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package com.turbomanage.httpclient;
/**
* An HTTP client that completes all requests asynchronously using
* {@link DoHttpRequestTask}. All methods take a callback argument which is
* passed to the task and whose methods are invoked when the request completes
* or throws on exception.
*
* @author David M. Chandler
*/
public class AsyncHttpClient extends AbstractHttpClient {
static int[] fib = new int[20];
static {
// Compute Fibonacci series for backoff
for (int i=0; i<20; i++) {
fib[i] = i<2 ? i : fib[i-2] + fib[i-1];
}
}
// Configurable default
private int maxRetries = 3;
/*
* The factory that will be used to obtain an async wrapper for the
* request. Usually set in a subclass that provides a platform-specific
* async wrapper such as a new thread or Android AsyncTask.
*/
protected final AsyncRequestExecutorFactory execFactory;
/**
* Constructs a new client with factory and empty baseUrl.
*
* @param factory
*/
public AsyncHttpClient(AsyncRequestExecutorFactory factory) {
this(factory, "");
}
/**
* Constructs a new client with factory and baseUrl.
*
* @param factory
* @param baseUrl
*/
public AsyncHttpClient(AsyncRequestExecutorFactory factory, String baseUrl) {
this(factory, baseUrl, new BasicRequestHandler() {
});
}
/**
* Constructs a new client with factory, baseUrl, and custom {@link RequestHandler}.
*
* @param factory
* @param baseUrl
* @param handler
*/
public AsyncHttpClient(AsyncRequestExecutorFactory factory, String baseUrl, RequestHandler handler) {
super(baseUrl, handler);
this.execFactory = factory;
}
/**
* Execute a HEAD request and invoke the callback on completion. The supplied
* parameters are URL encoded and sent as the query string.
*
* @param path
* @param params
* @param callback
*/
public void head(String path, ParameterMap params, AsyncCallback callback) {
HttpRequest req = new HttpHead(path, params);
executeAsync(req, callback);
}
/**
* Execute a GET request and invoke the callback on completion. The supplied
* parameters are URL encoded and sent as the query string.
*
* @param path
* @param params
* @param callback
*/
public void get(String path, ParameterMap params, AsyncCallback callback) {
HttpRequest req = new HttpGet(path, params);
executeAsync(req, callback);
}
/**
* Execute a POST request with parameter map and invoke the callback on
* completion.
*
* @param path
* @param params
* @param callback
*/
public void post(String path, ParameterMap params, AsyncCallback callback) {
HttpRequest req = new HttpPost(path, params);
executeAsync(req, callback);
}
/**
* Execute a POST request with a chunk of data and invoke the callback on
* completion.
*
* To include name-value pairs in the query string, add them to the path
* argument or use the constructor in {@link HttpPost}. This is not a
* common use case, so it is not included here.
*
* @param path
* @param contentType
* @param data
* @param callback
*/
public void post(String path, String contentType, byte[] data, AsyncCallback callback) {
HttpPost req = new HttpPost(path, null, contentType, data);
executeAsync(req, callback);
}
/**
* Execute a PUT request with the supplied content and invoke the callback
* on completion.
*
* To include name-value pairs in the query string, add them to the path
* argument or use the constructor in {@link HttpPut}. This is not a
* common use case, so it is not included here.
*
* @param path
* @param contentType
* @param data
* @param callback
*/
public void put(String path, String contentType, byte[] data, AsyncCallback callback) {
HttpRequest req = new HttpPut(path, null, contentType, data);
executeAsync(req, callback);
}
/**
* Execute a DELETE request and invoke the callback on completion. The
* supplied parameters are URL encoded and sent as the query string.
*
* @param path
* @param params
* @param callback
*/
public void delete(String path, ParameterMap params, AsyncCallback callback) {
HttpDelete req = new HttpDelete (path, params);
executeAsync(req, callback);
}
/**
* Execute an {@link HttpRequest} asynchronously. Uses a factory to obtain a
* suitable async wrapper in order to decouple from Android.
*
* @param httpRequest
* @param callback
*/
protected void executeAsync(HttpRequest httpRequest, AsyncCallback callback) {
AsyncRequestExecutor executor = execFactory.getAsyncRequestExecutor(this, callback);
executor.execute(httpRequest);
}
/**
* Tries several times until successful or maxRetries exhausted.
* Must throw exception in order for the async process to forward
* it to the callback's onError method.
*
* @param httpRequest
* @return Response object, may be null
* @throws HttpRequestException
*/
public HttpResponse tryMany(HttpRequest httpRequest) throws HttpRequestException {
int numTries = 0;
long startTime = System.currentTimeMillis();
HttpResponse res = null;
while (numTries < maxRetries) {
try {
setConnectionTimeout(getNextTimeout(numTries));
if (requestLogger.isLoggingEnabled()) {
requestLogger.log((numTries+1) + "of" + maxRetries + ", trying " + httpRequest.getPath());
}
startTime = System.currentTimeMillis();
res = doHttpMethod(httpRequest.getPath(),
httpRequest.getHttpMethod(), httpRequest.getContentType(),
httpRequest.getContent());
if (res != null) {
return res;
}
} catch (HttpRequestException e) {
if (isTimeoutException(e, startTime) && numTries < (maxRetries-1)) {
// Fall through loop, retry
// On last attempt, throw the exception regardless
} else {
boolean isRecoverable = requestHandler.onError(e);
if (isRecoverable && numTries < (maxRetries-1)) {
try {
// Wait a while and fall through loop to try again
Thread.sleep(connectionTimeout);
} catch (InterruptedException ie) {
// App stopping, perhaps? No point in further retries
throw e;
}
} else {
// Not recoverable or last attempt, time to bail
throw e;
}
}
}
numTries++;
}
return null;
}
/**
* Implements exponential backoff using the Fibonacci series, which
* has the effect of backing off with a multiplier of ~1.618
* (the golden mean) instead of 2, which is rather boring.
*
* @param numTries Current number of attempts completed
* @return Connection timeout in ms for next attempt
*/
protected int getNextTimeout(int numTries) {
// For n=0,1,2,3 returns 1000,2000,3000,5000
return 1000 * fib[numTries + 2];
}
/**
* Set maximum number of retries to attempt, capped at 18. On the
* 18th retry, the connection timeout will be 4,181 sec = 1 hr 9 min.
*
* @param maxRetries
*/
public void setMaxRetries(int maxRetries) {
if (maxRetries < 1 || maxRetries > 18) {
throw new IllegalArgumentException("Maximum retries must be between 1 and 18");
}
this.maxRetries = maxRetries;
}
}
