StringBlockEditor to help plugins with owning parts of files

lib/vagrant/util/string_block_editor.rb

@@ -0,0 +1,66 @@
+module Vagrant
+  module Util
+    # This class modifies strings by creating and managing Vagrant-owned
+    # "blocks" via wrapping them in specially formed comments.
+    #
+    # This is useful when modifying a file that someone else owns and adding
+    # automatic entries into it. Example: /etc/exports or some other
+    # configuration file.
+    #
+    # Vagrant marks ownership of a block in the string by wrapping it in
+    # VAGRANT-BEGIN and VAGRANT-END comments with a unique ID. Example:
+    #
+    #     foo
+    #     # VAGRANT-BEGIN: id
+    #     some contents
+    #     created by vagrant
+    #     # VAGRANT-END: id
+    #
+    # The goal of this class is to be able to insert and remove these
+    # blocks without modifying anything else in the string.
+    #
+    # The strings usually come from files but it is up to the caller to
+    # manage the file resource.
+    class StringBlockEditor
+      # The current string value. This is the value that is modified by
+      # the methods below.
+      #
+      # @return [String]
+      attr_reader :value
+
+      def initialize(string)
+        @value = string
+      end
+
+      # This returns the keys (or ids) that are in the string.
+      #
+      # @return [<Array<String>]
+      def keys
+        regexp = /^#\s*VAGRANT-BEGIN:\s*(.+?)$(.*)^#\s*VAGRANT-END:\s(\1)$/m
+        @value.scan(regexp).map do |match|
+          match[0]
+        end
+      end
+
+      # This deletes the block with the given key if it exists.
+      def delete(key)
+        regexp = /^#\s*VAGRANT-BEGIN:\s*#{key}$.*^#\s*VAGRANT-END:\s*#{key}$\r?\n?/m
+        @value.gsub!(regexp, "")
+      end
+
+      # This inserts a block with the given key and value.
+      #
+      # @param [String] key
+      # @param [String] value
+      def insert(key, value)
+        new_block = <<BLOCK
+# VAGRANT-BEGIN: #{key}
+#{value}
+# VAGRANT-END: #{key}
+BLOCK
+
+        @value << "\n#{new_block}"
+      end
+    end
+  end
+end

test/unit/vagrant/util/string_block_editor_test.rb

@@ -0,0 +1,78 @@
+require File.expand_path("../../../base", __FILE__)
+
+require "vagrant/util/string_block_editor"
+
+describe Vagrant::Util::StringBlockEditor do
+  describe "#keys" do
+    it "should return all the keys" do
+      data = <<DATA
+# VAGRANT-BEGIN: foo
+value
+# VAGRANT-END: foo
+another
+# VAGRANT-BEGIN: bar
+content
+# VAGRANT-END: bar
+DATA
+
+      described_class.new(data).keys.should == ["foo", "bar"]
+    end
+  end
+
+  describe "#delete" do
+    it "should delete nothing if the key doesn't exist" do
+      data = "foo"
+
+      instance = described_class.new(data)
+      instance.delete("key")
+      instance.value.should == data
+    end
+
+    it "should delete the matching blocks if they exist" do
+      data = <<DATA
+# VAGRANT-BEGIN: foo
+value
+# VAGRANT-END: foo
+# VAGRANT-BEGIN: foo
+another
+# VAGRANT-END: foo
+another
+# VAGRANT-BEGIN: bar
+content
+# VAGRANT-END: bar
+DATA
+
+      new_data = <<DATA
+another
+# VAGRANT-BEGIN: bar
+content
+# VAGRANT-END: bar
+DATA
+
+      instance = described_class.new(data)
+      instance.delete("foo")
+      instance.value.should == new_data
+    end
+  end
+
+  describe "#insert" do
+    it "should insert the given key and value" do
+      data = <<DATA
+# VAGRANT-BEGIN: bar
+content
+# VAGRANT-END: bar
+DATA
+
+      new_data = <<DATA
+#{data}
+# VAGRANT-BEGIN: foo
+value
+# VAGRANT-END: foo
+DATA
+
+      instance = described_class.new(data)
+      instance.insert("foo", "value")
+      instance.value.should == new_data
+    end
+  end
+end