Function ReadFromCursorFile

pg_documentdb/src/infrastructure/cursor_store.c:497–523

* Given a cursor file state, reads the next document from the * cursor file. The file is expected to be in the cursor directory. * Blocks are pre-buffered in BLCKSZ chunks. * * Also updates the flush state of the cursor file state based on the * prior value read. This ensures that if we return a document, that we * only advance the cursor to include that when the next Read is called. */

 * only advance the cursor to include that when the next Read is called.
 */
pgbson *
ReadFromCursorFile(CursorFileState *cursorFileState)
{
	/* First step, advance the file stream forward with what was buffered before */
	cursorFileState->cursorState.file_offset = cursorFileState->next_offset;

	int32_t length = 0;
	if (!FillBuffer(cursorFileState, (char *) &length, 4))
	{
		return NULL;
	}

	if ((Size) length > BSON_MAX_SIZE)
	{
		ereport(ERROR, (errcode(ERRCODE_DOCUMENTDB_INTERNALERROR),
						errmsg("Invalid BSON size in cursor file %d", length)));
	}

	pgbson *bson = palloc(length);
	if (!FillBuffer(cursorFileState, (char *) bson, length))
	{
		pfree(bson);
		return NULL;
	}

	return bson;
}


/*