Revert "Jonmv/reapply leaner token buffer"

7 files changed, 131 insertions, 230 deletions

diff --git a/document/src/main/java/com/yahoo/document/json/JsonReader.java b/document/src/main/java/com/yahoo/document/json/JsonReader.java
index b6cf8c6e18b..3e1743b8d45 100644
--- a/document/src/main/java/com/yahoo/document/json/JsonReader.java
+++ b/document/src/main/java/com/yahoo/document/json/JsonReader.java
@@ -6,10 +6,8 @@ import com.fasterxml.jackson.core.JsonParser;
 import com.fasterxml.jackson.core.JsonToken;
 import com.yahoo.document.DocumentId;
 import com.yahoo.document.DocumentOperation;
-import com.yahoo.document.DocumentPut;
 import com.yahoo.document.DocumentType;
 import com.yahoo.document.DocumentTypeManager;
-import com.yahoo.document.DocumentUpdate;
 import com.yahoo.document.TestAndSetCondition;
 import com.yahoo.document.json.document.DocumentParser;
 import com.yahoo.document.json.readers.DocumentParseInfo;
@@ -20,9 +18,6 @@ import java.io.InputStream;
 import java.util.Optional;
 
 import static com.yahoo.document.json.JsonReader.ReaderState.END_OF_FEED;
-import static com.yahoo.document.json.document.DocumentParser.CONDITION;
-import static com.yahoo.document.json.document.DocumentParser.CREATE_IF_NON_EXISTENT;
-import static com.yahoo.document.json.document.DocumentParser.FIELDS;
 import static com.yahoo.document.json.readers.JsonParserHelpers.expectArrayStart;
 
 /**
@@ -65,7 +60,7 @@ public class JsonReader {
      * @param docIdString document ID
      * @return the parsed document operation
      */
-    ParsedDocumentOperation readSingleDocument(DocumentOperationType operationType, String docIdString) {
+    public ParsedDocumentOperation readSingleDocument(DocumentOperationType operationType, String docIdString) {
         DocumentId docId = new DocumentId(docIdString);
         DocumentParseInfo documentParseInfo;
         try {
@@ -83,79 +78,6 @@ public class JsonReader {
         return operation;
     }
 
-    /**
-     * Reads a JSON which is expected to contain a single document operation,
-     * and where other parameters, like the document ID and operation type, are supplied by other means.
-     *
-     * @param operationType the type of operation (update or put)
-     * @param docIdString document ID
-     * @return the parsed document operation
-     */
-    public ParsedDocumentOperation readSingleDocumentStreaming(DocumentOperationType operationType, String docIdString) {
-        try {
-            DocumentId docId = new DocumentId(docIdString);
-            DocumentParseInfo documentParseInfo = new DocumentParseInfo();
-            documentParseInfo.documentId = docId;
-            documentParseInfo.operationType = operationType;
-
-            if (JsonToken.START_OBJECT != parser.nextValue())
-                throw new IllegalArgumentException("expected start of root object, got " + parser.currentToken());
-
-            Boolean create = null;
-            String condition = null;
-            ParsedDocumentOperation operation = null;
-            while (JsonToken.END_OBJECT != parser.nextValue()) {
-                switch (parser.getCurrentName()) {
-                    case FIELDS -> {
-                        documentParseInfo.fieldsBuffer = new LazyTokenBuffer(parser);
-                        VespaJsonDocumentReader vespaJsonDocumentReader = new VespaJsonDocumentReader(typeManager.getIgnoreUndefinedFields());
-                        operation = vespaJsonDocumentReader.createDocumentOperation(
-                                getDocumentTypeFromString(documentParseInfo.documentId.getDocType(), typeManager), documentParseInfo);
-
-                        if ( ! documentParseInfo.fieldsBuffer.isEmpty())
-                            throw new IllegalArgumentException("expected all content to be consumed by document parsing, but " +
-                                                               documentParseInfo.fieldsBuffer.nesting() + " levels remain");
-
-                    }
-                    case CONDITION -> {
-                        if ( ! JsonToken.VALUE_STRING.equals(parser.currentToken()) && ! JsonToken.VALUE_NULL.equals(parser.currentToken()))
-                            throw new IllegalArgumentException("expected string value for condition, got " + parser.currentToken());
-
-                        condition = parser.getValueAsString();
-                    }
-                    case CREATE_IF_NON_EXISTENT -> {
-                        create = parser.getBooleanValue(); // Throws if not boolean.
-                    }
-                    default -> {
-                        // We ignore stray fields, but need to ensure structural balance in doing do.
-                        if (parser.currentToken().isStructStart()) parser.skipChildren();
-                    }
-                }
-            }
-
-            if (null != parser.nextToken())
-                throw new IllegalArgumentException("expected end of input, got " + parser.currentToken());
-
-            if (null == operation)
-                throw new IllegalArgumentException("document is missing the required \"fields\" field");
-
-            if (null != create) {
-                switch (operationType) {
-                    case PUT -> ((DocumentPut) operation.operation()).setCreateIfNonExistent(create);
-                    case UPDATE -> ((DocumentUpdate) operation.operation()).setCreateIfNonExistent(create);
-                    case REMOVE -> throw new IllegalArgumentException(CREATE_IF_NON_EXISTENT + " is not supported for remove operations");
-                }
-            }
-
-            operation.operation().setCondition(TestAndSetCondition.fromConditionString(Optional.ofNullable(condition)));
-
-            return operation;
-        }
-        catch (IOException e) {
-            throw new IllegalArgumentException("failed parsing document", e);
-        }
-    }
-
     /** Returns the next document operation, or null if we have reached the end */
     public DocumentOperation next() {
         switch (state) {
diff --git a/document/src/main/java/com/yahoo/document/json/LazyTokenBuffer.java b/document/src/main/java/com/yahoo/document/json/LazyTokenBuffer.java
deleted file mode 100644
index 0fbdd0b28c7..00000000000
--- a/document/src/main/java/com/yahoo/document/json/LazyTokenBuffer.java
+++ /dev/null
@@ -1,64 +0,0 @@
-package com.yahoo.document.json;
-
-import com.fasterxml.jackson.core.JsonParser;
-import com.fasterxml.jackson.core.JsonToken;
-
-import java.io.IOException;
-import java.util.function.Supplier;
-
-/**
- * A {@link TokenBuffer} which only buffers tokens when needed, i.e., when peeking.
- *
- * @author jonmv
- */
-public class LazyTokenBuffer extends TokenBuffer {
-
-    private final JsonParser parser;
-
-    public LazyTokenBuffer(JsonParser parser) {
-        this.parser = parser;
-        try { addFromParser(parser); }
-        catch (IOException e) { throw new IllegalArgumentException("failed parsing document JSON", e); }
-        if (JsonToken.START_OBJECT != current())
-            throw new IllegalArgumentException("expected start of JSON object, but got " + current());
-        updateNesting(current());
-    }
-
-    void advance() {
-        super.advance();
-        if (tokens.isEmpty() && nesting() > 0) tokens.add(nextToken()); // Fill current token if needed and possible.
-    }
-
-    @Override
-    public Supplier<Token> lookahead() {
-        return new Supplier<>() {
-            int localNesting = nesting();
-            Supplier<Token> buffered = LazyTokenBuffer.super.lookahead();
-            @Override public Token get() {
-                if (localNesting == 0)
-                    return null;
-
-                Token token = buffered.get();
-                if (token == null) {
-                    token = nextToken();
-                    tokens.add(token);
-                }
-                localNesting += nestingOffset(token.token);
-                return token;
-            }
-        };
-    }
-
-    private Token nextToken() {
-        try {
-            JsonToken token = parser.nextValue();
-            if (token == null)
-                throw new IllegalStateException("no more JSON tokens");
-            return new Token(token, parser.getCurrentName(), parser.getText());
-        }
-        catch (IOException e) {
-            throw new IllegalArgumentException("failed reading document JSON", e);
-        }
-    }
-
-}
diff --git a/document/src/main/java/com/yahoo/document/json/TokenBuffer.java b/document/src/main/java/com/yahoo/document/json/TokenBuffer.java
index 3a48f71c4cd..dec84e46b77 100644
--- a/document/src/main/java/com/yahoo/document/json/TokenBuffer.java
+++ b/document/src/main/java/com/yahoo/document/json/TokenBuffer.java
@@ -1,16 +1,15 @@
 // Copyright Vespa.ai. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 package com.yahoo.document.json;
 
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
+
 import com.fasterxml.jackson.core.JsonParser;
 import com.fasterxml.jackson.core.JsonToken;
 import com.google.common.base.Preconditions;
 
-import java.io.IOException;
-import java.util.ArrayDeque;
-import java.util.Deque;
-import java.util.Iterator;
-import java.util.function.Supplier;
-
 /**
  * Helper class to enable lookahead in the token stream.
  *
@@ -18,76 +17,101 @@ import java.util.function.Supplier;
  */
 public class TokenBuffer {
 
-    final Deque<Token> tokens = new ArrayDeque<>();
+    private final List<Token> tokens;
 
+    private int position = 0;
     private int nesting = 0;
 
-    public TokenBuffer() { }
+    public TokenBuffer() {
+        this(new ArrayList<>());
+    }
+
+    public TokenBuffer(List<Token> tokens) {
+        this.tokens = tokens;
+        if (tokens.size() > 0)
+            updateNesting(tokens.get(position).token);
+    }
 
     /** Returns whether any tokens are available in this */
-    public boolean isEmpty() { return tokens.isEmpty(); }
+    public boolean isEmpty() { return remaining() == 0; }
+
+    public JsonToken previous() {
+        updateNestingGoingBackwards(current());
+        position--;
+        return current();
+    }
+
+    /** Returns the current token without changing position, or null if none */
+    public JsonToken current() {
+        if (isEmpty()) return null;
+        Token token = tokens.get(position);
+        if (token == null) return null;
+        return token.token;
+    }
 
-    /** Returns the next token, or null, and updates the nesting count of this. */
     public JsonToken next() {
-        advance();
+        position++;
         JsonToken token = current();
         updateNesting(token);
         return token;
     }
 
-    void advance() {
-        tokens.poll();
-    }
-
-    /** Returns the current token without changing position, or null if none */
-    public JsonToken current() {
-        return isEmpty() ? null : tokens.peek().token;
+    /** Returns a given number of tokens ahead, or null if none */
+    public JsonToken peek(int ahead) {
+        if (tokens.size() <= position + ahead) return null;
+        return tokens.get(position + ahead).token;
     }
 
     /** Returns the current token name without changing position, or null if none */
     public String currentName() {
-        return isEmpty() ? null : tokens.peek().name;
+        if (isEmpty()) return null;
+        Token token = tokens.get(position);
+        if (token == null) return null;
+        return token.name;
     }
 
     /** Returns the current token text without changing position, or null if none */
     public String currentText() {
-        return isEmpty() ? null : tokens.peek().text;
+        if (isEmpty()) return null;
+        Token token = tokens.get(position);
+        if (token == null) return null;
+        return token.text;
     }
 
-    /**
-     * Returns a sequence of remaining tokens in this, or nulls when none remain.
-     * This may fill the token buffer, but not otherwise modify it.
-     */
-    public Supplier<Token> lookahead() {
-        Iterator<Token> iterator = tokens.iterator();
-        if (iterator.hasNext()) iterator.next();
-        return () -> iterator.hasNext() ? iterator.next() : null;
+    public int remaining() {
+        return tokens.size() - position;
     }
 
     private void add(JsonToken token, String name, String text) {
-        tokens.add(new Token(token, name, text));
+        tokens.add(tokens.size(), new Token(token, name, text));
     }
 
-    public void bufferObject(JsonParser parser) {
-        bufferJsonStruct(parser, JsonToken.START_OBJECT);
+    public void bufferObject(JsonToken first, JsonParser tokens) {
+        bufferJsonStruct(first, tokens, JsonToken.START_OBJECT);
     }
 
-    private void bufferJsonStruct(JsonParser parser, JsonToken firstToken) {
-        JsonToken token = parser.currentToken();
-        Preconditions.checkArgument(token == firstToken,
-                                    "Expected %s, got %s.", firstToken.name(), token);
-        updateNesting(token);
+    private void bufferJsonStruct(JsonToken first, JsonParser tokens, JsonToken firstToken) {
+        int localNesting = 0;
+        JsonToken t = first;
 
-        try {
-            for (int nesting = addFromParser(parser); nesting > 0; nesting += addFromParser(parser))
-                parser.nextValue();
+        Preconditions.checkArgument(first == firstToken,
+                "Expected %s, got %s.", firstToken.name(), t);
+        if (remaining() == 0) {
+            updateNesting(t);
         }
-        catch (IOException e) {
-            throw new IllegalArgumentException(e);
+        localNesting = storeAndPeekNesting(t, localNesting, tokens);
+        while (localNesting > 0) {
+            t = nextValue(tokens);
+            localNesting = storeAndPeekNesting(t, localNesting, tokens);
         }
     }
 
-    int nestingOffset(JsonToken token) {
+    private int storeAndPeekNesting(JsonToken t, int nesting, JsonParser tokens) {
+        addFromParser(t, tokens);
+        return nesting + nestingOffset(t);
+    }
+
+    private int nestingOffset(JsonToken token) {
         if (token == null) return 0;
         if (token.isStructStart()) {
             return 1;
@@ -98,23 +122,43 @@ public class TokenBuffer {
         }
     }
 
-    int addFromParser(JsonParser tokens) throws IOException {
-        add(tokens.currentToken(), tokens.getCurrentName(), tokens.getText());
-        return nestingOffset(tokens.currentToken());
+    private void addFromParser(JsonToken t, JsonParser tokens) {
+        try {
+            add(t, tokens.getCurrentName(), tokens.getText());
+        } catch (IOException e) {
+            throw new IllegalArgumentException(e);
+        }
+    }
+
+    private JsonToken nextValue(JsonParser tokens) {
+        try {
+            return tokens.nextValue();
+        } catch (IOException e) {
+            throw new IllegalArgumentException(e);
+        }
     }
 
-    void updateNesting(JsonToken token) {
+    private void updateNesting(JsonToken token) {
         nesting += nestingOffset(token);
     }
 
+    private void updateNestingGoingBackwards(JsonToken token) {
+        nesting -= nestingOffset(token);
+    }
+
     public int nesting() {
         return nesting;
     }
 
     public void skipToRelativeNesting(int relativeNesting) {
         int initialNesting = nesting();
-        do next();
-        while (nesting() > initialNesting + relativeNesting);
+        do {
+            next();
+        } while ( nesting() > initialNesting + relativeNesting);
+    }
+
+    public List<Token> rest() {
+        return tokens.subList(position, tokens.size());
     }
 
     public static final class Token {
diff --git a/document/src/main/java/com/yahoo/document/json/document/DocumentParser.java b/document/src/main/java/com/yahoo/document/json/document/DocumentParser.java
index 77e11dcf2a8..74656762fe1 100644
--- a/document/src/main/java/com/yahoo/document/json/document/DocumentParser.java
+++ b/document/src/main/java/com/yahoo/document/json/document/DocumentParser.java
@@ -20,7 +20,7 @@ public class DocumentParser {
     private static final String UPDATE = "update";
     private static final String PUT = "put";
     private static final String ID = "id";
-    public static final String CONDITION = "condition";
+    private static final String CONDITION = "condition";
     public static final String CREATE_IF_NON_EXISTENT = "create";
     public static final String FIELDS = "fields";
     public static final String REMOVE = "remove";
@@ -86,6 +86,16 @@ public class DocumentParser {
     private void handleIdentLevelOne(DocumentParseInfo documentParseInfo, boolean docIdAndOperationIsSetExternally)
             throws IOException {
         JsonToken currentToken = parser.getCurrentToken();
+        if (currentToken == JsonToken.VALUE_TRUE || currentToken == JsonToken.VALUE_FALSE) {
+            try {
+                if (CREATE_IF_NON_EXISTENT.equals(parser.getCurrentName())) {
+                    documentParseInfo.create = Optional.ofNullable(parser.getBooleanValue());
+                    return;
+                }
+            } catch (IOException e) {
+                throw new RuntimeException("Got IO exception while parsing document", e);
+            }
+        }
         if ((currentToken == JsonToken.VALUE_TRUE || currentToken == JsonToken.VALUE_FALSE) &&
                 CREATE_IF_NON_EXISTENT.equals(parser.getCurrentName())) {
             documentParseInfo.create = Optional.of(currentToken == JsonToken.VALUE_TRUE);
@@ -101,11 +111,12 @@ public class DocumentParser {
         }
     }
 
-    private void handleIdentLevelTwo(DocumentParseInfo documentParseInfo) {
+    private  void handleIdentLevelTwo(DocumentParseInfo documentParseInfo) {
         try {
+            JsonToken currentToken = parser.getCurrentToken();
             // "fields" opens a dictionary and is therefore on level two which might be surprising.
-            if (parser.currentToken() == JsonToken.START_OBJECT && FIELDS.equals(parser.getCurrentName())) {
-                documentParseInfo.fieldsBuffer.bufferObject(parser);
+            if (currentToken == JsonToken.START_OBJECT && FIELDS.equals(parser.getCurrentName())) {
+                documentParseInfo.fieldsBuffer.bufferObject(currentToken, parser);
                 processIndent();
             }
         } catch (IOException e) {
diff --git a/document/src/main/java/com/yahoo/document/json/readers/DocumentParseInfo.java b/document/src/main/java/com/yahoo/document/json/readers/DocumentParseInfo.java
index e859306f04d..2dce07cdbe6 100644
--- a/document/src/main/java/com/yahoo/document/json/readers/DocumentParseInfo.java
+++ b/document/src/main/java/com/yahoo/document/json/readers/DocumentParseInfo.java
@@ -8,7 +8,6 @@ import com.yahoo.document.json.TokenBuffer;
 import java.util.Optional;
 
 public class DocumentParseInfo {
-    public DocumentParseInfo() { }
     public DocumentId documentId;
     public Optional<Boolean> create = Optional.empty();
     public Optional<String> condition = Optional.empty();
diff --git a/document/src/main/java/com/yahoo/document/json/readers/TensorReader.java b/document/src/main/java/com/yahoo/document/json/readers/TensorReader.java
index 1fd4029b1a5..0b7b1ae9996 100644
--- a/document/src/main/java/com/yahoo/document/json/readers/TensorReader.java
+++ b/document/src/main/java/com/yahoo/document/json/readers/TensorReader.java
@@ -4,15 +4,13 @@ package com.yahoo.document.json.readers;
 import com.fasterxml.jackson.core.JsonToken;
 import com.yahoo.document.datatypes.TensorFieldValue;
 import com.yahoo.document.json.TokenBuffer;
-import com.yahoo.document.json.TokenBuffer.Token;
+import com.yahoo.slime.Inspector;
+import com.yahoo.slime.Type;
 import com.yahoo.tensor.IndexedTensor;
 import com.yahoo.tensor.MixedTensor;
 import com.yahoo.tensor.Tensor;
 import com.yahoo.tensor.TensorAddress;
 import com.yahoo.tensor.TensorType;
-import com.yahoo.tensor.TensorType.Dimension;
-
-import java.util.function.Supplier;
 
 import static com.yahoo.document.json.readers.JsonParserHelpers.*;
 import static com.yahoo.tensor.serialization.JsonFormat.decodeHexString;
@@ -39,43 +37,36 @@ public class TensorReader {
         Tensor.Builder builder = Tensor.Builder.of(tensorFieldValue.getDataType().getTensorType());
         expectOneOf(buffer.current(), JsonToken.START_OBJECT, JsonToken.START_ARRAY);
         int initNesting = buffer.nesting();
-        while (true) {
-            Supplier<Token> lookahead = buffer.lookahead();
-            Token next = lookahead.get();
-            if (TENSOR_CELLS.equals(next.name) && ! primitiveContent(next.token, lookahead.get().token)) {
-                buffer.next();
+        for (buffer.next(); buffer.nesting() >= initNesting; buffer.next()) {
+            if (TENSOR_CELLS.equals(buffer.currentName()) && ! primitiveContent(buffer)) {
                 readTensorCells(buffer, builder);
             }
-            else if (TENSOR_VALUES.equals(next.name) && builder.type().dimensions().stream().allMatch(Dimension::isIndexed)) {
-                buffer.next();
+            else if (TENSOR_VALUES.equals(buffer.currentName()) && builder.type().dimensions().stream().allMatch(d -> d.isIndexed())) {
                 readTensorValues(buffer, builder);
             }
-            else if (TENSOR_BLOCKS.equals(next.name)) {
-                buffer.next();
+            else if (TENSOR_BLOCKS.equals(buffer.currentName())) {
                 readTensorBlocks(buffer, builder);
             }
-            else if (TENSOR_TYPE.equals(next.name) && next.token == JsonToken.VALUE_STRING) {
-                buffer.next();
+            else if (TENSOR_TYPE.equals(buffer.currentName()) && buffer.current() == JsonToken.VALUE_STRING) {
                 // Ignore input tensor type
             }
-            else if (buffer.nesting() == initNesting && JsonToken.END_OBJECT == next.token) {
-                buffer.next();
-                break;
-            }
             else {
+                buffer.previous(); // Back up to the start of the enclosing block
                 readDirectTensorValue(buffer, builder);
-                break;
+                buffer.previous(); // ... and back up to the end of the enclosing block
             }
         }
         expectOneOf(buffer.current(), JsonToken.END_OBJECT, JsonToken.END_ARRAY);
         tensorFieldValue.assign(builder.build());
     }
 
-    static boolean primitiveContent(JsonToken current, JsonToken next) {
-        if (current.isScalarValue()) return true;
-        if (current == JsonToken.START_ARRAY) {
-            if (next == JsonToken.END_ARRAY) return false;
-            if (next.isScalarValue()) return true;
+    static boolean primitiveContent(TokenBuffer buffer) {
+        JsonToken cellsValue = buffer.current();
+        if (cellsValue.isScalarValue()) return true;
+        if (cellsValue == JsonToken.START_ARRAY) {
+            JsonToken firstArrayValue = buffer.peek(1);
+            if (firstArrayValue == JsonToken.END_ARRAY) return false;
+            if (firstArrayValue.isScalarValue()) return true;
         }
         return false;
     }
@@ -195,7 +186,7 @@ public class TensorReader {
         boolean hasIndexed = builder.type().dimensions().stream().anyMatch(TensorType.Dimension::isIndexed);
         boolean hasMapped = builder.type().dimensions().stream().anyMatch(TensorType.Dimension::isMapped);
 
-        if (isArrayOfObjects(buffer))
+        if (isArrayOfObjects(buffer, 0))
             readTensorCells(buffer, builder);
         else if ( ! hasMapped)
             readTensorValues(buffer, builder);
@@ -205,12 +196,10 @@ public class TensorReader {
             readTensorCells(buffer, builder);
     }
 
-    private static boolean isArrayOfObjects(TokenBuffer buffer) {
-        if (buffer.current() != JsonToken.START_ARRAY) return false;
-        Supplier<Token> lookahead = buffer.lookahead();
-        Token next;
-        while ((next = lookahead.get()).token == JsonToken.START_ARRAY) { }
-        return next.token == JsonToken.START_OBJECT;
+    private static boolean isArrayOfObjects(TokenBuffer buffer, int ahead) {
+        if (buffer.peek(ahead++) != JsonToken.START_ARRAY) return false;
+        if (buffer.peek(ahead) == JsonToken.START_ARRAY) return isArrayOfObjects(buffer, ahead); // nested array
+        return buffer.peek(ahead) == JsonToken.START_OBJECT;
     }
 
     private static TensorAddress readAddress(TokenBuffer buffer, TensorType type) {
diff --git a/document/src/main/java/com/yahoo/document/json/readers/VespaJsonDocumentReader.java b/document/src/main/java/com/yahoo/document/json/readers/VespaJsonDocumentReader.java
index 067dabdbdab..113b8732b23 100644
--- a/document/src/main/java/com/yahoo/document/json/readers/VespaJsonDocumentReader.java
+++ b/document/src/main/java/com/yahoo/document/json/readers/VespaJsonDocumentReader.java
@@ -230,7 +230,7 @@ public class VespaJsonDocumentReader {
 
 
     private static boolean isFieldPath(String field) {
-        return field.matches("^.*?[.\\[{].*$");
+        return field.matches("^.*?[.\\[\\{].*$");
     }
 
     private static void verifyEndState(TokenBuffer buffer, JsonToken expectedFinalToken) {
@@ -238,7 +238,7 @@ public class VespaJsonDocumentReader {
                                  "Expected end of JSON struct (%s), got %s", expectedFinalToken, buffer.current());
         Preconditions.checkState(buffer.nesting() == 0, "Nesting not zero at end of operation");
         Preconditions.checkState(buffer.next() == null, "Dangling data at end of operation");
-        Preconditions.checkState(buffer.isEmpty(), "Dangling data at end of operation");
+        Preconditions.checkState(buffer.remaining() == 0, "Dangling data at end of operation");
     }
 
 }