EXC_BAD_ACCESS in Amplitude.m due to dereferencing nil after refreshing dynamic config

[jaltreuter]

Expected Behavior

If Amplitude is deallocated while dynamic config is being refreshed, the completion block should no-op.

Current Behavior

If Amplitude is deallocated while dynamic config is being refreshed, the completion block will dereference nil and crash the app.

Possible Solution

This is a snippet of the existing code in Amplitude.m:

- (void)refreshDynamicConfig {
    if (self.useDynamicConfig) {
        __weak typeof(self) weakSelf = self;
        [[AMPConfigManager sharedInstance] refresh:^{
            __strong typeof(self) strongSelf = weakSelf;
            strongSelf->_serverUrl = [AMPConfigManager sharedInstance].ingestionEndpoint;
        }];
    }
}

The block avoids a retain cycle by creating a weak reference to self, but incorrectly uses that reference. If weakSelf becomes nil, the block will then dereference that value and crash. It should be replaced with

- (void)refreshDynamicConfig {
    if (self.useDynamicConfig) {
        __weak typeof(self) weakSelf = self;
        [[AMPConfigManager sharedInstance] refresh:^{
            __strong typeof(self) strongSelf = weakSelf;
            if strongSelf == nil {
                return;
            }
            strongSelf->_serverUrl = [AMPConfigManager sharedInstance].ingestionEndpoint;
        }];
    }
}

Steps to Reproduce

1. Create an instance of Amplitude
2. Set useDynamicConfig to true
3. Call initializeApiKey
4. Remove all references to this instance of Amplitude

Environment

• SDK Version: 7.1.0
• Device: iPhone XS Simulator
• OS Version: iOS 12.0

[haoliu-amp]

Merged. Thanks!