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parquet-read: add support to read parquet data from stdin #2482

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merged 1 commit into from Aug 18, 2022
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parquet-read: add support to read parquet data from stdin #2482

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21 changes: 16 additions & 5 deletions parquet/src/bin/parquet-read.rs
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Expand Up @@ -41,12 +41,13 @@ extern crate parquet;
use clap::Parser;
use parquet::file::reader::{FileReader, SerializedFileReader};
use parquet::record::Row;
use std::io::{self, Read};
use std::{fs::File, path::Path};

#[derive(Debug, Parser)]
#[clap(author, version, about("Binary file to read data from a Parquet file"), long_about = None)]
struct Args {
#[clap(short, long, help("Path to a parquet file"))]
#[clap(short, long, help("Path to a parquet file, or - for stdin"))]
file_name: String,
#[clap(
short,
Expand All @@ -66,10 +67,20 @@ fn main() {
let num_records = args.num_records;
let json = args.json;

let path = Path::new(&filename);
let file = File::open(&path).expect("Unable to open file");
let parquet_reader =
SerializedFileReader::new(file).expect("Failed to create reader");
let parquet_reader: Box<dyn FileReader> = if filename == "-" {
let mut buf = Vec::new();
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It may surprise people who aren't familiar with parquet that this will buffer the entire file in memory, as opposed to streaming it. Perhaps we could add a note to the help text to alert people?

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As @tustvold suggests, I think it is inevitable that reading from stdin requires buffering (because the parquet footer is at the end of the file and we need to get past all the data to get to the footer).

io::stdin()
.read_to_end(&mut buf)
.expect("Failed to read stdin into a buffer");
Box::new(
SerializedFileReader::new(bytes::Bytes::from(buf))
.expect("Failed to create reader"),
)
} else {
let path = Path::new(&filename);
let file = File::open(&path).expect("Unable to open file");
Box::new(SerializedFileReader::new(file).expect("Failed to create reader"))
};

// Use full schema as projected schema
let mut iter = parquet_reader
Expand Down