Janus

Node.js Handler for All Library Searches

code{4}lib 2016, March 9

David Naughton - UMN Libraries Web Development

naughton@umn.edu

Slides

http://z.umn.edu/c4ljanus

Common Problem

Many Search Targets

What to do for UMN's Library Data and Student Success?

A Solution - One Search Form to Rule them All

aka Bento Box

One example: Quick Search from NCSU
Very nice, but what if it doesn't meet your needs?

An Alternative - One Handler to Rule All the Search Forms

Privacy and Security

Single code-base to maintain.

Automate deleting of search data! We use logrotate.

Simpler Search Form Targets

Replaced this...

http://primo.lib.umn.edu/primo_library/libweb/action/dlSearch.do?institution=TWINCITIES&vid=TWINCITIES&indx=1&dym=true&highlight=true&lang=eng&search_scope=mncat_discovery&query=any%2Ccontains%2Cdarwin

...with this:

https://stacks.lib.umn.edu/janus?target=mncatdiscovery&search=darwin

Challenges - Testing

First attempt, with PHP/Guzzle: JavaScrip problems.

Solution? node.js!

Some people, when confronted with a problem, think "I know, I'll use node.js."

Now they have ω₁ problems.

Challenges - node.js

The rest of the talk.

Installing node.js

OS Package

Will your sys-admins allow/support it?
Even if they do, version could be very old.

Installer/Version Manager

ndenv
nvm
n (Requires already-existing node.js)

node.js - Not a robust HTTP server.

Need a reverse proxy. Most common recommendation is nginx.

Still need to keep node.js running: forever or Supervisor or ...

May seem daunting. And what about risk-averse orgs?

Our Solution: Apache + Passenger

Phusion Passenger: Node.js tutorial

Configuring Passenger for node.js

Undocumented, but this works:


      Alias /janus /path/to/janus/public
      <Directory /path/to/janus/public>
        PassengerNodejs /path/to/node
        PassengerAppRoot /path/to/janus
        PassengerBaseURI /janus
      </Directory>

Asynchrony

Running multiple async ops sequentially is problematic.
What the heck is the event loop anyway?
What Color is Your Function?

Rapid Evolution of Approaches

Callbacks, Promises, and Coroutines (oh my!): Asynchronous Programming Patterns in JavaScript
ES 5-6-7: From Callbacks to Promises to Generators to Async/await
aysnc/await proposal for ES7, building on generators and promises.

Coroutines

"...computer program components that generalize subroutines for nonpreemptive multitasking, by allowing multiple entry points for suspending and resuming execution at certain locations." — Wikipedia
Coroutines, like ES7's async/await, make asynchronous code look synchronous.
Fundamentally different from previous approaches, which all use continuation-passing style.

Coroutines in ES(5|6)

koa

"next generation web framework for node.js", based on generators/coroutines.
Designed by the team behind Express.
Coroutines all the way down in koa v2, which will be alpha "until async/await hits node.js", but seems stable.