Add DOTENV_LINEBREAK_MODE=legacy to preserve newline expansion

lib/dotenv/parser.rb

@@ -80,7 +80,11 @@ def unescape_characters(value)
     end
 
     def expand_newlines(value)
-      value.gsub('\n', "\\\\\\n").gsub('\r', "\r")
+      if (@hash["DOTENV_LINEBREAK_MODE"] || ENV["DOTENV_LINEBREAK_MODE"]) == "legacy"
+        value.gsub('\n', "\n").gsub('\r', "\r")
+      else
+        value.gsub('\n', "\\\\\\n").gsub('\r', "\\\\\\r")
+      end
     end
 
     def variable_not_set?(line)

spec/dotenv/parser_spec.rb

@@ -120,8 +120,25 @@ def env(string)
     end.to raise_error(Dotenv::FormatError, 'Line "export OH_NO_NOT_SET" has an unset variable')
   end
 
-  it "expands newlines in quoted strings" do
+  it 'escapes \n in quoted strings' do
     expect(env('FOO="bar\nbaz"')).to eql("FOO" => "bar\\nbaz")
+    expect(env('FOO="bar\\nbaz"')).to eql("FOO" => "bar\\nbaz")
+  end
+
+  it 'expands \n and \r in quoted strings with DOTENV_LINEBREAK_MODE=legacy in current file' do
+    ENV["DOTENV_LINEBREAK_MODE"] = "strict"
+
+    contents = [
+      'DOTENV_LINEBREAK_MODE=legacy',
+      'FOO="bar\nbaz\rfizz"'
+    ].join("\n")
+    expect(env(contents)).to eql("DOTENV_LINEBREAK_MODE" => "legacy", "FOO" => "bar\nbaz\rfizz")
+  end
+
+  it 'expands \n and \r in quoted strings with DOTENV_LINEBREAK_MODE=legacy in ENV' do
+    ENV['DOTENV_LINEBREAK_MODE'] = 'legacy'
+    contents = 'FOO="bar\nbaz\rfizz"'
+    expect(env(contents)).to eql("FOO" => "bar\nbaz\rfizz")
   end
 
   it 'parses variables with "." in the name' do
@@ -259,8 +276,8 @@ def env(string)
       expect(env("FOO=bar\r\nbaz=fbb")).to eql("FOO" => "bar", "baz" => "fbb")
     end
 
-    it "expands carriage return in quoted strings" do
-      expect(env('FOO="bar\rbaz"')).to eql("FOO" => "bar\rbaz")
+    it "escapes carriage return in quoted strings" do
+      expect(env('FOO="bar\rbaz"')).to eql("FOO" => "bar\\rbaz")
     end
 
     it "escape $ properly when no alphabets/numbers/_  are followed by it" do