Add next page navigation for RDAP nameserver searches

Domain and entity searches will be handled in future CLs.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=178912832

java/google/registry/rdap/RdapSearchActionBase.java

@@ -0,0 +1,115 @@
+// 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.rdap;
+
+import static java.nio.charset.StandardCharsets.UTF_8;
+
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableListMultimap;
+import google.registry.request.Parameter;
+import google.registry.request.ParameterMap;
+import google.registry.request.RequestUrl;
+import java.io.UnsupportedEncodingException;
+import java.net.URLEncoder;
+import java.util.Base64;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+import javax.inject.Inject;
+
+/**
+ * Base RDAP (new WHOIS) action for domain, nameserver and entity search requests.
+ *
+ * @see <a href="https://tools.ietf.org/html/rfc7482">
+ *        RFC 7482: Registration Data Access Protocol (RDAP) Query Format</a>
+ */
+public abstract class RdapSearchActionBase extends RdapActionBase {
+
+  @Inject @RequestUrl String requestUrl;
+  @Inject @ParameterMap ImmutableListMultimap<String, String> parameterMap;
+  @Inject @Parameter("cursor") Optional<String> cursorTokenParam;
+
+  protected Optional<String> cursorString;
+
+  /**
+   * Decodes the cursor token passed in the HTTP request.
+   *
+   * <p>The cursor token is just the Base 64 encoded value of the last data item returned. To fetch
+   * the next page, the code can just decode the cursor, and return only data whose value is greater
+   * than the cursor value.
+   */
+  protected void decodeCursorToken() {
+    if (!cursorTokenParam.isPresent()) {
+      cursorString = Optional.empty();
+    } else {
+      cursorString =
+          Optional.of(
+              new String(
+                  Base64.getDecoder().decode(cursorTokenParam.get().getBytes(UTF_8)), UTF_8));
+    }
+  }
+
+  /** Returns an encoded cursor token to pass back in the RDAP JSON link strings. */
+  protected String encodeCursorToken(String nextCursorString) {
+    return new String(Base64.getEncoder().encode(nextCursorString.getBytes(UTF_8)), UTF_8);
+  }
+
+  /** Returns the original request URL, but with the specified parameter added or overridden. */
+  protected String getRequestUrlWithExtraParameter(String parameterName, String parameterValue) {
+    return getRequestUrlWithExtraParameter(parameterName, ImmutableList.of(parameterValue));
+  }
+
+  /**
+   * Returns the original request URL, but with the specified parameter added or overridden.
+   *
+   * <p>This version handles a list of parameter values, all associated with the same name.
+   *
+   * <p>Example: If the original parameters were "a=w&a=x&b=y&c=z", and this method is called with
+   * parameterName = "b" and parameterValues of "p" and "q", the result will be
+   * "a=w&a=x&c=z&b=p&b=q". The new values of parameter "b" replace the old ones.
+   *
+   */
+  protected String getRequestUrlWithExtraParameter(
+      String parameterName, List<String> parameterValues) {
+    StringBuilder stringBuilder = new StringBuilder(requestUrl);
+    boolean first = true;
+    // Step one: loop through the existing parameters, copying all of them except for the parameter
+    // we want to explicitly set.
+    for (Map.Entry<String, String> entry : parameterMap.entries()) {
+      if (!entry.getKey().equals(parameterName)) {
+        appendParameter(stringBuilder, entry.getKey(), entry.getValue(), first);
+        first = false;
+      }
+    }
+    // Step two: tack on all values of the explicit parameter.
+    for (String parameterValue : parameterValues) {
+      appendParameter(stringBuilder, parameterName, parameterValue, first);
+      first = false;
+    }
+    return stringBuilder.toString();
+  }
+
+  private void appendParameter(
+      StringBuilder stringBuilder, String name, String value, boolean first) {
+    try {
+      stringBuilder.append(first ? '?' : '&');
+      stringBuilder.append(URLEncoder.encode(name, "UTF-8"));
+      stringBuilder.append('=');
+      stringBuilder.append(URLEncoder.encode(value, "UTF-8"));
+    } catch (UnsupportedEncodingException e) {
+      throw new RuntimeException(e);
+    }
+  }
+}