Function infer_json_schema 

pub fn infer_json_schema<R: BufRead>(
    reader: R,
    max_read_records: Option<usize>,
) -> Result<(Schema, usize), ArrowError>

Infer the fields of a JSON file by reading the first n records of the buffer, with max_read_records controlling the maximum number of records to read.

If max_read_records is not set, the whole file is read to infer its field types.

Returns inferred schema and number of records read.

This function will not seek back to the start of the reader. The user has to manage the original file’s cursor. This function is useful when the reader’s cursor is not available (does not implement Seek), such is the case for compressed streams decoders.

Note that JSON is not able to represent all Arrow data types exactly. So the inferred schema might be different from the schema of the original data that was encoded as JSON. For example, JSON does not have different integer types, so all integers are inferred as Int64. Another example is binary data, which is encoded as a Base16 string in JSON and therefore inferred as String type by this function.

Examples

use std::fs::File;
use std::io::{BufReader, SeekFrom, Seek};
use flate2::read::GzDecoder;
use arrow_json::reader::infer_json_schema;

let mut file = File::open("test/data/mixed_arrays.json.gz").unwrap();

// file's cursor's offset at 0
let mut reader = BufReader::new(GzDecoder::new(&file));
let inferred_schema = infer_json_schema(&mut reader, None).unwrap();
// cursor's offset at end of file

// seek back to start so that the original file is usable again
file.seek(SeekFrom::Start(0)).unwrap();