使用校验和执行函数。

有了这些理论基础以后，就可以看看上面的代码都做了什么了！
首先是获取参数，这个参数赋值给i；然后创建了一个对象res；紧接着调用llen命令，获得指定list的长度；如果list的长度大于i，则什么也不做；如果小于i，那么i就等于lenth；然后执行命令lpop，取出list中的元素，一共取i次，放入res中，最后返回。

说得通俗点，就是比较一下list元素个数与设置batch_count的值。如果batch_count为5，列表list中有5条以上的数据，那么直接取5条，一次性返回；否则取length条返回。

可以看到这段脚本的作用，就是让logstash一次请求，最多获得batch_count条事件，减小了服务器处理请求的压力。

讲完这段代码，可以看看不同的工作模式的实现代码了：

首先是list的代码，其实就是执行BLPOP命令，获取数据。如果在list模式中，还会去判断batch_count的值，如果是1直接退出；如果大于1，则使用evalsha命令调用之前保存的脚本方法。

至于channel和pattern_channel,就没啥解释的了，就是分别调用subscribe和psubsribe命令而已。

其实最难理解的，就是中间那段lua脚本~明白它的用处，redis插件也就不难理解了。

代码

# encoding: utf-8
require "logstash/inputs/base"
require "logstash/inputs/threadable"
require "logstash/namespace"# This input will read events from a Redis instance; it supports both Redis channels and lists.
# The list command (BLPOP) used by Logstash is supported in Redis v1.3.1+, and
# the channel commands used by Logstash are found in Redis v1.3.8+.
# While you may be able to make these Redis versions work, the best performance
# and stability will be found in more recent stable versions.  Versions 2.6.0+
# are recommended.
#
# For more information about Redis, see <http://redis.io/>
#
# `batch_count` note: If you use the `batch_count` setting, you *must* use a Redis version 2.6.0 or
# newer. Anything older does not support the operations used by batching.
#
class LogStash::Inputs::Redis < LogStash::Inputs::Threadableconfig_name "redis"default :codec, "json"# The `name` configuration is used for logging in case there are multiple instances.# This feature has no real function and will be removed in future versions.config :name, :validate => :string, :default => "default", :deprecated => true# The hostname of your Redis server.config :host, :validate => :string, :default => "127.0.0.1"# The port to connect on.config :port, :validate => :number, :default => 6379# The Redis database number.config :db, :validate => :number, :default => 0# Initial connection timeout in seconds.config :timeout, :validate => :number, :default => 5# Password to authenticate with. There is no authentication by default.config :password, :validate => :password# The name of the Redis queue (we'll use BLPOP against this).# TODO: remove soon.config :queue, :validate => :string, :deprecated => true# The name of a Redis list or channel.# TODO: change required to trueconfig :key, :validate => :string, :required => false# Specify either list or channel.  If `redis\_type` is `list`, then we will BLPOP the# key.  If `redis\_type` is `channel`, then we will SUBSCRIBE to the key.# If `redis\_type` is `pattern_channel`, then we will PSUBSCRIBE to the key.# TODO: change required to trueconfig :data_type, :validate => [ "list", "channel", "pattern_channel" ], :required => false# The number of events to return from Redis using EVAL.config :batch_count, :validate => :number, :default => 1publicdef registerrequire 'redis'@redis = nil@redis_url = "redis://#{@password}@#{@host}:#{@port}/#{@db}"# TODO remove after setting key and data_type to trueif @queueif @key or @data_typeraise RuntimeError.new("Cannot specify queue parameter and key or data_type")end@key = @queue@data_type = 'list'endif not @key or not @data_typeraise RuntimeError.new("Must define queue, or key and data_type parameters")end# end TODO@logger.info("Registering Redis", :identity => identity)end # def register# A string used to identify a Redis instance in log messages# TODO(sissel): Use instance variables for this once the @name config# option is removed.privatedef identity@name || "#{@redis_url} #{@data_type}:#{@key}"endprivatedef connectredis = Redis.new(:host => @host,:port => @port,:timeout => @timeout,:db => @db,:password => @password.nil? ? nil : @password.value)load_batch_script(redis) if @data_type == 'list' && (@batch_count > 1)return redisend # def connectprivatedef load_batch_script(redis)#A Redis Lua EVAL script to fetch a count of keys#in case count is bigger than current items in queue whole queue will be returned without extra nil valuesredis_script = <<EOFlocal i = tonumber(ARGV[1])local res = {}local length = redis.call('llen',KEYS[1])if length < i then i = length endwhile (i > 0) dolocal item = redis.call("lpop", KEYS[1])if (not item) thenbreakendtable.insert(res, item)i = i-1endreturn res
EOF@redis_script_sha = redis.script(:load, redis_script)endprivatedef queue_event(msg, output_queue)begin@codec.decode(msg) do |event|decorate(event)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               output_queue << eventendrescue LogStash::ShutdownSignal => e# propagate upraise(e)rescue => e # parse or event creation error@logger.error("Failed to create event", :message => msg, :exception => e, :backtrace => e.backtrace);endendprivatedef list_listener(redis, output_queue)item = redis.blpop(@key, 0, :timeout => 1)return unless item # from timeout or other conditions# blpop returns the 'key' read from as well as the item result# we only care about the result (2nd item in the list).queue_event(item[1], output_queue)# If @batch_count is 1, there's no need to continue.return if @batch_count == 1beginredis.evalsha(@redis_script_sha, [@key], [@batch_count-1]).each do |item|queue_event(item, output_queue)end# Below is a commented-out implementation of 'batch fetch'# using pipelined LPOP calls. This in practice has been observed to# perform exactly the same in terms of event throughput as# the evalsha method. Given that the EVALSHA implementation uses# one call to Redis instead of N (where N == @batch_count) calls,# I decided to go with the 'evalsha' method of fetching N items# from Redis in bulk.#redis.pipelined do#error, item = redis.lpop(@key)#(@batch_count-1).times { redis.lpop(@key) }#end.each do |item|#queue_event(item, output_queue) if item#end# --- End commented out implementation of 'batch fetch'rescue Redis::CommandError => eif e.to_s =~ /NOSCRIPT/ then@logger.warn("Redis may have been restarted, reloading Redis batch EVAL script", :exception => e);load_batch_script(redis)retryelseraise eendendendprivatedef channel_listener(redis, output_queue)redis.subscribe @key do |on|on.subscribe do |channel, count|@logger.info("Subscribed", :channel => channel, :count => count)endon.message do |channel, message|queue_event message, output_queueendon.unsubscribe do |channel, count|@logger.info("Unsubscribed", :channel => channel, :count => count)endendendprivatedef pattern_channel_listener(redis, output_queue)redis.psubscribe @key do |on|on.psubscribe do |channel, count|@logger.info("Subscribed", :channel => channel, :count => count)endon.pmessage do |ch, event, message|queue_event message, output_queueendon.punsubscribe do |channel, count|@logger.info("Unsubscribed", :channel => channel, :count => count)endendend# Since both listeners have the same basic loop, we've abstracted the outer# loop.privatedef listener_loop(listener, output_queue)while !@shutdown_requestedbegin@redis ||= connectself.send listener, @redis, output_queuerescue Redis::BaseError => e@logger.warn("Redis connection problem", :exception => e)# Reset the redis variable to trigger reconnect@redis = nilsleep 1endendend # listener_looppublicdef run(output_queue)if @data_type == 'list'listener_loop :list_listener, output_queueelsif @data_type == 'channel'listener_loop :channel_listener, output_queueelselistener_loop :pattern_channel_listener, output_queueendrescue LogStash::ShutdownSignal# ignore and quitend # def runpublicdef teardown@shutdown_requested = trueif @redisif @data_type == 'list'@redis.quit rescue nilelsif @data_type == 'channel'@redis.unsubscribe rescue nil@redis.connection.disconnectelsif @data_type == 'pattern_channel'@redis.punsubscribe rescue nil@redis.connection.disconnectend@redis = nilendend
end # class LogStash::Inputs::Redis