Initial implementation of the hook feature

The current implementation is modular and allows users to define hooks
in several ways:
  * Use one of the built-in hook types (currently only 'exec')
  * Define their own Hook classes inside ~/.config/oxidized/hook

Exec hook type runs a user defined command with or without shell. It
populates a bunch of environment variables with metadata. The command
can either be run as synchronous or asynchronous. The default is
synchronous.

1 files changed, 88 insertions, 0 deletions

diff --git a/lib/oxidized/hook.rb b/lib/oxidized/hook.rb
new file mode 100644
index 0000000..2763c4f
--- /dev/null
+++ b/lib/oxidized/hook.rb
@@ -0,0 +1,88 @@
+module Oxidized
+class HookManager
+  class << self
+    def from_config cfg
+      mgr = new
+      cfg.hooks.each do |name,h_cfg|
+        h_cfg.events.each do |event|
+          mgr.register event.to_sym, name, h_cfg.type, h_cfg
+        end
+      end
+      mgr
+    end
+  end
+
+  # HookContext is passed to each hook. It can contain anything related to the
+  # event in question. At least it contains the event name
+  class HookContext < OpenStruct; end
+
+  # RegisteredHook is a container for a Hook instance
+  class RegisteredHook < Struct.new(:name, :hook); end
+
+  Events = [ 
+    :node_success,
+    :node_fail,
+    :post_store,
+  ]
+  attr_reader :registered_hooks
+
+  def initialize
+    @registered_hooks = Hash.new {|h,k| h[k] = []}
+  end
+
+  def register event, name, hook_type, cfg
+    unless Events.include? event
+      raise ArgumentError,
+        "unknown event #{event}, available: #{Events.join ','}"
+    end
+
+    Oxidized.mgr.add_hook hook_type
+    begin
+      hook = Oxidized.mgr.hook.fetch(hook_type).new
+    rescue KeyError
+      raise KeyError, "cannot find hook #{hook_type.inspect}"
+    end
+
+    hook.cfg = cfg
+
+    @registered_hooks[event] << RegisteredHook.new(name, hook)
+    Log.debug "Hook #{name.inspect} registered #{hook.class} for event #{event.inspect}"
+  end
+
+  def handle event, **ctx_params
+    ctx = HookContext.new ctx_params
+    ctx.event = event
+
+    @registered_hooks[event].each do |r_hook|
+      begin
+        r_hook.hook.run_hook ctx
+      rescue => e
+        Log.error "Hook #{r_hook.name} (#{r_hook.hook}) failed " +
+                  "(#{e.inspect}) for event #{event.inspect}"
+      end
+    end
+  end
+end
+
+# Hook abstract base class
+class Hook
+  attr_accessor :cfg
+
+  def initialize
+  end
+
+  def cfg=(cfg)
+    @cfg = cfg
+    validate_cfg! if self.respond_to? :validate_cfg!
+  end
+
+  def run_hook ctx
+    raise NotImplementedError
+  end
+
+  def log(msg, level=:info)
+    Log.send(level, "#{self.class.name}: #{msg}")
+  end
+
+end
+end