[GitHub] [iceberg] samredai commented on a diff in pull request #4792: Python: Add BotoFileIO, a FileIO that wraps boto3

[GitBox <gi...@apache.org>]

samredai commented on code in PR #4792:
URL: https://github.com/apache/iceberg/pull/4792#discussion_r884938730


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python/src/iceberg/io/boto.py:
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@@ -0,0 +1,294 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+"""FileIO implementation for reading and writing table files that uses boto3"""
+
+from typing import Literal, Optional, Union
+from urllib.parse import urlparse
+
+from boto3 import Session
+from boto3.resources.factory import s3
+from botocore.exceptions import ClientError
+
+from iceberg.io.base import FileIO, InputFile, InputStream, OutputFile, OutputStream
+
+class BotoInputStream:
+    """A seekable wrapper for reading an S3 Object that abides by the InputStream protocol
+        
+        Args:
+        s3_object(boto3.resources.factory.s3.Object): An s3 object
+    """
+
+    def __init__(self, s3_object: s3.Object):
+        self._s3_object = s3_object
+        self._position = 0
+
+    def read(self, size: int = -1) -> bytes:
+        """Read the byte content of the s3 object
+
+        This uses the `Range` argument when reading the S3 Object that allows setting a range of bytes to the headers of the request to S3.
+
+        Args:
+            size (int, optional): The number of bytes to read. Defaults to -1 which reads the entire file.
+
+        Returns:
+            bytes: The byte content of the file
+        """
+        if size == -1:  # Read the entire file from the current position
+            range_header = f"bytes={self._position}-"
+            self.seek(offset=0, whence=2)
+        else:
+            position_new = self._position + size
+
+            if position_new >= self.size:  # If more bytes are requested than exists, just read the entire file from the current position
+                return self.read(size=-1)
+
+            range_header = f"bytes={self._position}-{position_new -1}"
+            self.seek(offset=size, whence=1)
+
+        return self._s3_object.get(Range=range_header)["Body"].read()
+
+    def seek(self, offset: int, whence: Literal[0, 1, 2] = 0) -> None:
+        position_new = offset if whence == 0 else self._position + offset if whence == 1 else self._s3_object.content_length + offset if whence == 2 else None
+
+        if not position_new:
+            raise ValueError(f"Cannot seek to position {offset}, invalid whence: {whence}")
+
+        self._position = position_new
+        return self._position
+
+    def tell(self) -> int:
+        return self._position
+
+    def closed(self) -> bool:
+        return False
+
+    def close(self) -> None:
+        pass
+
+class BotoOutputStream:
+    """A wrapper for writing an S3 Object that abides by the OutputStream protocol
+        
+        Args:
+        s3_object(boto3.resources.factory.s3.Object): An s3 object
+    """
+
+    def __init__(self, s3_object):
+        self._s3_object = s3_object
+
+    def write(self, b: bytes) -> None:
+        """Write to the S3 Object
+        
+        Args:
+            b(bytes): The bytes to write to the S3 Object
+        """
+        self._s3_object.put(Body=b)
+
+    def closed(self) -> bool:
+        """Returns where the stream is closed or not
+
+        Since this is a wrapper for requests to S3, there is no concept of closing, therefore this always returns False
+        """
+        return False
+
+    def close(self) -> None:
+        """Closes the stream
+        
+        Since this is a wrapper for requests to S3, there is no concept of closing, therefore this method does nothing
+        """
+        pass
+
+class BotoInputFile(InputFile):
+    """An input file implementation for the BotoFileIO
+
+    Args:
+        location(str): An S3 URI
+
+    Attributes:
+        location(str): An S3 URI
+
+    Examples:
+        >>> from iceberg.io.boto import BotoInputFile
+        >>> input_file = BotoInputFile("s3://foo/bar.txt")
+        >>> file_content = input_file.open().read()  # Read the contents of the BotoInputFile instance
+    """
+
+    def __init__(self, location: str, session: Session):
+        parsed_location = urlparse(location)  # Create a ParseResult from the uri
+
+        if not parsed_location.scheme.startswith('s3'):
+            raise ValueError(f"Cannot create BotoInputFile, scheme not supported: {parsed_location.scheme}")
+
+        self._bucket = parsed_location.netloc
+        self._path = parsed_location.path.strip("/")
+        self._session = session
+        super().__init__(location=location)
+
+    def __len__(self) -> int:
+        """Returns the total length of the file, in bytes"""
+        file_info = self._file_info()
+        return file_info.size
+
+    def exists(self) -> bool:
+        """Checks whether the location exists"""
+        try:
+            self._session.resource('s3').Bucket(self._bucket).Object(self._path).load()  # raises botocore.exceptions.ClientError with a 404 if it does not exist

Review Comment:
   Ah you're absolutely right. But since we use the session object directly to create resource clients we'll probably need to add an endpoint argument to the `BotoFileIO` init and then consistently pass it to `resource(...)` which also has an [endpoint_url](https://boto3.amazonaws.com/v1/documentation/api/latest/reference/core/session.html#boto3.session.Session.resource) argument. Let me update this, thanks @joshuarobinson!



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