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Feign Core
There is a newer version: 13.5
/*
 * Copyright 2013 Netflix, Inc.
 *
 * 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 feign.codec;

import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Collection;
import java.util.Date;
import java.util.Map;

import feign.FeignException;
import feign.Response;
import feign.RetryableException;

import static feign.FeignException.errorStatus;
import static feign.Util.RETRY_AFTER;
import static feign.Util.checkNotNull;
import static java.util.Locale.US;
import static java.util.concurrent.TimeUnit.NANOSECONDS;
import static java.util.concurrent.TimeUnit.SECONDS;

/**
 * Allows you to massage an exception into a application-specific one. Converting out to a throttle
 * exception are examples of this in use.
 *
 * Ex:
 * 
 * class IllegalArgumentExceptionOn404Decoder implements ErrorDecoder {
 *
 *   @Override
 *   public Exception decode(String methodKey, Response response) {
 *    if (response.status() == 400)
 *        throw new IllegalArgumentException("bad zone name");
 *    return new ErrorDecoder.Default().decode(methodKey, response);
 *   }
 *
 * }
 * 
 *
 * Error handling
 *
 * 
Responses where {@link Response#status()} is not in the 2xx
 * range are classified as errors, addressed by the {@link ErrorDecoder}. That said, certain RPC
 * apis return errors defined in the {@link Response#body()} even on a 200 status. For example, in
 * the DynECT api, a job still running condition is returned with a 200 status, encoded in json.
 * When scenarios like this occur, you should raise an application-specific exception (which may be
 * {@link feign.RetryableException retryable}).
 *
 * 
Not Found Semantics
 *  It is commonly the case that 404 (Not Found) status has semantic value in HTTP apis. While
 * the default behavior is to raise exeception, users can alternatively enable 404 processing via
 * {@link feign.Feign.Builder#decode404()}.
 */
public interface ErrorDecoder {

  /**
   * Implement this method in order to decode an HTTP {@link Response} when {@link
   * Response#status()} is not in the 2xx range. Please raise  application-specific exceptions where
   * possible. If your exception is retryable, wrap or subclass {@link RetryableException}
   *
   * @param methodKey {@link feign.Feign#configKey} of the java method that invoked the request.
   *                  ex. {@code IAM#getUser()}
   * @param response  HTTP response where {@link Response#status() status} is greater than or equal
   *                  to {@code 300}.
   * @return Exception IOException, if there was a network error reading the response or an
   * application-specific exception decoded by the implementation. If the throwable is retryable, it
   * should be wrapped, or a subtype of {@link RetryableException}
   */
  public Exception decode(String methodKey, Response response);

  public static class Default implements ErrorDecoder {

    private final RetryAfterDecoder retryAfterDecoder = new RetryAfterDecoder();

    @Override
    public Exception decode(String methodKey, Response response) {
      FeignException exception = errorStatus(methodKey, response);
      Date retryAfter = retryAfterDecoder.apply(firstOrNull(response.headers(), RETRY_AFTER));
      if (retryAfter != null) {
        return new RetryableException(exception.getMessage(), exception, retryAfter);
      }
      return exception;
    }

    private  T firstOrNull(Map> map, String key) {
      if (map.containsKey(key) && !map.get(key).isEmpty()) {
        return map.get(key).iterator().next();
      }
      return null;
    }
  }

  /**
   * Decodes a {@link feign.Util#RETRY_AFTER} header into an absolute date, if possible. 
 See Retry-After format
   */
  static class RetryAfterDecoder {

    static final DateFormat
        RFC822_FORMAT =
        new SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss 'GMT'", US);
    private final DateFormat rfc822Format;

    RetryAfterDecoder() {
      this(RFC822_FORMAT);
    }

    RetryAfterDecoder(DateFormat rfc822Format) {
      this.rfc822Format = checkNotNull(rfc822Format, "rfc822Format");
    }

    protected long currentTimeMillis() {
      return System.currentTimeMillis();
    }

    /**
     * returns a date that corresponds to the first time a request can be retried.
     *
     * @param retryAfter String in Retry-After format
     */
    public Date apply(String retryAfter) {
      if (retryAfter == null) {
        return null;
      }
      if (retryAfter.matches("^[0-9]+$")) {
        long deltaMillis = SECONDS.toMillis(Long.parseLong(retryAfter));
        return new Date(currentTimeMillis() + deltaMillis);
      }
      synchronized (rfc822Format) {
        try {
          return rfc822Format.parse(retryAfter);
        } catch (ParseException ignored) {
          return null;
        }
      }
    }
  }
}