Handle unknown b-value encoding

by treating it as ascii as well as ignoring any invalid chars

Author: kjg

lib/mail/version_specific/ruby_1_8.rb

@@ -56,7 +56,18 @@ def Ruby18.get_constant(klass, string)
     end
 
     def Ruby18.transcode_charset(str, from_encoding, to_encoding = 'UTF-8')
-      Iconv.conv("#{normalize_iconv_charset_encoding(to_encoding)}//IGNORE", normalize_iconv_charset_encoding(from_encoding), str)
+      retried = false
+      begin
+        Iconv.conv("#{normalize_iconv_charset_encoding(to_encoding)}//IGNORE", normalize_iconv_charset_encoding(from_encoding), str)
+      rescue Iconv::InvalidEncoding
+        if retried
+          raise
+        else
+          from_encoding = 'ASCII'
+          retried = true
+          retry
+        end
+      end
     end
 
     def Ruby18.b_value_encode(str, encoding)

lib/mail/version_specific/ruby_1_9.rb

@@ -90,7 +90,7 @@ def Ruby19.b_value_decode(str)
         str = Ruby19.decode_base64(match[2])
         str = charset_encoder.encode(str, charset)
       end
-      decoded = str.encode(Encoding::UTF_8, :invalid => :replace, :replace => "")
+      decoded = str.encode(Encoding::UTF_8, :undef => :replace, :invalid => :replace, :replace => "")
       decoded.valid_encoding? ? decoded : decoded.encode(Encoding::UTF_16LE, :invalid => :replace, :replace => "").encode(Encoding::UTF_8)
     rescue Encoding::UndefinedConversionError, ArgumentError, Encoding::ConverterNotFoundError
       warn "Encoding conversion failed #{$!}"

spec/mail/encoding_spec.rb

@@ -196,6 +196,12 @@
     end
   end
 
+  it "should skip characters of unknown and invalid encoding" do
+    m = Mail.new
+    m['Subject'] = Mail::SubjectField.new("Hello=?UNKNOWN?B?4g==?=")
+    expect(m.subject).to eq "Hello"
+  end
+
   if RUBY_VERSION > '1.9'
     describe "#pick_encoding" do
       it "picks binary for nil" do