Allow clients to send stereotypes to help determine what to get from the new session queue

This is the first step in preventing the distributor from needing to
maintain a list of request ids, which can easily get out of alignment
with reality, and can contain stale entries if requests time out of
the queue.

Author: shs96c

java/server/src/org/openqa/selenium/grid/commands/Hub.java

@@ -28,7 +28,6 @@
 import org.openqa.selenium.grid.distributor.Distributor;
 import org.openqa.selenium.grid.distributor.config.DistributorOptions;
 import org.openqa.selenium.grid.distributor.local.LocalDistributor;
-import org.openqa.selenium.grid.distributor.selector.DefaultSlotSelector;
 import org.openqa.selenium.grid.graphql.GraphqlHandler;
 import org.openqa.selenium.grid.log.LoggingOptions;
 import org.openqa.selenium.grid.router.ProxyCdpIntoGrid;
@@ -141,16 +140,17 @@ protected Handlers createHandlers(Config config) {
       handler,
       networkOptions.getHttpClientFactory(tracer));
 
+    DistributorOptions distributorOptions = new DistributorOptions(config);
     SessionRequestOptions sessionRequestOptions = new SessionRequestOptions(config);
     NewSessionQueue queue = new LocalNewSessionQueue(
       tracer,
-       bus,
+      bus,
+      distributorOptions.getSlotMatcher(),
       sessionRequestOptions.getSessionRequestRetryInterval(),
       sessionRequestOptions.getSessionRequestTimeout(),
       secret);
     handler.addHandler(queue);
 
-    DistributorOptions distributorOptions = new DistributorOptions(config);
     Distributor distributor = new LocalDistributor(
       tracer,
       bus,

java/server/src/org/openqa/selenium/grid/commands/Standalone.java

@@ -138,16 +138,17 @@ protected Handlers createHandlers(Config config) {
     SessionMap sessions = new LocalSessionMap(tracer, bus);
     combinedHandler.addHandler(sessions);
 
+    DistributorOptions distributorOptions = new DistributorOptions(config);
     SessionRequestOptions sessionRequestOptions = new SessionRequestOptions(config);
     NewSessionQueue queue = new LocalNewSessionQueue(
       tracer,
       bus,
+      distributorOptions.getSlotMatcher(),
       sessionRequestOptions.getSessionRequestRetryInterval(),
       sessionRequestOptions.getSessionRequestTimeout(),
       registrationSecret);
     combinedHandler.addHandler(queue);
 
-    DistributorOptions distributorOptions = new DistributorOptions(config);
     Distributor distributor = new LocalDistributor(
       tracer,
       bus,

java/server/src/org/openqa/selenium/grid/data/SessionRequest.java

@@ -33,7 +33,9 @@
 import java.util.HashSet;
 import java.util.LinkedHashSet;
 import java.util.Map;
+import java.util.Objects;
 import java.util.Set;
+import java.util.StringJoiner;
 import java.util.TreeMap;
 import java.util.stream.Collectors;
 
@@ -99,6 +101,34 @@ public Instant getEnqueued() {
     return enqueued;
   }
 
+  @Override
+  public String toString() {
+    return new StringJoiner(", ", SessionRequest.class.getSimpleName() + "[", "]")
+      .add("requestId=" + requestId)
+      .add("desiredCapabilities=" + desiredCapabilities)
+      .add("downstreamDialects=" + downstreamDialects)
+      .add("metadata=" + metadata)
+      .toString();
+  }
+
+  @Override
+  public boolean equals(Object o) {
+    if (!(o instanceof SessionRequest)) {
+      return false;
+    }
+    SessionRequest that = (SessionRequest) o;
+
+    return this.requestId.equals(that.requestId) &&
+      this.desiredCapabilities.equals(that.desiredCapabilities) &&
+      this.downstreamDialects.equals(that.downstreamDialects) &&
+      this.metadata.equals(that.metadata);
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hash(requestId, enqueued, desiredCapabilities, downstreamDialects, metadata);
+  }
+
   private Map<String, Object> toJson() {
     Map<String, Object> toReturn = new HashMap<>();
     toReturn.put("requestId", requestId);

java/server/src/org/openqa/selenium/grid/data/SlotMatcher.java

@@ -19,7 +19,8 @@
 
 import org.openqa.selenium.Capabilities;
 
-/** Used to determine how a {@link Slot} can match its
+/**
+ * Used to determine how a {@link Slot} can match its
  * stereotype to the capabilities sent in a particular
  * New Session request.
  */

java/server/src/org/openqa/selenium/grid/distributor/config/BUILD.bazel

@@ -10,6 +10,7 @@ java_library(
     deps = [
         "//java:auto-service",
         "//java/server/src/org/openqa/selenium/grid/config",
+        "//java/server/src/org/openqa/selenium/grid/data",
         "//java/server/src/org/openqa/selenium/grid/distributor",
         "//java/server/src/org/openqa/selenium/grid/distributor/selector",
         artifact("com.beust:jcommander"),

java/server/src/org/openqa/selenium/grid/distributor/config/DistributorFlags.java

@@ -21,6 +21,7 @@
 import static org.openqa.selenium.grid.config.StandardGridRoles.DISTRIBUTOR_ROLE;
 import static org.openqa.selenium.grid.distributor.config.DistributorOptions.DEFAULT_DISTRIBUTOR_IMPLEMENTATION;
 import static org.openqa.selenium.grid.distributor.config.DistributorOptions.DEFAULT_HEALTHCHECK_INTERVAL;
+import static org.openqa.selenium.grid.distributor.config.DistributorOptions.DEFAULT_SLOT_MATCHER;
 import static org.openqa.selenium.grid.distributor.config.DistributorOptions.DEFAULT_SLOT_SELECTOR_IMPLEMENTATION;
 import static org.openqa.selenium.grid.distributor.config.DistributorOptions.DISTRIBUTOR_SECTION;
 
@@ -65,7 +66,15 @@ public class DistributorFlags implements HasRoles {
     example = DEFAULT_DISTRIBUTOR_IMPLEMENTATION)
   private String implementation = DEFAULT_DISTRIBUTOR_IMPLEMENTATION;
 
-  @Parameter(names = {"--slot-selector"}, description = "Full classname of non-default slot selector implementation")
+  @Parameter(
+    names = {"--slot-matcher"},
+    description = "Full classname of non-default slot matcher to use. This is used to determine whether a Node can support a particular session.")
+  @ConfigValue(section = DISTRIBUTOR_SECTION, name = "slot-matcher", example = DEFAULT_SLOT_MATCHER)
+  private String slotMatcher = DEFAULT_SLOT_MATCHER;
+
+  @Parameter(
+    names = {"--slot-selector"},
+    description = "Full classname of non-default slot selector. This is used to select a slot in a Node once the Node has been matched.")
   @ConfigValue(section = DISTRIBUTOR_SECTION, name = "slot-selector", example = DEFAULT_SLOT_SELECTOR_IMPLEMENTATION)
   private String slotSelector = DEFAULT_SLOT_SELECTOR_IMPLEMENTATION;
 

java/server/src/org/openqa/selenium/grid/distributor/config/DistributorOptions.java

@@ -19,6 +19,7 @@
 
 import org.openqa.selenium.grid.config.Config;
 import org.openqa.selenium.grid.config.ConfigException;
+import org.openqa.selenium.grid.data.SlotMatcher;
 import org.openqa.selenium.grid.distributor.Distributor;
 import org.openqa.selenium.grid.distributor.selector.SlotSelector;
 
@@ -32,6 +33,7 @@ public class DistributorOptions {
   static final String DISTRIBUTOR_SECTION = "distributor";
   static final String DEFAULT_DISTRIBUTOR_IMPLEMENTATION =
     "org.openqa.selenium.grid.distributor.local.LocalDistributor";
+  static final String DEFAULT_SLOT_MATCHER = "org.openqa.selenium.grid.data.DefaultSlotMatcher";
   static final String DEFAULT_SLOT_SELECTOR_IMPLEMENTATION =
     "org.openqa.selenium.grid.distributor.selector.DefaultSlotSelector";
 
@@ -96,6 +98,14 @@ public Distributor getDistributor() {
       DEFAULT_DISTRIBUTOR_IMPLEMENTATION);
   }
 
+  public SlotMatcher getSlotMatcher() {
+    return config.getClass(
+      DISTRIBUTOR_SECTION,
+      "slot-matcher",
+      SlotMatcher.class,
+      DEFAULT_SLOT_MATCHER);
+  }
+
   public SlotSelector getSlotSelector() {
     return config.getClass(
       DISTRIBUTOR_SECTION,

java/server/src/org/openqa/selenium/grid/sessionqueue/GetNextMatchingRequest.java

@@ -0,0 +1,53 @@
+// Licensed to the Software Freedom Conservancy (SFC) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The SFC 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 org.openqa.selenium.grid.sessionqueue;
+
+import org.openqa.selenium.Capabilities;
+import org.openqa.selenium.grid.data.SessionRequest;
+import org.openqa.selenium.internal.Require;
+import org.openqa.selenium.json.TypeToken;
+import org.openqa.selenium.remote.http.Contents;
+import org.openqa.selenium.remote.http.HttpHandler;
+import org.openqa.selenium.remote.http.HttpRequest;
+import org.openqa.selenium.remote.http.HttpResponse;
+
+import java.io.UncheckedIOException;
+import java.lang.reflect.Type;
+import java.util.Optional;
+import java.util.Set;
+
+import static java.util.Collections.singletonMap;
+
+class GetNextMatchingRequest implements HttpHandler {
+  private static final Type SET_OF_CAPABILITIES = new TypeToken<Set<Capabilities>>() {}.getType();
+
+  private final NewSessionQueue queue;
+
+  public GetNextMatchingRequest(NewSessionQueue queue) {
+    this.queue = Require.nonNull("New session queue", queue);
+  }
+
+  @Override
+  public HttpResponse execute(HttpRequest req) throws UncheckedIOException {
+    Set<Capabilities> stereotypes = Contents.fromJson(req, SET_OF_CAPABILITIES);
+
+    Optional<SessionRequest> maybeRequest = queue.getNextAvailable(stereotypes);
+
+    return new HttpResponse().setContent(Contents.asJson(singletonMap("value", maybeRequest.orElse(null))));
+  }
+}

java/server/src/org/openqa/selenium/grid/sessionqueue/NewSessionQueue.java

@@ -90,9 +90,12 @@ protected NewSessionQueue(Tracer tracer, Secret registrationSecret) {
       post("/se/grid/newsessionqueue/session/{requestId}/success")
         .to(params -> new SessionCreated(tracer, this, requestIdFrom(params)))
         .with(requiresSecret),
-      get("/se/grid/newsessionqueue/session/{requestId}")
+      post("/se/grid/newsessionqueue/session/{requestId}")
         .to(params -> new RemoveFromSessionQueue(tracer, this, requestIdFrom(params)))
         .with(requiresSecret),
+      post("/se/grid/newsessionqueue/session/next")
+        .to(() -> new GetNextMatchingRequest(this))
+        .with(requiresSecret),
       get("/se/grid/newsessionqueue/queue")
         .to(() -> new GetSessionQueue(tracer, this)),
       delete("/se/grid/newsessionqueue/queue")
@@ -110,6 +113,8 @@ private RequestId requestIdFrom(Map<String, String> params) {
 
   public abstract Optional<SessionRequest> remove(RequestId reqId);
 
+  public abstract Optional<SessionRequest> getNextAvailable(Set<Capabilities> stereotypes);
+
   public abstract void complete(RequestId reqId, Either<SessionNotCreatedException, CreateSessionResponse> result);
 
   public abstract int clearQueue();

java/server/src/org/openqa/selenium/grid/sessionqueue/local/BUILD.bazel

@@ -15,6 +15,7 @@ java_library(
         "//java/server/src/org/openqa/selenium/events",
         "//java/server/src/org/openqa/selenium/grid/config",
         "//java/server/src/org/openqa/selenium/grid/data",
+        "//java/server/src/org/openqa/selenium/grid/distributor/config",
         "//java/server/src/org/openqa/selenium/grid/jmx",
         "//java/server/src/org/openqa/selenium/grid/log",
         "//java/server/src/org/openqa/selenium/grid/security",