This is a quick and dirty script to compare two different s3-compatible buckets, just dorp in the bucket name and credentials, and optionally change the endpoint host

compare_buckets.py

#!/usr/bin/python

import boto, json

from boto.s3.connection import S3Connection
from boto.gs.connection import GSConnection

def compare_buckets(bucket_one_bucket_name, 
                    bucket_two_bucket_name, 
                    bucket_one_access_key_id, 
                    bucket_one_secret_access_key, 
                    bucket_two_access_key_id, 
                    bucket_two_secret_access_key, 
                    bucket_one_host="s3.amazonaws.com",
                    bucket_two_host="s3.amazonaws.com",
                    print_status=False, 
                    confirm_matches=False):
    '''
        This function compares the file contents of two S3-compatible
        buckets, skipping multi-part uploads, and returning files that
        are missing or that differ (via etag md5 hash).
        It may be helpful for migrating from S3 to GS.
    '''

    bucket_one_conn = S3Connection(aws_access_key_id=bucket_one_access_key_id, aws_secret_access_key=bucket_one_secret_access_key, host=bucket_one_host)
    bucket_two_conn = S3Connection(aws_access_key_id=bucket_two_access_key_id, aws_secret_access_key=bucket_two_secret_access_key, host=bucket_two_host)

    bucket_one_bucket=bucket_one_conn.get_bucket(bucket_one_bucket_name)
    bucket_two_bucket=bucket_two_conn.get_bucket(bucket_two_bucket_name)

    results = {}
    results["present"]              = []
    results["missing"]              = []
    results["different"]            = []
    results["skipped_bucket_one"]   = []
    results["skipped_bucket_two"]   = []

    bucket_one_keys = bucket_one_bucket.get_all_keys()
    numer_of_keys = len(bucket_one_keys)
    for i, bucket_one_key in enumerate(bucket_one_keys):
        if print_status:
            print( "Processing. {percent:.2%} complete.".format(percent=float(i+1)/float(numer_of_keys)) )

        if not bucket_one_key.name.endswith("/"):
            if "-" not in str(bucket_one_key.etag):
                bucket_two_key = bucket_two_bucket.get_key(bucket_one_key.name)
                if bucket_two_key:
                    if "-" not in str(bucket_two_key.etag):
                        if bucket_two_key.etag == bucket_one_key.etag:
                            if print_status and confirm_matches:
                                print("etag matches for:", bucket_one_key.name, bucket_one_key.etag, "==", bucket_two_key.etag)
                            results["present"].append(bucket_one_key.name)
                            pass
                        else:
                            if print_status:
                                print("etag differs for:", bucket_one_key.name, bucket_one_key.etag, "==", bucket_two_key.etag)
                            results["different"].append(bucket_one_key.name)
                    else:
                        if print_status:
                            print("multipart upload for file, skipping:", bucket_two_key.name)
                        results["skipped_bucket_two"].append(bucket_one_key.name)
                else:
                    if print_status:
                        print("object does not exist in GS:", bucket_one_key.name)
                    results["missing"].append(bucket_one_key.name)
            else:
                if print_status:
                    print("multipart upload for file, skipping:", bucket_one_key.name)
                results["skipped_bucket_one"].append(bucket_one_key.name)

    return results

if __name__ == "__main__":
    bucket_name = "bucket-name"
    results = compare_buckets(
                    bucket_one_bucket_name        = bucket_name, 
                    bucket_two_bucket_name        = bucket_name, 
                    bucket_one_access_key_id      = "", 
                    bucket_one_secret_access_key  = "",
                    bucket_two_access_key_id      = "",
                    bucket_two_secret_access_key  = "", 
                    bucket_two_host               = "storage.googleapis.com",
                    print_status                  = False, 
                    confirm_matches               = False)

    print(json.dumps(results, sort_keys=True, indent=4, separators=(',', ': ')))

This function is awesome, thanks for sharing. One thing I found was that get_all_keys requires you to handle paging yourself, so as is the script is limited to 1000 keys. If you want something that will take care this for you, you can replace

bucket_one_keys = bucket_one_bucket.get_all_keys()

with

bucket_one_keys = list(bucket_one_bucket.list())

The list function returns a BucketListResultSet which is iterable. The list function creates a new list with all of the elements of the iterator.

This script is cool but it could be improved for JSON files as the etag changes with changing order of keys inside json.