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README.markdown

What is Hallon? Build Status

Hallon (Swedish for “Raspberry”) is the ruby gem for interacting with the official Spotify C API. It is the only ruby gem for libspotify that is up-to-date and usable. My goal with Hallon is to make libspotify a joy to use.

Code samples can be found under the examples/ directory. An explanation on how to run them can be found on the Hallon wiki on GitHub.

Important to consider before using Hallon

First off, Hallon is no longer being maintained.

Hallon’s model was from the start something along the lines of a synchronous Ruby binding to libspotify, and I no longer believe the way Hallon achieve this to be a good way of doing things. Because of this, development of Hallon has been stagnant for a long time. An additional reason is that I am no longer personally using Hallon for anything myself.

Most of my effort towards libspotify and Ruby have been focused on the spotify gem that powers Hallon: https://github.com/Burgestrand/spotify. For new projects, and possibly even existing projects, I would strongly suggest using the spotify gem instead of using Hallon, because:

  • Less of an abstraction around libspotify.
  • Less bugs, because of 1.
  • Less risk of e.g. deadlocks in the library because of 1.
  • Less confusing, because of 1.
  • Better than C (it’s in ruby, has automatic garbage collection, thread safe).
  • It’s still seeing new features and improvements, Hallon currently isn’t.

However, the spotify gem also has a few cons in comparison to Hallon:

  • Less of an abstraction around libspotify.
  • Requires (even if rudimentary) knowledge of FFI.
  • Some things are still annoying to do (e.g. calling certain functions, and callbacks) because of 2 and 1.

Please consider the above points before using Hallon.

Contact details

If you for some reason cannot use the mailing list or GitHub issue tracker you may contact me directly. My email is found on my GitHub profile.

Prerequisites

Before you start using Hallon you’ll need to complete the following steps.

  1. Get yourself a Spotify premium account, which is required for libspotify to work. You username and password (either classic Spotify, or facebook credentials) will be used to connect to Spotify later.
  2. Download your application key from developer.spotify.com, and place it in a known location. You’ll have the option of downloading it either in binary or c-code. You want the binary one. If you do not have an application key already, you will be asked to create one.
  3. Once the above are done, you are ready to try out Hallon.

Using Hallon

First, begin by installing the latest version of Hallon.

gem install hallon

Great! Now you’re ready to start experimenting. Everything in Hallon, from searching to looking up tracks, requires you to have an active Spotify session. You create it by initializing it with your application key.

require 'hallon'

session = Hallon::Session.initialize IO.read('./spotify_appkey.key')

Now that you have your session you may also want to login (even though you can still do a few things without logging in).

session.login!('username', 'password')

You may now experiment with just about anything. For an API reference, please see Hallon’s page at rdoc.info. As a starter tip, many objects can be constructed by giving it a Spotify URI, like this.

track = Hallon::Track.new("spotify:track:1ZPsdTkzhDeHjA5c2Rnt2I").load
artist = track.artist.load

puts "#{track.name} by #{artist.name}"

If you want to play audio…

If you want to play audio you’ll need to install an audio driver. As of current writing there is only one driver in existence. You can install it with:

gem install hallon-openal

For more information about audio support in Hallon, see the section "Audio support" below.

Hallon and Spotify objects

All objects from libspotify have a counterpart in Hallon, and just like in libspotify the objects are populated with information as it becomes available. All objects that behave in this way respond to #loaded?, which’ll return true if the object has been populated with data.

To ease loading objects, all loadable objects also respond to #load. This method simply polls on the target object, repeatedly calling Session#process_events until either a time limit is reached or the object has finished loading.

user = Hallon::User.new("spotify:user:burgestrand").load
puts user.loaded? # => true

As far as usage of the library goes, what applies to libspotify also applies to Hallon, so I would suggest you also read the libspotify library overview and related documentation.

Callbacks

Some objects may fire callbacks, most of the time as a direct result of Session#process_events. In libspotify the callbacks are only fired once for every object, but in Hallon you may have more than one object attached to the same libspotify object. As a result, callbacks are handled individually for each Hallon object.

imageA = Hallon::Image.new("spotify:image:548957670a3e9950e87ce61dc0c188debd22b0cb")
imageB = Hallon::Image.new("spotify:image:548957670a3e9950e87ce61dc0c188debd22b0cb")

imageA.pointer == imageB.pointer # => true, same spotify pointer
imageA.object_id == imageB.object_id # => false, different objects

imageA.on(:load) do
  puts "imageA loaded!"
end

imageB.on(:load) do
  puts "imageB loaded!"
end

imageA.load # might load imageB as well, we don’t know
imageB.load # but the callbacks will both fire on load

A list of all objects that may fire callbacks can be found on the API page for Hallon::Observable.

Errors

On failed libspotify API calls, a Hallon::Error will be raised with a message explaining the error. Methods that might fail in this way (e.g. Session.initialize) should have this clearly stated in its’ documentation.

For a full list of possible errors, see the official libspotify documentation on error handling.

Enumerators

Some methods (e.g. Track#artists) return a Hallon::Enumerator object. Enumerators are lazily loaded, which means that calling track.artists won’t create any artist objects until you try to retrieve one of the records out of the returned enumerator. If you want to load all artists for a track you should retrieve them all then load them in bulk.

artists = track.artists.to_a # avoid laziness, instantiate all artist objects
artists.map(&:load)

An additional note is that the size of an enumerator may change, and its contents may move as libspotify updates its information.

For the API reference and existing subclasses, see Hallon::Enumerator.

Garbage collection

Hallon makes use of Ruby’s own garbage collection to automatically release libspotify objects when they are no longer in use. There is no need to retain or release the spotify objects manually.

Audio support

Hallon supports streaming audio from Spotify via Hallon::Player. When you create the player you give it your audio driver of choice, which the player will then use for audio playback.

require 'hallon'
require 'hallon-openal'

session = Hallon::Session.initialize(IO.read('./spotify_appkey.key'))
session.login!('username', 'password')

track = Hallon::Track.new("spotify:track:1ZPsdTkzhDeHjA5c2Rnt2I")
track.load

player = Hallon::Player.new(Hallon::OpenAL)
player.play!(track)

Available drivers are:

For information on how to write your own audio driver, see Hallon::ExampleAudioDriver.

Finally, here are some important notes

Contributing to Hallon

Fork Hallon, write tests for everything you do (so I don’t break your stuff during my own development) and send a pull request. If you modify existing files, please adhere to the coding standard surrounding your code.

Hallon uses semantic versioning as of v0.0.0

As long as Hallon stays at major version 0 its API should be considered experimental. I expect it to change a lot to version v1.0.0.

Hallon is not without version policy, however. As of version v0.18.0 I aim to only increase the minor version when backwards-incompatible changes are made. Therefore, it should be safe to upgrade between minor versions, i.e. specify version constraints with the patch version as the variable version: hallon ~> v0.18.0.

Hallon only supports one session per process

You can only keep one session with Spotify alive at a time within the same process, due to a limitation of libspotify.

When forking, you need to be extra careful

If you fork, you need to instantiate the session within the process you plan to use Hallon in. You want to use Hallon in the parent? Create the session in the parent. You want to use it in the child? Create the session in the child! This is a limitation of libspotify itself.

You must not share cache directory between processes

Hallon uses tmp/hallon as both cache and settings directory by default. If you launch Hallon in multiple processes, you must make sure that cache_location is not shared between them, by changing it in the call to Session.initialize, or libspotify will lock up.

Hallon and platforms

Hallon aims to support the available platforms of the Spotify gem, which in turn depends somewhat on the platforms that libspotify support. As of current, Hallon officially supports Mac OS and Linux distributions that libspotify supports. Windows support is possible, but is yet to have been needed.

Having trouble with libspotify missing?

If so, it may be the case that your platform is not supported by the libspotify gem. Hallon’s wiki has an article on How to install libspotify for you. However, please also report an issue on the libspotify gem, I’d appreciate it, thank you!

Credits

  • Per Reimers, cracking synchronization bugs with me deep in the night (4 AM), thanks. :)
  • Jesper Särnesjö, unknowingly providing me a starting point with Greenstripes
  • Linus Oleander, originally inspiring me to write Hallon (for the radiofy.se project)
  • Emil “@mrevilme” Palm, for his patience in helping me debug Hallon deadlock issues

License

Hallon is licensed under a 2-clause (Simplified) BSD license.

Copyright 2012 Kim Burgestrand. All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

  1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

  2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY KIM BURGESTRAND ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL KIM BURGESTRAND OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.