[BUG] Cosmos | Direct TCP | Address null pointer exception in RntbdClientChannelPool.computeLoadFactor (#12339)

* Port from v4

* Corrected package misspelling in log4j.properties and removed System.exit from Main.java

* Responded to code review comments

* Updated sdk/cosmos/README.md with info on using system properties to modify default Direct TCP options

* Addresses a NullPointerException raised when an available channel closes since it became available, improves two log messages, and increases the value of maxChannelsPerEndpoint from 10 to 130. The latter is based on performance runs that indicate this is a better value in syncrhonous and asynchronous point read scenarios

* Tweaked logger message

* Removed README.md because it was deleted on master and was not removed when I pulled from master

Author: David Noble

sdk/cosmos/azure-cosmos/src/main/java/com/azure/cosmos/DirectConnectionConfig.java

@@ -18,8 +18,8 @@ public final class DirectConnectionConfig {
     private static final Duration DEFAULT_IDLE_ENDPOINT_TIMEOUT = Duration.ofSeconds(70L);
     private static final Duration DEFAULT_CONNECT_TIMEOUT = Duration.ofSeconds(60L);
     private static final Duration DEFAULT_REQUEST_TIMEOUT = Duration.ofSeconds(5L);
-    private static final int DEFAULT_MAX_CONNECTIONS_PER_ENDPOINT = 30;
-    private static final int DEFAULT_MAX_REQUESTS_PER_CONNECTION = 10;
+    private static final int DEFAULT_MAX_CONNECTIONS_PER_ENDPOINT = 130;
+    private static final int DEFAULT_MAX_REQUESTS_PER_CONNECTION = 30;
 
     private Duration connectTimeout;
     private Duration idleConnectionTimeout;
@@ -29,7 +29,7 @@ public final class DirectConnectionConfig {
     private int maxRequestsPerConnection;
 
     /**
-     * Constructor.
+     * Constructor
      */
     public DirectConnectionConfig() {
         this.connectTimeout = DEFAULT_CONNECT_TIMEOUT;

sdk/cosmos/azure-cosmos/src/main/java/com/azure/cosmos/implementation/directconnectivity/RntbdTransportClient.java

@@ -15,6 +15,7 @@
 import com.azure.cosmos.implementation.directconnectivity.rntbd.RntbdRequestRecord;
 import com.azure.cosmos.implementation.directconnectivity.rntbd.RntbdServiceEndpoint;
 import com.azure.cosmos.implementation.guava25.base.Strings;
+import com.fasterxml.jackson.annotation.JsonCreator;
 import com.fasterxml.jackson.annotation.JsonIgnore;
 import com.fasterxml.jackson.annotation.JsonProperty;
 import com.fasterxml.jackson.core.JsonGenerator;
@@ -221,6 +222,11 @@ public static final class Options {
 
         // region Constructors
 
+        @JsonCreator
+        private Options() {
+            this(ConnectionPolicy.getDefaultPolicy());
+        }
+
         private Options(final Builder builder) {
 
             this.bufferPageSize = builder.bufferPageSize;

sdk/cosmos/azure-cosmos/src/main/java/com/azure/cosmos/implementation/directconnectivity/rntbd/RntbdClientChannelPool.java

@@ -623,6 +623,12 @@ private double computeLoadFactor() {
         for (Channel channel : this.availableChannels) {
 
             final RntbdRequestManager manager = channel.pipeline().get(RntbdRequestManager.class);
+
+            if (manager == null) {
+                logger.debug("Channel({}) connection lost", channel);
+                continue;
+            }
+
             final long pendingRequestCount = manager.pendingRequestCount();
 
             if (pendingRequestCount < pendingRequestCountMin) {

sdk/cosmos/azure-cosmos/src/main/java/com/azure/cosmos/implementation/directconnectivity/rntbd/RntbdServiceEndpoint.java

@@ -7,7 +7,6 @@
 import com.azure.cosmos.implementation.GoneException;
 import com.azure.cosmos.implementation.directconnectivity.RntbdTransportClient;
 import com.azure.cosmos.implementation.guava25.collect.ImmutableMap;
-import com.azure.cosmos.implementation.guava27.Strings;
 import com.fasterxml.jackson.core.JsonGenerator;
 import com.fasterxml.jackson.databind.SerializerProvider;
 import com.fasterxml.jackson.databind.annotation.JsonSerialize;
@@ -40,6 +39,7 @@
 import static com.azure.cosmos.implementation.directconnectivity.RntbdTransportClient.Options;
 import static com.azure.cosmos.implementation.guava25.base.Preconditions.checkNotNull;
 import static com.azure.cosmos.implementation.guava25.base.Preconditions.checkState;
+import static com.azure.cosmos.implementation.guava27.Strings.lenientFormat;
 import static java.util.concurrent.TimeUnit.NANOSECONDS;
 
 @JsonSerialize(using = RntbdServiceEndpoint.JsonSerializer.class)
@@ -261,11 +261,11 @@ private RntbdRequestRecord writeWhenConnected(
         } else {
 
             logger.debug("\n  [{}]\n  {}\n  write failed due to {} ", this, requestArgs, cause);
-            final String reason = cause.getMessage();
+            final String reason = cause.toString();
 
             final GoneException goneException = new GoneException(
-                Strings.lenientFormat("failed to establish connection to %s: %s", this.remoteAddress, reason),
-                cause instanceof Exception ? (Exception)cause : new IOException(reason, cause),
+                lenientFormat("failed to establish connection to %s due to %s", this.remoteAddress, reason),
+                cause instanceof Exception ? (Exception) cause : new IOException(reason, cause),
                 ImmutableMap.of(HttpHeaders.ACTIVITY_ID, activityId.toString()),
                 requestArgs.replicaPath()
             );