Freeze all string values coming out of Ohai.

This both helps avoid weird mutation bugs and saves a bit of RAM.

Refs https://github.com/chef/chef/issues/4930

Signed-off-by: Noah Kantrowitz <noah@coderanger.net>

2 files changed, 27 insertions, 0 deletions

diff --git a/lib/ohai/system.rb b/lib/ohai/system.rb
index e66ba90b..d2a8243a 100644
--- a/lib/ohai/system.rb
+++ b/lib/ohai/system.rb
@@ -107,6 +107,9 @@ module Ohai
         Ohai::Log.error("Encountered error while running plugins: #{e.inspect}")
         raise
       end
+
+      # Freeze all strings.
+      freeze_strings!
     end
 
     def have_v6_plugin?(name)
@@ -231,5 +234,25 @@ module Ohai
         Ohai::Log.level = Ohai.config[:log_level]
       end
     end
+
+    # Freeze all string values in @data. This makes them immutable and saves
+    # a bit of RAM.
+    #
+    # @api private
+    # @return [void]
+    def freeze_strings!
+      # Recursive visitor pattern helper.
+      visitor = lambda do |val|
+        case val
+        when Hash
+          val.each_value {|v| visitor.call(v) }
+        when Array
+          val.each {|v| visitor.call(v) }
+        when String
+          val.freeze
+        end
+      end
+      visitor.call(@data)
+    end
   end
 end
diff --git a/spec/unit/system_spec.rb b/spec/unit/system_spec.rb
index 3bfafcf1..0941b1f0 100644
--- a/spec/unit/system_spec.rb
+++ b/spec/unit/system_spec.rb
@@ -166,6 +166,8 @@ EOF
         ohai.all_plugins
         expect(ohai.data[:zoo]).to eq("animals")
         expect(ohai.data[:park]).to eq("plants")
+        expect(ohai.data[:zoo]).to be_frozen
+        expect(ohai.data[:park]).to be_frozen
       end
 
       describe "when using :disabled_plugins" do
@@ -312,6 +314,8 @@ EOF
         ohai.all_plugins
         expect(ohai.data[:zoo]).to eq("animals")
         expect(ohai.data[:park]).to eq("plants")
+        expect(ohai.data[:zoo]).to be_frozen
+        expect(ohai.data[:park]).to be_frozen
       end
 
       it "should write an error to Ohai::Log" do