Generate CRC32 base64 encoded hash the same way google does

generate_local_crc32c.py

"""
Google makes it difficult to verify if local files match the ones on their cloud storage.
This snippet takes a file path to run the CRC32C hashing and then base64 encode it so it matches the results
from the google-cloud-storage python blob api

You will need pip install:
  - google-cloud-storage
 
"""
import google_crc32c
import collections

def generate_file_crc32c(path, blocksize=2**20):
    """
    Generate a base64 encoded crc32c checksum for a file to compare with google cloud storage.
    
    Returns a string like "4jvPnQ=="
    
    Compare with a google storage blob instance:
      blob.crc32c == generate_file_crc32c("path/to/local/file.txt")
    """
    crc = google_crc32c.Checksum()
    read_stream = open(path, "rb")
    collections.deque(crc.consume(read_stream, blocksize), maxlen=0)
    read_stream.close()
    return base64.b64encode(crc.digest()).decode("utf-8")