houqp commented on a change in pull request #950: URL: https://github.com/apache/arrow-datafusion/pull/950#discussion_r697158713
########## File path: datafusion/src/datasource/object_store/mod.rs ########## @@ -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>, +} + +/// Stream of files get listed from object store +pub type FileMetaStream = + Pin<Box<dyn Stream<Item = Result<FileMeta>> + Send + Sync + 'static>>; + +/// A ObjectStore abstracts access to an underlying file/object storage. +/// It maps strings (e.g. URLs, filesystem paths, etc) to sources of bytes +#[async_trait] +pub trait ObjectStore: Sync + Send + Debug { + /// Returns all the files in path `prefix` asynchronously + async fn list(&self, prefix: &str) -> Result<FileMetaStream>; + + /// Get object reader for one file + async fn get_reader(&self, file: FileMeta) -> Result<Arc<dyn ObjectReader>>; +} + +static LOCAL_SCHEME: &str = "file"; + +/// A Registry holds all the object stores at runtime with a scheme for each store. +/// This allows the user to extend DataFusion with different storage systems such as S3 or HDFS +/// and query data inside these systems. +pub struct ObjectStoreRegistry { + /// A map from scheme to object store that serve list / read operations for the store + pub object_stores: RwLock<HashMap<String, Arc<dyn ObjectStore>>>, +} + +impl ObjectStoreRegistry { + /// Create the registry that object stores can registered into. + /// ['LocalFileSystem'] store is registered in by default to support read local files natively. + pub fn new() -> Self { + let mut map: HashMap<String, Arc<dyn ObjectStore>> = HashMap::new(); + map.insert(LOCAL_SCHEME.to_string(), Arc::new(LocalFileSystem)); + + Self { + object_stores: RwLock::new(map), + } + } + + /// Adds a new store to this registry. + /// If a store of the same prefix existed before, it is replaced in the registry and returned. + pub fn register_store( + &self, + scheme: String, + store: Arc<dyn ObjectStore>, + ) -> Option<Arc<dyn ObjectStore>> { + let mut stores = self.object_stores.write().unwrap(); + stores.insert(scheme, store) + } + + /// Get the store registered for scheme + pub fn get(&self, scheme: &str) -> Option<Arc<dyn ObjectStore>> { + let stores = self.object_stores.read().unwrap(); + stores.get(scheme).cloned() + } + + /// Get a suitable store for the URI based on it's scheme. For example: + /// URI with scheme file or no schema will return the default LocalFS store, + /// URI with scheme s3 will return the S3 store if it's registered. + pub fn get_by_uri(&self, uri: &str) -> Result<Arc<dyn ObjectStore>> { + if let Some((scheme, _)) = uri.split_once(':') { + let stores = self.object_stores.read().unwrap(); + if let Some(store) = stores.get(&*scheme.to_lowercase()) { + Ok(store.clone()) + } else { + Err(DataFusionError::Internal(format!( + "No suitable object store found for {}", + scheme + ))) + } Review comment: You can probably use ok_or_else to simplify the code: ```suggestion stores.get(&*scheme.to_lowercase()).ok_or_else(|| DataFusionError::Internal(format!( "No suitable object store found for {}", scheme ))) ``` -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. 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