zhuqi-lucas commented on code in PR #19924:
URL: https://github.com/apache/datafusion/pull/19924#discussion_r2785437673
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datafusion/datasource-json/Cargo.toml:
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@@ -43,8 +43,11 @@ datafusion-physical-expr-common = { workspace = true }
datafusion-physical-plan = { workspace = true }
datafusion-session = { workspace = true }
futures = { workspace = true }
+log = "0.4.29"
Review Comment:
Addressed in latest commit!
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datafusion/datasource-json/src/utils.rs:
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@@ -0,0 +1,734 @@
+// 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.
+
+//! Utility types for JSON processing
+
+use std::io::{BufRead, Read};
+use std::sync::mpsc::Receiver;
+
+use bytes::Bytes;
+
+// ============================================================================
+// JsonArrayToNdjsonReader - Streaming JSON Array to NDJSON Converter
+// ============================================================================
+//
+// Architecture:
+//
+// ```text
+// ┌─────────────────────────────────────────────────────────────┐
+// │ JSON Array File (potentially very large, e.g. 33GB) │
+// │ [{"a":1}, {"a":2}, {"a":3}, ...... {"a":1000000}] │
+// └─────────────────────────────────────────────────────────────┘
+// │
+// ▼ read chunks via ChannelReader
+// ┌───────────────────┐
+// │ JsonArrayToNdjson │ ← character substitution only:
+// │ Reader │ '[' skip, ',' → '\n', ']' stop
+// └───────────────────┘
+// │
+// ▼ outputs NDJSON format
+// ┌───────────────────┐
+// │ Arrow Reader │ ← internal buffer, batch parsing
+// │ batch_size=8192 │
+// └───────────────────┘
+// │
+// ▼ outputs RecordBatch
+// ┌───────────────────┐
+// │ RecordBatch │
+// └───────────────────┘
+// ```
+//
+// Memory Efficiency:
+//
+// | Approach | Memory for 33GB file | Parse
count |
+//
|---------------------------------------|----------------------|-------------|
+// | Load entire file + serde_json | ~100GB+ | 3x
|
+// | Streaming with JsonArrayToNdjsonReader| ~32MB (configurable) | 1x
|
+//
+// Design Note:
+//
+// This implementation uses `inner: R` directly (not `BufReader<R>`) and
manages
+// its own input buffer. This is critical for compatibility with `SyncIoBridge`
+// and `ChannelReader` in `spawn_blocking` contexts.
+//
+
+/// Default buffer size for JsonArrayToNdjsonReader (2MB for better throughput)
+const DEFAULT_BUF_SIZE: usize = 2 * 1024 * 1024;
+
+/// Parser state for JSON array streaming
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+enum JsonArrayState {
+ /// Initial state, looking for opening '['
+ Start,
+ /// Inside the JSON array, processing objects
+ InArray,
+ /// Reached the closing ']', finished
+ Done,
+}
+
+/// A streaming reader that converts JSON array format to NDJSON format.
+///
+/// This reader wraps an underlying reader containing JSON array data
+/// `[{...}, {...}, ...]` and transforms it on-the-fly to newline-delimited
+/// JSON format that Arrow's JSON reader can process.
+///
+/// Implements both `Read` and `BufRead` traits for compatibility with Arrow's
+/// `ReaderBuilder::build()` which requires `BufRead`.
+///
+/// # Transformation Rules
+///
+/// - Skip leading `[` and whitespace before it
+/// - Convert top-level `,` (between objects) to `\n`
+/// - Skip whitespace at top level (between objects)
+/// - Stop at trailing `]`
+/// - Preserve everything inside objects (including nested `[`, `]`, `,`)
+/// - Properly handle strings (ignore special chars inside quotes)
+///
+/// # Example
+///
+/// ```text
+/// Input: [{"a":1}, {"b":[1,2]}, {"c":"x,y"}]
+/// Output: {"a":1}
+/// {"b":[1,2]}
+/// {"c":"x,y"}
+/// ```
+pub struct JsonArrayToNdjsonReader<R: Read> {
+ /// Inner reader - we use R directly (not `BufReader<R>`) for SyncIoBridge
compatibility
+ inner: R,
+ state: JsonArrayState,
+ /// Tracks nesting depth of `{` and `[` to identify top-level commas
+ depth: i32,
+ /// Whether we're currently inside a JSON string
+ in_string: bool,
+ /// Whether the next character is escaped (after `\`)
+ escape_next: bool,
+ /// Input buffer - stores raw bytes read from inner reader
+ input_buffer: Vec<u8>,
+ /// Current read position in input buffer
+ input_pos: usize,
+ /// Number of valid bytes in input buffer
+ input_filled: usize,
+ /// Output buffer - stores transformed NDJSON bytes
+ output_buffer: Vec<u8>,
+ /// Current read position in output buffer
+ output_pos: usize,
+ /// Number of valid bytes in output buffer
+ output_filled: usize,
+ /// Whether trailing non-whitespace content was detected after ']'
+ has_trailing_content: bool,
Review Comment:
Addressed in latest commit!
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