From 942d213191918ed0bc7aa5a6b62a1f0bc8d96bbb Mon Sep 17 00:00:00 2001
From: Mitchell Hashimoto <mitchell.hashimoto@gmail.com>
Date: Wed, 8 Dec 2010 11:03:49 -0800
Subject: [PATCH] Raise a unique exception if libvirt C library not available.

---
 CHANGELOG.md                 |  3 ++-
 Gemfile.lock                 |  2 +-
 lib/ffi/libvirt.rb           | 13 +++++++++++--
 lib/ffi/libvirt/exception.rb | 10 ++++++++++
 4 files changed, 24 insertions(+), 4 deletions(-)
 create mode 100644 lib/ffi/libvirt/exception.rb

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5117e51..ab4f934 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,7 @@
 ## 0.2.1 (unreleased)
 
-
+  - `FFI::Libvirt::MissingLibError` is raised if libvirt C library
+    is not available.
 
 ## 0.2.0 (December 7, 2010)
 
diff --git a/Gemfile.lock b/Gemfile.lock
index f7fe370..41ba4a9 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -1,7 +1,7 @@
 PATH
   remote: .
   specs:
-    libvirt (0.2.0)
+    libvirt (0.2.1.dev)
       ffi (~> 0.6.3)
       nokogiri (~> 1.4.3)
 
diff --git a/lib/ffi/libvirt.rb b/lib/ffi/libvirt.rb
index 25848f2..16f1fa3 100644
--- a/lib/ffi/libvirt.rb
+++ b/lib/ffi/libvirt.rb
@@ -7,10 +7,19 @@ module FFI
   # that it is up to you to manage all the pointers and so on that come
   # with this power.
   module Libvirt
+    autoload :MissingLibError, 'ffi/libvirt/exception'
+    autoload :Util, 'ffi/libvirt/util'
+
     extend FFI::Library
-    ffi_lib "libvirt"
 
-    autoload :Util, 'ffi/libvirt/util'
+    # Attempt to load the libvirt lib and raise a more specific exception
+    # if it doesn't exist. (Normally a LoadError, which is ambiguous, is
+    # raised)
+    begin
+      ffi_lib "libvirt"
+    rescue LoadError
+      raise MissingLibError
+    end
   end
 end
 
diff --git a/lib/ffi/libvirt/exception.rb b/lib/ffi/libvirt/exception.rb
new file mode 100644
index 0000000..a57b7b4
--- /dev/null
+++ b/lib/ffi/libvirt/exception.rb
@@ -0,0 +1,10 @@
+module FFI
+  module Libvirt
+    # Error raised when the libvirt C library is missing.
+    class MissingLibError < StandardError
+      def initialize
+        super("The libvirt C library could not be loaded. Is it properly installed?")
+      end
+    end
+  end
+end