Expose NBT hashes of items to users

This just uses the same approach as Plethora, so we should have aparity
for .list() now.

src/main/java/dan200/computercraft/shared/peripheral/generic/data/ItemData.java

@@ -7,6 +7,8 @@
 package dan200.computercraft.shared.peripheral.generic.data;
 
 import com.google.gson.JsonParseException;
+import dan200.computercraft.ComputerCraft;
+import dan200.computercraft.shared.util.NBTUtil;
 import net.minecraft.enchantment.Enchantment;
 import net.minecraft.enchantment.EnchantmentHelper;
 import net.minecraft.item.EnchantedBookItem;
@@ -22,13 +24,29 @@ import javax.annotation.Nullable;
 import java.util.*;
 import java.util.stream.Collectors;
 
+/**
+ * Data providers for items.
+ *
+ * We guard using {@link ComputerCraft#genericPeripheral} in several places, as advanced functionality should not be
+ * exposed for {@code turtle.getItemDetail} when generic peripehrals are disabled.
+ */
 public class ItemData
 {
     @Nonnull
-    public static <T extends Map<? super String, Object>> T fillBasic( @Nonnull T data, @Nonnull ItemStack stack )
+    public static <T extends Map<? super String, Object>> T fillBasicSafe( @Nonnull T data, @Nonnull ItemStack stack )
     {
         data.put( "name", DataHelpers.getId( stack.getItem() ) );
         data.put( "count", stack.getCount() );
+
+        return data;
+    }
+
+    @Nonnull
+    public static <T extends Map<? super String, Object>> T fillBasic( @Nonnull T data, @Nonnull ItemStack stack )
+    {
+        fillBasicSafe( data, stack );
+        String hash = NBTUtil.getNBTHash( stack.getTag() );
+        if( hash != null ) data.put( "nbt", hash );
         return data;
     }
 
@@ -55,6 +73,8 @@ public class ItemData
 
         data.put( "tags", DataHelpers.getTags( stack.getItem().getTags() ) );
 
+        if( !ComputerCraft.genericPeripheral ) return data;
+
         CompoundNBT tag = stack.getTag();
         if( tag != null && tag.contains( "display", Constants.NBT.TAG_COMPOUND ) )
         {

src/main/java/dan200/computercraft/shared/turtle/apis/TurtleAPI.java

@@ -605,7 +605,7 @@ public class TurtleAPI implements ILuaAPI
 
         Map<String, Object> table = detailed
             ? ItemData.fill( new HashMap<>(), stack )
-            : ItemData.fillBasic( new HashMap<>(), stack );
+            : ItemData.fillBasicSafe( new HashMap<>(), stack );
 
         TurtleActionEvent event = new TurtleInspectItemEvent( turtle, stack, table, detailed );
         if( MinecraftForge.EVENT_BUS.post( event ) ) return new Object[] { false, event.getFailureMessage() };

src/main/java/dan200/computercraft/shared/util/NBTUtil.java

@@ -5,9 +5,19 @@
  */
 package dan200.computercraft.shared.util;
 
+import dan200.computercraft.ComputerCraft;
 import net.minecraft.nbt.*;
 import net.minecraftforge.common.util.Constants;
+import org.apache.commons.codec.binary.Hex;
 
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+import java.io.DataOutput;
+import java.io.DataOutputStream;
+import java.io.IOException;
+import java.io.OutputStream;
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
 import java.util.HashMap;
 import java.util.Map;
 
@@ -159,4 +169,46 @@ public final class NBTUtil
         }
         return objects;
     }
+
+    @Nullable
+    public static String getNBTHash( @Nullable CompoundNBT tag )
+    {
+        if( tag == null ) return null;
+
+        try
+        {
+            MessageDigest digest = MessageDigest.getInstance( "MD5" );
+            DataOutput output = new DataOutputStream( new DigestOutputStream( digest ) );
+            CompressedStreamTools.write( tag, output );
+            byte[] hash = digest.digest();
+            return new String( Hex.encodeHex( hash ) );
+        }
+        catch( NoSuchAlgorithmException | IOException e )
+        {
+            ComputerCraft.log.error( "Cannot hash NBT", e );
+            return null;
+        }
+    }
+
+    private static class DigestOutputStream extends OutputStream
+    {
+        private final MessageDigest digest;
+
+        private DigestOutputStream( MessageDigest digest )
+        {
+            this.digest = digest;
+        }
+
+        @Override
+        public void write( @Nonnull byte[] b, int off, int len )
+        {
+            digest.update( b, off, len );
+        }
+
+        @Override
+        public void write( int b )
+        {
+            digest.update( (byte) b );
+        }
+    }
 }