content: /*
   * 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 org.apache.kafka.common.config.provider;
  
  import org.apache.kafka.common.config.ConfigData;
  import org.apache.kafka.common.config.ConfigException;
  
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import java.io.IOException;
  import java.util.HashMap;
  import java.util.Map;
  import java.util.Set;
  import java.util.regex.Pattern;
  import java.util.stream.Collectors;
  
  /**
   * An implementation of {@link ConfigProvider} based on environment variables.
   * Keys correspond to the names of the environment variables, paths are currently not being used.
   * Using an allowlist pattern {@link EnvVarConfigProvider#ALLOWLIST_PATTERN_CONFIG} that supports regular expressions,
   * it is possible to limit access to specific environment variables. Default allowlist pattern is ".*".
   */
  public class EnvVarConfigProvider implements ConfigProvider {
  
      private static final Logger log = LoggerFactory.getLogger(EnvVarConfigProvider.class);
  
      public static final String ALLOWLIST_PATTERN_CONFIG = "allowlist.pattern";
      public static final String ALLOWLIST_PATTERN_CONFIG_DOC = "A pattern / regular expression that needs to match for environment variables" +
              " to be used by this config provider.";
      private final Map<String, String> envVarMap;
      private Map<String, String> filteredEnvVarMap;
  
      public EnvVarConfigProvider() {
          envVarMap = getEnvVars();
      }
  
      public EnvVarConfigProvider(Map<String, String> envVarsAsArgument) {
          envVarMap = envVarsAsArgument;
      }
  
      @Override
      public void configure(Map<String, ?> configs) {
          Pattern envVarPattern;
  
          if (configs.containsKey(ALLOWLIST_PATTERN_CONFIG)) {
              envVarPattern = Pattern.compile(
                      String.valueOf(configs.get(ALLOWLIST_PATTERN_CONFIG))
              );
          } else {
              envVarPattern = Pattern.compile(".*");
              log.info("No pattern for environment variables provided. Using default pattern '(.*)'.");
          }
  
          filteredEnvVarMap = envVarMap.entrySet().stream()
                  .filter(envVar -> envVarPattern.matcher(envVar.getKey()).matches())
                  .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue)
                  );
      }
  
      @Override
      public void close() throws IOException {
      }
  
      /**
       * @param path unused
       * @return returns environment variables as configuration
       */
      @Override
      public ConfigData get(String path) {
          return get(path, null);
      }
  
      /**
       * @param path    path, not used for environment variables
       * @param keys the keys whose values will be retrieved.
       * @return the configuration data.
       */
      @Override
      public ConfigData get(String path, Set<String> keys) {
  
          if (path != null && !path.isEmpty()) {
              log.error("Path is not supported for EnvVarConfigProvider, invalid value '{}'", path);
              throw new ConfigException("Path is not supported for EnvVarConfigProvider, invalid value '" + path + "'");
          }
  
          if (keys == null) {
              return new ConfigData(filteredEnvVarMap);
          }
  
          Map<String, String> filteredData = new HashMap<>(filteredEnvVarMap);
          filteredData.keySet().retainAll(keys);
  
          return new ConfigData(filteredData);
      }
  
      private Map<String, String> getEnvVars() {
          try {
              return System.getenv();
          } catch (Exception e) {
              log.error("Could not read environment variables", e);
              throw new ConfigException("Could not read environment variables");
          }
      }
  }
  