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/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
// This implements logic for stopping requests if the server starts to return
// too many errors. If we get MAX_ERRORS errors in ERROR_PERIOD minutes, we
// back off for TIMEOUT_INCREMENT minutes. If we get another error
// immediately after we restart, we double the timeout and add
// TIMEOUT_INCREMENT minutes, etc.
//
// This is similar to the logic used by the search suggestion service.
// HTTP responses that count as an error. We also include any 5xx response
// as an error.
this.HTTP_FOUND = 302;
this.HTTP_SEE_OTHER = 303;
this.HTTP_TEMPORARY_REDIRECT = 307;
/**
* @param maxErrors Number of times to request before backing off.
* @param retryIncrement Time (ms) for each retry before backing off.
* @param maxRequests Number the number of requests needed to trigger backoff
* @param requestPeriod Number time (ms) in which maxRequests have to occur to
* trigger the backoff behavior (0 to disable maxRequests)
* @param timeoutIncrement Number time (ms) the starting timeout period
* we double this time for consecutive errors
* @param maxTimeout Number time (ms) maximum timeout period
*/
this.RequestBackoff =
function RequestBackoff(maxErrors, retryIncrement,
maxRequests, requestPeriod,
timeoutIncrement, maxTimeout) {
this.MAX_ERRORS_ = maxErrors;
this.RETRY_INCREMENT_ = retryIncrement;
this.MAX_REQUESTS_ = maxRequests;
this.REQUEST_PERIOD_ = requestPeriod;
this.TIMEOUT_INCREMENT_ = timeoutIncrement;
this.MAX_TIMEOUT_ = maxTimeout;
// Queue of ints keeping the time of all requests
this.requestTimes_ = [];
this.numErrors_ = 0;
this.errorTimeout_ = 0;
this.nextRequestTime_ = 0;
}
/**
* Reset the object for reuse. This deliberately doesn't clear requestTimes_.
*/
RequestBackoff.prototype.reset = function() {
this.numErrors_ = 0;
this.errorTimeout_ = 0;
this.nextRequestTime_ = 0;
}
/**
* Check to see if we can make a request.
*/
RequestBackoff.prototype.canMakeRequest = function() {
var now = Date.now();
if (now < this.nextRequestTime_) {
return false;
}
return (this.requestTimes_.length < this.MAX_REQUESTS_ ||
(now - this.requestTimes_[0]) > this.REQUEST_PERIOD_);
}
RequestBackoff.prototype.noteRequest = function() {
var now = Date.now();
this.requestTimes_.push(now);
// We only care about keeping track of MAX_REQUESTS
if (this.requestTimes_.length > this.MAX_REQUESTS_)
this.requestTimes_.shift();
}
RequestBackoff.prototype.nextRequestDelay = function() {
return Math.max(0, this.nextRequestTime_ - Date.now());
}
/**
* Notify this object of the last server response. If it's an error,
*/
RequestBackoff.prototype.noteServerResponse = function(status) {
if (this.isErrorStatus(status)) {
this.numErrors_++;
if (this.numErrors_ < this.MAX_ERRORS_)
this.errorTimeout_ = this.RETRY_INCREMENT_;
else if (this.numErrors_ == this.MAX_ERRORS_)
this.errorTimeout_ = this.TIMEOUT_INCREMENT_;
else
this.errorTimeout_ *= 2;
this.errorTimeout_ = Math.min(this.errorTimeout_, this.MAX_TIMEOUT_);
this.nextRequestTime_ = Date.now() + this.errorTimeout_;
} else {
// Reset error timeout, allow requests to go through.
this.reset();
}
}
/**
* We consider 302, 303, 307, 4xx, and 5xx http responses to be errors.
* @param status Number http status
* @return Boolean true if we consider this http status an error
*/
RequestBackoff.prototype.isErrorStatus = function(status) {
return ((400 <= status && status <= 599) ||
HTTP_FOUND == status ||
HTTP_SEE_OTHER == status ||
HTTP_TEMPORARY_REDIRECT == status);
}
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