Figure 1 shows the sequence of events for a URL session task, which correspond to the temporal metrics captured by NSURLSessionTaskTransactionMetrics.
For all metrics with a start and end date, if an aspect of the task was not completed, then its corresponding end date metric is nil. This can happen if name lookup begins, but the operation either times out, fails, or the client cancels the task before the name can be resolved. In this case, the domainLookupEndDate property is nil, along with all metrics for aspects that occurred afterwards.
The number of redirects that occurred during the execution of the task.
This documentation contains preliminary information about an API or technology in development. This information is subject to change, and software implemented according to this documentation should be tested with final operating system software.