Debugging HTTP

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

Transcript

1. Debugging HTTP
   Lorna Mitchell, ZendCon 2014
   

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2. 6 Stages of Debugging
   

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3. Denial
   That can't happen.
   

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

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5. Disbelief
   That shouldn't happen.
   

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6. Testing
   Why does that happen?
   

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7. Gotcha
   Oh, I see.
   

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8. Relief
   How did that ever work?
   

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9. Fault-Finding HTTP
   ... is just like fault-finding elsewhere in a web project
   Seeing the problem is usually harder than fixing it
   

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10. Tools
    

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11. Developer Tools
    Get to know the tools in your browser.
    Demo: My favourite browser tool
    

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

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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
    

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14. Meet Curl
    Demo: I'd like to introduce you to curl
    

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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
    

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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/
    

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17. Debugging Across Layers
    

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

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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)
    

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20. Charles Proxy
    Demo: Charles Proxy on web and mobile
    

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

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

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23. Make Debugging Your Super Power
    

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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/
    

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25. Questions?
    Feedback (please?) https://m.joind.in/talk/1d5ee
    Contact: http://lornajane.net - @lornajane
    

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