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TracingFilter.java
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TracingFilter.java
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package io.opentracing.contrib.web.servlet.filter;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.logging.Logger;
import java.util.regex.Pattern;
import javax.servlet.AsyncEvent;
import javax.servlet.AsyncListener;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import io.opentracing.Scope;
import io.opentracing.SpanContext;
import io.opentracing.Tracer;
import io.opentracing.propagation.Format;
import io.opentracing.tag.Tags;
import io.opentracing.util.GlobalTracer;
/**
* Tracing servlet filter.
*
* Filter can be programmatically added to {@link ServletContext} or initialized via web.xml.
*
* Following code examples show possible initialization:
*
* <pre>
* {@code
* TracingFilter filter = new TracingFilter(tracer);
* servletContext.addFilter("tracingFilter", filter);
* }
* </pre>
*
* Or include filter in web.xml and:
* <pre>
* {@code
* GlobalTracer.register(tracer);
* servletContext.setAttribute({@link TracingFilter#SPAN_DECORATORS}, listOfDecorators); // optional, if no present ServletFilterSpanDecorator.STANDARD_TAGS is applied
* }
* </pre>
*
* Current server span context is accessible via {@link HttpServletRequest#getAttribute(String)} with name
* {@link TracingFilter#SERVER_SPAN_CONTEXT}.
*
* @author Pavol Loffay
*/
public class TracingFilter implements Filter {
private static final Logger log = Logger.getLogger(TracingFilter.class.getName());
/**
* Use as a key of {@link ServletContext#setAttribute(String, Object)} to set span decorators
*/
public static final String SPAN_DECORATORS = TracingFilter.class.getName() + ".spanDecorators";
/**
* Use as a key of {@link ServletContext#setAttribute(String, Object)} to skip pattern
*/
public static final String SKIP_PATTERN = TracingFilter.class.getName() + ".skipPattern";
/**
* Used as a key of {@link HttpServletRequest#setAttribute(String, Object)} to inject server span context
*/
public static final String SERVER_SPAN_CONTEXT = TracingFilter.class.getName() + ".activeSpanContext";
private FilterConfig filterConfig;
protected Tracer tracer;
private List<ServletFilterSpanDecorator> spanDecorators;
private Pattern skipPattern;
/**
* Tracer instance has to be registered with {@link GlobalTracer#register(Tracer)}.
*/
public TracingFilter() {
this(GlobalTracer.get());
}
/**
* @param tracer
*/
public TracingFilter(Tracer tracer) {
this(tracer, Collections.singletonList(ServletFilterSpanDecorator.STANDARD_TAGS), null);
}
/**
*
* @param tracer tracer
* @param spanDecorators decorators
* @param skipPattern null or pattern to exclude certain paths from tracing e.g. "/health"
*/
public TracingFilter(Tracer tracer, List<ServletFilterSpanDecorator> spanDecorators, Pattern skipPattern) {
this.tracer = tracer;
this.spanDecorators = new ArrayList<>(spanDecorators);
this.spanDecorators.removeAll(Collections.singleton(null));
this.skipPattern = skipPattern;
}
@Override
public void init(FilterConfig filterConfig) throws ServletException {
this.filterConfig = filterConfig;
ServletContext servletContext = filterConfig.getServletContext();
// Check whether the servlet context provides a tracer
Object tracerObj = servletContext.getAttribute(Tracer.class.getName());
if (tracerObj instanceof Tracer) {
tracer = (Tracer)tracerObj;
} else {
// Add current tracer to servlet context, so available to webapp
servletContext.setAttribute(Tracer.class.getName(), tracer);
}
// use decorators from context attributes
Object contextAttribute = servletContext.getAttribute(SPAN_DECORATORS);
if (contextAttribute instanceof Collection) {
List<ServletFilterSpanDecorator> decorators = new ArrayList<>();
for (Object decorator: (Collection)contextAttribute) {
if (decorator instanceof ServletFilterSpanDecorator) {
decorators.add((ServletFilterSpanDecorator) decorator);
} else {
log.severe(decorator + " is not an instance of " + ServletFilterSpanDecorator.class);
}
}
this.spanDecorators = decorators.size() > 0 ? decorators : this.spanDecorators;
}
contextAttribute = servletContext.getAttribute(SKIP_PATTERN);
if (contextAttribute instanceof Pattern) {
skipPattern = (Pattern) contextAttribute;
}
}
@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain chain)
throws IOException, ServletException {
HttpServletRequest httpRequest = (HttpServletRequest) servletRequest;
HttpServletResponse httpResponse = (HttpServletResponse) servletResponse;
if (!isTraced(httpRequest, httpResponse)) {
chain.doFilter(httpRequest, httpResponse);
return;
}
/**
* If request is traced then do not start new span.
*/
if (servletRequest.getAttribute(SERVER_SPAN_CONTEXT) != null) {
chain.doFilter(servletRequest, servletResponse);
} else {
SpanContext extractedContext = tracer.extract(Format.Builtin.HTTP_HEADERS,
new HttpServletRequestExtractAdapter(httpRequest));
final Scope scope = tracer.buildSpan(httpRequest.getMethod())
.asChildOf(extractedContext)
.withTag(Tags.SPAN_KIND.getKey(), Tags.SPAN_KIND_SERVER)
.startActive(false);
httpRequest.setAttribute(SERVER_SPAN_CONTEXT, scope.span().context());
for (ServletFilterSpanDecorator spanDecorator: spanDecorators) {
spanDecorator.onRequest(httpRequest, scope.span());
}
try {
chain.doFilter(servletRequest, servletResponse);
if (!httpRequest.isAsyncStarted()) {
for (ServletFilterSpanDecorator spanDecorator : spanDecorators) {
spanDecorator.onResponse(httpRequest, httpResponse, scope.span());
}
}
// catch all exceptions (e.g. RuntimeException, ServletException...)
} catch (Throwable ex) {
for (ServletFilterSpanDecorator spanDecorator : spanDecorators) {
spanDecorator.onError(httpRequest, httpResponse, ex, scope.span());
}
throw ex;
} finally {
if (httpRequest.isAsyncStarted()) {
// what if async is already finished? This would not be called
httpRequest.getAsyncContext()
.addListener(new AsyncListener() {
@Override
public void onComplete(AsyncEvent event) throws IOException {
HttpServletRequest httpRequest = (HttpServletRequest) event.getSuppliedRequest();
HttpServletResponse httpResponse = (HttpServletResponse) event.getSuppliedResponse();
for (ServletFilterSpanDecorator spanDecorator: spanDecorators) {
spanDecorator.onResponse(httpRequest,
httpResponse,
scope.span());
}
scope.span().finish();
}
@Override
public void onTimeout(AsyncEvent event) throws IOException {
HttpServletRequest httpRequest = (HttpServletRequest) event.getSuppliedRequest();
HttpServletResponse httpResponse = (HttpServletResponse) event.getSuppliedResponse();
for (ServletFilterSpanDecorator spanDecorator : spanDecorators) {
spanDecorator.onTimeout(httpRequest,
httpResponse,
event.getAsyncContext().getTimeout(),
scope.span());
}
}
@Override
public void onError(AsyncEvent event) throws IOException {
HttpServletRequest httpRequest = (HttpServletRequest) event.getSuppliedRequest();
HttpServletResponse httpResponse = (HttpServletResponse) event.getSuppliedResponse();
for (ServletFilterSpanDecorator spanDecorator: spanDecorators) {
spanDecorator.onError(httpRequest,
httpResponse,
event.getThrowable(),
scope.span());
}
}
@Override
public void onStartAsync(AsyncEvent event) throws IOException {
}
});
} else {
// If not async, then need to explicitly finish the span associated with the scope.
// This is necessary, as we don't know whether this request is being handled
// asynchronously until after the scope has already been started.
scope.span().finish();
}
scope.close();
}
}
}
@Override
public void destroy() {
this.filterConfig = null;
}
/**
* It checks whether a request should be traced or not.
*
* @param httpServletRequest request
* @param httpServletResponse response
* @return whether request should be traced or not
*/
protected boolean isTraced(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse) {
// skip URLs matching skip pattern
// e.g. pattern is defined as '/health|/status' then URL 'http://localhost:5000/context/health' won't be traced
if (skipPattern != null) {
String url = httpServletRequest.getRequestURI().substring(httpServletRequest.getContextPath().length());
return !skipPattern.matcher(url).matches();
}
return true;
}
/**
* Get context of server span.
*
* @param servletRequest request
* @return server span context
*/
public static SpanContext serverSpanContext(ServletRequest servletRequest) {
return (SpanContext) servletRequest.getAttribute(SERVER_SPAN_CONTEXT);
}
}