fix decoding of 7bit messages with extra padding on UDH

Gemfile.lock

@@ -1,16 +1,15 @@
 GEM
   remote: https://rubygems.org/
   specs:
-    activesupport (4.2.2)
+    activesupport (5.1.5)
+      concurrent-ruby (~> 1.0, >= 1.0.2)
       i18n (~> 0.7)
-      json (~> 1.7, >= 1.7.7)
       minitest (~> 5.1)
-      thread_safe (~> 0.3, >= 0.3.4)
       tzinfo (~> 1.1)
     coderay (1.1.0)
+    concurrent-ruby (1.1.7)
     diff-lcs (1.2.5)
     i18n (0.7.0)
-    json (1.8.3)
     method_source (0.8.2)
     minitest (5.7.0)
     phone (1.2.3)

lib/pdu_tools/decoder.rb

@@ -171,6 +171,13 @@ def parse_user_data data_length
         @udh_length = take(2, :integer) * 2
         udh = take(@udh_length)
         @user_data_header = parse_user_data_header udh
+
+        if (@data_coding_scheme[:alphabet] === :a7bit)
+          udh_bit_length = ((@udh_length/2) + 1) * 8
+          next_septet_start =  ( udh_bit_length.to_f / 7 ).ceil * 7
+          offset = next_septet_start > udh_bit_length ? next_septet_start - udh_bit_length : 0
+          @offset_7bit = offset if offset > 1
+        end
       end
       case @data_coding_scheme[:alphabet]
       when :a7bit

lib/pdu_tools/helpers.rb

@@ -84,6 +84,12 @@ def decode7bit textdata, length = nil, offset = 1
       next_septet = ""
       last_char = ""
 
+      if offset > 1 && bytes.length
+        cur_septet = bytes.shift
+        cur_septet = cur_septet.slice( 0, cur_septet.length - offset )
+        offset = cur_septet.length + 1
+      end
+
       bytes.each_with_index do |byte, index|
         to_take = ([0,1].include? offset) ? 7 : 8-offset
         cur_septet.prepend byte[offset, to_take]

spec/decoder_spec.rb

@@ -31,6 +31,19 @@
       expect(message_part.user_data_header[:multipart]).to be_present
       expect(message_part.user_data_header[:multipart][:parts]).to eq 2
       expect(message_part.user_data_header[:multipart][:part_number]).to eq 1
+      expect(message_part.body).to eq 'This is a test messageThis is a test messageThis is a test messageThis is a test messageThis is a test messageThis is a test messageThis is a test messa'
+    end
+
+    context "with extra padding" do
+      let(:pdu) { "07912933035011804409D055F3DB5D060000411120712071022A080701030003990202A09976D7E9E5390B640FB3D364103DCD668364B3562CD692C1623417" }
+      it "should decode" do
+        message_part = decoder.decode
+        expect(message_part.user_data_header).to be_present
+        expect(message_part.user_data_header[:multipart]).to be_present
+        expect(message_part.user_data_header[:multipart][:parts]).to eq 2
+        expect(message_part.user_data_header[:multipart][:part_number]).to eq 2
+        expect(message_part.body).to eq 'Minutes, valid till 23-11-2014.'
+      end
     end
   end