Add test to validate we can survive giving the fountain sink the wron…

…g data

... since we're using that as the detection mechanism for auto-detect.

Also, a simplification to Decoder::do_decode()

src/lib/encoder/Decoder.h

@@ -80,7 +80,6 @@ inline unsigned Decoder::do_decode(CimbReader& reader, STREAM& ostream, bool leg
  colorPositions.resize(reader.num_reads()); // the number of cells == reader.num_reads(). Can we calculate this from config at compile time? Do we care?
 
  unsigned bitsPerSymbol = cimbar::Config::symbol_bits();
- unsigned bytesDecoded = 0;
  {
  bitbuffer symbolBits(cimbar::Config::capacity(bitsPerSymbol));
  // read symbols first
@@ -116,8 +115,8 @@ inline unsigned Decoder::do_decode(CimbReader& reader, STREAM& ostream, bool leg
  }
 
  reed_solomon_stream rss(ostream, _eccBytes, _eccBlockSize);
- bytesDecoded += colorBits.flush(rss); // will return the pos after this flush(), which includes the previous flush()...
- return bytesDecoded;
+ // flush() will return the (good) cumulative bytes written to the underlying stream
+ return colorBits.flush(rss);
 }
 
 template <typename STREAM>

src/lib/encoder/test/EncoderRoundTripTest.cpp

@@ -46,6 +46,42 @@ TEST_CASE( "EncoderRoundTripTest/testFountain.Pad", "[unit]" )
 
  std::string decodedContents = File(tempdir.path() / "0.626").read_all();
  assertEquals( "hello", decodedContents );
+
+ assertEquals( 1, fds.num_done() );
+}
+
+TEST_CASE( "EncoderRoundTripTest/testFountain.SinkMismatch", "[unit]" )
+{
+ MakeTempDirectory tempdir;
+
+ std::string inputFile = tempdir.path() / "hello.txt";
+ std::string outPrefix = tempdir.path() / "encoder.fountain";
+
+ {
+ std::ofstream f(inputFile);
+ f << "hello"; // 5 bytes!
+ }
+
+ // will be padded so the fountain encoding is happy. The encoded image looks suspiciously non-random!
+ Encoder enc(30, 4, 2);
+ assertEquals( 1, enc.encode_fountain(inputFile, outPrefix) );
+
+ uint64_t hash = 0xeecc8800efce8c48;
+ std::string path = fmt::format("{}_0.png", outPrefix);
+ cv::Mat encodedImg = cv::imread(path);
+ cv::cvtColor(encodedImg, encodedImg, cv::COLOR_BGR2RGB);
+ assertEquals( hash, image_hash::average_hash(encodedImg) );
+
+ // decoder
+ Decoder dec(30);
+ // sink with a mismatched fountain_chunk_size
+ // importantly, the sink expects a *larger* chunk than we'll give it...
+ fountain_decoder_sink<cimbar::zstd_decompressor<std::ofstream>> fds(tempdir.path(), cimbar::Config::fountain_chunk_size(30, 6, true));
+
+ unsigned bytesDecoded = dec.decode_fountain(encodedImg, fds, 1);
+ assertEquals( 7500, bytesDecoded );
+
+ assertEquals( 0, fds.num_done() );
 }
 
 TEST_CASE( "EncoderRoundTripTest/testStreaming", "[unit]" )