Decompress content using Rust and flate2 without headaches

A few days ago I had to deflate some compressed content using Rust. I quickly found the flate2 crate, it is well maintained and has a very high usage. I decided it would be a great fit for my little project, a CLI tool to download, decompress, and store in a local SQLite3 some content from AWS S3.

I wrote my small CLI tool, and it seemed to work perfectly on the first run. It was all nice until some time later. I have noticed that some lines of my compressed file were missing. The code was running fine and didn’t provide any warnings. After a few hours of debugging, I was sure there was a bug in my code somewhere. I went on and wrote a bunch more test to try to isolate in a reproducible way, where the problem was present, without any luck. All tests passing and no indication of problems anywhere.

At some point, I decided to use a sample from the original compressed files, and that is how I managed to reproduce the bug. The sample code in the README of the flate2 crate was what I used in my code:

use std::io::prelude::*;
use flate2::read::GzDecoder;

fn main() {
    let mut d = GzDecoder::new("...".as_bytes());
    let mut s = String::new();
    d.read_to_string(&mut s).unwrap();
    println!("{}", s);
}

Unfortunately, the GzDecoder cannot successfully decompress my files. I went then to the official library repository and found this issue which describes exactly my problem. I had to use the MultiGzDecoder instead, it all worked as expected after this change and I could decompress successfully my files. The example in the README of flate2 should probably be this:

use std::io::prelude::*;
use flate2::read::GzDecoder;

fn main() {
    let mut d = MultiGzDecoder::new("...".as_bytes());
    let mut s = String::new();
    d.read_to_string(&mut s).unwrap();
    println!("{}", s);
}

Finally, I still don’t know why the MultiGzDecoder works when the GzDecoder don’t. If you know, I will update this blog with your answer.