Refactor out creation of server TRIDs so they can be tested

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=152837185

java/google/registry/flows/ServerTridProviderImpl.java

@@ -0,0 +1,50 @@
+// Copyright 2017 The Nomulus Authors. All Rights Reserved.
+//
+// Licensed 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 google.registry.flows;
+
+import static com.google.common.primitives.Longs.BYTES;
+
+import com.google.common.io.BaseEncoding;
+import java.nio.ByteBuffer;
+import java.util.UUID;
+import java.util.concurrent.atomic.AtomicLong;
+import javax.inject.Inject;
+
+/** A server Trid provider that generates globally incrementing UUIDs. */
+public class ServerTridProviderImpl implements ServerTridProvider {
+
+  private static final String SERVER_ID = getServerId();
+  private static final AtomicLong idCounter = new AtomicLong();
+
+  @Inject public ServerTridProviderImpl() {}
+
+  /** Creates a unique id for this server instance, as a base64 encoded UUID. */
+  private static String getServerId() {
+    UUID uuid = UUID.randomUUID();
+    ByteBuffer buffer =
+        ByteBuffer.allocate(BYTES * 2)
+            .putLong(uuid.getMostSignificantBits())
+            .putLong(uuid.getLeastSignificantBits());
+    return BaseEncoding.base64().encode(buffer.array());
+  }
+
+  @Override
+  public String createServerTrid() {
+    // The server id can be at most 64 characters. The SERVER_ID is at most 22 characters (128
+    // bits in base64), plus the dash. That leaves 41 characters, so we just append the counter in
+    // hex.
+    return String.format("%s-%x", SERVER_ID, idCounter.incrementAndGet());
+  }
+}