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# This file is part of daf_butler. 

# 

# Developed for the LSST Data Management System. 

# This product includes software developed by the LSST Project 

# (http://www.lsst.org). 

# See the COPYRIGHT file at the top-level directory of this distribution 

# for details of code ownership. 

# 

# This program is free software: you can redistribute it and/or modify 

# it under the terms of the GNU General Public License as published by 

# the Free Software Foundation, either version 3 of the License, or 

# (at your option) any later version. 

# 

# This program is distributed in the hope that it will be useful, 

# but WITHOUT ANY WARRANTY; without even the implied warranty of 

# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 

# GNU General Public License for more details. 

# 

# You should have received a copy of the GNU General Public License 

# along with this program. If not, see <http://www.gnu.org/licenses/>. 

 

__all__ = ("s3CheckFileExists", "bucketExists") 

 

try: 

import boto3 

except ImportError: 

boto3 = None 

 

from lsst.daf.butler.core.location import ButlerURI, Location 

 

 

def s3CheckFileExists(path, bucket=None, client=None): 

"""Returns (True, filesize) if file exists in the bucket and (False, -1) if 

the file is not found. 

 

Parameters 

---------- 

path : `Location`, `ButlerURI`, `str` 

Location or ButlerURI containing the bucket name and filepath. 

bucket : `str`, optional 

Name of the bucket in which to look. If provided, path will be assumed 

to correspond to be relative to the given bucket. 

client : `boto3.client`, optional 

S3 Client object to query, if not supplied boto3 will try to resolve 

the credentials as in order described in its manual_. 

 

Returns 

------- 

exists : `bool` 

True if key exists, False otherwise. 

size : `int` 

Size of the key, if key exists, in bytes, otherwise -1 

 

Notes 

----- 

S3 Paths are sensitive to leading and trailing path separators. 

 

.. _manual: https://boto3.amazonaws.com/v1/documentation/api/latest/guide/\ 

configuration.html#configuring-credentials 

""" 

if boto3 is None: 

raise ModuleNotFoundError(("Could not find boto3. " 

"Are you sure it is installed?")) 

 

if client is None: 

client = boto3.client('s3') 

 

if isinstance(path, str): 

if bucket is not None: 

filepath = path 

else: 

uri = ButlerURI(path) 

bucket = uri.netloc 

filepath = uri.relativeToPathRoot 

elif isinstance(path, (ButlerURI, Location)): 

bucket = path.netloc 

filepath = path.relativeToPathRoot 

 

try: 

obj = client.head_object(Bucket=bucket, Key=filepath) 

return (True, obj["ContentLength"]) 

except client.exceptions.ClientError as err: 

# resource unreachable error means key does not exist 

if err.response["ResponseMetadata"]["HTTPStatusCode"] == 404: 

return (False, -1) 

# head_object returns 404 when object does not exist only when user has 

# s3:ListBucket permission. If list permission does not exist a 403 is 

# returned. In practical terms this generally means that the file does 

# not exist, but it could also mean user lacks s3:GetObject permission: 

# https://docs.aws.amazon.com/AmazonS3/latest/API/RESTObjectHEAD.html 

# I don't think its possible to discern which case is it with certainty 

if err.response["ResponseMetadata"]["HTTPStatusCode"] == 403: 

raise PermissionError("Forbidden HEAD operation error occured. " 

"Verify s3:ListBucket and s3:GetObject " 

"permissions are granted for your IAM user. ") from err 

raise 

 

 

def bucketExists(bucketName, client=None): 

"""Check if the S3 bucket with the given name actually exists. 

 

Parameters 

---------- 

bucketName : `str` 

Name of the S3 Bucket 

client : `boto3.client`, optional 

S3 Client object to query, if not supplied boto3 will try to resolve 

the credentials as in order described in its manual_. 

 

Returns 

------- 

exists : `bool` 

True if it exists, False if no Bucket with specified parameters is 

found. 

 

.. _manual: https://boto3.amazonaws.com/v1/documentation/api/latest/guide/\ 

configuration.html#configuring-credentials 

""" 

if boto3 is None: 

raise ModuleNotFoundError(("Could not find boto3. " 

"Are you sure it is installed?")) 

 

s3 = boto3.client("s3") 

try: 

s3.get_bucket_location(Bucket=bucketName) 

return True 

except s3.exceptions.NoSuchBucket: 

return False