ARROW-7971: [Rust] Create rowcount utility

This utility introduces a way to count the number of rows present in one or more Parquet files.  This was tested against the Parquet payloads in the `python/pyarrow/tests/data/parquet/` directory.  I created this utility out of necessity, as the `parquet-tools` project introduces applications written using Java.  This is a much faster alternative, and allows for multiple files to be counted at a time, rather than `parquet-tools` ability to only count one file at a time.

Closes #6511 from KenSuenobu/parquet-rowcount-rust and squashes the following commits:

76ce2d2 <Ken Suenobu> Renamed variable.
794237e <Ken Suenobu> Changed code to use row_groups() from metadata as suggested by @andygrove
31ebd36 <Ken Suenobu> Removed formatted space.
819df7a <Ken Suenobu> Creation of parquet-rowcount tool to help count number of rows in a Parquet file.

Authored-by: Ken Suenobu <ksuenobu@fastmail.com>
Signed-off-by: Krisztián Szűcs <szucs.krisztian@gmail.com>

rust/parquet/README.md

@@ -97,6 +97,10 @@ and optional `verbose` is the boolean flag that allows to print full metadata or
 and `num-records` is the number of records to read from a file (when not specified all records will
 be printed).
 
+- **parquet-rowcount** for reporting the number of records in one or more Parquet files.
+`Usage: parquet-rowcount <file-path> ...`, where `file-path` is the path to a Parquet file, and `...`
+indicates any number of additional parquet files.
+
 If you see `Library not loaded` error, please make sure `LD_LIBRARY_PATH` is set properly:
 ```
 export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:$(rustc --print sysroot)/lib

rust/parquet/src/bin/parquet-rowcount.rs

@@ -0,0 +1,74 @@
+// 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.
+
+//! Binary file to return the number of rows found from Parquet file(s).
+//!
+//! # Install
+//!
+//! `parquet-rowcount` can be installed using `cargo`:
+//! ```
+//! cargo install parquet
+//! ```
+//! After this `parquet-rowcount` should be globally available:
+//! ```
+//! parquet-rowcount XYZ.parquet
+//! ```
+//!
+//! The binary can also be built from the source code and run as follows:
+//! ```
+//! cargo run --bin parquet-rowcount XYZ.parquet ABC.parquet ZXC.parquet
+//! ```
+//!
+//! # Usage
+//!
+//! ```
+//! parquet-rowcount <file-path> ...
+//! ```
+//! where `file-path` is the path to a Parquet file and `...` is any additional number of
+//! parquet files to count the number of rows from.
+//!
+//! Note that `parquet-rowcount` reads full file schema, no projection or filtering is
+//! applied.
+
+extern crate parquet;
+
+use std::{env, fs::File, path::Path, process};
+
+use parquet::file::reader::{FileReader, SerializedFileReader};
+
+fn main() {
+    let args: Vec<String> = env::args().collect();
+    if args.len() < 2 {
+        println!("Usage: parquet-rowcount <file-path> ...");
+        process::exit(1);
+    }
+
+    for i in 1..args.len() {
+        let filename = args[i].clone();
+        let path = Path::new(&filename);
+        let file = File::open(&path).unwrap();
+        let parquet_reader = SerializedFileReader::new(file).unwrap();
+        let row_group_metadata = parquet_reader.metadata().row_groups();
+        let mut total_num_rows = 0;
+
+        for group_metadata in row_group_metadata {
+            total_num_rows += group_metadata.num_rows();
+        }
+
+        eprintln!("File {}: rowcount={}", filename, total_num_rows);
+    }
+}