[GitHub] [arrow-rs] viirya commented on a diff in pull request #1803: Add AsyncChunkReader trait

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

viirya commented on code in PR #1803:
URL: https://github.com/apache/arrow-rs/pull/1803#discussion_r890453518


##########
parquet/src/arrow/async_reader.rs:
##########
@@ -101,8 +103,63 @@ use crate::file::footer::parse_metadata_buffer;
 use crate::file::metadata::ParquetMetaData;
 use crate::file::reader::SerializedPageReader;
 use crate::file::PARQUET_MAGIC;
-use crate::schema::types::{ColumnDescPtr, SchemaDescPtr};
-use crate::util::memory::ByteBufferPtr;
+use crate::schema::types::{ColumnDescPtr, SchemaDescPtr, SchemaDescriptor};
+
+/// A reader that can asynchronously read a range of bytes
+pub trait AsyncChunkReader: Send + Unpin + 'static {
+    /// Retrieve the bytes in `range`
+    fn get_bytes(&mut self, range: Range<usize>) -> BoxFuture<'_, Result<Bytes>>;
+
+    /// Retrieve the [`ParquetMetaData`] for this file
+    fn get_metadata(&mut self) -> BoxFuture<'_, Result<Arc<ParquetMetaData>>>;
+}
+
+impl<T: AsyncRead + AsyncSeek + Unpin + Send + 'static> AsyncChunkReader for T {
+    fn get_bytes(&mut self, range: Range<usize>) -> BoxFuture<'_, Result<Bytes>> {
+        async move {
+            self.seek(SeekFrom::Start(range.start as u64)).await?;

Review Comment:
   Hmm, as `get_bytes` and `get_metadata` both async, and they both call `seek`. Is any chance there will be race condition between then? For example, calling `get_bytes` first but the file pos is changed by call `get_metadata` next?



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