[GitHub] [arrow-datafusion] tustvold commented on a diff in pull request #2936: Add streaming JSON and CSV reading, `NewlineDelimitedStream' (#2935)

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

tustvold commented on code in PR #2936:
URL: https://github.com/apache/arrow-datafusion/pull/2936#discussion_r923437122


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datafusion/core/src/physical_plan/file_format/delimited_stream.rs:
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@@ -0,0 +1,215 @@
+// 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.
+
+use crate::error::{DataFusionError, Result};
+use bytes::Bytes;
+use futures::{Stream, StreamExt};
+use std::collections::VecDeque;
+
+/// The ASCII encoding of `"`
+const QUOTE: u8 = 34;
+
+/// The ASCII encoding of `\n`
+const NEWLINE: u8 = 10;
+
+/// The ASCII encoding of `\`
+const ESCAPE: u8 = 92;
+
+/// [`LineDelimiter`] is provided with a stream of [`Bytes`] and returns an iterator
+/// of [`Bytes`] containing a whole number of new line delimited records
+#[derive(Debug, Default)]
+struct LineDelimiter {
+    /// Complete chunks of [`Bytes`]
+    complete: VecDeque<Bytes>,
+    /// Remainder bytes that form the next record
+    remainder: Vec<u8>,

Review Comment:
   I think the copy is unavoidable as the nature of the remainder, is you need to take data from two separate `Bytes`. It should only be a single "line" though, and so should be relatively minor from a performance standpoint



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