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Debugging HTTP

Debugging HTTP

ZendCon session on using various tools to observe and diagnose issues in HTTP connection between applications (the original also included screencasts)


Lorna Mitchell

October 28, 2014

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  1. Debugging HTTP Lorna Mitchell, ZendCon 2014

  2. 6 Stages of Debugging

  3. Denial That can't happen.

  4. Frustration That doesn't happen on my machine.

  5. Disbelief That shouldn't happen.

  6. Testing Why does that happen?

  7. Gotcha Oh, I see.

  8. Relief How did that ever work?

  9. Fault-Finding HTTP ... is just like fault-finding elsewhere in a

    web project Seeing the problem is usually harder than fixing it
  10. Tools

  11. Developer Tools Get to know the tools in your browser.

    Demo: My favourite browser tool
  12. Curl Curl (or cURL) is command-line multitool for HTTP http://curl.haxx.se/

  13. Lornajane's Curl Cheat Sheet -X [verb] The verb to use

    for this request -H "[Header: value]" A header to send. Repeat as needed -d [value] Either the whole body data as a string, a filename, or a key/value pair -s The "silent" switch, to hide curl's progress meter when piping the output to something else -c [filename] Where to store any incoming cookies for future use -b [filename] Cookies to send with the request -v to show headers for both request and response
  14. Meet Curl Demo: I'd like to introduce you to curl

  15. Python's JSON Library A python tool, handily available via CLI

    [some json] | python -mjson.tool http://docs.python.org/2/library/json.html
  16. Wireshark Copies traffic from your network card to allow you

    to view it • Observe without changing • Can capture on a server, inspect later • Or tunnel the data over SSH (http://lrnja.net/1gEMLiE) • Save and load sessions https://www.wireshark.org/
  17. Debugging Across Layers

  18. Debugging Across Layers Demo: why doesn't this work? ... oh.

  19. Charles Proxy Multi-platform Web Debugging Proxy http://www.charlesproxy.com/ • Observe requests

    • Firefox plugin • Change requests • Use Charles as a network proxy • Repeat/save requests (detailed article: http://lrnja.net/ZuiDYJ)
  20. Charles Proxy Demo: Charles Proxy on web and mobile

  21. Debugging SSL Charles can perform a man-in-the-middle attack

  22. Debugging SSL You need to authorise the "attack"

  23. Make Debugging Your Super Power

  24. Other Excellent Tools • httpie https://github.com/jkbr/httpie • Fiddler http://www.telerik.com/fiddler •

    Postman (Chrome) http://getpostman.com/ • RESTClient (Firefox) http://restclient.net/ • mitmproxy http://mitmproxy.org/ • jq http://stedolan.github.io/jq/ • hurl.it http://www.hurl.it/
  25. Questions? Feedback (please?) https://m.joind.in/talk/1d5ee Contact: http://lornajane.net - @lornajane