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JUnit rule to spin-up a Zipkin server during tests
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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package zipkin2.junit;

import java.io.IOException;
import java.util.List;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.atomic.AtomicInteger;
import okhttp3.mockwebserver.Dispatcher;
import okhttp3.mockwebserver.MockResponse;
import okhttp3.mockwebserver.MockWebServer;
import okhttp3.mockwebserver.RecordedRequest;
import org.junit.rules.TestRule;
import org.junit.runner.Description;
import org.junit.runners.model.Statement;
import zipkin2.DependencyLink;
import zipkin2.Span;
import zipkin2.collector.InMemoryCollectorMetrics;
import zipkin2.internal.Nullable;
import zipkin2.internal.Platform;
import zipkin2.storage.InMemoryStorage;

import static okhttp3.mockwebserver.SocketPolicy.KEEP_OPEN;

/**
 * Starts up a local Zipkin server, listening for http requests on {@link #httpUrl}.
 *
 * This can be used to test instrumentation. For example, you can POST spans directly to this
 * server.
 *
 * 
See http://openzipkin.github.io/zipkin-api/#/
 */
public final class ZipkinRule implements TestRule {
  private final InMemoryStorage storage = InMemoryStorage.newBuilder().build();
  private final InMemoryCollectorMetrics metrics = new InMemoryCollectorMetrics();
  private final MockWebServer server = new MockWebServer();
  private final BlockingQueue failureQueue = new LinkedBlockingQueue<>();
  private final AtomicInteger receivedSpanBytes = new AtomicInteger();

  public ZipkinRule() {
    Dispatcher dispatcher =
        new Dispatcher() {
          final ZipkinDispatcher successDispatch = new ZipkinDispatcher(storage, metrics, server);

          @Override
          public MockResponse dispatch(RecordedRequest request) {
            MockResponse maybeFailure = failureQueue.poll();
            if (maybeFailure != null) return maybeFailure;
            MockResponse result = successDispatch.dispatch(request);
            if (request.getMethod().equals("POST")) {
              receivedSpanBytes.addAndGet((int) request.getBodySize());
            }
            return result;
          }

          @Override
          public MockResponse peek() {
            MockResponse maybeFailure = failureQueue.peek();
            if (maybeFailure != null) return maybeFailure.clone();
            return new MockResponse().setSocketPolicy(KEEP_OPEN);
          }
        };
    server.setDispatcher(dispatcher);
  }

  /** Use this to connect. The zipkin v1 interface will be under "/api/v1" */
  public String httpUrl() {
    return String.format("http://%s:%s", server.getHostName(), server.getPort());
  }

  /** Use this to see how many requests you've sent to any zipkin http endpoint. */
  public int httpRequestCount() {
    return server.getRequestCount();
  }

  /** Use this to see how many spans or serialized bytes were collected on the http endpoint. */
  public InMemoryCollectorMetrics collectorMetrics() {
    return metrics;
  }

  /**
   * Stores the given spans directly, to setup preconditions for a test.
   *
   * 
For example, if you are testing what happens when instrumentation adds a child to a trace,
   * you'd add the parent here.
   */
  public ZipkinRule storeSpans(List spans) {
    try {
      storage.accept(spans).execute();
    } catch (IOException e) {
      throw Platform.get().uncheckedIOException(e);
    }
    return this;
  }

  /**
   * Adds a one-time failure to the http endpoint.
   *
   * 
Ex. If you want to test that you don't repeatedly send bad data, you could send a 400 back.
   *
   * 
{@code
   * zipkin.enqueueFailure(sendErrorResponse(400, "bad format"));
   * }
   *
   * @param failure type of failure the next call to the http endpoint responds with
   */
  public ZipkinRule enqueueFailure(HttpFailure failure) {
    failureQueue.add(failure.response);
    return this;
  }

  /** Retrieves all traces this zipkin server has received. */
  public List> getTraces() {
    return storage.spanStore().getTraces();
  }

  /** Retrieves a trace by ID which zipkin server has received, or null if not present. */
  @Nullable
  public List getTrace(String traceId) {
    try {
      return storage.spanStore().getTrace(traceId).execute();
    } catch (IOException e) {
      throw Platform.get().assertionError("I/O exception in in-memory storage", e);
    }
  }

  /** Retrieves all service links between traces this zipkin server has received. */
  public List getDependencies() {
    return storage.spanStore().getDependencies();
  }

  /**
   * Used to manually start the server.
   *
   * @param httpPort choose 0 to select an available port
   */
  public void start(int httpPort) throws IOException {
    server.start(httpPort);
  }

  /** Used to manually stop the server. */
  public void shutdown() throws IOException {
    server.shutdown();
  }

  @Override
  public Statement apply(Statement base, Description description) {
    return server.apply(base, description);
  }
}