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fix: write the Schema message into the stream embedded in IPC files #514

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fix: write the Schema message into the stream embedded in IPC files #514

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6 changes: 4 additions & 2 deletions src/ipc/writer.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -439,9 +439,11 @@ export class RecordBatchFileWriter<T extends TypeMap = any> extends RecordBatchW
this._writeLegacyIpcFormat = false;
}

// @ts-ignore
protected _writeSchema(schema: Schema<T>) {
return this._writeMagic()._writePadding(2);
// The file format embeds a complete IPC stream after the leading
// magic and padding, so the Schema message has to be written here too.
this._writeMagic()._writePadding(2);
return super._writeSchema(schema);
}

protected _writeDictionaryBatch(dictionary: Data, id: number, isDelta = false) {
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18 changes: 18 additions & 0 deletions test/unit/ipc/writer/file-writer-tests.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -31,6 +31,7 @@ import {
RecordBatch,
RecordBatchFileWriter,
RecordBatchReader,
RecordBatchStreamReader,
Table,
tableFromArrays,
Uint32,
Expand Down Expand Up @@ -134,6 +135,23 @@ describe('RecordBatchFileWriter', () => {
expect(dictionary).toBeInstanceOf(Vector);
expect(dictionary.data).toHaveLength(20);
});

describe('embedded IPC stream', () => {
const cases: [string, Table][] = [
['all types', generate.table([10, 20, 30]).table],
['dictionaries', generateDictionaryTables([10, 20, 30]).next().value!],
];
for (const [name, source] of cases) {
it(`can be read by a stream reader after the leading magic (${name})`, async () => {
const bytes = await RecordBatchFileWriter.writeAll(source).toUint8Array();
// Skip the leading "ARROW1" magic and its two bytes of padding.
const reader = RecordBatchStreamReader.from(bytes.subarray(FILE_FORMAT_HEADER_LENGTH));
const result = new Table(reader);
expect(result.schema.fields).toHaveLength(source.schema.fields.length);
expect(result).toEqualTable(source);
});
}
});
});

function testFileWriter(table: Table, name: string, options?: RecordBatchStreamWriterOptions) {
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