Library instrumentation for Java Servlet 3.0 Filters.

Includes handling for attaching all the async stuff, but can't support everything the java agent does.

I could use help figuring out the right way to shadow all the necessary dependencies.  I'm a bit rusty with our shadow usage.
Depending on how aggressive we want to be, the dependency could be reversed so that `:servlet-3.0:javaagent` depends on this new module, but that's more aggressive.  Perhaps shadow could prune unused classes (with `minimize()`) instead.

Once we get the modules figured out, I can work on adding some unit tests.

If we like this approach, it could probably be copied and modified pretty easily to support servlet 5, but I'm not familiar with that instrumentation.

Author: tylerbenson

instrumentation/servlet/servlet-3.0/library/build.gradle.kts

@@ -0,0 +1,11 @@
+plugins {
+  id("otel.library-instrumentation")
+}
+
+dependencies {
+  library("javax.servlet:javax.servlet-api:3.0.1")
+
+  // FIXME: These dependencies need to be shadowed into the library.
+  library(project(":instrumentation:servlet:servlet-3.0:javaagent"))
+  library(project(":instrumentation:servlet:servlet-common:javaagent"))
+}

instrumentation/servlet/servlet-3.0/library/src/main/java/io/opentelemetry/javaagent/instrumentation/servlet/v3_0/OpenTelemetryServletFilter.java

@@ -0,0 +1,69 @@
+package io.opentelemetry.javaagent.instrumentation.servlet.v3_0;
+
+import static io.opentelemetry.javaagent.instrumentation.servlet.v3_0.Servlet3Singletons.helper;
+
+import io.opentelemetry.context.Context;
+import io.opentelemetry.context.Scope;
+import io.opentelemetry.javaagent.instrumentation.servlet.ServletRequestContext;
+import java.io.IOException;
+import javax.servlet.Filter;
+import javax.servlet.FilterChain;
+import javax.servlet.FilterConfig;
+import javax.servlet.ServletException;
+import javax.servlet.ServletRequest;
+import javax.servlet.ServletResponse;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+
+/**
+ * OpenTelemetry Library instrumentation for Java Servlet based applications that can't use a Java
+ * Agent. Due to inherit limitations in the servlet filter API, instrumenting at the filter level
+ * will miss anything that happens earlier in the filter stack or problems handled directly by the
+ * app server. For this reason, Java Agent instrumentation is preferred when possible.
+ */
+public class OpenTelemetryServletFilter implements Filter {
+
+  @Override
+  public void init(FilterConfig filterConfig) throws ServletException {}
+
+  @Override
+  public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
+      throws IOException, ServletException {
+    // Only HttpServlets are supported.
+    if (!(request instanceof HttpServletRequest && response instanceof HttpServletResponse)) {
+      chain.doFilter(request, response);
+      return;
+    }
+
+    HttpServletRequest httpRequest = (HttpServletRequest) request;
+    HttpServletResponse httpResponse = (HttpServletResponse) response;
+    ServletRequestContext<HttpServletRequest> requestContext =
+        new ServletRequestContext<>(httpRequest, this);
+
+    // Bail if we shouldn't start a new span.
+    if (!helper().shouldStart(Context.current(), requestContext)) {
+      chain.doFilter(request, response);
+      return;
+    }
+
+    Context spanContext = helper().start(Context.current(), requestContext);
+    helper().setAsyncListenerResponse(spanContext, (HttpServletResponse) response);
+
+    // Not using try-with-resources to match the api usage of Servlet3Advice.
+    // (helper().end is responsible for closing the scope.)
+    Scope scope = spanContext.makeCurrent();
+    Throwable throwable = null;
+    try {
+      chain.doFilter(
+          new OtelHttpServletRequest((HttpServletRequest) request), response);
+    } catch (Throwable e) {
+      throwable = e;
+      throw e;
+    } finally {
+      helper().end(requestContext, httpRequest, httpResponse, throwable, true, spanContext, scope);
+    }
+  }
+
+  @Override
+  public void destroy() {}
+}

instrumentation/servlet/servlet-3.0/library/src/main/java/io/opentelemetry/javaagent/instrumentation/servlet/v3_0/OtelAsyncContext.java

@@ -0,0 +1,85 @@
+package io.opentelemetry.javaagent.instrumentation.servlet.v3_0;
+
+import static io.opentelemetry.javaagent.instrumentation.servlet.v3_0.Servlet3Singletons.helper;
+
+import javax.servlet.AsyncContext;
+import javax.servlet.AsyncListener;
+import javax.servlet.ServletContext;
+import javax.servlet.ServletException;
+import javax.servlet.ServletRequest;
+import javax.servlet.ServletResponse;
+
+/// Delegates all methods except [#start(Runnable) which wraps the [Runnable].
+public class OtelAsyncContext implements AsyncContext {
+  private final AsyncContext delegate;
+
+  public OtelAsyncContext(AsyncContext delegate) {
+    this.delegate = delegate;
+  }
+
+  @Override
+  public ServletRequest getRequest() {
+    return delegate.getRequest();
+  }
+
+  @Override
+  public ServletResponse getResponse() {
+    return delegate.getResponse();
+  }
+
+  @Override
+  public boolean hasOriginalRequestAndResponse() {
+    return delegate.hasOriginalRequestAndResponse();
+  }
+
+  @Override
+  public void dispatch() {
+    delegate.dispatch();
+  }
+
+  @Override
+  public void dispatch(String path) {
+    delegate.dispatch(path);
+  }
+
+  @Override
+  public void dispatch(ServletContext context, String path) {
+    delegate.dispatch(context, path);
+  }
+
+  @Override
+  public void complete() {
+    delegate.complete();
+  }
+
+  @Override
+  public void start(Runnable run) {
+    delegate.start(helper().wrapAsyncRunnable(run));
+  }
+
+  @Override
+  public void addListener(AsyncListener listener) {
+    delegate.addListener(listener);
+  }
+
+  @Override
+  public void addListener(
+      AsyncListener listener, ServletRequest servletRequest, ServletResponse servletResponse) {
+    delegate.addListener(listener, servletRequest, servletResponse);
+  }
+
+  @Override
+  public <T extends AsyncListener> T createListener(Class<T> clazz) throws ServletException {
+    return delegate.createListener(clazz);
+  }
+
+  @Override
+  public void setTimeout(long timeout) {
+    delegate.setTimeout(timeout);
+  }
+
+  @Override
+  public long getTimeout() {
+    return delegate.getTimeout();
+  }
+}

instrumentation/servlet/servlet-3.0/library/src/main/java/io/opentelemetry/javaagent/instrumentation/servlet/v3_0/OtelHttpServletRequest.java

@@ -0,0 +1,43 @@
+package io.opentelemetry.javaagent.instrumentation.servlet.v3_0;
+
+import static io.opentelemetry.javaagent.instrumentation.servlet.v3_0.Servlet3Singletons.helper;
+
+import io.opentelemetry.context.Context;
+import javax.servlet.AsyncContext;
+import javax.servlet.ServletRequest;
+import javax.servlet.ServletResponse;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletRequestWrapper;
+
+/// Wrapper around [HttpServletRequest] that attaches an async listener if [#startAsync()] is
+/// invoked and a wrapper around [#getAsyncContext()] to capture exceptions from async [Runnable]s.
+public class OtelHttpServletRequest extends HttpServletRequestWrapper {
+
+  public OtelHttpServletRequest(HttpServletRequest request) {
+    super(request);
+  }
+
+  @Override
+  public AsyncContext getAsyncContext() {
+    return new OtelAsyncContext(super.getAsyncContext());
+  }
+
+  @Override
+  public AsyncContext startAsync() throws IllegalStateException {
+    try {
+      return super.startAsync();
+    } finally {
+      helper().attachAsyncListener(this, Context.current());
+    }
+  }
+
+  @Override
+  public AsyncContext startAsync(ServletRequest servletRequest, ServletResponse servletResponse)
+      throws IllegalStateException {
+    try {
+      return super.startAsync(servletRequest, servletResponse);
+    } finally {
+      helper().attachAsyncListener(this, Context.current());
+    }
+  }
+}

settings.gradle.kts

@@ -590,6 +590,7 @@ include(":instrumentation:scala-fork-join-2.8:javaagent")
 include(":instrumentation:servlet:servlet-2.2:javaagent")
 include(":instrumentation:servlet:servlet-3.0:javaagent")
 include(":instrumentation:servlet:servlet-3.0:javaagent-unit-tests")
+include(":instrumentation:servlet:servlet-3.0:library")
 include(":instrumentation:servlet:servlet-3.0:testing")
 include(":instrumentation:servlet:servlet-5.0:javaagent")
 include(":instrumentation:servlet:servlet-5.0:javaagent-unit-tests")