Hi , we are a network SDK develop company, our SDK is helping other apps optimize their network performance. We start a proxy server in the iOS device, and app's network request via our proxy server.
Recently, we found request sometimes happen -1200 error (error NSURLErrorDomain / -1200 /) . After capture package between app and our proxy server. Found something strange:(please see the .pcap file https://github.com/icefirewang/share_file)
After handshake success, app receive h2`s setting frame then initiate terminate the connection. ( see No.14 package) Then, retry, and failed, same as first time (see No. 15 package). After second failed, app try to handshake again, but failed. The fail reason is handshake agreement decline from 1.2 to 1.0 (out proxy server log: "handshake libssl error: error:140A1175:SSL routines:ssl_bytes_to_cipher_list:inappropriate fallback" , see No.16 package)
The app request is started by URLSession in a NSURLProtocol. Out proxy server is base on openssl. Could you help us, find out what cause
URLSession close the connection twice. And why the https agreement decline.