martin-g commented on code in PR #19924:
URL: https://github.com/apache/datafusion/pull/19924#discussion_r2726811083
##########
datafusion/common/src/config.rs:
##########
@@ -3065,6 +3065,25 @@ config_namespace! {
/// If not specified, the default level for the compression algorithm
is used.
pub compression_level: Option<u32>, default = None
pub schema_infer_max_rec: Option<usize>, default = None
+ /// The JSON format to use when reading files.
+ ///
+ /// When `true` (default), expects newline-delimited JSON (NDJSON):
+ /// ```text
+ /// {"key1": 1, "key2": "val"}
+ /// {"key1": 2, "key2": "vals"}
+ /// ```
+ ///
+ /// When `false`, expects JSON array format:
+ /// ```text
+ /// [
+ /// {"key1": 1, "key2": "val"},
+ /// {"key1": 2, "key2": "vals"}
+ /// ]
+ /// ```
+ ///
+ /// Note: JSON array format requires loading the entire file into
memory.
Review Comment:
This is no more true
##########
datafusion/datasource-json/src/utils.rs:
##########
@@ -0,0 +1,389 @@
+// 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};
+
+// ============================================================================
+// JsonArrayToNdjsonReader - Streaming JSON Array to NDJSON Converter
+// ============================================================================
+//
+// Architecture:
+//
+// ```text
+// ┌─────────────────────────────────────────────────────────────┐
+// │ JSON Array File (potentially very large, e.g. 1GB) │
+// │ [{"a":1}, {"a":2}, {"a":3}, ...... {"a":1000000}] │
+// └─────────────────────────────────────────────────────────────┘
+// │
+// ▼ read small chunks at a time (e.g. 64KB)
+// ┌───────────────────┐
+// │ JsonArrayToNdjson │ ← character substitution only:
+// │ Reader │ '[' skip, ',' → '\n', ']' stop
+// └───────────────────┘
+// │
+// ▼ outputs NDJSON format
+// ┌───────────────────┐
+// │ Arrow Reader │ ← internal buffer, batch parsing
+// │ batch_size=1024 │
+// └───────────────────┘
+// │
+// ▼ outputs RecordBatch for every batch_size rows
+// ┌───────────────────┐
+// │ RecordBatch │
+// │ (1024 rows) │
+// └───────────────────┘
+// ```
+//
+// Memory Efficiency:
+//
+// | Approach | Memory for 1GB file | Parse count
|
+//
|---------------------------------------|---------------------|-------------|
+// | Load entire file + serde_json | ~5GB | 3x
|
+// | Streaming with JsonArrayToNdjsonReader| ~few MB | 1x
|
+//
+
+/// Default buffer size for JsonArrayToNdjsonReader (64KB)
+const DEFAULT_BUF_SIZE: usize = 64 * 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: 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,
+ /// Internal buffer for BufRead implementation
+ buffer: Vec<u8>,
+ /// Current position in the buffer
+ pos: usize,
+ /// Number of valid bytes in the buffer
+ filled: usize,
+}
+
+impl<R: Read> JsonArrayToNdjsonReader<R> {
+ /// Create a new streaming reader that converts JSON array to NDJSON.
+ pub fn new(reader: R) -> Self {
+ Self {
+ inner: reader,
+ state: JsonArrayState::Start,
+ depth: 0,
+ in_string: false,
+ escape_next: false,
+ buffer: vec![0; DEFAULT_BUF_SIZE],
+ pos: 0,
+ filled: 0,
+ }
+ }
+
+ /// Check if the JSON array was properly terminated.
+ ///
+ /// Returns an error if:
+ /// - Unbalanced braces/brackets (depth != 0)
+ /// - Unterminated string
+ /// - Missing closing `]`
+ pub fn validate_complete(&self) -> std::io::Result<()> {
Review Comment:
This new method seems unused.
Please add some tests with invalid JSON to trigger the failures.
##########
datafusion/proto-common/proto/datafusion_common.proto:
##########
@@ -469,6 +469,7 @@ message JsonOptions {
CompressionTypeVariant compression = 1; // Compression type
optional uint64 schema_infer_max_rec = 2; // Optional max records for schema
inference
optional uint32 compression_level = 3; // Optional compression level
+ bool newline_delimited = 4; // Whether to read as newline-delimited JSON
(default true). When false, expects JSON array format [{},...]
Review Comment:
if an old message is decoded it won't have the new property and it will
initialized to `false`, i.e. JSON array
```suggestion
optional bool newline_delimited = 4; // Whether to read as
newline-delimited JSON (default true). When false, expects JSON array format
[{},...]
```
##########
datafusion/core/src/datasource/file_format/options.rs:
##########
@@ -442,7 +442,9 @@ impl<'a> AvroReadOptions<'a> {
}
}
-/// Options that control the reading of Line-delimited JSON files (NDJson)
+/// Options that control the reading of JSON files.
+///
+/// Supports both newline-delimited JSON (NDJSON) and JSON array formats.
Review Comment:
The struct name is still `NdJsonReadOptions`. I guess it is not renamed
(e.g. to `JsonReadOptions`) to prevent API breaks.
Maybe you could rename it and add a deprecated type alias that will be
usable for a while ?!
##########
datafusion/datasource-json/src/utils.rs:
##########
@@ -0,0 +1,389 @@
+// 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};
+
+// ============================================================================
+// JsonArrayToNdjsonReader - Streaming JSON Array to NDJSON Converter
+// ============================================================================
+//
+// Architecture:
+//
+// ```text
+// ┌─────────────────────────────────────────────────────────────┐
+// │ JSON Array File (potentially very large, e.g. 1GB) │
+// │ [{"a":1}, {"a":2}, {"a":3}, ...... {"a":1000000}] │
+// └─────────────────────────────────────────────────────────────┘
+// │
+// ▼ read small chunks at a time (e.g. 64KB)
+// ┌───────────────────┐
+// │ JsonArrayToNdjson │ ← character substitution only:
+// │ Reader │ '[' skip, ',' → '\n', ']' stop
+// └───────────────────┘
+// │
+// ▼ outputs NDJSON format
+// ┌───────────────────┐
+// │ Arrow Reader │ ← internal buffer, batch parsing
+// │ batch_size=1024 │
+// └───────────────────┘
+// │
+// ▼ outputs RecordBatch for every batch_size rows
+// ┌───────────────────┐
+// │ RecordBatch │
+// │ (1024 rows) │
+// └───────────────────┘
+// ```
+//
+// Memory Efficiency:
+//
+// | Approach | Memory for 1GB file | Parse count
|
+//
|---------------------------------------|---------------------|-------------|
+// | Load entire file + serde_json | ~5GB | 3x
|
+// | Streaming with JsonArrayToNdjsonReader| ~few MB | 1x
|
+//
+
+/// Default buffer size for JsonArrayToNdjsonReader (64KB)
+const DEFAULT_BUF_SIZE: usize = 64 * 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: 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,
+ /// Internal buffer for BufRead implementation
+ buffer: Vec<u8>,
+ /// Current position in the buffer
+ pos: usize,
+ /// Number of valid bytes in the buffer
+ filled: usize,
+}
+
+impl<R: Read> JsonArrayToNdjsonReader<R> {
+ /// Create a new streaming reader that converts JSON array to NDJSON.
+ pub fn new(reader: R) -> Self {
+ Self {
+ inner: reader,
+ state: JsonArrayState::Start,
+ depth: 0,
+ in_string: false,
+ escape_next: false,
+ buffer: vec![0; DEFAULT_BUF_SIZE],
+ pos: 0,
+ filled: 0,
+ }
+ }
+
+ /// Check if the JSON array was properly terminated.
+ ///
+ /// Returns an error if:
+ /// - Unbalanced braces/brackets (depth != 0)
+ /// - Unterminated string
+ /// - Missing closing `]`
+ pub fn validate_complete(&self) -> std::io::Result<()> {
+ if self.depth != 0 {
+ return Err(std::io::Error::new(
+ std::io::ErrorKind::InvalidData,
+ "Malformed JSON array: unbalanced braces or brackets",
+ ));
+ }
+ if self.in_string {
+ return Err(std::io::Error::new(
+ std::io::ErrorKind::InvalidData,
+ "Malformed JSON array: unterminated string",
+ ));
+ }
+ if self.state != JsonArrayState::Done {
+ return Err(std::io::Error::new(
+ std::io::ErrorKind::InvalidData,
+ "Malformed JSON array: missing closing ']'",
+ ));
+ }
+ Ok(())
+ }
+
+ /// Process a single byte and return the transformed byte (if any)
+ fn process_byte(&mut self, byte: u8) -> Option<u8> {
+ match self.state {
+ JsonArrayState::Start => {
+ // Looking for the opening '[', skip whitespace
+ if byte == b'[' {
+ self.state = JsonArrayState::InArray;
+ }
+ // Skip whitespace and the '[' itself
+ None
+ }
+ JsonArrayState::InArray => {
+ // Handle escape sequences in strings
+ if self.escape_next {
+ self.escape_next = false;
+ return Some(byte);
+ }
+
+ if self.in_string {
+ // Inside a string: handle escape and closing quote
+ match byte {
+ b'\\' => self.escape_next = true,
+ b'"' => self.in_string = false,
+ _ => {}
+ }
+ Some(byte)
+ } else {
+ // Outside strings: track depth and transform
+ match byte {
+ b'"' => {
+ self.in_string = true;
+ Some(byte)
+ }
+ b'{' | b'[' => {
+ self.depth += 1;
+ Some(byte)
+ }
+ b'}' => {
+ self.depth -= 1;
+ Some(byte)
+ }
+ b']' => {
+ if self.depth == 0 {
+ // Top-level ']' means end of array
+ self.state = JsonArrayState::Done;
+ None
+ } else {
+ // Nested ']' inside an object
+ self.depth -= 1;
+ Some(byte)
+ }
+ }
+ b',' if self.depth == 0 => {
+ // Top-level comma between objects → newline
+ Some(b'\n')
+ }
+ _ => {
+ // At depth 0, skip whitespace between objects
+ if self.depth == 0 && byte.is_ascii_whitespace() {
+ None
+ } else {
+ Some(byte)
+ }
+ }
+ }
+ }
+ }
+ JsonArrayState::Done => None,
+ }
+ }
+
+ /// Fill the internal buffer with transformed data
+ fn fill_internal_buffer(&mut self) -> std::io::Result<()> {
+ if self.state == JsonArrayState::Done {
+ return Ok(());
+ }
+
+ // Read raw data from inner reader
+ let mut raw_buf = vec![0u8; DEFAULT_BUF_SIZE];
+ let mut write_pos = 0;
+
+ loop {
+ if write_pos >= self.buffer.len() {
+ break;
+ }
+
+ let bytes_read = self.inner.read(&mut raw_buf)?;
+ if bytes_read == 0 {
+ break; // EOF
+ }
+
+ for &byte in &raw_buf[..bytes_read] {
+ if self.state == JsonArrayState::Done {
+ break;
+ }
+ if let Some(transformed) = self.process_byte(byte)
+ && write_pos < self.buffer.len()
+ {
+ self.buffer[write_pos] = transformed;
+ write_pos += 1;
+ }
+ }
+
+ if self.state == JsonArrayState::Done {
+ break;
+ }
+ }
+
+ self.pos = 0;
+ self.filled = write_pos;
+ Ok(())
+ }
+}
+
+impl<R: Read> Read for JsonArrayToNdjsonReader<R> {
+ fn read(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
+ // If buffer is empty, fill it
+ if self.pos >= self.filled {
+ self.fill_internal_buffer()?;
+ if self.filled == 0 {
+ return Ok(0); // EOF
+ }
+ }
+
+ // Copy from internal buffer to output
+ let available = self.filled - self.pos;
+ let to_copy = std::cmp::min(available, buf.len());
+ buf[..to_copy].copy_from_slice(&self.buffer[self.pos..self.pos +
to_copy]);
+ self.pos += to_copy;
+ Ok(to_copy)
+ }
+}
+
+impl<R: Read> BufRead for JsonArrayToNdjsonReader<R> {
+ fn fill_buf(&mut self) -> std::io::Result<&[u8]> {
+ if self.pos >= self.filled {
+ self.fill_internal_buffer()?;
+ }
+ Ok(&self.buffer[self.pos..self.filled])
+ }
+
+ fn consume(&mut self, amt: usize) {
+ self.pos = std::cmp::min(self.pos + amt, self.filled);
+ }
+}
+
+#[cfg(test)]
+mod tests {
+ use super::*;
+
+ #[test]
+ fn test_json_array_to_ndjson_simple() {
+ let input = r#"[{"a":1}, {"a":2}, {"a":3}]"#;
+ let mut reader = JsonArrayToNdjsonReader::new(input.as_bytes());
+ let mut output = String::new();
+ reader.read_to_string(&mut output).unwrap();
+ assert_eq!(output, "{\"a\":1}\n{\"a\":2}\n{\"a\":3}");
+ }
+
+ #[test]
+ fn test_json_array_to_ndjson_nested() {
+ let input = r#"[{"a":{"b":1}}, {"c":[1,2,3]}]"#;
+ let mut reader = JsonArrayToNdjsonReader::new(input.as_bytes());
+ let mut output = String::new();
+ reader.read_to_string(&mut output).unwrap();
+ assert_eq!(output, "{\"a\":{\"b\":1}}\n{\"c\":[1,2,3]}");
+ }
+
+ #[test]
+ fn test_json_array_to_ndjson_strings_with_special_chars() {
+ let input = r#"[{"a":"[1,2]"}, {"b":"x,y"}]"#;
+ let mut reader = JsonArrayToNdjsonReader::new(input.as_bytes());
+ let mut output = String::new();
+ reader.read_to_string(&mut output).unwrap();
+ assert_eq!(output, "{\"a\":\"[1,2]\"}\n{\"b\":\"x,y\"}");
+ }
+
+ #[test]
+ fn test_json_array_to_ndjson_escaped_quotes() {
+ let input = r#"[{"a":"say \"hello\""}, {"b":1}]"#;
+ let mut reader = JsonArrayToNdjsonReader::new(input.as_bytes());
+ let mut output = String::new();
+ reader.read_to_string(&mut output).unwrap();
+ assert_eq!(output, "{\"a\":\"say \\\"hello\\\"\"}\n{\"b\":1}");
+ }
+
+ #[test]
+ fn test_json_array_to_ndjson_empty() {
+ let input = r#"[]"#;
+ let mut reader = JsonArrayToNdjsonReader::new(input.as_bytes());
+ let mut output = String::new();
+ reader.read_to_string(&mut output).unwrap();
+ assert_eq!(output, "");
+ }
+
+ #[test]
+ fn test_json_array_to_ndjson_single_element() {
+ let input = r#"[{"a":1}]"#;
+ let mut reader = JsonArrayToNdjsonReader::new(input.as_bytes());
+ let mut output = String::new();
+ reader.read_to_string(&mut output).unwrap();
+ assert_eq!(output, "{\"a\":1}");
+ }
+
+ #[test]
+ fn test_json_array_to_ndjson_bufread() {
+ let input = r#"[{"a":1}, {"a":2}]"#;
+ let mut reader = JsonArrayToNdjsonReader::new(input.as_bytes());
+
+ let buf = reader.fill_buf().unwrap();
+ assert!(!buf.is_empty());
+
+ let first_len = buf.len();
+ reader.consume(first_len);
+
+ let mut output = String::new();
+ reader.read_to_string(&mut output).unwrap();
+ }
+
+ #[test]
+ fn test_json_array_to_ndjson_whitespace() {
+ let input = r#" [ {"a":1} , {"a":2} ] "#;
+ let mut reader = JsonArrayToNdjsonReader::new(input.as_bytes());
+ let mut output = String::new();
+ reader.read_to_string(&mut output).unwrap();
+ // Top-level whitespace is skipped, internal whitespace preserved
+ assert_eq!(output, "{\"a\":1}\n{\"a\":2}");
+ }
Review Comment:
Please also add a test case for ` let input = r#" [ {"a":1} , {"a":2} ]
some { junk [ here ] "#;`
--
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.
To unsubscribe, e-mail: [email protected]
For queries about this service, please contact Infrastructure at:
[email protected]
---------------------------------------------------------------------
To unsubscribe, e-mail: [email protected]
For additional commands, e-mail: [email protected]
