hyparquet/src/datapageV2.js

import { decompressPage } from './column.js'
import { Encoding } from './constants.js'
import { readPlain, readRleBitPackedHybrid, widthFromMaxInt } from './encoding.js'
import { getMaxDefinitionLevel, getMaxRepetitionLevel, schemaElement } from './schema.js'
import { readVarInt, readZigZag } from './thrift.js'

/**
 * @typedef {import("./types.d.ts").Decoded<T>} Decoded
 * @template T
 */

/**
 * Read a data page from the given Uint8Array.
 *
 * @typedef {import("./types.d.ts").DataPage} DataPage
 * @typedef {import("./types.d.ts").ColumnMetaData} ColumnMetaData
 * @typedef {import("./types.d.ts").DataPageHeaderV2} DataPageHeaderV2
 * @typedef {import("./types.d.ts").PageHeader} PageHeader
 * @typedef {import("./types.d.ts").SchemaElement} SchemaElement
 * @param {Uint8Array} compressedBytes raw page data (should already be decompressed)
 * @param {PageHeader} ph page header
 * @param {SchemaElement[]} schema schema for the file
 * @param {ColumnMetaData} columnMetadata metadata for the column
 * @returns {DataPage} definition levels, repetition levels, and array of values
 */
export function readDataPageV2(compressedBytes, ph, schema, columnMetadata) {
  const dataView = new DataView(compressedBytes.buffer, compressedBytes.byteOffset, compressedBytes.byteLength)
  let offset = 0
  /** @type {any} */
  let values = []

  const daph2 = ph.data_page_header_v2
  if (!daph2) throw new Error('parquet data page header v2 is undefined')

  // repetition levels
  const repetitionLevels = readRepetitionLevelsV2(dataView, offset, daph2, schema, columnMetadata)

  // definition levels
  offset += daph2.repetition_levels_byte_length
  const maxDefinitionLevel = getMaxDefinitionLevel(schema, columnMetadata.path_in_schema)
  const definitionLevels = readDefinitionLevelsV2(dataView, offset, daph2, maxDefinitionLevel)
  offset += daph2.definition_levels_byte_length

  const uncompressedPageSize = ph.uncompressed_page_size - daph2.definition_levels_byte_length - daph2.repetition_levels_byte_length

  // read values based on encoding
  const nValues = daph2.num_values - daph2.num_nulls
  if (daph2.encoding === Encoding.PLAIN) {
    const se = schemaElement(schema, columnMetadata.path_in_schema)
    const utf8 = se.converted_type === 'UTF8'
    const plainObj = readPlain(dataView, columnMetadata.type, nValues, offset, utf8)
    values = plainObj.value
  } else if (daph2.encoding === Encoding.RLE) {
    const page = decompressPage(compressedBytes, uncompressedPageSize, columnMetadata.codec)
    const pageView = new DataView(page.buffer, page.byteOffset, page.byteLength)
    const bitWidth = 1
    if (daph2.num_nulls) {
      throw new Error('parquet RLE encoding with nulls not supported')
    } else {
      values = readRleBitPackedHybrid(
        pageView, 4, bitWidth, uncompressedPageSize, nValues
      ).value
    }
  } else if (
    daph2.encoding === Encoding.PLAIN_DICTIONARY ||
    daph2.encoding === Encoding.RLE_DICTIONARY
  ) {
    compressedBytes = compressedBytes.subarray(offset)
    const page = decompressPage(compressedBytes, uncompressedPageSize, columnMetadata.codec)
    const pageView = new DataView(page.buffer, page.byteOffset, page.byteLength)

    const bitWidth = pageView.getUint8(0)
    const { value } = readRleBitPackedHybrid(
      pageView, 1, bitWidth, uncompressedPageSize, nValues
    )
    values = value
  } else if (daph2.encoding === Encoding.DELTA_BINARY_PACKED) {
    if (daph2.num_nulls) throw new Error('parquet delta-int not supported')
    const codec = daph2.is_compressed ? columnMetadata.codec : 'UNCOMPRESSED'
    const page = decompressPage(compressedBytes, uncompressedPageSize, codec)
    deltaBinaryUnpack(page, nValues, values)
  } else {
    throw new Error(`parquet unsupported encoding: ${daph2.encoding}`)
  }

  return { definitionLevels, repetitionLevels, value: values }
}

/**
 * Read the repetition levels from this page, if any.
 *
 * @param {DataView} dataView data view for the page
 * @param {number} offset offset to start reading from
 * @param {DataPageHeaderV2} daph2 data page header
 * @param {SchemaElement[]} schema schema for the file
 * @param {ColumnMetaData} columnMetadata metadata for the column
 * @returns {any[]} repetition levels and number of bytes read
 */
export function readRepetitionLevelsV2(dataView, offset, daph2, schema, columnMetadata) {
  const maxRepetitionLevel = getMaxRepetitionLevel(schema, columnMetadata.path_in_schema)
  if (maxRepetitionLevel) {
    const bitWidth = widthFromMaxInt(maxRepetitionLevel)
    // num_values is index 1 for either type of page header
    return readRleBitPackedHybrid(
      dataView, offset, bitWidth, daph2.repetition_levels_byte_length, daph2.num_values
    ).value
  }
  return []
}

/**
 * Read the definition levels from this page, if any.
 *
 * @param {DataView} dataView data view for the page
 * @param {number} offset offset to start reading from
 * @param {DataPageHeaderV2} daph2 data page header v2
 * @param {number} maxDefinitionLevel maximum definition level for this column
 * @returns {number[] | undefined} definition levels and number of bytes read
 */
function readDefinitionLevelsV2(dataView, offset, daph2, maxDefinitionLevel) {
  if (maxDefinitionLevel) {
    // not the same as V1, because we know the length
    const bitWidth = widthFromMaxInt(maxDefinitionLevel)
    return readRleBitPackedHybrid(
      dataView, offset, bitWidth, daph2.definition_levels_byte_length, daph2.num_values
    ).value
  }
}

/**
 * Unpack the delta binary packed encoding.
 *
 * @param {Uint8Array} page page data
 * @param {number} nValues number of values to read
 * @param {any[]} values array to write to
 */
function deltaBinaryUnpack(page, nValues, values) {
  const dataView = new DataView(page.buffer, page.byteOffset, page.byteLength)
  const [blockSize, index1] = readVarInt(dataView, 0)
  const [miniblockPerBlock, index2] = readVarInt(dataView, index1)
  const [count, index3] = readVarInt(dataView, index2)
  let [value, offset] = readZigZag(dataView, index3)

  const valuesPerMiniblock = blockSize / miniblockPerBlock

  for (let valueIndex = 0; valueIndex < nValues;) {
    const [minDelta, index4] = readZigZag(dataView, offset)
    offset = index4
    const bitWidths = new Uint8Array(miniblockPerBlock)
    for (let i = 0; i < miniblockPerBlock; i++, offset++) {
      bitWidths[i] = page[offset]
    }

    for (let i = 0; i < miniblockPerBlock; i++) {
      const bitWidth = bitWidths[i]
      if (bitWidth) {
        if (count > 1) {
          // no more diffs if on last value, delta read bitpacked
          let data = 0
          let stop = -bitWidth
          // TODO: possible loss of precision
          const mask = 0xffffffffffffffff >> (64 - bitWidth)
          while (count) {
            if (stop < 0) {
              data = ((data & 0x00ffffffffffffff) << 8) | dataView.getUint8(offset++)
              stop += 8
            } else {
              values.push((data >> stop) & mask)
            }
          }
        }
      } else {
        for (let j = 0; j < valuesPerMiniblock && valueIndex < nValues; j++, valueIndex++) {
          values[valueIndex] = value
          value += minDelta
        }
      }
    }
  }
}