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Locally calculate dropbox hash of files

Dropbox rest api, in function metatada has a parameter named "hash" https://www.dropbox.com/developers/reference/api#metadata

Can I calculate this hash locally without call any remote api rest function?

I need know this value to reduce upload bandwidth.

Solution

  • https://www.dropbox.com/developers/reference/content-hash explains how Dropbox computes their file hashes. A Python implementation of this is below:

    import hashlib
import math
import os

DROPBOX_HASH_CHUNK_SIZE = 4*1024*1024

def compute_dropbox_hash(filename):
    file_size = os.stat(filename).st_size
    with open(filename, 'rb') as f:
        block_hashes = b''
        while True:
            chunk = f.read(DROPBOX_HASH_CHUNK_SIZE)
            if not chunk:
                break
            block_hashes += hashlib.sha256(chunk).digest()
        return hashlib.sha256(block_hashes).hexdigest()