thread 'main' panicked at 'Box<Any>' - rust

Question

I am trying to learn Rust. I am following a book online which implements the unix program cat. Right now I trying to read the content of files passed as an argument like that cargo run file1.txt file2.txt but the program panics:
D:\rust\cat> cargo run .\src\test.txt
Compiling cat v0.1.0 (D:\rust\cat)
Finished dev [unoptimized + debuginfo] target(s) in 0.62s
Running `target\debug\cat.exe .\src\test.txt`
thread 'main' panicked at 'Box<Any>', src\main.rs:12:28
this is my program:
use std::env;
use std::fs::File;
use std::io;
use std::io::prelude::*;
fn main() {
let args: Vec<String> = env::args().collect();
if args.len() > 1 {
match read_file(&args) {
Ok(content) => println!("{}", content),
Err(reason) => panic!(reason),
}
}
}
fn read_file(filenames: &Vec<String>) -> Result<String, io::Error> {
let mut content = String::new();
for filename in filenames {
let mut file = File::open(filename)?;
file.read_to_string(&mut content)?;
}
Ok(content)
}
Can anyone explain what I am missing here?

Answer 1

The first element of the Args iterator returned by std::env::args is tipically the path of executable (see the docs
for more details).
The error arises because you do not skip the first arg: the program binary is not a sequence of valid UTF-8 bytes.
The apparently non sense error thread 'main' panicked at 'Box<Any>' is because panic! is not used with the same arguments of
the format! syntax.
use std::env;
use std::fs::File;
use std::io;
use std::io::prelude::*;
fn main() {
for filename in env::args().skip(1) {
match read_file(filename) {
Ok(content) => println!("{}", content),
Err(reason) => panic!("{}", reason),
}
}
}
fn read_file(filename: String) -> Result<String, io::Error> {
let mut content = String::new();
let mut file = File::open(filename)?;
file.read_to_string(&mut content)?;
Ok(content)
}