(MovieCart) Limit reading of image data to single frame

when its likely an MVC file. This avoids reading of GB of data.

src/emucore/CartDetector.cxx

@@ -19,6 +19,7 @@
 #include "Logger.hxx"
 
 #include "CartDetector.hxx"
+#include "MovieCart/StreamReader.hxx"
 
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 Bankswitch::Type CartDetector::autodetectType(const ByteBuffer& image, size_t size)
@@ -694,11 +695,34 @@ bool CartDetector::isProbablyMDM(const ByteBuffer& image, size_t size)
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 bool CartDetector::isProbablyMVC(const ByteBuffer& image, size_t size)
 {
-  // MVC version 0, frame 0
+  // MVC version 0
   uInt8 sig[] = { 'M', 'V', 'C', 0 };
-  return searchForBytes(image, std::min<size_t>(size, 5), sig, 4);
+  int	sigSize = sizeof(sig);
+  return searchForBytes(image, std::min<size_t>(size, sigSize+1), sig, sigSize);
 }
 
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+size_t CartDetector::isProbablyMVC(std::istream &in, size_t maxSize)
+{
+  const size_t	frameSize = 2 * MVC_FIELD_PAD_SIZE;
+  bool			found = false;
+
+  // Returns size of field if stream is probably an MVC movie cartridge
+  
+  if (maxSize >= frameSize)
+  {
+	auto	pos = in.tellg();
+
+	ByteBuffer	image = make_unique<uInt8[]>(frameSize);
+	in.read(reinterpret_cast<char*>(image.get()), frameSize);
+
+	in.seekg(pos);
+
+	found = isProbablyMVC(image, frameSize);
+  }
+
+  return found ? frameSize : 0;
+}
 
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 bool CartDetector::isProbablySB(const ByteBuffer& image, size_t size)

src/emucore/CartDetector.hxx

@@ -40,6 +40,13 @@ class CartDetector
     */
     static Bankswitch::Type autodetectType(const ByteBuffer& image, size_t size);
 
+
+    /**
+	  MVC cartridges are of arbitary large length
+      Returns size of frame if stream is probably an MVC movie cartridge
+    */
+    static size_t isProbablyMVC(std::istream &in, size_t size);
+
   private:
     /**
       Search the image for the specified byte signature

src/emucore/FSNode.cxx

@@ -17,6 +17,7 @@
 
 #include "FSNodeFactory.hxx"
 #include "FSNode.hxx"
+#include "CartDetector.hxx"
 
 // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 FilesystemNode::FilesystemNode(const AbstractFSNodePtr& realNode)
@@ -355,6 +356,12 @@ size_t FilesystemNode::read(ByteBuffer& buffer) const
     if (sizeRead == 0)
       throw runtime_error("Zero-byte file");
 
+	// In the case of MVC (MovieCart) files, contents are streaming data
+	// of arbitrary length, so just read first frame.
+	size_t subSize = CartDetector::isProbablyMVC(in, sizeRead);
+	if (subSize > 0)
+		sizeRead = subSize;
+
     buffer = make_unique<uInt8[]>(sizeRead);
     in.read(reinterpret_cast<char*>(buffer.get()), sizeRead);
   }