ES源码分析Transport模块之REST的解析与处理
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文章目录
Transport模块之REST的解析与处理
基于ES源码6.7.2
注册REST处理
借由上图回顾一下通信模块的初始化过程，在ActionModule下对Rest请求处理进行了注册，注册过程在initRestHandlers方法中。可以发现对REST请求执行处理的类的命名是Rest*Action，同时可以发现这些处理类都继承了BaseRestHandler，而BaseRestHandler继承了RestHandler。
public void initRestHandlers(Supplier<DiscoveryNodes> nodesInCluster)
List<AbstractCatAction> catActions = new ArrayList<>();
Consumer<RestHandler> registerHandler = a ->
if (a instanceof AbstractCatAction)
catActions.add((AbstractCatAction) a);
;
registerHandler.accept(new RestMainAction(settings, restController));
registerHandler.accept(new RestNodesInfoAction(settings, restController, settingsFilter));
registerHandler.accept(new RestRemoteClusterInfoAction(settings, restController));
registerHandler.accept(new RestNodesStatsAction(settings, restController));
registerHandler.accept(new RestNodesUsageAction(settings, restController));
registerHandler.accept(new RestNodesHotThreadsAction(settings, restController));
registerHandler.accept(new RestClusterAllocationExplainAction(settings, restController));
registerHandler.accept(new RestClusterStatsAction(settings, restController));
registerHandler.accept(new RestClusterStateAction(settings, restController, settingsFilter));
registerHandler.accept(new RestClusterHealthAction(settings, restController));
...
...
...
for (ActionPlugin plugin : actionPlugins)
for (RestHandler handler : plugin.getRestHandlers(settings, restController, clusterSettings, indexScopedSettings,
settingsFilter, indexNameExpressionResolver, nodesInCluster))
registerHandler.accept(handler);
registerHandler.accept(new RestCatAction(settings, restController, catActions));
以RestClusterHealthAction为例，在其构造函数中对请求头中请求方法为GET，URI为/_cluster/health和拥有占位符/_cluster/health/index的处理类为this（即自己）。
public RestClusterHealthAction(Settings settings, RestController controller)
super(settings);
controller.registerHandler(RestRequest.Method.GET, "/_cluster/health", this);
controller.registerHandler(RestRequest.Method.GET, "/_cluster/health/index", this);
由于继承了BaseRestHandler，所以必须实现prepareRequest方法，用于在接收到请求时，做一些前置工作，比如验证参数，转换为内部RPC请求等。
处理请求
HTTP请求执行路径
BaseRestHandler的handleRequest方法
@Override
public final void handleRequest(RestRequest request, RestChannel channel, NodeClient client) throws Exception
// 对请求的预处理
final RestChannelConsumer action = prepareRequest(request, client);
// validate unconsumed params, but we must exclude params used to format the response
// use a sorted set so the unconsumed parameters appear in a reliable sorted order
final SortedSet<String> unconsumedParams =
request.unconsumedParams().stream().filter(p -> !responseParams().contains(p)).collect(Collectors.toCollection(TreeSet::new));
// validate the non-response params
if (!unconsumedParams.isEmpty())
final Set<String> candidateParams = new HashSet<>();
candidateParams.addAll(request.consumedParams());
candidateParams.addAll(responseParams());
throw new IllegalArgumentException(unrecognized(request, unconsumedParams《Elasticsearch 源码解析与优化实战》第15章：Transport模块分析
ElasticSearchEs 源码之 Transport 和 TransportService 源码解读