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zst.py
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zst.py
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from datetime import datetime
import json
import logging
from pprint import pprint
import zstandard
log = logging.getLogger(__name__)
log.setLevel(logging.INFO)
def read_and_decode(reader, chunk_size, max_window_size, previous_chunk=None, bytes_read=0, file_name=None):
chunk = reader.read(chunk_size)
bytes_read += chunk_size
if previous_chunk is not None:
chunk = previous_chunk + chunk
try:
return chunk.decode()
except UnicodeDecodeError:
if bytes_read > max_window_size:
raise UnicodeError(f"Unable to decode frame after reading {bytes_read:,} bytes")
log.info(f"Decoding error: {file_name} with {bytes_read:,} bytes, reading another chunk")
return read_and_decode(reader, chunk_size, max_window_size, chunk, bytes_read)
def read_lines_zst(file_name):
with open(file_name, 'rb') as file_handle:
buffer = ''
reader = zstandard.ZstdDecompressor(max_window_size=2**31).stream_reader(file_handle)
while True:
chunk = read_and_decode(reader, 2**27, (2**29) * 2, file_name=file_name)
if not chunk:
break
lines = (buffer + chunk).split("\n")
for line in lines[:-1]:
yield line, file_handle.tell()
buffer = lines[-1]
reader.close()