High-Performance iOS Networking

Talk about building fast networking iOS apps and how to debug them at UIKonf in Berlin on 23 May 2016.

Transcript

1. High Performance
   iOS Networking
   @smithclay · New Relic
   UIKonf · 23 May 2016 · Berlin
   

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2. This talk: tech notes
   • iOS 9 only (changes in iOS 10?)
   • NSURLSession is assumed (AFNetworking
   2.0+)
   • Not about the absence of a network
   connection.
   • No code—focus on the network layer and
   server-side. Don't block the main thread.
   

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3. Your App Backend
   HTTP(S)
   Vintage client—server
   

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4. Your App
   Authentication
   Messaging
   Dynamic
   Content
   Analytics
   Advertising
   HTTP
   2016 reality:
   

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5. c
   Max speed limit
   

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6. Full TCP handshake
   Device Server
   1. SYN
   2. SYN/ACK
   3. ACK
   Data
   {
   Round trip
   {
   

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7. San Francisco 9142 km
   Singapore 16093 km
   Latency
   

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8. How do we reduce
   network latency?
   

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9. TCP Fast Open
   http://static.googleusercontent.com/media/research.google.com/en//pubs/archive/37517.pdf
   https://datatracker.ietf.org/doc/rfc7413/
   

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10. TCP handshake + TFO
    Device Server
    1. SYN
    2. SYN/ACK+cookie
    3. ACK
    Data
    {
    Round trip
    {
    

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11. TCP handshake, #2 Request
    Device Server
    1. SYN+cookie
    2. SYN/ACK+data
    {
    Round trip
    

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12. TCP Fast Open Guide
    • Only for idempotent data (HTTP GET)
    • Needs Linux Kernel v4.1
    • https://developer.apple.com/videos/play/
    wwdc2015/719/
    • http://devstreaming.apple.com/videos/wwdc/
    2015/719ui2k57m/
    719/719_your_app_and_next_generation_net
    works.pdf?dl=1 (Implementation details)
    

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13. Does it work with
    NSURLSession?
    No :(
    

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14. Transport Layer
    Security (TLS)
    

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15. App Transport Security
    nscurl --ats-
    diagnostics
    
    TLS 1.2,
    Strong
    certificates
    

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16. Full TCP + TLS handshake
    Device Server
    Data Transfer
    {
    Round trip
    1. SYN
    2. SYN/ACK
    3. ACK
    {
    {
    TLS, +2 RTTs
    Cool demo (browser-based): https://tls.openmirage.org/
    

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17. Use a CDN if possible
    TLS tuning for iOS (server-side)
    Reduce RTTs (False start, session resumption)
    Coming soon (?): TLS 1.3
    Visit istlsfastyet.com
    https://developer.apple.com/library/ios/qa/qa1727/_index.html
    

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18. HTTP/2
    

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20. TCP Multiplexing in HTTP/2
    Device Server*
    Connection closes
    Connection opens
    https://blog.newrelic.com/2016/02/09/http2-best-practices-web-performance/
    *TLS Required
    

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21. Nice H2 features
    Header
    Compression
    (HPACK)
    Server Push
    (not supported on
    iOS... yet)
    Stream Priorities
    (not supported on
    iOS)
    

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22. HTTP/2 backend support?
    https://tools.keycdn.com/http2-test
    openssl s_client -alpn h2 -connect google.com:443 | grep ALPN
    ·
    https://blog.newrelic.com/2016/02/17/http2-production/
    * OpenSSL 1.0.2g or greater needed
    *
    

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23. Use a CDN (shortcut)
    H2 implementation tips
    Consider server-side TCP tuning (initcwnd)
    Use keep-alive for HTTP 1.1 clients
    Measure before + after
    https://tools.ietf.org/html/draft-stenberg-httpbis-tcp-00
    

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24. Caching with
    NSURLSession
    

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25. Use the Cache-Control
    header
    • NSURLRequestUseProtocolCachePolicy
    (default policy for NSURLSession)
    observes the protocol spec.
    • Cache-Control: max-age=,
    public
    http://nshipster.com/nsurlcache/
    https://tools.ietf.org/html/rfc7234
    

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26. The ETag Header
    Device Server
    200 OK
    Last-Modified: Mon, 22
    ETag: ad87...
    GET /fave-cats.json
    https://en.wikipedia.org/wiki/HTTP_ETag
    GET /fave-cats.json
    If-None-Matched: ad87..
    304 Not Modified
    

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27. Debugging
    

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28. CFNETWORK_DIAGNOSTICS
    https://developer.apple.com/library/ios/qa/qa1887/_index.html
    

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29. Example log
    

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30. Remote Virtual Interface
    • rvictl creates an interface
    for packet capture tools (i.e.
    wireshark)
    • Device must be plugged in
    using USB
    https://developer.apple.com/library/mac/qa/qa1176/_index.html
    http://useyourloaf.com/blog/remote-packet-capture-for-ios-devices/
    

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31. Wireshark setup
    Download: http://wireshark.com/
    

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32. ...see all the packets
    

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33. Instruments: Network
    Must test on a real device.
    

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34. Meh.
    Must test on a real device.
    

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35. HTTP Proxies
    • mitmproxy: mitmproxy.org
    (0.16 supports HTTP/2!)
    • charlesproxy.com/Fiddler
    (Nice UI, paid, no HTTP/2
    support yet)
    http://jasdev.me/intercepting-ios-traffic
    

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36. mitmproxy: install notes
    1.El Capitan python issues: use brew
    install python
    2. For simulator, must set proxy on OS X to
    127.0.0.1:8080 to start capturing HTTP(S)
    traffic.
    3.Must install certificate after running proxy:
    go to http://mitm.it on simulator.
    

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37. Inspect request/response
    http://docs.mitmproxy.org/en/latest/mitmproxy.html
    

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38. Other tools: bad networks
    • https://github.com/facebook/
    augmented-traffic-control
    • http://nshipster.com/
    network-link-conditioner/
    

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39. Checklist
    Repeat this 5 times: the network is unreliable*.
    Reduce the number of TCP connections.
    Don't implement your own caching
    scheme: use the protocol features.
    Test and measure network traffic regularly.
    *https://en.wikipedia.org/wiki/Fallacies_of_distributed_computing
    

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40. Last thought
    The person who uses your app doesn't care about
    network stuff. They just want it to be fast.
    

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41. Thanks.
    @smithclay · New Relic
    UIKonf · 23 May 2016 · Berlin
    Slides will posted on Twitter.
    

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