Keeping Software Soft

Keeping Software Soft John Kary @johnkary Lawrence Coders, January 2015

Hardware

Software

Program

Program Data In

Program Data In Data Out

Program Program Program

$ ls -l | grep "b" fabien.txt rabid-bear.rb sunk-cost.bl zabbazabba.do
! ! $ tail -f logs/prod.log | grep "error" [2015-01-16 21:15:45] app.error — Uncaught Exception [2015-01-16 23:22:42] app.error — Invalid argument "1" expected "2" [2015-01-17 00:01:52] app.error — SQL parse error "); DROP TABLE St

$ ls -l | grep "b" fabien.txt rabid-bear.rb sunk-cost.bl zabbazabba.do
! ! $ tail -f logs/prod.log | grep "error" [2015-01-16 21:15:45] app.error — Uncaught Exception [2015-01-16 23:22:42] app.error — Invalid argument "1" expected "2" [2015-01-17 00:01:52] app.error — SQL parse error "); DROP TABLE St Unix Pipes

https://www.ﬂickr.com/photos/billybrown00/4982722491

http://www.xcalak.info/images/misc/voip_network_l.gif

http://www.xcalak.info/images/misc/voip_network_l.gif +1 785-979-8176

GET /index.html HTTP/1.1 Host: www.lmgtfy.com

GET /index.html HTTP/1.1 Host: www.lmgtfy.com www.lmgtfy.com

GET /index.html HTTP/1.1 Host: www.lmgtfy.com www.lmgtfy.com HTTP/1.1 200 OK Date:
Mon, 23 May 2005 22:38:34 GMT Last-Modiﬁed: Wed, 08 Jan 2003 23:11:55 GMT ETag: "3f80f-1b6-3e1cb03b" Content-Type: text/html; charset=UTF-8 ! <html><head><title>An Example Page</title></head> <body>Hello World</body></html>

RFC2616

RFC2616 http://www.w3.org/Protocols/rfc2616/rfc2616-sec4.html#sec4 4. HTTP Message

Program Message Protocol

Program Message Protocol Interface

Interface "[Prohibits] access to all resources by default, allowing access
only through well-deﬁned entry points" http://en.wikipedia.org/wiki/Interface_(computing) "[A] shared boundary across which two separate components of a computer system exchange information."

https://www.ﬂickr.com/photos/dominicotine/7187354723

https://www.ﬂickr.com/photos/toasty/330752049

https://www.ﬂickr.com/photos/brilliantmichael/4172218074

http://www.ﬂickr.com/photos/amcgore/5518551326/

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Program Processing Program Program Program Your Thing Message Boundary Their
Thing You Don't Know

Server

Server Processes

Server Processes Packages

Server Processes Packages Classes

Server Processes Packages Classes Functions

Server Processes Packages Classes Functions Network IO

Your Package Not Your Package

Program Message Protocol

Program Message Protocol Interface

Program Message Protocol Interface Adapter

Message Passing Between Processes ls grep Keyboard STDIN Terminal STDOUT
C C

Further Study Basic of the Unix Philosophy! http://www.catb.org/esr/writings/taoup/html/ch01s06.html The Art
of Unix Programming (2003) ! The Art of Destroying Software! Talk by Greg Young (Unsure location/date) http://vimeo.com/108441214 ! Stop Writing Classes! Jack Diederich @ PyCon 2012 https://www.youtube.com/watch?v=o9pEzgHorH0 ! Architecture the Lost Years Robert C Martin (Uncle Bob) @ Ruby Midwest 2011 http://confreaks.com/videos/759-rubymidwest2011-keynote-architecture-the-lost-years ! Seven Languages in Seven Weeks (Erlang chapter)! https://pragprog.com/book/btlang/seven-languages-in-seven-weeks

Homework • Build small things • Build simple things and
compose them together • Connect things by generic messages • Isolate complexity into more small things • Build things that can be thrown away

ﬁn http://johnkary.net/talks @johnkary

Keeping Software Soft

Keeping Software Soft

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