springcloud-sleuth源码解析2-TraceFilter
基于spring cloud 1.2.1版本spring
本章将分析server接收一个请求，trace到底是怎么处理的。api
span的生命周期
首先介绍下一个span的生命周期：mvc
- start
建立一个span，这时候会记录建立时间以及设置span name。若是当前线程已经存在一个span，则建立的新的span是childSpan。
// Start a span. If there was a span present in this thread it will become
// the `newSpan`'s parent.
Span newSpan = this.tracer.createSpan("calculateTax");
try {
// ...
// You can tag a span
this.tracer.addTag("taxValue", taxValue);
// ...
// You can log an event on a span
newSpan.logEvent("taxCalculated");
} finally {
// Once done remember to close the span. This will allow collecting
// the span to send it to Zipkin
this.tracer.close(newSpan);
}
- close
若是一个span已经准备好将自身发送到zipkin server或者其余collect的时候，便会调用close方法，记录endTime，上报span，而后从当前线程中移除span。 - continue
将一个新的span设置到当前线程中，成为continueSpan。该方法做用是传递不一样线程之间的span。对于一些异步处理代码，就须要 将span设置到异步处理线程中了。
Span continuedSpan = this.tracer.continueSpan(spanToContinue);
- detach
从当前线程中删除span，剥离出去，但不会stop或者close span。通常跟continue方法结合使用。
// let's assume that we're in a thread Y and we've received
// the `initialSpan` from thread X
Span continuedSpan = this.tracer.continueSpan(initialSpan);
try {
// ...
// You can tag a span
this.tracer.addTag("taxValue", taxValue);
// ...
// You can log an event on a span
continuedSpan.logEvent("taxCalculated");
} finally {
// Once done remember to detach the span. That way you'll
// safely remove it from the current thread without closing it
this.tracer.detach(continuedSpan);
}
- create with explicit parent
建立一个span而且指定它的parent span。该方法的使用场景是在当前线程中想建立一个span，但parent span存在另外一个线程当中，这样你 就能够获取到parent span，明确指定该span为要建立的span的parent。
// let's assume that we're in a thread Y and we've received
// the `initialSpan` from thread X. `initialSpan` will be the parent
// of the `newSpan`
Span newSpan = this.tracer.createSpan("calculateCommission", initialSpan);
try {
// ...
// You can tag a span
this.tracer.addTag("commissionValue", commissionValue);
// ...
// You can log an event on a span
newSpan.logEvent("commissionCalculated");
} finally {
// Once done remember to close the span. This will allow collecting
// the span to send it to Zipkin. The tags and events set on the
// newSpan will not be present on the parent
this.tracer.close(newSpan);
}
下面介绍TraceFilter过滤器，它拦截全部请求，咱们直接看它的doFilter方法。app
TraceFilter.doFilter:
@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse,
FilterChain filterChain) throws IOException, ServletException {
if (!(servletRequest instanceof HttpServletRequest) || !(servletResponse instanceof HttpServletResponse)) {
throw new ServletException("Filter just supports HTTP requests");
}
HttpServletRequest request = (HttpServletRequest) servletRequest;
HttpServletResponse response = (HttpServletResponse) servletResponse;
//首先从request获取到uri
String uri = this.urlPathHelper.getPathWithinApplication(request);
//判断是否忽略本次trace。根据两个条件判断是否忽略本次trace：
//A、根据skipPattern判断此uri是不是skip uri，若是是返回true
//B、从request、response的head中获取X-B3-Sampled属性，若是值为0则返回true，即不进行采样
boolean skip = this.skipPattern.matcher(uri).matches()
|| Span.SPAN_NOT_SAMPLED.equals(ServletUtils.getHeader(request, response, Span.SAMPLED_NAME));
//从request中getAttribute span。表示在一个request中，若是发生了转发那直接能够在request中获取span，不须要从新生成。
Span spanFromRequest = getSpanFromAttribute(request);
if (spanFromRequest != null) {
//不为空的话则continueSpan，下面看看continueSpan方法。
continueSpan(request, spanFromRequest);
}
if (log.isDebugEnabled()) {
log.debug("Received a request to uri [" + uri + "] that should not be sampled [" + skip + "]");
}
// in case of a response with exception status a exception controller will close the span
//正如上面的注释所说，这是请求出现异常时，跳转到异常controller时处理逻辑，而后关闭span当即结束filter。
if (!httpStatusSuccessful(response) && isSpanContinued(request)) {
Span parentSpan = parentSpan(spanFromRequest);
processErrorRequest(filterChain, request, new TraceHttpServletResponse(response, parentSpan), spanFromRequest);
return;
}
//设置span name
String name = HTTP_COMPONENT + ":" + uri;
Throwable exception = null;
try {
//根据request建立span，下面分析createSpan代码。
spanFromRequest = createSpan(request, skip, spanFromRequest, name);
//这里会触发springmvc的trace拦截器TraceHandlerInterceptor的一些方法，下一章会分析。
filterChain.doFilter(request, new TraceHttpServletResponse(response, spanFromRequest));
} catch (Throwable e) {
exception = e;
this.tracer.addTag(Span.SPAN_ERROR_TAG_NAME, ExceptionUtils.getExceptionMessage(e));
throw e;
} finally {
//对于异步request则不进行处理
if (isAsyncStarted(request) || request.isAsyncStarted()) {
if (log.isDebugEnabled()) {
log.debug("The span " + spanFromRequest + " will get detached by a HandleInterceptor");
}
// TODO: how to deal with response annotations and async?
return;
}
//若是该请求没有被spring mvc的trace拦截器拦截到，则会人工的生成一个lc类型span，做为spanFromRequest的child span，
//弥补springmvc的trace拦截器缺失的部分，这样能保证对于zipkin来讲是一个合理的调用链路。
spanFromRequest = createSpanIfRequestNotHandled(request, spanFromRequest, name, skip);
//分离获取关闭span，最后来分析下该方法
detachOrCloseSpans(request, response, spanFromRequest, exception);
}
}
TraceFilter.continueSpan:
private void continueSpan(HttpServletRequest request, Span spanFromRequest) {
//tracer的continueSpan方法的做用是将新的span设置到当前线程中。
//好比span a 在线程X中，span b在线程Y中，如今上下文处于线程b中，而后操做continueSpan(a),
//即将线程Y中的span b替换成span a，而后span a中的saved span属性设置成span b，即设置当前线程span以前的current span。
//下面分析下continueSpan方法。
this.tracer.continueSpan(spanFromRequest);
request.setAttribute(TraceRequestAttributes.SPAN_CONTINUED_REQUEST_ATTR, "true");
if (log.isDebugEnabled()) {
log.debug("There has already been a span in the request " + spanFromRequest);
}
}
DefaultTracer.continueSpan：
public Span continueSpan(Span span) {
if (span != null) {
//日志组件，主要用于MDC输出的
this.spanLogger.logContinuedSpan(span);
} else {
return null;
}
//createContinuedSpan方法第一个参数span是request中保存的span，或者其余上下文传递下来的。
//第二个span，SpanContextHolder.getCurrentSpan()是从ThreadLocal获取当前线程中的span。
//下面看下createContinuedSpan方法
Span newSpan = createContinuedSpan(span, SpanContextHolder.getCurrentSpan());
//将新的span保存到当前线程中
SpanContextHolder.setCurrentSpan(newSpan);
return newSpan;
}
//若是当前线程span为空且被传递过来的span的saved span属性不为空，则设置新的saved span为被传递过来的span的saved span，
//不然saved span使用当前线程中的span。
private Span createContinuedSpan(Span span, Span saved) {
if (saved == null && span.getSavedSpan() != null) {
saved = span.getSavedSpan();
}
return new Span(span, saved);
}
对于new Span(span, saved)这种构造span的形式咱们来分析下saved span有何做用：
saved的span是在建立该新的span以前就已经存在当前线程中的span。有两种状况会调用该api：异步
- 正如以前所说的，span从线程X复制到线程Y中
- 当前线程中已有span，而后建立child span，child span的saved span就是parent span
TraceFilter.createSpan
/**
* Creates a span and appends it as the current request's attribute
*/
private Span createSpan(HttpServletRequest request,
boolean skip, Span spanFromRequest, String name) {
//若是spanFromRequest不为空，即发生了转发等状况，那直接返回，不须要建立新的span。
if (spanFromRequest != null) {
if (log.isDebugEnabled()) {
log.debug("Span has already been created - continuing with the previous one");
}
return spanFromRequest;
}
//抽取request中的header、path等信息建立span，下面将分析joinTrace方法。
Span parent = this.spanExtractor.joinTrace(new HttpServletRequestTextMap(request));
//若是成功从request中提取了trace信息，生成了parent
if (parent != null) {
if (log.isDebugEnabled()) {
log.debug("Found a parent span " + parent + " in the request");
}
//正常tags中信息不会在server端添加，而是在client端添加tags。
//可是若是request header中不存在span name信息，说明client没有生成span信息，致使span信息不完整，
//那么就须要在server端生成tags。
addRequestTagsForParentSpan(request, parent);
spanFromRequest = parent;
//将生成的span保存到当前线程中，详情看DefaultTracer.continueSpan方法，前面已分析。
this.tracer.continueSpan(spanFromRequest);
//判断该span是否跨进程，是的话会加SR标识，即span生命周期中server recive阶段
if (parent.isRemote()) {
parent.logEvent(Span.SERVER_RECV);
}
//将span保存到request中。
request.setAttribute(TRACE_REQUEST_ATTR, spanFromRequest);
if (log.isDebugEnabled()) {
log.debug("Parent span is " + parent + "");
}
} else {
//parent为空须要生成新的span
//若是skip为true，则会生成一个不采样标识的span
if (skip) {
spanFromRequest = this.tracer.createSpan(name, NeverSampler.INSTANCE);
}
else {
//根据request header中的采样标识判断直接采样，仍是根据本地设置的采样器判断是否采样
//下面分析下DefaultTracer.createSpan方法
String header = request.getHeader(Span.SPAN_FLAGS);
if (Span.SPAN_SAMPLED.equals(header)) {
spanFromRequest = this.tracer.createSpan(name, new AlwaysSampler());
} else {
spanFromRequest = this.tracer.createSpan(name);
}
}
spanFromRequest.logEvent(Span.SERVER_RECV);
request.setAttribute(TRACE_REQUEST_ATTR, spanFromRequest);
if (log.isDebugEnabled()) {
log.debug("No parent span present - creating a new span");
}
}
return spanFromRequest;
}
ZipkinHttpSpanExtractor.joinTrace
public Span joinTrace(SpanTextMap textMap) {
//carrier中保存request header、uri信息
Map<String, String> carrier = TextMapUtil.asMap(textMap);
//判断header中是否有Span.SPAN_FLAGS标识，且值为1，即须要采样。
boolean debug = Span.SPAN_SAMPLED.equals(carrier.get(Span.SPAN_FLAGS));
if (debug) {
// we're only generating Trace ID since if there's no Span ID will assume
// that it's equal to Trace ID
//header中若是不存在trace id，则生成一个。
generateIdIfMissing(carrier, Span.TRACE_ID_NAME);
} else if (carrier.get(Span.TRACE_ID_NAME) == null) {
// can't build a Span without trace id
//header中没有trace id则直接返回null，不能从reqeust中提取信息构建span
return null;
}
try {
String uri = carrier.get(URI_HEADER);
//根据uri判断是够skip
boolean skip = this.skipPattern.matcher(uri).matches()
|| Span.SPAN_NOT_SAMPLED.equals(carrier.get(Span.SAMPLED_NAME));
//若是header中span id为空则根据trace id生成一个，不然直接返回header中的span id。
long spanId = spanId(carrier);
//构建span
return buildParentSpan(carrier, uri, skip, spanId);
} catch (Exception e) {
log.error("Exception occurred while trying to extract span from carrier", e);
return null;
}
}
DefaultTracer.createSpan
public Span createSpan(String name, Sampler sampler) {
String shortenedName = SpanNameUtil.shorten(name);
Span span;
//若是本地即当前线程已经存在span，则建立child span，当前线程中的span为parent span
//若是不存在span，则建立一个彻底新的span
if (isTracing()) {
span = createChild(getCurrentSpan(), shortenedName);
}
else {
long id = createId();
span = Span.builder().name(shortenedName)
.traceIdHigh(this.traceId128 ? createId() : 0L)
.traceId(id)
.spanId(id).build();
if (sampler == null) {
sampler = this.defaultSampler;
}
span = sampledSpan(span, sampler);
this.spanLogger.logStartedSpan(null, span);
}
//将建立的span保存在当前线程
return continueSpan(span);
}
TraceFilter.detachOrCloseSpans
private void detachOrCloseSpans(HttpServletRequest request,
HttpServletResponse response, Span spanFromRequest, Throwable exception) {
Span span = spanFromRequest;
if (span != null) {
//添加response status到tags中
addResponseTags(response, exception);
//这里判断span中savedSpan不为空且请求被TraceHandlerInterceptor拦截器拦截处理过则上报savedSpan信息
//这里上报savedSpan,个人理解是traceFilter在filter一个request的时候会建立第一个parentSpan，
//期间不会建立childSpan，但进入springmvc handler处理期间可能会建立一些childSpan，而后设置为current span，
//但这种span不是traceFilter关注的，它只关注server reciver时即刚接收到请求建立的span。
if (span.hasSavedSpan() && requestHasAlreadyBeenHandled(request)) {
//首先中止span的clock，即记录结束时间，算下开始时间与结束时间的duration。
//而后记录server send event，代表做为server端，何时响应请求返回结果的。
//最后上报span，好比上报到zipkin或者打印log，这就取决于初始化哪一种spanReporter的了。
recordParentSpan(span.getSavedSpan());
} else if (!requestHasAlreadyBeenHandled(request)) {
//若是该请求没有被TraceHandlerInterceptor拦截器拦截处理，则直接把span从当前线程中移除，中止span的clock，而后上报
//这里的span多是createSpanIfRequestNotHandled建立的span。
//close返回savedSpan，即parentSpan
span = this.tracer.close(span);
}
//上报parentSpan
recordParentSpan(span);
// in case of a response with exception status will close the span when exception dispatch is handled
// checking if tracing is in progress due to async / different order of view controller processing
if (httpStatusSuccessful(response) && this.tracer.isTracing()) {
if (log.isDebugEnabled()) {
log.debug("Closing the span " + span + " since the response was successful");
}
this.tracer.close(span);
} else if (errorAlreadyHandled(request) && this.tracer.isTracing()) {
if (log.isDebugEnabled()) {
log.debug(
"Won't detach the span " + span + " since error has already been handled");
}
} else if (shouldCloseSpan(request) && this.tracer.isTracing() && stillTracingCurrentSapn(span)) {
if (log.isDebugEnabled()) {
log.debug(
"Will close span " + span + " since some component marked it for closure");
}
this.tracer.close(span);
} else if (this.tracer.isTracing()) {
if (log.isDebugEnabled()) {
log.debug("Detaching the span " + span + " since the response was unsuccessful");
}
this.tracer.detach(span);
}
}
}
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