Parse logical types from metadata

src/constants.js

@@ -1,3 +1,7 @@
+/**
+ * @typedef {import('./types.js').ParquetType} ParquetTypeType
+ * @type {ParquetTypeType[]}
+ */
 export const ParquetType = [
   'BOOLEAN',
   'INT32',
@@ -28,6 +32,10 @@ export const FieldRepetitionType = [
   'REPEATED',
 ]
 
+/**
+ * @typedef {import('./types.js').ConvertedType} ConvertedTypeType
+ * @type {ConvertedTypeType[]}
+ */
 export const ConvertedType = [
   'UTF8',
   'MAP',
@@ -53,6 +61,28 @@ export const ConvertedType = [
   'INTERVAL',
 ]
 
+/**
+ * @typedef {import('./types.js').LogicalTypeType} LogicalTypeType
+ * @type {LogicalTypeType[]}
+ */
+export const logicalTypeType = [
+  'NULL',
+  'STRING',
+  'MAP',
+  'LIST',
+  'ENUM',
+  'DECIMAL',
+  'DATE',
+  'TIME',
+  'TIMESTAMP',
+  'INTERVAL',
+  'INTEGER',
+  'NULL',
+  'JSON',
+  'BSON',
+  'UUID',
+]
+
 export const CompressionCodec = [
   'UNCOMPRESSED',
   'SNAPPY',

src/metadata.js

@@ -105,6 +105,7 @@ export function parquetMetadata(arrayBuffer) {
     scale: field.field_7,
     precision: field.field_8,
     field_id: field.field_9,
+    logical_type: logicalType(field.field_10),
   }))
   const num_rows = metadata.field_3
   const row_groups = metadata.field_4.map((/** @type {any} */ rowGroup) => ({
@@ -171,3 +172,32 @@ export function parquetMetadata(arrayBuffer) {
 export function parquetSchema(metadata) {
   return schemaTree(metadata.schema, 0)
 }
+
+/**
+ * Parse logical type by type.
+ *
+ * @typedef {import("./types.d.ts").LogicalType} LogicalType
+ * @param {any} logicalType
+ * @returns {LogicalType | undefined}
+ */
+function logicalType(logicalType) {
+  if (logicalType?.field_5) {
+    return {
+      logicalType: 'DECIMAL',
+      scale: logicalType.field_5.field_1,
+      precision: logicalType.field_5.field_2,
+    }
+  }
+  // TODO: TimestampType
+  // TOFO: TimeType
+  if (logicalType?.field_10) {
+    return {
+      logicalType: 'INTEGER',
+      bitWidth: logicalType.field_10.field_1,
+      isSigned: logicalType.field_10.field_2,
+    }
+  }
+  if (logicalType) {
+    return logicalType
+  }
+}

src/types.d.ts

@@ -42,6 +42,7 @@ export interface SchemaElement {
   scale?: number
   precision?: number
   field_id?: number
+  logicalType?: LogicalType
 }
 
 export type ParquetType =
@@ -83,6 +84,40 @@ export type ConvertedType =
   'BSON' |
   'INTERVAL'
 
+type LogicalDecimalType = {
+  logicalType: 'DECIMAL'
+  precision: number
+  scale: number
+}
+
+type LogicalIntType = {
+  logicalType: 'INTEGER'
+  bitWidth: number
+  isSigned: boolean
+}
+
+export type LogicalType =
+  { logicalType: LogicalTypeType } |
+  LogicalDecimalType |
+  LogicalIntType
+
+export type LogicalTypeType =
+  'STRING' | // convertedType UTF8
+  'MAP' | // convertedType MAP
+  'LIST' | // convertedType LIST
+  'ENUM' | // convertedType ENUM
+  'DECIMAL' | // convertedType DECIMAL + precision/scale
+  'DATE' | // convertedType DATE
+  'TIME' | // convertedType TIME_MILLIS or TIME_MICROS
+  'TIMESTAMP' | // convertedType TIMESTAMP_MILLIS or TIMESTAMP_MICROS
+  'INTEGER' | // convertedType INT or UINT
+  'INTERVAL' | // convertedType INT or UINT
+  'NULL' | // no convertedType
+  'JSON' | // convertedType JSON
+  'BSON' | // convertedType BSON
+  'UUID' | // no convertedType
+  'FLOAT16' // no convertedType
+
 export interface RowGroup {
   columns: ColumnChunk[]
   total_byte_size: number

test/files/concatenated_gzip_members.metadata.json

@@ -36,6 +36,11 @@
     },
     {
       "converted_type": "UINT_64",
+      "logical_type": {
+        "logicalType": "INTEGER",
+        "bitWidth": 64,
+        "isSigned": false
+      },
       "name": "long_col",
       "repetition_type": "OPTIONAL",
       "type": "INT64"