Daniel Compton danielcompton

Opening and closing an SSH tunnel in a shell script the smart way

I recently had the following problem:

From an unattended shell script (called by Jenkins), run a command-line tool that accesses the MySQL database on another host.
That tool doesn't know that the database is on another host, plus the MySQL port on that host is firewalled and not accessible from other machines.

We didn't want to open the MySQL port to the network, but it's possible to SSH from the Jenkins machine to the MySQL machine. So, basically you would do something like

ssh -L 3306:localhost:3306 remotehost

Make it real

Ideas are cheap. Make a prototype, sketch a CLI session, draw a wireframe. Discuss around concrete examples, not hand-waving abstractions. Don't say you did something, provide a URL that proves it.

Ship it

Nothing is real until it's being used by a real user. This doesn't mean you make a prototype in the morning and blog about it in the evening. It means you find one person you believe your product will help and try to get them to use it.

Do it with style

ClojureScript macros: kinda, sorta, not really.

ClojureScript does not have a standalone macro system. To write ClojureScript macros, one must write them in Clojure and then refer to them in ClojureScript code. This situation is workable, but at a minimum it forces one to keep ClojureScript code and the macros it invokes in separate files. I miss the locality of regular Clojure macros, so I wrote something called maptemplate that gives me back some of what I miss. The technique may be useful in other scenarios.

Problem

Suppose you're wrapping functionality in another namespace or package so that you can have your own namespace of identically named but otherwise decorated functions:

ClojureScript:

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	;;; Seed Dependencies for Clojure Projects

	;; This file contains Leiningen-style dependencies for many
	;; commonly-used Clojure and Java libraries.

	;; If you put all of these dependencies in a project.clj file, you
	;; will NOT get a working project! However, running `lein deps` will
	;; download all of these libraries as well as their transitive
	;; dependencies. This is a convenient way to "seed" the local Maven
	;; repository cache on a new machine.

	(ns my-cljs.macros.debug
	(:require [cljs.analyzer :as cljs]
	clojure.walk))

	(declare ap
	cljs-macroexpand*
	cljs-macroexpand-1*
	cljs-macroexpand-all*

	cljs-macroexpand

	(time
	(def data-thread
	(let [c (chan)
	res (atom [])]
	;; fetch em all
	(doseq [i (range 10 100)]
	(thread (>!! c (blocking-get (format "http://fssnip.net/%d" i)))))
	;; gather results
	(doseq [_ (range 10 100)]
	(swap! res conj (<!! c)))

	// nodewar.com library function…
	// o.lib.targeting.simpleTarget(ship, pos)
	//
	// mostly deobfuscated/deminified
	//
	function simpleTarget(ship, pos) {
	var i, r, h,
	torque = 0,
	thrust = 0,
	dir = o.lib.targeting.dir(ship, pos);

	require 'nokogiri'


	# Public: Find the absolute path to a file
	#
	# This method finds a file that is relative to the
	# location of the script, expanding anything that
	# needs expanding (~, etc.)
	#
	# filename - the filename to find