rdblue commented on code in PR #3397: URL: https://github.com/apache/parquet-java/pull/3397#discussion_r4099288647
########## parquet-column/src/main/java/org/apache/parquet/column/values/alp/AlpValuesReader.java: ########## @@ -0,0 +1,306 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one + * or more contributor license agreements. See the NOTICE file + * distributed with this work for additional information + * regarding copyright ownership. The ASF licenses this file + * to you under the Apache License, Version 2.0 (the + * "License"); you may not use this file except in compliance + * with the License. You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, + * software distributed under the License is distributed on an + * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY + * KIND, either express or implied. See the License for the + * specific language governing permissions and limitations + * under the License. + */ +package org.apache.parquet.column.values.alp; + +import static org.apache.parquet.column.values.alp.AlpConstants.ALP_COMPRESSION_MODE; +import static org.apache.parquet.column.values.alp.AlpConstants.ALP_HEADER_SIZE; +import static org.apache.parquet.column.values.alp.AlpConstants.ALP_INFO_SIZE; +import static org.apache.parquet.column.values.alp.AlpConstants.ALP_INTEGER_ENCODING_FOR; +import static org.apache.parquet.column.values.alp.AlpConstants.MAX_LOG_VECTOR_SIZE; +import static org.apache.parquet.column.values.alp.AlpConstants.MIN_LOG_VECTOR_SIZE; + +import java.io.IOException; +import java.nio.ByteBuffer; +import java.nio.ByteOrder; +import org.apache.parquet.bytes.ByteBufferInputStream; +import org.apache.parquet.column.values.ValuesReader; +import org.apache.parquet.io.ParquetDecodingException; + +/** + * Abstract base class for ALP values readers with lazy per-vector decoding. + * + * <p>Reads ALP-encoded values from the interleaved page layout: + * <pre> + * ┌─────────┬──────────────────────┬──────────────┬──────────────┬─────┐ + * │ Header │ Offset Array │ Vector 0 │ Vector 1 │ ... │ + * │ 7 bytes │ 4B × numVectors │ (interleaved)│ (interleaved)│ │ + * └─────────┴──────────────────────┴──────────────┴──────────────┴─────┘ + * </pre> + * + * <p>Each vector is decoded lazily on first access. Skipping values does not + * trigger decoding of intermediate vectors. + */ +abstract class AlpValuesReader extends ValuesReader { + + protected int vectorSize; + protected int totalCount; + protected int numVectors; + protected int pageValueIndex; + protected int currentVectorNumber; + + protected int[] vectorOffsets; + protected ByteBuffer vectorsData; + protected int offsetArraySize; + + // Scratch buffer for exception positions within a vector; shared by both readers (int[] in each). + protected int[] excPositionsBuffer; + + AlpValuesReader() { + this.pageValueIndex = 0; + this.totalCount = 0; + this.currentVectorNumber = -1; + } + + @Override + public void initFromPage(int valuesCount, ByteBufferInputStream stream) + throws ParquetDecodingException, IOException { + ByteBuffer headerBuf = stream.slice(ALP_HEADER_SIZE).order(ByteOrder.LITTLE_ENDIAN); + int compressionMode = headerBuf.get() & 0xFF; + int integerEncoding = headerBuf.get() & 0xFF; + int logVectorSize = headerBuf.get() & 0xFF; + int numElements = headerBuf.getInt(); + + if (compressionMode != ALP_COMPRESSION_MODE) { + throw new ParquetDecodingException("Unsupported ALP compression mode: " + compressionMode); + } + if (integerEncoding != ALP_INTEGER_ENCODING_FOR) { + throw new ParquetDecodingException("Unsupported ALP integer encoding: " + integerEncoding); + } + if (logVectorSize < MIN_LOG_VECTOR_SIZE || logVectorSize > MAX_LOG_VECTOR_SIZE) { + throw new ParquetDecodingException("Invalid ALP log vector size: " + logVectorSize + ", must be between " + + MIN_LOG_VECTOR_SIZE + " and " + MAX_LOG_VECTOR_SIZE); + } + if (numElements < 0) { + throw new ParquetDecodingException("Invalid ALP element count: " + numElements); + } + // ALP's num_elements is the count of non-null values that went through encoding; + // valuesCount is the page row count, which is larger when the column has nulls. + // The two are equal only for required (non-null) columns. + if (numElements > valuesCount) { + throw new ParquetDecodingException( + "ALP header element count " + numElements + " exceeds page valuesCount " + valuesCount); + } + + this.vectorSize = 1 << logVectorSize; + this.totalCount = numElements; + + // Bound the vector count against the bytes actually present before allocating anything. + // numElements is only capped by valuesCount, which a forged page can set as high as + // Integer.MAX_VALUE, so computing this in int would overflow to a negative count, and even + // without overflow a large count would drive a huge int[] and a huge stream.slice allocation. + // Every vector costs a 4-byte offset entry plus at least its ALP and FOR headers, which gives + // a hard ceiling on how many vectors the remaining bytes can possibly describe. + int minVectorBytes = ALP_INFO_SIZE + forInfoSize(); + long bodyBytes = stream.available(); + long numVectorsLong = ((long) numElements + vectorSize - 1) / vectorSize; + long minBodyBytes = numVectorsLong * (Integer.BYTES + minVectorBytes); + if (minBodyBytes > bodyBytes) { + throw new ParquetDecodingException("ALP header element count " + numElements + " requires at least " + + minBodyBytes + " bytes but only " + bodyBytes + " remain in the page"); + } + this.numVectors = (int) numVectorsLong; + this.pageValueIndex = 0; + this.currentVectorNumber = -1; Review Comment: Nit: I prefer constants for values like this, like `BEFORE_FIRST_VECTOR`. -- This is an automated message from the Apache Git Service. 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