Stuart Breckenridge

BoringSSL SSL ERROR ZERO RETURN

In an iOS app I’m building, I’m using URLSession to make API requests. However, shortly after the first request has completed successfully this error appears in the console log:

SSL_ERROR_ZERO_RETURN(6): operation failed because the connection was cleanly shut down with a close_notify alert

Enabling CFNETWORK_DIAGNOSTICS doesn’t reveal anything out of the ordinary, and I haven’t found anything on Stack Overflow that reveals the underlying cause of the issue. Strangely, testing the API through the app, browser, and Postman, works perfectly.

I just can’t stand seeing this pointless entry in the console log, the best description of which is available on Apple’s Developer Forums:

What’s happening here is that this log message relates to a common scenario that may or may not be correlated to any actual problem.

If anyone has any ideas as to how to resolve this error message, ping me on Twitter.

Config:

  • Server:
    • Ubuntu 16.04.4
    • Apache/2.4.18
    • OpenSSL 1.0.2g
  • Client:
    • iOS 11.3
    • Swift 4