polars_io/cloud/
adaptors.rs

1//! Interface with the object_store crate and define AsyncSeek, AsyncRead.
2
3use std::sync::Arc;
4
5use object_store::ObjectStore;
6use object_store::buffered::BufWriter;
7use object_store::path::Path;
8use polars_error::PolarsResult;
9use polars_utils::plpath::PlPathRef;
10use tokio::io::AsyncWriteExt;
11
12use super::{CloudOptions, object_path_from_str};
13use crate::pl_async::get_runtime;
14use crate::utils::file::WriteableTrait;
15
16fn clone_io_err(e: &std::io::Error) -> std::io::Error {
17    std::io::Error::new(e.kind(), e.to_string())
18}
19
20/// Adaptor which wraps the interface of [ObjectStore::BufWriter] exposing a synchronous interface
21/// which implements `std::io::Write`.
22///
23/// This allows it to be used in sync code which would otherwise write to a simple File or byte stream,
24/// such as with `polars::prelude::CsvWriter`.
25///
26/// [ObjectStore::BufWriter]: https://docs.rs/object_store/latest/object_store/buffered/struct.BufWriter.html
27pub struct BlockingCloudWriter {
28    state: std::io::Result<BufWriter>,
29}
30
31impl BlockingCloudWriter {
32    /// Construct a new BlockingCloudWriter, re-using the given `object_store`
33    ///
34    /// Creates a new (current-thread) Tokio runtime
35    /// which bridges the sync writing process with the async ObjectStore multipart uploading.
36    /// TODO: Naming?
37    pub fn new_with_object_store(
38        object_store: Arc<dyn ObjectStore>,
39        path: Path,
40        cloud_upload_chunk_size: usize,
41    ) -> PolarsResult<Self> {
42        let writer = BufWriter::with_capacity(object_store, path, cloud_upload_chunk_size);
43        Ok(BlockingCloudWriter { state: Ok(writer) })
44    }
45
46    /// Constructs a new BlockingCloudWriter from a path and an optional set of CloudOptions.
47    ///
48    /// Wrapper around `BlockingCloudWriter::new_with_object_store` that is useful if you only have a single write task.
49    /// TODO: Naming?
50    pub async fn new(
51        uri: PlPathRef<'_>,
52        cloud_options: Option<&CloudOptions>,
53        cloud_upload_chunk_size: usize,
54    ) -> PolarsResult<Self> {
55        let (cloud_location, object_store) =
56            crate::cloud::build_object_store(uri, cloud_options, false).await?;
57        Self::new_with_object_store(
58            object_store.to_dyn_object_store().await,
59            object_path_from_str(&cloud_location.prefix)?,
60            cloud_upload_chunk_size,
61        )
62    }
63
64    /// Returns the underlying [`object_store::buffered::BufWriter`]
65    pub fn try_into_inner(mut self) -> std::io::Result<BufWriter> {
66        // We can't just return self.state:
67        // * cannot move out of type `adaptors::BlockingCloudWriter`, which implements the `Drop` trait
68        std::mem::replace(&mut self.state, Err(std::io::Error::other("")))
69    }
70
71    /// Closes the writer, or returns the existing error if it exists. After this function is called
72    /// the writer is guaranteed to be in an error state.
73    pub fn close(&mut self) -> std::io::Result<()> {
74        match self.try_with_writer(|writer| get_runtime().block_in_place_on(writer.shutdown())) {
75            Ok(_) => {
76                self.state = Err(std::io::Error::other("closed"));
77                Ok(())
78            },
79            Err(e) => Err(e),
80        }
81    }
82
83    fn try_with_writer<F, O>(&mut self, func: F) -> std::io::Result<O>
84    where
85        F: Fn(&mut BufWriter) -> std::io::Result<O>,
86    {
87        let writer: &mut BufWriter = self.state.as_mut().map_err(|e| clone_io_err(e))?;
88        match func(writer) {
89            Ok(v) => Ok(v),
90            Err(e) => {
91                self.state = Err(clone_io_err(&e));
92                Err(e)
93            },
94        }
95    }
96}
97
98impl std::io::Write for BlockingCloudWriter {
99    fn write(&mut self, buf: &[u8]) -> std::io::Result<usize> {
100        // SAFETY:
101        // We extend the lifetime for the duration of this function. This is safe as we block the
102        // async runtime here
103        let buf = unsafe { std::mem::transmute::<&[u8], &'static [u8]>(buf) };
104
105        self.try_with_writer(|writer| {
106            get_runtime()
107                .block_in_place_on(async { writer.write_all(buf).await.map(|_t| buf.len()) })
108        })
109    }
110
111    fn flush(&mut self) -> std::io::Result<()> {
112        self.try_with_writer(|writer| get_runtime().block_in_place_on(writer.flush()))
113    }
114}
115
116impl WriteableTrait for BlockingCloudWriter {
117    fn close(&mut self) -> std::io::Result<()> {
118        BlockingCloudWriter::close(self)
119    }
120
121    fn sync_all(&self) -> std::io::Result<()> {
122        Ok(())
123    }
124
125    fn sync_data(&self) -> std::io::Result<()> {
126        Ok(())
127    }
128}
129
130impl Drop for BlockingCloudWriter {
131    fn drop(&mut self) {
132        if self.state.is_err() {
133            return;
134        }
135
136        // Note: We should not hit here - the writer should instead be explicitly closed.
137        // But we still have this here as a safety measure to prevent silently dropping errors.
138        match self.close() {
139            Ok(()) => {},
140            e @ Err(_) => {
141                if std::thread::panicking() {
142                    eprintln!("ERROR: CloudWriter errored on close: {e:?}")
143                } else {
144                    e.unwrap()
145                }
146            },
147        }
148    }
149}
150
151#[cfg(test)]
152mod tests {
153
154    use polars_core::df;
155    use polars_core::prelude::DataFrame;
156
157    use crate::get_upload_chunk_size;
158
159    fn example_dataframe() -> DataFrame {
160        df!(
161            "foo" => &[1, 2, 3],
162            "bar" => &[None, Some("bak"), Some("baz")],
163        )
164        .unwrap()
165    }
166
167    #[test]
168    #[cfg(feature = "csv")]
169    fn csv_to_local_objectstore_cloudwriter() {
170        use super::*;
171        use crate::csv::write::CsvWriter;
172        use crate::prelude::SerWriter;
173
174        let mut df = example_dataframe();
175
176        let object_store: Arc<dyn ObjectStore> = Arc::new(
177            object_store::local::LocalFileSystem::new_with_prefix(std::env::temp_dir())
178                .expect("Could not initialize connection"),
179        );
180
181        let path: object_store::path::Path = "cloud_writer_example.csv".into();
182
183        let mut cloud_writer =
184            BlockingCloudWriter::new_with_object_store(object_store, path, get_upload_chunk_size())
185                .unwrap();
186        CsvWriter::new(&mut cloud_writer)
187            .finish(&mut df)
188            .expect("Could not write DataFrame as CSV to remote location");
189    }
190
191    // Skip this tests on Windows since it does not have a convenient /tmp/ location.
192    #[cfg_attr(target_os = "windows", ignore)]
193    #[cfg(feature = "csv")]
194    #[test]
195    fn cloudwriter_from_cloudlocation_test() {
196        use super::*;
197        use crate::SerReader;
198        use crate::csv::write::CsvWriter;
199        use crate::prelude::{CsvReadOptions, SerWriter};
200
201        let mut df = example_dataframe();
202
203        let path = "/tmp/cloud_writer_example2.csv";
204
205        std::fs::File::create(path).unwrap();
206
207        let mut cloud_writer = get_runtime()
208            .block_on(BlockingCloudWriter::new(
209                PlPathRef::new(&format!("file://{path}")),
210                None,
211                get_upload_chunk_size(),
212            ))
213            .unwrap();
214
215        CsvWriter::new(&mut cloud_writer)
216            .finish(&mut df)
217            .expect("Could not write DataFrame as CSV to remote location");
218
219        cloud_writer.close().unwrap();
220
221        assert_eq!(
222            CsvReadOptions::default()
223                .try_into_reader_with_file_path(Some(path.into()))
224                .unwrap()
225                .finish()
226                .unwrap(),
227            df
228        );
229    }
230}
polars_io/cloud/adaptors.rs

polars_io/cloud/
adaptors.rs
