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1 files changed, 139 insertions, 0 deletions

diff --git a/Firebase/Database/Core/Utilities/FIRRetryHelper.m b/Firebase/Database/Core/Utilities/FIRRetryHelper.m
new file mode 100644
index 0000000..199e17d
--- /dev/null
+++ b/Firebase/Database/Core/Utilities/FIRRetryHelper.m
@@ -0,0 +1,139 @@
+/*
+ * Copyright 2017 Google
+ *
+ * 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.
+ */
+
+#import "FIRRetryHelper.h"
+#import "FUtilities.h"
+
+@interface FIRRetryHelperTask : NSObject
+
+@property (nonatomic, strong) void (^block)();
+
+@end
+
+@implementation FIRRetryHelperTask
+
+- (instancetype) initWithBlock:(void (^)())block {
+    self = [super init];
+    if (self != nil) {
+        self->_block = [block copy];
+    }
+    return self;
+}
+
+- (BOOL) isCanceled {
+    return self.block == nil;
+}
+
+- (void) cancel {
+    self.block = nil;
+}
+
+- (void) execute {
+    if (self.block) {
+        self.block();
+    }
+}
+
+@end
+
+
+
+@interface FIRRetryHelper ()
+
+@property (nonatomic, strong) dispatch_queue_t dispatchQueue;
+@property (nonatomic) NSTimeInterval minRetryDelayAfterFailure;
+@property (nonatomic) NSTimeInterval maxRetryDelay;
+@property (nonatomic) double retryExponent;
+@property (nonatomic) double jitterFactor;
+
+@property (nonatomic) BOOL lastWasSuccess;
+@property (nonatomic) NSTimeInterval currentRetryDelay;
+
+@property (nonatomic, strong) FIRRetryHelperTask *scheduledRetry;
+
+@end
+
+@implementation FIRRetryHelper
+
+- (instancetype) initWithDispatchQueue:(dispatch_queue_t)dispatchQueue
+             minRetryDelayAfterFailure:(NSTimeInterval)minRetryDelayAfterFailure
+                         maxRetryDelay:(NSTimeInterval)maxRetryDelay
+                         retryExponent:(double)retryExponent
+                          jitterFactor:(double)jitterFactor {
+    self = [super init];
+    if (self != nil) {
+        self->_dispatchQueue = dispatchQueue;
+        self->_minRetryDelayAfterFailure = minRetryDelayAfterFailure;
+        self->_maxRetryDelay = maxRetryDelay;
+        self->_retryExponent = retryExponent;
+        self->_jitterFactor = jitterFactor;
+        self->_lastWasSuccess = YES;
+    }
+    return self;
+}
+
+- (void) retry:(void (^)())block {
+    if (self.scheduledRetry != nil) {
+        FFLog(@"I-RDB054001", @"Canceling existing retry attempt");
+        [self.scheduledRetry cancel];
+        self.scheduledRetry = nil;
+    }
+
+    NSTimeInterval delay;
+    if (self.lastWasSuccess) {
+        delay = 0;
+    } else {
+        if (self.currentRetryDelay == 0) {
+            self.currentRetryDelay = self.minRetryDelayAfterFailure;
+        } else {
+            NSTimeInterval newDelay = (self.currentRetryDelay * self.retryExponent);
+            self.currentRetryDelay = MIN(newDelay, self.maxRetryDelay);
+        }
+
+        delay = ((1 - self.jitterFactor) * self.currentRetryDelay) +
+                (self.jitterFactor * self.currentRetryDelay * [FUtilities randomDouble]);
+        FFLog(@"I-RDB054002", @"Scheduling retry in %fs", delay);
+
+    }
+    self.lastWasSuccess = NO;
+    FIRRetryHelperTask *task = [[FIRRetryHelperTask alloc] initWithBlock:block];
+    self.scheduledRetry = task;
+    dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (long long)(delay * NSEC_PER_SEC));
+    dispatch_after(popTime, self.dispatchQueue, ^{
+        if (![task isCanceled]) {
+            self.scheduledRetry = nil;
+            [task execute];
+        }
+    });
+}
+
+- (void) signalSuccess {
+    self.lastWasSuccess = YES;
+    self.currentRetryDelay = 0;
+}
+
+- (void) cancel {
+    if (self.scheduledRetry != nil) {
+        FFLog(@"I-RDB054003", @"Canceling existing retry attempt");
+        [self.scheduledRetry cancel];
+        self.scheduledRetry = nil;
+    } else {
+        FFLog(@"I-RDB054004", @"No existing retry attempt to cancel");
+    }
+    self.currentRetryDelay = 0;
+}
+
+@end