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An Asynchronous HTTP Library for Android
There is a newer version: 1.4.11
/*
    Android Asynchronous Http Client
    Copyright (c) 2011 James Smith 
    http://loopj.com

    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.
*/

/*
    Some of the retry logic in this class is heavily borrowed from the
    fantastic droid-fu project: https://github.com/donnfelker/droid-fu
*/

package com.loopj.android.http;

import android.os.SystemClock;

import org.apache.http.NoHttpResponseException;
import org.apache.http.client.HttpRequestRetryHandler;
import org.apache.http.client.methods.HttpUriRequest;
import org.apache.http.protocol.ExecutionContext;
import org.apache.http.protocol.HttpContext;

import java.io.IOException;
import java.io.InterruptedIOException;
import java.net.SocketException;
import java.net.UnknownHostException;
import java.util.HashSet;

import javax.net.ssl.SSLException;

class RetryHandler implements HttpRequestRetryHandler {
    private static HashSet> exceptionWhitelist = new HashSet>();
    private static HashSet> exceptionBlacklist = new HashSet>();

    static {
        // Retry if the server dropped connection on us
        exceptionWhitelist.add(NoHttpResponseException.class);
        // retry-this, since it may happens as part of a Wi-Fi to 3G failover
        exceptionWhitelist.add(UnknownHostException.class);
        // retry-this, since it may happens as part of a Wi-Fi to 3G failover
        exceptionWhitelist.add(SocketException.class);

        // never retry timeouts
        exceptionBlacklist.add(InterruptedIOException.class);
        // never retry SSL handshake failures
        exceptionBlacklist.add(SSLException.class);
    }

    private final int maxRetries;
    private final int retrySleepTimeMS;

    public RetryHandler(int maxRetries, int retrySleepTimeMS) {
        this.maxRetries = maxRetries;
        this.retrySleepTimeMS = retrySleepTimeMS;
    }

    @Override
    public boolean retryRequest(IOException exception, int executionCount, HttpContext context) {
        boolean retry = true;

        Boolean b = (Boolean) context.getAttribute(ExecutionContext.HTTP_REQ_SENT);
        boolean sent = (b != null && b);

        if (executionCount > maxRetries) {
            // Do not retry if over max retry count
            retry = false;
        } else if (isInList(exceptionBlacklist, exception)) {
            // immediately cancel retry if the error is blacklisted
            retry = false;
        } else if (isInList(exceptionWhitelist, exception)) {
            // immediately retry if error is whitelisted
            retry = true;
        } else if (!sent) {
            // for most other errors, retry only if request hasn't been fully sent yet
            retry = true;
        }

        if (retry) {
            // resend all idempotent requests
            HttpUriRequest currentReq = (HttpUriRequest) context.getAttribute(ExecutionContext.HTTP_REQUEST);
            if (currentReq == null) {
                return false;
            }
            String requestType = currentReq.getMethod();
            retry = !requestType.equals("POST");
        }

        if (retry) {
            SystemClock.sleep(retrySleepTimeMS);
        } else {
            exception.printStackTrace();
        }

        return retry;
    }

    protected boolean isInList(HashSet> list, Throwable error) {
        for (Class aList : list) {
            if (aList.isInstance(error)) {
                return true;
            }
        }
        return false;
    }
}