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For discussion: Add suffixStart option to parquetMetadataAsync #142

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For discussion: Add suffixStart option to parquetMetadataAsync #142

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10 changes: 6 additions & 4 deletions src/metadata.js
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Original file line number Diff line number Diff line change
Expand Up @@ -32,14 +32,16 @@ function decode(/** @type {Uint8Array} */ value) {
* or a second request for up to the metadata size.
*
* @param {AsyncBuffer} asyncBuffer parquet file contents
* @param {MetadataOptions & { initialFetchSize?: number }} options initial fetch size in bytes (default 512kb)
* @param {import('../src/types.d.ts').MetadataAsyncOptions} options
* @returns {Promise<FileMetaData>} parquet metadata object
*/
export async function parquetMetadataAsync(asyncBuffer, { parsers, initialFetchSize = defaultInitialFetchSize, geoparquet = true } = {}) {
export async function parquetMetadataAsync(asyncBuffer, { parsers, initialFetchSize = defaultInitialFetchSize, suffixStart, geoparquet = true } = {}) {
if (!asyncBuffer || !(asyncBuffer.byteLength >= 0)) throw new Error('parquet expected AsyncBuffer')

// fetch last bytes (footer) of the file
const footerOffset = Math.max(0, asyncBuffer.byteLength - initialFetchSize)
// suffixStart overrides initialFetchSize - allows caller to specify exact start offset
const footerOffset = suffixStart ?? Math.max(0, asyncBuffer.byteLength - initialFetchSize)
const fetchSize = asyncBuffer.byteLength - footerOffset
const footerBuffer = await asyncBuffer.slice(footerOffset, asyncBuffer.byteLength)

// Check for parquet magic number "PAR1"
Expand All @@ -56,7 +58,7 @@ export async function parquetMetadataAsync(asyncBuffer, { parsers, initialFetchS
}

// check if metadata size fits inside the initial fetch
if (metadataLength + 8 > initialFetchSize) {
if (metadataLength + 8 > fetchSize) {
// fetch the rest of the metadata
const metadataOffset = asyncBuffer.byteLength - metadataLength - 8
const metadataBuffer = await asyncBuffer.slice(metadataOffset, footerOffset)
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8 changes: 8 additions & 0 deletions src/types.d.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,14 @@ export interface MetadataOptions {
geoparquet?: boolean // parse geoparquet metadata and set logical type to geometry/geography for geospatial columns (default true)
}

/**
* Options for parquetMetadataAsync
*/
export interface MetadataAsyncOptions extends MetadataOptions {
initialFetchSize?: number // fetch last N bytes from EOF (default 512kb)
suffixStart?: number // if provided, fetch from this byte offset to EOF (overrides initialFetchSize)
}

/**
* Parquet query options for reading data
*/
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