[GitHub] [arrow-datafusion] houqp commented on a change in pull request #950: ObjectStore API to read from remote storage systems

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

houqp commented on a change in pull request #950:
URL: https://github.com/apache/arrow-datafusion/pull/950#discussion_r697156961



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File path: datafusion/src/datasource/object_store/mod.rs
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@@ -0,0 +1,127 @@
+// 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.
+
+//! Object Store abstracts access to an underlying file/object storage.
+
+pub mod local;
+
+use std::collections::HashMap;
+use std::fmt::Debug;
+use std::pin::Pin;
+use std::sync::{Arc, RwLock};
+
+use async_trait::async_trait;
+use futures::{AsyncRead, Stream};
+
+use local::LocalFileSystem;
+
+use crate::error::{DataFusionError, Result};
+use chrono::Utc;
+
+/// Object Reader for one file in a object store
+#[async_trait]
+pub trait ObjectReader {
+    /// Get reader for a part [start, start + length] in the file asynchronously
+    async fn get_reader(&self, start: u64, length: usize) -> Result<Arc<dyn AsyncRead>>;
+
+    /// Get length for the file asynchronously
+    async fn length(&self) -> Result<u64>;
+}
+
+/// File meta we got from object store
+pub struct FileMeta {
+    /// Path of the file
+    pub path: String,
+    /// Last time the file was modified in UTC
+    pub last_modified: Option<chrono::DateTime<Utc>>,
+    /// File size in total
+    pub size: Option<u64>,

Review comment:
       I remember running into similar issues (null object size) with Golang SDK in the past, but I couldn't remember exactly what triggered it.
   
   What's interesting is the new official AWS SDK doesn't have size declared as optional anymore:
   https://awslabs.github.io/aws-sdk-rust/aws_sdk_s3/model/struct.Object.html.
   
   I think in general, if we expect the consumer of `FileMeta` needing to access `size` for core logic, we should declare it as non-optional and manage error propagation in the s3 object store's implementation. If it's used in non-core logic, then I think declaring it as optional is fine.




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