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In this note series, We will understand How to use CFNetwork diagnostic logging to investigate HTTP and HTTPS problems in iOS.
So Let’s begin.
If we’re using
URLSession and need to debug a complex networking issue, we can enable CFNetwork diagnostic logging to get detailed information about the progress of our network requests. CFNetwork diagnostic logging has unique advantages relative to other network debugging tools, including:
- Minimal setup
- The ability to look at network traffic that’s protected by Transport Layer Security (TLS).
- Information about CFNetwork’s internal state, like which cookies get saved and applied.
CFNetwork diagnostic logging is not exclusive to the CFNetwork framework. The core implementation of the
URLSession API lives within the CFNetwork framework, and thus we can and should use CFNetwork diagnostic logging if we’re using
Understand the Security Implications
CFNetwork diagnostic logs may contain decrypted TLS data and other security-sensitive information. Take these precautions:
- Restrict access to any logs we capture.
- If we build an app that enables this logging programmatically, make sure that anyone who receives that app understands the security implications of using it.
- If we send a log to Apple, redact any security-sensitive information.
CFNetwork diagnostic logs may contain information that is extremely security-sensitive. Protect these logs accordingly.
Enable Logging In Xcode
To enable CFNetwork diagnostic logging, edit the current scheme (choose Product > Scheme > Edit Scheme), navigate to the Arguments tab, and add a
CFNETWORK_DIAGNOSTICS item to the Environment Variables list. The value of this item can range from 0 to 3, where 0 turns logging off, and higher numbers give us progressively more logging. When we next run our app and use
URLSession, CFNetwork diagnostic log entries appear in Xcode’s debug console area. If the console area isn’t visible, choose View > Debug Area > Show Debug Area to show it.
Enable Logging Programmatically
To investigate problems outside of Xcode, programmatically enable CFNetwork diagnostic logging by setting the environment variable directly.
setenv("CFNETWORK_DIAGNOSTICS", "3", 1)
Do this right at the beginning of the app’s launch sequence:
- If we’re programming in Objective-C, put the code at the start of our
- If our program has a C++ component, make sure this code runs before any C++ static initializers that use CFNetwork or any APIs, like
URLSession, that use CFNetwork.
- If we’re programming in Swift, put this code in
main.swift. By default Swift apps don’t have a
main.swift. We need to add one.
View Log Entries
How we view the resulting log entries depends on our specific situation:
- In macOS, if we can reproduce the problem locally, run the Console utility on our Mac and view log entries there.
- In iOS, if we can reproduce the problem locally, and we’re able to connect the device to our Mac through USB, run the Console utility on our Mac and view log entries there. Make sure we select our iOS device from the source list on the left of the main Console window (choose View > Show Sources if the source list is not visible).
- If neither of the above work for us — for example, if we’re trying to debug a problem that can only be reproduced by one of our users in the field — get a sysdiagnose log from the machine exhibiting the problem and then extract the log entries from that.
In this note series, We understood How to use CFNetwork diagnostic logging to investigate HTTP and HTTPS problems in iOS.
Thanks for reading ! I hope you enjoyed and learned about CFNetwork diagnostic logging usage in iOS. Reading is one thing, but the only way to master it is to do it yourself.
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