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::file::WriteClose;
10use tokio::io::AsyncWriteExt;
11
12use super::{CloudOptions, object_path_from_str};
13use crate::pl_async::{get_runtime, get_upload_chunk_size};
14
15fn clone_io_err(e: &std::io::Error) -> std::io::Error {
16    std::io::Error::new(e.kind(), e.to_string())
17}
18
19/// Adaptor which wraps the interface of [ObjectStore::BufWriter] exposing a synchronous interface
20/// which implements `std::io::Write`.
21///
22/// This allows it to be used in sync code which would otherwise write to a simple File or byte stream,
23/// such as with `polars::prelude::CsvWriter`.
24///
25/// [ObjectStore::BufWriter]: https://docs.rs/object_store/latest/object_store/buffered/struct.BufWriter.html
26pub struct BlockingCloudWriter {
27    state: std::io::Result<BufWriter>,
28}
29
30impl BlockingCloudWriter {
31    /// Construct a new BlockingCloudWriter, re-using the given `object_store`
32    ///
33    /// Creates a new (current-thread) Tokio runtime
34    /// which bridges the sync writing process with the async ObjectStore multipart uploading.
35    /// TODO: Naming?
36    pub fn new_with_object_store(
37        object_store: Arc<dyn ObjectStore>,
38        path: Path,
39    ) -> PolarsResult<Self> {
40        let writer = BufWriter::with_capacity(object_store, path, get_upload_chunk_size());
41        Ok(BlockingCloudWriter { state: Ok(writer) })
42    }
43
44    /// Constructs a new BlockingCloudWriter from a path and an optional set of CloudOptions.
45    ///
46    /// Wrapper around `BlockingCloudWriter::new_with_object_store` that is useful if you only have a single write task.
47    /// TODO: Naming?
48    pub async fn new(uri: &str, cloud_options: Option<&CloudOptions>) -> PolarsResult<Self> {
49        if let Some(local_path) = uri.strip_prefix("file://") {
50            // Local paths must be created first, otherwise object store will not write anything.
51            if !matches!(std::fs::exists(local_path), Ok(true)) {
52                panic!("[BlockingCloudWriter] Expected local file to be created: {local_path}");
53            }
54        }
55
56        let (cloud_location, object_store) =
57            crate::cloud::build_object_store(uri, cloud_options, false).await?;
58        Self::new_with_object_store(
59            object_store.to_dyn_object_store().await,
60            object_path_from_str(&cloud_location.prefix)?,
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 WriteClose for BlockingCloudWriter {
117    fn close(mut self: Box<Self>) -> std::io::Result<()> {
118        BlockingCloudWriter::close(self.as_mut())
119    }
120}
121
122impl Drop for BlockingCloudWriter {
123    fn drop(&mut self) {
124        if self.state.is_err() {
125            return;
126        }
127
128        // Note: We should not hit here - the writer should instead be explicitly closed.
129        // But we still have this here as a safety measure to prevent silently dropping errors.
130        match self.close() {
131            Ok(()) => {},
132            e @ Err(_) => {
133                if std::thread::panicking() {
134                    eprintln!("ERROR: CloudWriter errored on close: {e:?}")
135                } else {
136                    e.unwrap()
137                }
138            },
139        }
140    }
141}
142
143#[cfg(test)]
144mod tests {
145
146    use polars_core::df;
147    use polars_core::prelude::DataFrame;
148
149    fn example_dataframe() -> DataFrame {
150        df!(
151            "foo" => &[1, 2, 3],
152            "bar" => &[None, Some("bak"), Some("baz")],
153        )
154        .unwrap()
155    }
156
157    #[test]
158    #[cfg(feature = "csv")]
159    fn csv_to_local_objectstore_cloudwriter() {
160        use super::*;
161        use crate::csv::write::CsvWriter;
162        use crate::prelude::SerWriter;
163
164        let mut df = example_dataframe();
165
166        let object_store: Arc<dyn ObjectStore> = Arc::new(
167            object_store::local::LocalFileSystem::new_with_prefix(std::env::temp_dir())
168                .expect("Could not initialize connection"),
169        );
170
171        let path: object_store::path::Path = "cloud_writer_example.csv".into();
172
173        let mut cloud_writer =
174            BlockingCloudWriter::new_with_object_store(object_store, path).unwrap();
175        CsvWriter::new(&mut cloud_writer)
176            .finish(&mut df)
177            .expect("Could not write DataFrame as CSV to remote location");
178    }
179
180    // Skip this tests on Windows since it does not have a convenient /tmp/ location.
181    #[cfg_attr(target_os = "windows", ignore)]
182    #[cfg(feature = "csv")]
183    #[test]
184    fn cloudwriter_from_cloudlocation_test() {
185        use super::*;
186        use crate::SerReader;
187        use crate::csv::write::CsvWriter;
188        use crate::prelude::{CsvReadOptions, SerWriter};
189
190        let mut df = example_dataframe();
191
192        let path = "/tmp/cloud_writer_example2.csv";
193
194        std::fs::File::create(path).unwrap();
195
196        let mut cloud_writer = get_runtime()
197            .block_on(BlockingCloudWriter::new(
198                format!("file://{path}").as_str(),
199                None,
200            ))
201            .unwrap();
202
203        CsvWriter::new(&mut cloud_writer)
204            .finish(&mut df)
205            .expect("Could not write DataFrame as CSV to remote location");
206
207        cloud_writer.close().unwrap();
208
209        assert_eq!(
210            CsvReadOptions::default()
211                .try_into_reader_with_file_path(Some(path.into()))
212                .unwrap()
213                .finish()
214                .unwrap(),
215            df
216        );
217    }
218}
polars_io/cloud/adaptors.rs

polars_io/cloud/
adaptors.rs
