Alissa Bonas mikeyteva

“Run Forrest, Run”

When is it needed? ● Add a new feature ● Fix a bug ● Investigate a problem ● Maintain legacy code ● Integration with another system or component

“My momma always said, life was like a box of chocolates. You never know what you’re gonna get”

How can we succeed?

Ask the person who developed it

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However...

Is it an open source project? ● Check the docs / wiki ● Ask in the community ○ mailing list ○ forum ○ irc ○ open an issue / ticket with a question

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Back to basics

Back to basics ● Technology / Programming language ● Source control ● Running tests ● Build / Run / Deploy

Detecting languages on Github

Detecting languages on Github

Not 100% accurate

Look for hints ● File extensions ● .gitignore ● README.md

Look for more hints ● Requirements.txt / setup.py ● pom.xml / build.xml ● Gemfile / gemspec ● bower.json

Scope the task

Minor changes ● Fix typos ● Add more info to a log statement ● Persist a field that already exists in an object

In search we trust ● Search for strings in the code repository ● Search existing logs for object names

Medium size changes ● Add a new field to an object / model ○ process and persist ○ use it in all code layers ● Upgrade the version of a third party library ○ regression is your nemesis ○ minor version upgrade != major version upgrade

Follow the trail ● Follow existing fields ○ understand the flow ● Follow the tests ○ learn how to add new tests ○ check if tests pass after code changes

Major changes ● Refactor a module / component ● Add a new functionality which requires a deep understanding of the system ● Performance is key and must not be harmed

Understand ● The architecture of the system ● Relevant flows and use cases ● The main path ● Fallback, retries, etc.

Number 1 factor is...

Time

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Goal: Identify entry points ● UI / REST / Backend ● Class hierarchy ● Identify and learn frameworks

Get to know the code better ● Is there a dependency injection mechanism? ● How do the components communicate ● Configuration keys to enable more info in the logs

Get to know the system better ● Identify persistency ○ data store type ○ how the data is stored ● Know your container ○ web server ○ application server

Product configuration files ● Static files location ● Check how they are used and changed ○ directly ○ loaded into the database

Multi process system ● Identify the processes ● How do they communicate with each other ● High availability / symmetric

Multithreaded considerations ● Sync or async code flow ● Usage of thread pools

After several iterations ● Create a sequence diagram ● UML draw.io Free online Visio alternative

Iterating over the code is like solving a puzzle

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Creating anchors “In climbing, a piton (/ˈpiːtɒn/; also called a pin or peg) is a metal spike (usually steel) that is driven into a crack or seam in the rock with a hammer, and which acts as an anchor to protect the climber against the consequences of a fall, or to assist progress in aid climbing” (wikipedia)

Creating anchors ● Read the code ● If we can debug - put breakpoints ● Read existing logs ● Understand through unitests

Creating anchors continued ● Change the log level ● Add more logging statements ● Check history in source control - commits and comments

Creating anchors - IDE Bookmarks

Creating anchors - the analog way ● Works too!

Backend

Example - utilities to explore the JVM ● JConsole ● VisualVM ● (more tools exist)

Getting more hints ● Explore threads names ● Thread dump - check thread source ● Take a heap dump - explore classes ● Check which objects a map contains

Hint on the database Hint on the scheduler

Network analyzer / packet sniffer ● Software that intercepts and logs traffic ○ decodes data ○ shows packet fields ● For example - Wireshark ● Define filters for efficiency

Example

Goal ● Send a SOA envelope to a service ● Sender - Ruby code ● Target - Java SOA service

Reports Engine 1 Reports Engine 2 Reports Engine 3 UI Reports Engine 4 http /engine1 http /engine2 http /engine3 http /engine4 SOA Tomcat SOA SOA SOA SOA

Steps ● Basic understanding what SOA is ● Intercept traffic of the existing Java code ● Learn how a SOA envelope should look like ● Write Ruby code to create a SOA envelope

Frontend

Frontend ● Which libraries are used ● Search for strings / translation files ● Search for icon files location and usage ● Learn how UI calls backend

Browser developer tools ● FireBug ● Chrome developer tools

Following the code ● Which css and js are downloaded ● Add watches in the script tab ● Set a breakpoint ○ Use ‘debugger;’ keyword in code ○ Set a breakpoint ● Inspect elements

Inspect the logo 160px * 159px File type and location Press here to switch to element selection mode Inspecting elements

Inspect the logo 160px * 159px Inspecting elements

Useful options ● Network tab ● Copy as curl ● Copy response ● Copy link address

Following network requests Alissa Bonas @ PyTN 2016

Analyzing response Alissa Bonas @ PyTN 2016

Analyzing response - zoom in JSON response

REST Client ● Learn how REST API is designed

In short...

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Thank you! mikeyteva

Graphics credits ● Signpost by Lubos Volkov ● Clock by Kid Mountain ● Idea by Matt Wasser ● Gauge by Joel Avery from the Noun Project ● Tomcat-logo by The Apache Tomcat Project Team ● Loop by useiconic.com from the Noun Project ● Magnifying Glass by Musket from the Noun Project ● Puzzle Piece by icon 54 from the Noun Project ● Writing by Creative Stall from the Noun Project ● Sherlock by James Keuning, the Noun Project ● Twitter by Lubos Volkov, the Noun Project ● Mug by Alex Getty from the Noun Project ● Diamond by MarkieAnn Packer from the Noun Project ● Light Bulb by artworkbean, the Noun Project ● Questions by Rediffusion from the Noun Project ● cancel by Jevgeni Striganov from the Noun Project ● Movies posters - http://www.impawards.com/