ES系列(四)：http请求分发框架解析
上一篇讲解了es的网络通信模块实现过程，大致明白其工作原理。再总结一下，就是基于netty编程范式，形成es通信基础。从而，最终我们得到几个重要的handler: Netty4HttpPipeliningHandler/Netty4HttpRequestHandler/Netty4MessageChannelHandler...
实际上，这种范式类的东西，没必要花太多精力去关注。因为这对于我们理解一个系统业务，可能不是那么重要。（话多了，实际上es中核心lucene难道不值得花精力关注？）但现在，我们可以进一步花精力，看看es都是如何处理http请求的，这样至少，对于之后的每个细节实现的研究是有前提基础的。
1. 从handler开始
因为是处理http请求，自然是从网络入口开始。而因为使用netty, 则必然显现在一个handler上。即上篇中看到的 Netty4HttpRequestHandler ... 我们再来回顾下。
// org.elasticsearch.http.netty4.Netty4HttpServerTransport.HttpChannelHandler#HttpChannelHandler
protected HttpChannelHandler(final Netty4HttpServerTransport transport, final HttpHandlingSettings handlingSettings) {
this.transport = transport;
this.handlingSettings = handlingSettings;
this.byteBufSizer = new NettyByteBufSizer();
this.requestCreator = new Netty4HttpRequestCreator();
this.requestHandler = new Netty4HttpRequestHandler(transport);
this.responseCreator = new Netty4HttpResponseCreator();
}
// org.elasticsearch.http.netty4.Netty4HttpServerTransport.HttpChannelHandler#initChannel
@Override
protected void initChannel(Channel ch) throws Exception {
Netty4HttpChannel nettyHttpChannel = new Netty4HttpChannel(ch);
// 此处 handler 配置的相当多, 自然是因其功能复杂的原因
ch.attr(HTTP_CHANNEL_KEY).set(nettyHttpChannel);
ch.pipeline().addLast("byte_buf_sizer", byteBufSizer);
ch.pipeline().addLast("read_timeout", new ReadTimeoutHandler(transport.readTimeoutMillis, TimeUnit.MILLISECONDS));
final HttpRequestDecoder decoder = new HttpRequestDecoder(
handlingSettings.getMaxInitialLineLength(),
handlingSettings.getMaxHeaderSize(),
handlingSettings.getMaxChunkSize());
decoder.setCumulator(ByteToMessageDecoder.COMPOSITE_CUMULATOR);
ch.pipeline().addLast("decoder", decoder);
ch.pipeline().addLast("decoder_compress", new HttpContentDecompressor());
ch.pipeline().addLast("encoder", new HttpResponseEncoder());
final HttpObjectAggregator aggregator = new HttpObjectAggregator(handlingSettings.getMaxContentLength());
aggregator.setMaxCumulationBufferComponents(transport.maxCompositeBufferComponents);
ch.pipeline().addLast("aggregator", aggregator);
if (handlingSettings.isCompression()) {
ch.pipeline().addLast("encoder_compress", new HttpContentCompressor(handlingSettings.getCompressionLevel()));
}
ch.pipeline().addLast("request_creator", requestCreator);
ch.pipeline().addLast("response_creator", responseCreator);
// 最后两个处理器， pipelineing, handler, 则处理真正的业务
ch.pipeline().addLast("pipelining", new Netty4HttpPipeliningHandler(logger, transport.pipeliningMaxEvents));
// Netty4HttpRequestHandler
ch.pipeline().addLast("handler", requestHandler);
transport.serverAcceptedChannel(nettyHttpChannel);
}
抛却 pipelineing 不说，就只剩下 handler 这个核心处理器了。而 handler 我们看到它是 Netty4HttpRequestHandler 的一个实例，而其构造方法中传入一个 transport, 这里面保存了相当多的上下文信息，包括配置，如何分发等等功能，细节无须多说。
但其中有一个 dispatcher 需要说下，因为这会影响到后续的请求如何处理的问题。
实际上，在node初始化时，就会创建一个 dispatcher, 是一个 RestController 实例，而这会在后其他组件进行注册时使用到，因为请求分发是由 RestController 控制的。它的初始化过程如下：
// org.elasticsearch.node.Node#Node
protected Node(final Environment initialEnvironment,
Collection<Class<? extends Plugin>> classpathPlugins, boolean forbidPrivateIndexSettings) {
... ActionModule actionModule = new ActionModule(false, settings, clusterModule.getIndexNameExpressionResolver(),
settingsModule.getIndexScopedSettings(), settingsModule.getClusterSettings(), settingsModule.getSettingsFilter(),
threadPool, pluginsService.filterPlugins(ActionPlugin.class), client, circuitBreakerService, usageService, systemIndices);
modules.add(actionModule);
// restController 在 ActionModule 中初始化, 被 networkModule 使用
final RestController restController = actionModule.getRestController();
final NetworkModule networkModule = new NetworkModule(settings, false, pluginsService.filterPlugins(NetworkPlugin.class),
threadPool, bigArrays, pageCacheRecycler, circuitBreakerService, namedWriteableRegistry, xContentRegistry,
networkService, restController, clusterService.getClusterSettings());
Collection<UnaryOperator<Map<String, IndexTemplateMetadata>>> indexTemplateMetadataUpgraders =
pluginsService.filterPlugins(Plugin.class).stream()
.map(Plugin::getIndexTemplateMetadataUpgrader)
.collect(Collectors.toList()); ... } // org.elasticsearch.action.ActionModule#ActionModule
public ActionModule(boolean transportClient, Settings settings, IndexNameExpressionResolver indexNameExpressionResolver,
IndexScopedSettings indexScopedSettings, ClusterSettings clusterSettings, SettingsFilter settingsFilter,
ThreadPool threadPool, List<ActionPlugin> actionPlugins, NodeClient nodeClient,
CircuitBreakerService circuitBreakerService, UsageService usageService, SystemIndices systemIndices) {
this.transportClient = transportClient;
this.settings = settings;
this.indexNameExpressionResolver = indexNameExpressionResolver;
this.indexScopedSettings = indexScopedSettings;
this.clusterSettings = clusterSettings;
this.settingsFilter = settingsFilter;
this.actionPlugins = actionPlugins;
this.threadPool = threadPool;
actions = setupActions(actionPlugins);
actionFilters = setupActionFilters(actionPlugins);
autoCreateIndex = transportClient
? null
: new AutoCreateIndex(settings, clusterSettings, indexNameExpressionResolver, systemIndices);
destructiveOperations = new DestructiveOperations(settings, clusterSettings);
Set<RestHeaderDefinition> headers = Stream.concat(
actionPlugins.stream().flatMap(p -> p.getRestHeaders().stream()),
Stream.of(new RestHeaderDefinition(Task.X_OPAQUE_ID, false))
).collect(Collectors.toSet());
UnaryOperator<RestHandler> restWrapper = null;
for (ActionPlugin plugin : actionPlugins) {
UnaryOperator<RestHandler> newRestWrapper = plugin.getRestHandlerWrapper(threadPool.getThreadContext());
if (newRestWrapper != null) {
logger.debug("Using REST wrapper from plugin " + plugin.getClass().getName());
if (restWrapper != null) {
throw new IllegalArgumentException("Cannot have more than one plugin implementing a REST wrapper");
}
restWrapper = newRestWrapper;
}
}
mappingRequestValidators = new RequestValidators<>(
actionPlugins.stream().flatMap(p -> p.mappingRequestValidators().stream()).collect(Collectors.toList()));
indicesAliasesRequestRequestValidators = new RequestValidators<>(
actionPlugins.stream().flatMap(p -> p.indicesAliasesRequestValidators().stream()).collect(Collectors.toList())); if (transportClient) {
restController = null;
} else {
// 直接实例化 restController
restController = new RestController(headers, restWrapper, nodeClient, circuitBreakerService, usageService);
}
}
实例化好 dispatcher 后，需要接受其他组件的注册行为。(接受注册的有两个组件: RestController 和 Transport$RequestHandlers)
其中，RequestHandlers 的地址格式如: internal:transport/handshake, cluster:admin/snapshot/status[nodes], indices:admin/close[s][p] ; 而 RestController 的地址格式如: /{index}/_doc/{id}, /_nodes/{nodeId}/{metrics}, /_cluster/allocation/explain, /{index}/_alias/{name}
1.1. RequestHandlers 的注册
先来看看 RequestHandlers 的注册过程，这些注册更多的是用于集群内部通信使用：
// org.elasticsearch.transport.TransportService#registerRequestHandler
/**
* Registers a new request handler
*
* @param action The action the request handler is associated with
* @param requestReader The request class that will be used to construct new instances for streaming
* @param executor The executor the request handling will be executed on
* @param forceExecution Force execution on the executor queue and never reject it
* @param canTripCircuitBreaker Check the request size and raise an exception in case the limit is breached.
* @param handler The handler itself that implements the request handling
*/
public <Request extends TransportRequest> void registerRequestHandler(String action,
String executor, boolean forceExecution,
boolean canTripCircuitBreaker,
Writeable.Reader<Request> requestReader,
TransportRequestHandler<Request> handler) {
validateActionName(action);
handler = interceptor.interceptHandler(action, executor, forceExecution, handler);
RequestHandlerRegistry<Request> reg = new RequestHandlerRegistry<>(
action, requestReader, taskManager, handler, executor, forceExecution, canTripCircuitBreaker);
transport.registerRequestHandler(reg);
}
// org.elasticsearch.transport.Transport#registerRequestHandler
/**
* Registers a new request handler
*/
default <Request extends TransportRequest> void registerRequestHandler(RequestHandlerRegistry<Request> reg) {
getRequestHandlers().registerHandler(reg);
} synchronized <Request extends TransportRequest> void registerHandler(RequestHandlerRegistry<Request> reg) {
if (requestHandlers.containsKey(reg.getAction())) {
throw new IllegalArgumentException("transport handlers for action " + reg.getAction() + " is already registered");
}
requestHandlers = MapBuilder.newMapBuilder(requestHandlers).put(reg.getAction(), reg).immutableMap();
} // 注册样例1
// org.elasticsearch.transport.TransportService#TransportService
public TransportService(Settings settings, Transport transport, ThreadPool threadPool, TransportInterceptor transportInterceptor,
Function<BoundTransportAddress, DiscoveryNode> localNodeFactory, @Nullable ClusterSettings clusterSettings,
Set<String> taskHeaders, ConnectionManager connectionManager) {
...
registerRequestHandler(
HANDSHAKE_ACTION_NAME,
ThreadPool.Names.SAME,
false, false,
HandshakeRequest::new,
(request, channel, task) -> channel.sendResponse(
new HandshakeResponse(localNode.getVersion(), Build.CURRENT.hash(), localNode, clusterName)));
...
}
// 注册样例2
// org.elasticsearch.repositories.VerifyNodeRepositoryAction#VerifyNodeRepositoryAction
public VerifyNodeRepositoryAction(TransportService transportService, ClusterService clusterService,
RepositoriesService repositoriesService) {
this.transportService = transportService;
this.clusterService = clusterService;
this.repositoriesService = repositoriesService;
transportService.registerRequestHandler(ACTION_NAME, ThreadPool.Names.SNAPSHOT, VerifyNodeRepositoryRequest::new,
new VerifyNodeRepositoryRequestHandler());
}
// 注册样例3
// org.elasticsearch.discovery.PeerFinder#PeerFinder
public PeerFinder(Settings settings, TransportService transportService, TransportAddressConnector transportAddressConnector,
ConfiguredHostsResolver configuredHostsResolver) {
this.settings = settings;
findPeersInterval = DISCOVERY_FIND_PEERS_INTERVAL_SETTING.get(settings);
requestPeersTimeout = DISCOVERY_REQUEST_PEERS_TIMEOUT_SETTING.get(settings);
this.transportService = transportService;
this.transportAddressConnector = transportAddressConnector;
this.configuredHostsResolver = configuredHostsResolver; transportService.registerRequestHandler(REQUEST_PEERS_ACTION_NAME, Names.GENERIC, false, false,
PeersRequest::new,
(request, channel, task) -> channel.sendResponse(handlePeersRequest(request))); transportService.registerRequestHandler(UnicastZenPing.ACTION_NAME, Names.GENERIC, false, false,
UnicastZenPing.UnicastPingRequest::new, new Zen1UnicastPingRequestHandler());
}
整个 RequestHandlers 的注册，使用一个同步锁保证线程安全性，且使用一个类似写时复制的一个机制，保证读的安全性。然后，最终使用一个简单的 HashMap 包含handlers与path. 性能与安全性同时兼顾。
1.2. RestController 的注册
RestController 的注册则稍有不同，它主要用于处理客户端的请求如： /{index}/_doc/{id}
// org.elasticsearch.rest.RestController#registerHandler
/**
* Registers a REST handler with the controller. The REST handler declares the {@code method}
* and {@code path} combinations.
*/
public void registerHandler(final RestHandler restHandler) {
restHandler.routes().forEach(route -> registerHandler(route.getMethod(), route.getPath(), restHandler));
restHandler.deprecatedRoutes().forEach(route ->
registerAsDeprecatedHandler(route.getMethod(), route.getPath(), restHandler, route.getDeprecationMessage()));
restHandler.replacedRoutes().forEach(route -> registerWithDeprecatedHandler(route.getMethod(), route.getPath(),
restHandler, route.getDeprecatedMethod(), route.getDeprecatedPath()));
} /**
* Registers a REST handler to be executed when one of the provided methods and path match the request.
*
* @param path Path to handle (e.g., "/{index}/{type}/_bulk")
* @param handler The handler to actually execute
* @param method GET, POST, etc.
*/
protected void registerHandler(RestRequest.Method method, String path, RestHandler handler) {
if (handler instanceof BaseRestHandler) {
// 如果是 BaseRestHandler, 则添加到 usageService 中
usageService.addRestHandler((BaseRestHandler) handler);
}
registerHandlerNoWrap(method, path, handlerWrapper.apply(handler));
} private void registerHandlerNoWrap(RestRequest.Method method, String path, RestHandler maybeWrappedHandler) {
// 此处 handlers = new PathTrie<>(RestUtils.REST_DECODER);
handlers.insertOrUpdate(path, new MethodHandlers(path, maybeWrappedHandler, method),
(mHandlers, newMHandler) -> mHandlers.addMethods(maybeWrappedHandler, method));
} // org.elasticsearch.usage.UsageService#addRestHandler
/**
* Add a REST handler to this service.
*
* @param handler the {@link BaseRestHandler} to add to the usage service.
*/
public void addRestHandler(BaseRestHandler handler) {
Objects.requireNonNull(handler);
if (handler.getName() == null) {
throw new IllegalArgumentException("handler of type [" + handler.getClass().getName() + "] does not have a name");
}
// 以hashMap直接保存name与handler的关系
final BaseRestHandler maybeHandler = handlers.put(handler.getName(), handler);
/*
* Handlers will be registered multiple times, once for each route that the handler handles. This means that we will see handlers
* multiple times, so we do not have a conflict if we are seeing the same instance multiple times. So, we only reject if a handler
* with the same name was registered before, and it is not the same instance as before.
*/
if (maybeHandler != null && maybeHandler != handler) {
final String message = String.format(
Locale.ROOT,
"handler of type [%s] conflicts with handler of type [%s] as they both have the same name [%s]",
handler.getClass().getName(),
maybeHandler.getClass().getName(),
handler.getName()
);
throw new IllegalArgumentException(message);
}
}
PathTrie 的插入更新过程细节，感兴趣可以展开：
// org.elasticsearch.common.path.PathTrie#insertOrUpdate
/**
* Insert a value for the given path. If the path already exists, replace the value with:
* <pre>
* value = updater.apply(oldValue, newValue);
* </pre>
* allowing the value to be updated if desired.
*/
public void insertOrUpdate(String path, T value, BiFunction<T, T, T> updater) {
String[] strings = path.split(SEPARATOR);
if (strings.length == 0) {
if (rootValue != null) {
rootValue = updater.apply(rootValue, value);
} else {
rootValue = value;
}
return;
}
int index = 0;
// Supports initial delimiter.
if (strings[0].isEmpty()) {
index = 1;
}
root.insertOrUpdate(strings, index, value, updater);
}
// 类似字典树的路径查找实现
// 核心原理是以 '/' 分割路径，然后依次从前往后取key以 HashMap 形式存储
// 遇到 {xxx} 则特殊对待存储
// 此处的字典先后是以 // 分的先后为依据的，而非字母顺序
// org.elasticsearch.common.path.PathTrie.TrieNode#insertOrUpdate
private synchronized void insertOrUpdate(String[] path, int index, T value, BiFunction<T, T, T> updater) {
if (index >= path.length)
return; String token = path[index];
String key = token;
// 类似 {index} 这种格式
if (isNamedWildcard(token)) {
key = wildcard;
}
TrieNode node = children.get(key);
if (node == null) {
T nodeValue = index == path.length - 1 ? value : null;
node = new TrieNode(token, nodeValue, wildcard);
addInnerChild(key, node);
} else {
if (isNamedWildcard(token)) {
node.updateKeyWithNamedWildcard(token);
}
/*
* If the target node already exists, but is without a value,
* then the value should be updated.
*/
if (index == (path.length - 1)) {
if (node.value != null) {
node.value = updater.apply(node.value, value);
} else {
node.value = value;
}
}
} node.insertOrUpdate(path, index + 1, value, updater);
}
有了以上地址注册后，在进行请求分发时就有依据了。
2. 请求分发过程
当一个请求到达es, es是如何执行处理的呢？当然是各种场景各有不同了。但是，我们此处要看的，从框架微处看es是如何执行的。其实，必然和上一节我们讲的 RestController, RequestHandlers 有关。
具体细节的如何分发到 RestController, 有兴趣的同学可以展开阅读, 无则直接从 RestController 开始。
// org.elasticsearch.http.netty4.Netty4HttpRequestHandler#channelRead0
@Override
protected void channelRead0(ChannelHandlerContext ctx, HttpPipelinedRequest httpRequest) {
final Netty4HttpChannel channel = ctx.channel().attr(Netty4HttpServerTransport.HTTP_CHANNEL_KEY).get();
boolean success = false;
try {
serverTransport.incomingRequest(httpRequest, channel);
success = true;
} finally {
if (success == false) {
httpRequest.release();
}
}
}
// org.elasticsearch.http.AbstractHttpServerTransport#incomingRequest
/**
* This method handles an incoming http request.
*
* @param httpRequest that is incoming
* @param httpChannel that received the http request
*/
public void incomingRequest(final HttpRequest httpRequest, final HttpChannel httpChannel) {
final long startTime = threadPool.relativeTimeInMillis();
try {
handleIncomingRequest(httpRequest, httpChannel, httpRequest.getInboundException());
} finally {
final long took = threadPool.relativeTimeInMillis() - startTime;
final long logThreshold = slowLogThresholdMs;
if (logThreshold > 0 && took > logThreshold) {
logger.warn("handling request [{}][{}][{}][{}] took [{}ms] which is above the warn threshold of [{}ms]",
httpRequest.header(Task.X_OPAQUE_ID), httpRequest.method(), httpRequest.uri(), httpChannel, took, logThreshold);
}
}
} private void handleIncomingRequest(final HttpRequest httpRequest, final HttpChannel httpChannel, final Exception exception) {
if (exception == null) {
HttpResponse earlyResponse = corsHandler.handleInbound(httpRequest);
if (earlyResponse != null) {
httpChannel.sendResponse(earlyResponse, earlyResponseListener(httpRequest, httpChannel));
httpRequest.release();
return;
}
} Exception badRequestCause = exception; /*
* We want to create a REST request from the incoming request from Netty. However, creating this request could fail if there
* are incorrectly encoded parameters, or the Content-Type header is invalid. If one of these specific failures occurs, we
* attempt to create a REST request again without the input that caused the exception (e.g., we remove the Content-Type header,
* or skip decoding the parameters). Once we have a request in hand, we then dispatch the request as a bad request with the
* underlying exception that caused us to treat the request as bad.
*/
final RestRequest restRequest;
{
RestRequest innerRestRequest;
try {
innerRestRequest = RestRequest.request(xContentRegistry, httpRequest, httpChannel);
} catch (final RestRequest.ContentTypeHeaderException e) {
badRequestCause = ExceptionsHelper.useOrSuppress(badRequestCause, e);
innerRestRequest = requestWithoutContentTypeHeader(httpRequest, httpChannel, badRequestCause);
} catch (final RestRequest.BadParameterException e) {
badRequestCause = ExceptionsHelper.useOrSuppress(badRequestCause, e);
innerRestRequest = RestRequest.requestWithoutParameters(xContentRegistry, httpRequest, httpChannel);
}
restRequest = innerRestRequest;
} final HttpTracer trace = tracer.maybeTraceRequest(restRequest, exception); /*
* We now want to create a channel used to send the response on. However, creating this channel can fail if there are invalid
* parameter values for any of the filter_path, human, or pretty parameters. We detect these specific failures via an
* IllegalArgumentException from the channel constructor and then attempt to create a new channel that bypasses parsing of these
* parameter values.
*/
final RestChannel channel;
{
RestChannel innerChannel;
ThreadContext threadContext = threadPool.getThreadContext();
try {
innerChannel =
new DefaultRestChannel(httpChannel, httpRequest, restRequest, bigArrays, handlingSettings, threadContext, corsHandler,
trace);
} catch (final IllegalArgumentException e) {
badRequestCause = ExceptionsHelper.useOrSuppress(badRequestCause, e);
final RestRequest innerRequest = RestRequest.requestWithoutParameters(xContentRegistry, httpRequest, httpChannel);
innerChannel =
new DefaultRestChannel(httpChannel, httpRequest, innerRequest, bigArrays, handlingSettings, threadContext, corsHandler,
trace);
}
channel = innerChannel;
}
// 分发请求，到 controller
dispatchRequest(restRequest, channel, badRequestCause);
}
// org.elasticsearch.http.AbstractHttpServerTransport#dispatchRequest
// Visible for testing
void dispatchRequest(final RestRequest restRequest, final RestChannel channel, final Throwable badRequestCause) {
final ThreadContext threadContext = threadPool.getThreadContext();
try (ThreadContext.StoredContext ignore = threadContext.stashContext()) {
if (badRequestCause != null) {
dispatcher.dispatchBadRequest(channel, threadContext, badRequestCause);
} else {
// 分发到 restController
dispatcher.dispatchRequest(restRequest, channel, threadContext);
}
}
}
RestController 是以 dispatchRequest() 作为入口的，它负责找到能够处理该请求的处理器，然后分发过去。这很自然。
// org.elasticsearch.rest.RestController#dispatchRequest
@Override
public void dispatchRequest(RestRequest request, RestChannel channel, ThreadContext threadContext) {
try {
// 尝试所有可能的处理器
tryAllHandlers(request, channel, threadContext);
} catch (Exception e) {
try {
// 发生异常则响应异常信息
channel.sendResponse(new BytesRestResponse(channel, e));
} catch (Exception inner) {
inner.addSuppressed(e);
logger.error(() ->
new ParameterizedMessage("failed to send failure response for uri [{}]", request.uri()), inner);
}
}
}
// org.elasticsearch.rest.RestController#tryAllHandlers
private void tryAllHandlers(final RestRequest request, final RestChannel channel, final ThreadContext threadContext) throws Exception {
// 读取 header 信息
for (final RestHeaderDefinition restHeader : headersToCopy) {
final String name = restHeader.getName();
final List<String> headerValues = request.getAllHeaderValues(name);
if (headerValues != null && headerValues.isEmpty() == false) {
final List<String> distinctHeaderValues = headerValues.stream().distinct().collect(Collectors.toList());
if (restHeader.isMultiValueAllowed() == false && distinctHeaderValues.size() > 1) {
channel.sendResponse(
BytesRestResponse.
createSimpleErrorResponse(channel, BAD_REQUEST, "multiple values for single-valued header [" + name + "]."));
return;
} else {
threadContext.putHeader(name, String.join(",", distinctHeaderValues));
}
}
}
// error_trace cannot be used when we disable detailed errors
// we consume the error_trace parameter first to ensure that it is always consumed
if (request.paramAsBoolean("error_trace", false) && channel.detailedErrorsEnabled() == false) {
channel.sendResponse(
BytesRestResponse.createSimpleErrorResponse(channel, BAD_REQUEST, "error traces in responses are disabled."));
return;
} final String rawPath = request.rawPath();
final String uri = request.uri();
final RestRequest.Method requestMethod;
try {
// Resolves the HTTP method and fails if the method is invalid
requestMethod = request.method();
// Loop through all possible handlers, attempting to dispatch the request
// 获取可能的处理器，主要是有正则或者索引变量的存在，可能匹配多个处理器
Iterator<MethodHandlers> allHandlers = getAllHandlers(request.params(), rawPath);
while (allHandlers.hasNext()) {
final RestHandler handler;
// 一个处理器里支持多种请求方法
final MethodHandlers handlers = allHandlers.next();
if (handlers == null) {
handler = null;
} else {
handler = handlers.getHandler(requestMethod);
}
if (handler == null) {
// 未找到处理器不代表不能处理，有可能需要继续查找，如果确定不能处理，则直接响应客户端返回
if (handleNoHandlerFound(rawPath, requestMethod, uri, channel)) {
return;
}
} else {
// 找到了处理器，调用其方法
dispatchRequest(request, channel, handler);
return;
}
}
} catch (final IllegalArgumentException e) {
handleUnsupportedHttpMethod(uri, null, channel, getValidHandlerMethodSet(rawPath), e);
return;
}
// If request has not been handled, fallback to a bad request error.
// 降级方法调用
handleBadRequest(uri, requestMethod, channel);
}
// org.elasticsearch.rest.RestController#getAllHandlers
Iterator<MethodHandlers> getAllHandlers(@Nullable Map<String, String> requestParamsRef, String rawPath) {
final Supplier<Map<String, String>> paramsSupplier;
if (requestParamsRef == null) {
paramsSupplier = () -> null;
} else {
// Between retrieving the correct path, we need to reset the parameters,
// otherwise parameters are parsed out of the URI that aren't actually handled.
final Map<String, String> originalParams = new HashMap<>(requestParamsRef);
paramsSupplier = () -> {
// PathTrie modifies the request, so reset the params between each iteration
requestParamsRef.clear();
requestParamsRef.putAll(originalParams);
return requestParamsRef;
};
}
// we use rawPath since we don't want to decode it while processing the path resolution
// so we can handle things like:
// my_index/my_type/http%3A%2F%2Fwww.google.com
return handlers.retrieveAll(rawPath, paramsSupplier);
} /**
* Returns an iterator of the objects stored in the {@code PathTrie}, using
* all possible {@code TrieMatchingMode} modes. The {@code paramSupplier}
* is called between each invocation of {@code next()} to supply a new map
* of parameters.
*/
public Iterator<T> retrieveAll(String path, Supplier<Map<String, String>> paramSupplier) {
return new Iterator<T>() { private int mode; @Override
public boolean hasNext() {
return mode < TrieMatchingMode.values().length;
} @Override
public T next() {
if (hasNext() == false) {
throw new NoSuchElementException("called next() without validating hasNext()! no more modes available");
}
return retrieve(path, paramSupplier.get(), TrieMatchingMode.values()[mode++]);
}
};
}
其中，路径匹配是基于trie树的一种实现，获取路径匹配的一个节点。需要稍微理解下其算法，按需展开。
// org.elasticsearch.common.path.PathTrie.TrieNode#retrieve
public T retrieve(String[] path, int index, Map<String, String> params, TrieMatchingMode trieMatchingMode) {
if (index >= path.length)
return null; String token = path[index];
TrieNode node = children.get(token);
boolean usedWildcard; if (node == null) {
if (trieMatchingMode == TrieMatchingMode.WILDCARD_NODES_ALLOWED) {
node = children.get(wildcard);
if (node == null) {
return null;
}
usedWildcard = true;
} else if (trieMatchingMode == TrieMatchingMode.WILDCARD_ROOT_NODES_ALLOWED && index == 1) {
/*
* Allow root node wildcard matches.
*/
node = children.get(wildcard);
if (node == null) {
return null;
}
usedWildcard = true;
} else if (trieMatchingMode == TrieMatchingMode.WILDCARD_LEAF_NODES_ALLOWED && index + 1 == path.length) {
/*
* Allow leaf node wildcard matches.
*/
node = children.get(wildcard);
if (node == null) {
return null;
}
usedWildcard = true;
} else {
return null;
}
} else {
if (index + 1 == path.length && node.value == null && children.get(wildcard) != null
&& EXPLICIT_OR_ROOT_WILDCARD.contains(trieMatchingMode) == false) {
/*
* If we are at the end of the path, the current node does not have a value but
* there is a child wildcard node, use the child wildcard node.
*/
node = children.get(wildcard);
usedWildcard = true;
} else if (index == 1 && node.value == null && children.get(wildcard) != null
&& trieMatchingMode == TrieMatchingMode.WILDCARD_ROOT_NODES_ALLOWED) {
/*
* If we are at the root, and root wildcards are allowed, use the child wildcard
* node.
*/
node = children.get(wildcard);
usedWildcard = true;
} else {
usedWildcard = token.equals(wildcard);
}
}
// 思考：params 的目的是啥？
put(params, node, token); if (index == (path.length - 1)) {
return node.value;
} T nodeValue = node.retrieve(path, index + 1, params, trieMatchingMode);
if (nodeValue == null && !usedWildcard && trieMatchingMode != TrieMatchingMode.EXPLICIT_NODES_ONLY) {
node = children.get(wildcard);
if (node != null) {
put(params, node, token);
nodeValue = node.retrieve(path, index + 1, params, trieMatchingMode);
}
} return nodeValue;
}
找到处理器之后，就是核心调用了。
// org.elasticsearch.rest.RestController#dispatchRequest
private void dispatchRequest(RestRequest request, RestChannel channel, RestHandler handler) throws Exception {
final int contentLength = request.contentLength();
if (contentLength > 0) {
final XContentType xContentType = request.getXContentType();
if (xContentType == null) {
sendContentTypeErrorMessage(request.getAllHeaderValues("Content-Type"), channel);
return;
}
if (handler.supportsContentStream() && xContentType != XContentType.JSON && xContentType != XContentType.SMILE) {
channel.sendResponse(BytesRestResponse.createSimpleErrorResponse(channel, RestStatus.NOT_ACCEPTABLE,
"Content-Type [" + xContentType + "] does not support stream parsing. Use JSON or SMILE instead"));
return;
}
}
RestChannel responseChannel = channel;
try {
// 熔断判定
if (handler.canTripCircuitBreaker()) {
inFlightRequestsBreaker(circuitBreakerService).addEstimateBytesAndMaybeBreak(contentLength, "<http_request>");
} else {
inFlightRequestsBreaker(circuitBreakerService).addWithoutBreaking(contentLength);
}
// iff we could reserve bytes for the request we need to send the response also over this channel
responseChannel = new ResourceHandlingHttpChannel(channel, circuitBreakerService, contentLength);
// TODO: Count requests double in the circuit breaker if they need copying?
if (handler.allowsUnsafeBuffers() == false) {
request.ensureSafeBuffers();
}
if (handler.allowSystemIndexAccessByDefault() == false && request.header(ELASTIC_PRODUCT_ORIGIN_HTTP_HEADER) == null) {
// The ELASTIC_PRODUCT_ORIGIN_HTTP_HEADER indicates that the request is coming from an Elastic product with a plan
// to move away from direct access to system indices, and thus deprecation warnings should not be emitted.
// This header is intended for internal use only.
client.threadPool().getThreadContext().putHeader(SYSTEM_INDEX_ACCESS_CONTROL_HEADER_KEY, Boolean.FALSE.toString());
}
// 调用handler处理方法，该handler可能会被过滤器先执行
handler.handleRequest(request, responseChannel, client);
} catch (Exception e) {
responseChannel.sendResponse(new BytesRestResponse(responseChannel, e));
}
}
// org.elasticsearch.xpack.security.rest.SecurityRestFilter#handleRequest
@Override
public void handleRequest(RestRequest request, RestChannel channel, NodeClient client) throws Exception {
if (licenseState.isSecurityEnabled() && request.method() != Method.OPTIONS) {
// CORS - allow for preflight unauthenticated OPTIONS request
if (extractClientCertificate) {
HttpChannel httpChannel = request.getHttpChannel();
SSLEngineUtils.extractClientCertificates(logger, threadContext, httpChannel);
} final String requestUri = request.uri();
authenticationService.authenticate(maybeWrapRestRequest(request), ActionListener.wrap(
authentication -> {
if (authentication == null) {
logger.trace("No authentication available for REST request [{}]", requestUri);
} else {
logger.trace("Authenticated REST request [{}] as {}", requestUri, authentication);
}
secondaryAuthenticator.authenticateAndAttachToContext(request, ActionListener.wrap(
secondaryAuthentication -> {
if (secondaryAuthentication != null) {
logger.trace("Found secondary authentication {} in REST request [{}]", secondaryAuthentication, requestUri);
}
RemoteHostHeader.process(request, threadContext);
restHandler.handleRequest(request, channel, client);
},
e -> handleException("Secondary authentication", request, channel, e)));
}, e -> handleException("Authentication", request, channel, e)));
} else {
// 转发到下一处理器责任链
restHandler.handleRequest(request, channel, client);
}
}
// 我们以 RestNodeAction 为例，如请求 /_cat/nodes，看handler如何处理请求
// org.elasticsearch.rest.BaseRestHandler#handleRequest
@Override
public final void handleRequest(RestRequest request, RestChannel channel, NodeClient client) throws Exception {
// prepare the request for execution; has the side effect of touching the request parameters
// 看起来叫准备请求，实际非常重要，它会组装后续的请求逻辑
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, candidateParams, "parameter"));
} if (request.hasContent() && request.isContentConsumed() == false) {
throw new IllegalArgumentException("request [" + request.method() + " " + request.path() + "] does not support having a body");
} usageCount.increment();
// execute the action
// 即此处仅为调用前面设置好的方法
action.accept(channel);
}
// org.elasticsearch.rest.action.cat.AbstractCatAction#prepareRequest
@Override
public RestChannelConsumer prepareRequest(final RestRequest request, final NodeClient client) throws IOException {
boolean helpWanted = request.paramAsBoolean("help", false);
// 帮助信息打印
if (helpWanted) {
return channel -> {
Table table = getTableWithHeader(request);
int[] width = buildHelpWidths(table, request);
BytesStream bytesOutput = Streams.flushOnCloseStream(channel.bytesOutput());
UTF8StreamWriter out = new UTF8StreamWriter().setOutput(bytesOutput);
for (Table.Cell cell : table.getHeaders()) {
// need to do left-align always, so create new cells
pad(new Table.Cell(cell.value), width[0], request, out);
out.append(" | ");
pad(new Table.Cell(cell.attr.containsKey("alias") ? cell.attr.get("alias") : ""), width[1], request, out);
out.append(" | ");
pad(new Table.Cell(cell.attr.containsKey("desc") ? cell.attr.get("desc") : "not available"), width[2], request, out);
out.append("\n");
}
out.close();
channel.sendResponse(new BytesRestResponse(RestStatus.OK, BytesRestResponse.TEXT_CONTENT_TYPE, bytesOutput.bytes()));
};
} else {
return doCatRequest(request, client);
}
}
// org.elasticsearch.rest.action.cat.RestNodesAction#doCatRequest
@Override
public RestChannelConsumer doCatRequest(final RestRequest request, final NodeClient client) {
final ClusterStateRequest clusterStateRequest = new ClusterStateRequest();
clusterStateRequest.clear().nodes(true);
if (request.hasParam("local")) {
deprecationLogger.deprecate("cat_nodes_local_parameter", LOCAL_DEPRECATED_MESSAGE);
}
clusterStateRequest.local(request.paramAsBoolean("local", clusterStateRequest.local()));
clusterStateRequest.masterNodeTimeout(request.paramAsTime("master_timeout", clusterStateRequest.masterNodeTimeout()));
final boolean fullId = request.paramAsBoolean("full_id", false);
// 向集群发起请求，获得各节点状态
return channel -> client.admin().cluster().state(clusterStateRequest, new RestActionListener<ClusterStateResponse>(channel) {
@Override
public void processResponse(final ClusterStateResponse clusterStateResponse) {
NodesInfoRequest nodesInfoRequest = new NodesInfoRequest();
nodesInfoRequest.clear().addMetrics(
NodesInfoRequest.Metric.JVM.metricName(),
NodesInfoRequest.Metric.OS.metricName(),
NodesInfoRequest.Metric.PROCESS.metricName(),
NodesInfoRequest.Metric.HTTP.metricName());
client.admin().cluster().nodesInfo(nodesInfoRequest, new RestActionListener<NodesInfoResponse>(channel) {
@Override
public void processResponse(final NodesInfoResponse nodesInfoResponse) {
NodesStatsRequest nodesStatsRequest = new NodesStatsRequest();
nodesStatsRequest.clear().indices(true).addMetrics(
NodesStatsRequest.Metric.JVM.metricName(),
NodesStatsRequest.Metric.OS.metricName(),
NodesStatsRequest.Metric.FS.metricName(),
NodesStatsRequest.Metric.PROCESS.metricName(),
NodesStatsRequest.Metric.SCRIPT.metricName()
);
client.admin().cluster().nodesStats(nodesStatsRequest, new RestResponseListener<NodesStatsResponse>(channel) {
@Override
public RestResponse buildResponse(NodesStatsResponse nodesStatsResponse) throws Exception {
return RestTable.buildResponse(buildTable(fullId, request, clusterStateResponse, nodesInfoResponse,
nodesStatsResponse), channel);
}
});
}
});
}
});
}
以上的整个 /_cat/nodes 的整体处理框架，即其会先发起 state 请求，然后是 nodesInfo 请求，最后是 nodesStats 请求，然后再统一响应。所以，我们也会三阶段来分析。
2.1. state的处理过程
state即获取集群当前状态信息，它的入口在 ClusterAdmin 中。因为是第一接触es的处理流程，我们将其抽象方法中的过程也一起看了。后续则不再讲述此部分，而只看业务核心实现部分。
// org.elasticsearch.client.support.AbstractClient.ClusterAdmin#state
@Override
public void state(final ClusterStateRequest request, final ActionListener<ClusterStateResponse> listener) {
execute(ClusterStateAction.INSTANCE, request, listener);
}
// org.elasticsearch.client.support.AbstractClient.ClusterAdmin#execute
@Override
public <Request extends ActionRequest, Response extends ActionResponse> void execute(
ActionType<Response> action, Request request, ActionListener<Response> listener) {
client.execute(action, request, listener);
}
// org.elasticsearch.client.support.AbstractClient#execute
/**
* This is the single execution point of *all* clients.
*/
@Override
public final <Request extends ActionRequest, Response extends ActionResponse> void execute(
ActionType<Response> action, Request request, ActionListener<Response> listener) {
try {
listener = threadedWrapper.wrap(listener);
doExecute(action, request, listener);
} catch (Exception e) {
assert false : new AssertionError(e);
listener.onFailure(e);
}
}
// org.elasticsearch.client.node.NodeClient#doExecute
@Override
public <Request extends ActionRequest, Response extends ActionResponse>
void doExecute(ActionType<Response> action, Request request, ActionListener<Response> listener) {
// Discard the task because the Client interface doesn't use it.
try {
executeLocally(action, request, listener);
} catch (TaskCancelledException | IllegalArgumentException | IllegalStateException e) {
// #executeLocally returns the task and throws TaskCancelledException if it fails to register the task because the parent
// task has been cancelled, IllegalStateException if the client was not in a state to execute the request because it was not
// yet properly initialized or IllegalArgumentException if header validation fails we forward them to listener since this API
// does not concern itself with the specifics of the task handling
listener.onFailure(e);
}
} /**
* Execute an {@link ActionType} locally, returning that {@link Task} used to track it, and linking an {@link ActionListener}.
* Prefer this method if you don't need access to the task when listening for the response. This is the method used to implement
* the {@link Client} interface.
*
* @throws TaskCancelledException if the request's parent task has been cancelled already
*/
public <Request extends ActionRequest,
Response extends ActionResponse
> Task executeLocally(ActionType<Response> action, Request request, ActionListener<Response> listener) {
return transportAction(action).execute(request, listener);
}
//
/**
* Get the {@link TransportAction} for an {@link ActionType}, throwing exceptions if the action isn't available.
*/
@SuppressWarnings("unchecked")
private < Request extends ActionRequest,
Response extends ActionResponse
> TransportAction<Request, Response> transportAction(ActionType<Response> action) {
if (actions == null) {
throw new IllegalStateException("NodeClient has not been initialized");
}
// action = "cluster:monitor/state"
// actions 即前面注册的一系列行为
// 此处将得到 TransportClusterStateAction
TransportAction<Request, Response> transportAction = actions.get(action);
if (transportAction == null) {
throw new IllegalStateException("failed to find action [" + action + "] to execute");
}
return transportAction;
}
// org.elasticsearch.action.support.TransportAction#execute
/**
* Use this method when the transport action call should result in creation of a new task associated with the call.
*
* This is a typical behavior.
*/
public final Task execute(Request request, ActionListener<Response> listener) {
/*
* While this version of execute could delegate to the TaskListener
* version of execute that'd add yet another layer of wrapping on the
* listener and prevent us from using the listener bare if there isn't a
* task. That just seems like too many objects. Thus the two versions of
* this method.
*/
final Releasable unregisterChildNode = registerChildNode(request.getParentTask());
final Task task;
try {
// 向taskManager 中注册任务
task = taskManager.register("transport", actionName, request);
} catch (TaskCancelledException e) {
unregisterChildNode.close();
throw e;
}
execute(task, request, new ActionListener<Response>() {
@Override
public void onResponse(Response response) {
try {
Releasables.close(unregisterChildNode, () -> taskManager.unregister(task));
} finally {
listener.onResponse(response);
}
} @Override
public void onFailure(Exception e) {
try {
Releasables.close(unregisterChildNode, () -> taskManager.unregister(task));
} finally {
listener.onFailure(e);
}
}
});
return task;
}
// org.elasticsearch.tasks.TaskManager#register
/**
* Registers a task without parent task
*/
public Task register(String type, String action, TaskAwareRequest request) {
Map<String, String> headers = new HashMap<>();
long headerSize = 0;
long maxSize = maxHeaderSize.getBytes();
ThreadContext threadContext = threadPool.getThreadContext();
for (String key : taskHeaders) {
String httpHeader = threadContext.getHeader(key);
if (httpHeader != null) {
headerSize += key.length() * 2 + httpHeader.length() * 2;
if (headerSize > maxSize) {
throw new IllegalArgumentException("Request exceeded the maximum size of task headers " + maxHeaderSize);
}
headers.put(key, httpHeader);
}
}
Task task = request.createTask(taskIdGenerator.incrementAndGet(), type, action, request.getParentTask(), headers);
Objects.requireNonNull(task);
assert task.getParentTaskId().equals(request.getParentTask()) : "Request [ " + request + "] didn't preserve it parentTaskId";
if (logger.isTraceEnabled()) {
logger.trace("register {} [{}] [{}] [{}]", task.getId(), type, action, task.getDescription());
} if (task instanceof CancellableTask) {
registerCancellableTask(task);
} else {
Task previousTask = tasks.put(task.getId(), task);
assert previousTask == null;
}
return task;
}
// org.elasticsearch.action.support.TransportAction#execute
/**
* Use this method when the transport action should continue to run in the context of the current task
*/
public final void execute(Task task, Request request, ActionListener<Response> listener) {
ActionRequestValidationException validationException = request.validate();
if (validationException != null) {
listener.onFailure(validationException);
return;
} if (task != null && request.getShouldStoreResult()) {
listener = new TaskResultStoringActionListener<>(taskManager, task, listener);
} RequestFilterChain<Request, Response> requestFilterChain = new RequestFilterChain<>(this, logger);
requestFilterChain.proceed(task, actionName, request, listener);
}
// org.elasticsearch.action.support.TransportAction.RequestFilterChain#proceed
@Override
public void proceed(Task task, String actionName, Request request, ActionListener<Response> listener) {
int i = index.getAndIncrement();
try {
if (i < this.action.filters.length) {
// 先执行filter, 再执行 action
// filter 实现 ActionFilter
this.action.filters[i].apply(task, actionName, request, listener, this);
} else if (i == this.action.filters.length) {
this.action.doExecute(task, request, listener);
} else {
listener.onFailure(new IllegalStateException("proceed was called too many times"));
}
} catch(Exception e) {
logger.trace("Error during transport action execution.", e);
listener.onFailure(e);
}
}
// org.elasticsearch.action.support.master.TransportMasterNodeAction#doExecute
@Override
protected void doExecute(Task task, final Request request, ActionListener<Response> listener) {
// 获取state
ClusterState state = clusterService.state();
logger.trace("starting processing request [{}] with cluster state version [{}]", request, state.version());
if (task != null) {
request.setParentTask(clusterService.localNode().getId(), task.getId());
}
// 启动一个新的状态获取请求
new AsyncSingleAction(task, request, listener).doStart(state);
}
// org.elasticsearch.cluster.service.ClusterService#state
/**
* The currently applied cluster state.
* TODO: Should be renamed to appliedState / appliedClusterState
*/
public ClusterState state() {
return clusterApplierService.state();
}
// org.elasticsearch.cluster.service.ClusterApplierService#state
/**
* The current cluster state.
* Should be renamed to appliedClusterState
*/
public ClusterState state() {
assert assertNotCalledFromClusterStateApplier("the applied cluster state is not yet available");
// AtomicReference, 当前的集群状态
ClusterState clusterState = this.state.get();
assert clusterState != null : "initial cluster state not set yet";
return clusterState;
} // org.elasticsearch.action.support.master.TransportMasterNodeAction.AsyncSingleAction#doStart
protected void doStart(ClusterState clusterState) {
try {
final DiscoveryNodes nodes = clusterState.nodes();
// 本地是 master 直接处理，否则像远程master发起请求处理
if (nodes.isLocalNodeElectedMaster() || localExecute(request)) {
// check for block, if blocked, retry, else, execute locally
final ClusterBlockException blockException = checkBlock(request, clusterState);
if (blockException != null) {
if (!blockException.retryable()) {
listener.onFailure(blockException);
} else {
logger.debug("can't execute due to a cluster block, retrying", blockException);
retry(clusterState, blockException, newState -> {
try {
ClusterBlockException newException = checkBlock(request, newState);
return (newException == null || !newException.retryable());
} catch (Exception e) {
// accept state as block will be rechecked by doStart() and listener.onFailure() then called
logger.trace("exception occurred during cluster block checking, accepting state", e);
return true;
}
});
}
} else {
ActionListener<Response> delegate = ActionListener.delegateResponse(listener, (delegatedListener, t) -> {
if (t instanceof FailedToCommitClusterStateException || t instanceof NotMasterException) {
logger.debug(() -> new ParameterizedMessage("master could not publish cluster state or " +
"stepped down before publishing action [{}], scheduling a retry", actionName), t);
retryOnMasterChange(clusterState, t);
} else {
delegatedListener.onFailure(t);
}
});
threadPool.executor(executor)
.execute(ActionRunnable.wrap(delegate, l -> masterOperation(task, request, clusterState, l)));
}
} else {
if (nodes.getMasterNode() == null) {
logger.debug("no known master node, scheduling a retry");
retryOnMasterChange(clusterState, null);
} else {
DiscoveryNode masterNode = nodes.getMasterNode();
final String actionName = getMasterActionName(masterNode);
transportService.sendRequest(masterNode, actionName, request,
new ActionListenerResponseHandler<Response>(listener, responseReader) {
@Override
public void handleException(final TransportException exp) {
Throwable cause = exp.unwrapCause();
if (cause instanceof ConnectTransportException ||
(exp instanceof RemoteTransportException && cause instanceof NodeClosedException)) {
// we want to retry here a bit to see if a new master is elected
logger.debug("connection exception while trying to forward request with action name [{}] to " +
"master node [{}], scheduling a retry. Error: [{}]",
actionName, nodes.getMasterNode(), exp.getDetailedMessage());
retryOnMasterChange(clusterState, cause);
} else {
listener.onFailure(exp);
}
}
});
}
}
} catch (Exception e) {
listener.onFailure(e);
}
}
以上，是一个 state() 命令的处理过程，总结起来就是通过具体的handler, 找到可以执行的线程池, 然后执行状态本机查询返回，如果本机不是master节点则会向远程节点发起请求，以得到集群当前状态。从上面的实现来看，state() 只是第一步的操作，后面还有 nodesInfo 请求，nodesStats 请求。
2.2. nodesInfo的处理过程
当state处理完成后，它会再发起一个 nodesInfo 请求，这个看起来更像nodes相关的信息。
// org.elasticsearch.client.support.AbstractClient.ClusterAdmin#nodesInfo
@Override
public void nodesInfo(final NodesInfoRequest request, final ActionListener<NodesInfoResponse> listener) {
execute(NodesInfoAction.INSTANCE, request, listener);
}
// 最终调用 TransportNodesAction 的doExecute 方法
// org.elasticsearch.action.support.nodes.TransportNodesAction#doExecute
@Override
protected void doExecute(Task task, NodesRequest request, ActionListener<NodesResponse> listener) {
new AsyncAction(task, request, listener).start();
}
// org.elasticsearch.action.support.nodes.TransportNodesAction.AsyncAction#start
void start() {
final DiscoveryNode[] nodes = request.concreteNodes();
if (nodes.length == 0) {
// nothing to notify
threadPool.generic().execute(() -> listener.onResponse(newResponse(request, responses)));
return;
}
final TransportRequestOptions transportRequestOptions = TransportRequestOptions.timeout(request.timeout());
// 依次向各节点发送状态请求，最终收集结果
for (int i = 0; i < nodes.length; i++) {
final int idx = i;
final DiscoveryNode node = nodes[i];
final String nodeId = node.getId();
try {
TransportRequest nodeRequest = newNodeRequest(request);
if (task != null) {
nodeRequest.setParentTask(clusterService.localNode().getId(), task.getId());
}
// action = inner:monitor/node/info[n]
transportService.sendRequest(node, getTransportNodeAction(node), nodeRequest, transportRequestOptions,
new TransportResponseHandler<NodeResponse>() {
@Override
public NodeResponse read(StreamInput in) throws IOException {
return newNodeResponse(in);
}
// 远端响应之后会进行回调该方法
@Override
public void handleResponse(NodeResponse response) {
onOperation(idx, response);
} @Override
public void handleException(TransportException exp) {
onFailure(idx, node.getId(), exp);
}
});
} catch (Exception e) {
onFailure(idx, nodeId, e);
}
}
}
完成后，会得到一个 NodesInfoResponse 信息。备用。
2.3. nodesStats的处理流程
一个集群有一个集群状态，n个集群节点，n个节点状态。就是这样了，即每获取到一个节点的信息，就会去拉取一次节点的状态 nodesStats . 事实上，它们执行是同一方法逻辑。
// org.elasticsearch.action.support.nodes.TransportNodesAction#doExecute
@Override
protected void doExecute(Task task, NodesRequest request, ActionListener<NodesResponse> listener) {
new AsyncAction(task, request, listener).start();
} void start() {
final DiscoveryNode[] nodes = request.concreteNodes();
if (nodes.length == 0) {
// nothing to notify
threadPool.generic().execute(() -> listener.onResponse(newResponse(request, responses)));
return;
}
final TransportRequestOptions transportRequestOptions = TransportRequestOptions.timeout(request.timeout());
for (int i = 0; i < nodes.length; i++) {
final int idx = i;
final DiscoveryNode node = nodes[i];
final String nodeId = node.getId();
try {
TransportRequest nodeRequest = newNodeRequest(request);
if (task != null) {
nodeRequest.setParentTask(clusterService.localNode().getId(), task.getId());
}
// action = cluster:monitor/nodes/stats[n]
transportService.sendRequest(node, getTransportNodeAction(node), nodeRequest, transportRequestOptions,
new TransportResponseHandler<NodeResponse>() {
@Override
public NodeResponse read(StreamInput in) throws IOException {
return newNodeResponse(in);
} @Override
public void handleResponse(NodeResponse response) {
onOperation(idx, response);
} @Override
public void handleException(TransportException exp) {
onFailure(idx, node.getId(), exp);
}
});
} catch (Exception e) {
onFailure(idx, nodeId, e);
}
}
}
// org.elasticsearch.action.admin.cluster.node.stats.TransportNodesStatsAction#nodeOperation
@Override
protected NodeStats nodeOperation(NodeStatsRequest nodeStatsRequest) {
NodesStatsRequest request = nodeStatsRequest.request;
Set<String> metrics = request.requestedMetrics();
return nodeService.stats(
request.indices(),
NodesStatsRequest.Metric.OS.containedIn(metrics),
NodesStatsRequest.Metric.PROCESS.containedIn(metrics),
NodesStatsRequest.Metric.JVM.containedIn(metrics),
NodesStatsRequest.Metric.THREAD_POOL.containedIn(metrics),
NodesStatsRequest.Metric.FS.containedIn(metrics),
NodesStatsRequest.Metric.TRANSPORT.containedIn(metrics),
NodesStatsRequest.Metric.HTTP.containedIn(metrics),
NodesStatsRequest.Metric.BREAKER.containedIn(metrics),
NodesStatsRequest.Metric.SCRIPT.containedIn(metrics),
NodesStatsRequest.Metric.DISCOVERY.containedIn(metrics),
NodesStatsRequest.Metric.INGEST.containedIn(metrics),
NodesStatsRequest.Metric.ADAPTIVE_SELECTION.containedIn(metrics),
NodesStatsRequest.Metric.SCRIPT_CACHE.containedIn(metrics),
NodesStatsRequest.Metric.INDEXING_PRESSURE.containedIn(metrics));
}
// org.elasticsearch.transport.RequestHandlerRegistry#processMessageReceived
public void processMessageReceived(Request request, TransportChannel channel) throws Exception {
final Task task = taskManager.register(channel.getChannelType(), action, request);
Releasable unregisterTask = () -> taskManager.unregister(task);
try {
if (channel instanceof TcpTransportChannel && task instanceof CancellableTask) {
final TcpChannel tcpChannel = ((TcpTransportChannel) channel).getChannel();
final Releasable stopTracking = taskManager.startTrackingCancellableChannelTask(tcpChannel, (CancellableTask) task);
unregisterTask = Releasables.wrap(unregisterTask, stopTracking);
}
final TaskTransportChannel taskTransportChannel = new TaskTransportChannel(channel, unregisterTask);
handler.messageReceived(request, taskTransportChannel, task);
unregisterTask = null;
} finally {
Releasables.close(unregisterTask);
}
}
// org.elasticsearch.action.support.nodes.TransportNodesAction.NodeTransportHandler
class NodeTransportHandler implements TransportRequestHandler<NodeRequest> { @Override
public void messageReceived(NodeRequest request, TransportChannel channel, Task task) throws Exception {
// 响应客户端
channel.sendResponse(nodeOperation(request, task));
}
}
// org.elasticsearch.rest.action.RestResponseListener#processResponse
@Override
protected final void processResponse(Response response) throws Exception {
// 响应客户端
channel.sendResponse(buildResponse(response));
}
到此，整个es的处理流程框架就讲完了。且我们以 /_cat/nodes 为例，讲解了es如何获取集群节点信息的。值得重提的是，es的状态操作，有时会向集群各节点发起请求，有时则不会。比如获取节点信息，并没有向集群中所有节点发送请求，而只是向其中一个master请求其本地当前状态即可。
3. 客户端响应
其实客户端响应，在前面的处理中，我们经常有看到。只不过没有完整的拿出来讨论。比如：
// 发生异常则响应异常信息
channel.sendResponse(new BytesRestResponse(channel, e)); // 直接发送错误信息
channel.sendResponse(
BytesRestResponse.createSimpleErrorResponse(channel, BAD_REQUEST, "error traces in responses are disabled.")); /**
* Handle HTTP OPTIONS requests to a valid REST endpoint. A 200 HTTP
* response code is returned, and the response 'Allow' header includes a
* list of valid HTTP methods for the endpoint (see
* <a href="https://tools.ietf.org/html/rfc2616#section-9.2">HTTP/1.1 - 9.2
* - Options</a>).
*/
private void handleOptionsRequest(RestChannel channel, Set<RestRequest.Method> validMethodSet) {
BytesRestResponse bytesRestResponse = new BytesRestResponse(OK, TEXT_CONTENT_TYPE, BytesArray.EMPTY);
// When we have an OPTIONS HTTP request and no valid handlers, simply send OK by default (with the Access Control Origin header
// which gets automatically added).
if (validMethodSet.isEmpty() == false) {
bytesRestResponse.addHeader("Allow", Strings.collectionToDelimitedString(validMethodSet, ","));
}
// 直接响应头信息
channel.sendResponse(bytesRestResponse);
}
// org.elasticsearch.transport.TaskTransportChannel#sendResponse
@Override
public void sendResponse(TransportResponse response) throws IOException {
try {
onTaskFinished.close();
} finally {
channel.sendResponse(response);
}
}
更多写客户端逻辑可展开阅读，总结一句就是最终的netty的channel.wrtie();
// org.elasticsearch.transport.TransportService.DirectResponseChannel#sendResponse
@Override
public void sendResponse(TransportResponse response) throws IOException {
service.onResponseSent(requestId, action, response);
final TransportResponseHandler handler = service.responseHandlers.onResponseReceived(requestId, service);
// ignore if its null, the service logs it
if (handler != null) {
final String executor = handler.executor();
if (ThreadPool.Names.SAME.equals(executor)) {
processResponse(handler, response);
} else {
threadPool.executor(executor).execute(new Runnable() {
@Override
public void run() {
processResponse(handler, response);
} @Override
public String toString() {
return "delivery of response to [" + requestId + "][" + action + "]: " + response;
}
});
}
}
}
// org.elasticsearch.transport.Transport.ResponseHandlers#onResponseReceived
/**
* called by the {@link Transport} implementation when a response or an exception has been received for a previously
* sent request (before any processing or deserialization was done). Returns the appropriate response handler or null if not
* found.
*/
public TransportResponseHandler<? extends TransportResponse> onResponseReceived(final long requestId,
final TransportMessageListener listener) {
ResponseContext<? extends TransportResponse> context = handlers.remove(requestId);
listener.onResponseReceived(requestId, context);
if (context == null) {
return null;
} else {
return context.handler();
}
}
// org.elasticsearch.transport.TransportService.DirectResponseChannel#processResponse
@SuppressWarnings("unchecked")
protected void processResponse(TransportResponseHandler handler, TransportResponse response) {
try {
handler.handleResponse(response);
} catch (Exception e) {
processException(handler, wrapInRemote(new ResponseHandlerFailureTransportException(e)));
}
}
// org.elasticsearch.transport.TransportService.ContextRestoreResponseHandler#handleResponse
@Override
public void handleResponse(T response) {
if(handler != null) {
handler.cancel();
}
try (ThreadContext.StoredContext ignore = contextSupplier.get()) {
delegate.handleResponse(response);
}
}
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