Refactor various components

core/src/main/java/io/xpipe/core/data/node/TupleNode.java

@@ -11,12 +11,12 @@ public abstract class TupleNode extends DataStructureNode {
         return new Builder();
     }
 
-    public static TupleNode of(List<DataStructureNode> nodes) {
+    public static TupleNode of(List<? extends DataStructureNode> nodes) {
         if (nodes == null) {
             throw new IllegalArgumentException("Nodes must be not null");
         }
 
-        return new NoKeyTupleNode(true, nodes);
+        return new NoKeyTupleNode(true, (List<DataStructureNode>) nodes);
     }
 
     public static TupleNode of(List<String> names, List<DataStructureNode> nodes) {

core/src/main/java/io/xpipe/core/source/DataSourceConnection.java

@@ -3,6 +3,4 @@ package io.xpipe.core.source;
 public interface DataSourceConnection extends AutoCloseable {
 
     void init() throws Exception;
-
-    void close() throws Exception;
 }

core/src/main/java/io/xpipe/core/source/TableDataReadConnection.java

@@ -10,9 +10,9 @@ import java.io.OutputStream;
 
 public interface TableDataReadConnection extends DataSourceConnection {
 
-    TupleType determineDataType() throws Exception;
+    TupleType getDataType() throws Exception;
 
-    int determineRowCount() throws Exception;
+    int getRowCount() throws Exception;
 
     void withLines(DataStructureNodeAcceptor<TupleNode> lineAcceptor) throws Exception;
 

core/src/main/java/io/xpipe/core/source/TableDataSourceDescriptor.java

@@ -4,9 +4,21 @@ import io.xpipe.core.store.DataStore;
 
 public abstract class TableDataSourceDescriptor<DS extends DataStore> implements DataSourceDescriptor<DS> {
 
-    public abstract TableDataWriteConnection newWriteConnection(DS store);
+    public final TableDataReadConnection openReadConnection(DS store) throws Exception {
+        var con = newReadConnection(store);
+        con.init();
+        return con;
+    }
 
-    public abstract TableDataReadConnection newReadConnection(DS store);
+    public final TableDataWriteConnection openWriteConnection(DS store) throws Exception {
+        var con = newWriteConnection(store);
+        con.init();
+        return con;
+    }
+
+    protected abstract TableDataWriteConnection newWriteConnection(DS store);
+
+    protected abstract TableDataReadConnection newReadConnection(DS store);
 
     @Override
     public DataSourceType getType() {

core/src/main/java/io/xpipe/core/store/InputStreamDataStore.java

@@ -1,11 +1,14 @@
 package io.xpipe.core.store;
 
+import java.io.BufferedInputStream;
 import java.io.InputStream;
 import java.io.OutputStream;
 
-public abstract class InputStreamDataStore implements StreamDataStore {
+public class InputStreamDataStore implements StreamDataStore {
 
     private final InputStream in;
+    private BufferedInputStream bufferedInputStream;
+    private boolean opened = false;
 
     public InputStreamDataStore(InputStream in) {
         this.in = in;
@@ -13,11 +16,17 @@ public abstract class InputStreamDataStore implements StreamDataStore {
 
     @Override
     public InputStream openInput() throws Exception {
-        return in;
+        if (opened) {
+            return bufferedInputStream;
+        }
+
+        opened = true;
+        bufferedInputStream = new BufferedInputStream(in);
+        return bufferedInputStream;
     }
 
     @Override
     public OutputStream openOutput() throws Exception {
-        throw new UnsupportedOperationException();
+        throw new UnsupportedOperationException("No output available");
     }
 }

core/src/main/java/io/xpipe/core/store/LocalFileDataStore.java

@@ -5,6 +5,7 @@ import com.fasterxml.jackson.annotation.JsonIgnore;
 import com.fasterxml.jackson.annotation.JsonTypeName;
 import org.apache.commons.io.FilenameUtils;
 
+import java.io.BufferedInputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
@@ -65,7 +66,7 @@ public class LocalFileDataStore extends FileDataStore {
 
     @Override
     public InputStream openInput() throws Exception {
-        return Files.newInputStream(file);
+        return new BufferedInputStream(Files.newInputStream(file));
     }
 
     @Override