This actually does work if you don't try to load encrypted archives. Begin work to allow saving/loading in memory for tests. woo.

src/main/java/net/runelite/cache/fs/Index.java

@@ -36,6 +36,11 @@ public class Index implements Closeable
 	//	throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.
 	}
 
+	public IndexFile getIndex()
+	{
+		return index;
+	}
+	
 	public void load() throws IOException
 	{	
 		// read data from index255
@@ -243,7 +248,7 @@ public class Index implements Closeable
 			assert this.index.getIndexFileId() == this.id;
 			byte[] b = store.getData().read(this.id, entry.getId(), entry.getSector(), entry.getLength()); // needs decompress etc...
 			
-			if (b == null) continue;
+			//if (b == null) continue;
 			
 			InputStream stream = new InputStream(b);
 
@@ -273,11 +278,11 @@ public class Index implements Closeable
 				default:
 				{
 					int length = stream.readInt();
-					if(length > 0 && length <= 1000000000) {
+//					if(length > 0 && length <= 1000000000) {
 						data = new byte[length];
 						this.checkRevision(stream, compressedLength);
 						GZipDecompressor.decompress(stream, data);
-					} else continue;//data = null;
+//					} else continue;//data = null;
 				}
 			}
 			

src/main/java/net/runelite/cache/fs/Store.java

@@ -12,13 +12,15 @@ public class Store implements Closeable
 	private static final String MAIN_FILE_CACHE_DAT = "main_file_cache.dat2";
 	private static final String MAIN_FILE_CACHE_IDX = "main_file_cache.idx";
 	
+	private final File folder;
 	private final DataFile data;
 	private final IndexFile index255;
 	private final List<Index> indexes = new ArrayList<>();
-	//private final List<IndexFile> indexFiles = new ArrayList<>();
 	
 	public Store(File folder) throws IOException
 	{
+		this.folder = folder;
+		
 		data = new DataFile(this, new File(folder, MAIN_FILE_CACHE_DAT));
 		index255 = new IndexFile(this, 255, new File(folder, MAIN_FILE_CACHE_IDX + "255"));
 		
@@ -29,7 +31,6 @@ public class Store implements Closeable
 			
 			indexes.add(index);
 		}
-			//indexFiles.add(new IndexFile(this, i, new File(folder, MAIN_FILE_CACHE_IDX + i)));
 	}
 
 	@Override
@@ -42,10 +43,26 @@ public class Store implements Closeable
 			i.close();
 	}
 	
+	public void addIndex(int id) throws FileNotFoundException
+	{
+		for (Index i : indexes)
+			if (i.getIndex().getIndexFileId() == id)
+				throw new IllegalArgumentException("index " + id + " already exists");
+		
+		IndexFile indexFile = new IndexFile(this, id, new File(folder, MAIN_FILE_CACHE_IDX + id));
+		Index index = new Index(this, indexFile, id);
+		
+		this.indexes.add(index);
+	}
+	
 	public void load() throws IOException
 	{
 		for (Index i : indexes)
-			i.load();
+		{
+			int id = i.getIndex().getIndexFileId();
+			if (id == 3 || id == 7) // XXXXXXXXXXXXX
+				i.load();
+		}
 	}
 
 	public DataFile getData()

src/test/java/net/runelite/cache/fs/DataFileTest.java

@@ -4,6 +4,7 @@ import java.io.File;
 import java.io.IOException;
 import java.nio.ByteBuffer;
 import org.junit.Assert;
+import org.junit.BeforeClass;
 import org.junit.Rule;
 import org.junit.Test;
 import org.junit.rules.TemporaryFolder;
@@ -13,6 +14,12 @@ public class DataFileTest
 	@Rule
 	public TemporaryFolder folder = new TemporaryFolder();
 	
+	@BeforeClass
+	public static void before()
+	{
+		System.setProperty("java.io.tmpdir", "d:/temp");
+	}
+  
 	@Test
 	public void test1() throws IOException
 	{

src/test/java/net/runelite/cache/fs/IndexFileTest.java

@@ -3,6 +3,7 @@ package net.runelite.cache.fs;
 import java.io.File;
 import java.io.IOException;
 import org.junit.Assert;
+import org.junit.BeforeClass;
 import org.junit.Rule;
 import org.junit.Test;
 import org.junit.rules.TemporaryFolder;
@@ -12,6 +13,12 @@ public class IndexFileTest
 	@Rule
 	public TemporaryFolder folder = new TemporaryFolder();
 	
+	@BeforeClass
+	public static void before()
+	{
+		System.setProperty("java.io.tmpdir", "d:/temp");
+	}
+	
 	@Test
 	public void test1() throws IOException
 	{

src/test/java/net/runelite/cache/fs/StoreLoadTest.java

@@ -8,7 +8,8 @@ public class StoreLoadTest
 	@Test
 	public void test() throws IOException
 	{
-		Store store = new Store(new java.io.File("c:/rs/cache"));
+		Store store = new Store(new java.io.File("d:/rs/07/cache"));//c:/rs/cache"));
 		store.load();
+		System.out.println(store);
 	}
 }

src/test/java/net/runelite/cache/fs/StoreTest.java

@@ -0,0 +1,25 @@
+package net.runelite.cache.fs;
+
+import java.io.IOException;
+import org.junit.BeforeClass;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.TemporaryFolder;
+
+public class StoreTest
+{
+	@Rule
+	public TemporaryFolder folder = new TemporaryFolder();
+	
+	@BeforeClass
+	public static void before()
+	{
+		System.setProperty("java.io.tmpdir", "d:/temp");
+	}
+	
+	@Test
+	public void testCreate() throws IOException
+	{
+		Store store = new Store(folder.getRoot());
+	}
+}