Replace characters undefined in target encoding with empty strings

lib/savon/builder.rb

@@ -34,15 +34,14 @@ def pretty
 
     def to_s
       return @locals[:xml] if @locals.include? :xml
-
-
+
       string = tag(builder, :Envelope, namespaces_with_globals) do |xml|
         tag(xml, :Header) { xml << header.to_s } unless header.empty?
         tag(xml, :Body)   { xml.tag!(*namespaced_message_tag) { xml << message.to_s } }
       end
-      
+
       if @globals[:encoding] && @globals[:encode_message]
-        string.encode!(@globals[:encoding])
+        string.encode!(@globals[:encoding], undef: :replace, replace:'')
       end
       string
     end

spec/savon/builder_spec.rb

@@ -90,7 +90,15 @@
       expect(builder.to_s.encoding.name).to eq "ISO-8859-1"
       expect(builder.to_s).to include("<username>lüke</username>".encode("ISO-8859-1"))
     end
-
+
+    it "ignores characters not found in the target encoding" do
+      globals[:encoding] = "ISO-8859-1"
+      globals[:encode_message] = true
+      locals[:message] = { :username => "lüke\u2122", :password => "secret" }
+      expect(builder.to_s.encoding.name).to eq "ISO-8859-1"
+      expect(builder.to_s).to include("<username>lüke</username>".encode("ISO-8859-1"))
+    end
+
     context "with encode_message unset" do
       before :each do
         globals[:encoding] = "ISO-8859-1"