How do I handle gzip or deflate compressed responses in Reqwest?

When you make a web request using reqwest, which is a popular HTTP client for Rust, the response you receive might be compressed using gzip or deflate encoding. By default, reqwest handles these encodings automatically and decompresses the response body for you, so you don't have to manually handle the decompression most of the time.

However, if you need to manually handle the compressed response for some reason, you can do so by disabling the automatic decompression feature provided by reqwest. After disabling this feature, you can manually decompress the response using the flate2 crate for gzip or deflate compressed content.

Here's how to handle gzip or deflate compressed responses manually:

1. First, add the dependencies in your Cargo.toml:

[dependencies]
reqwest = { version = "0.11", default-features = false, features = ["blocking", "json"] }
flate2 = "1.0"

1. Then, you can write a function to make a request and handle the decompression manually:

use reqwest;
use flate2::read::{GzDecoder, DeflateDecoder};
use std::io::Read;

fn fetch_and_decompress(url: &str) -> Result<Vec<u8>, Box<dyn std::error::Error>> {
    // Build the client and disable automatic decompression
    let client = reqwest::blocking::Client::builder()
        .gzip(false)
        .deflate(false)
        .build()?;

    // Make the request and get the response
    let mut response = client.get(url).send()?;

    // Check the Content-Encoding header to determine the compression method
    let content_encoding = response.headers().get(reqwest::header::CONTENT_ENCODING);

    // Create a buffer to hold the decompressed data
    let mut decompressed_data = Vec::new();

    match content_encoding.and_then(|v| v.to_str().ok()) {
        Some("gzip") => {
            // The response is gzip-compressed, so decode it accordingly
            let body = response.text()?;
            let mut decoder = GzDecoder::new(body.as_bytes());
            decoder.read_to_end(&mut decompressed_data)?;
        },
        Some("deflate") => {
            // The response is deflate-compressed, so decode it accordingly
            let body = response.text()?;
            let mut decoder = DeflateDecoder::new(body.as_bytes());
            decoder.read_to_end(&mut decompressed_data)?;
        },
        _ => {
            // The response is not compressed, or the encoding is not supported
            // You can read it directly
            decompressed_data = response.bytes()?.to_vec();
        }
    }

    Ok(decompressed_data)
}

fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Replace with the actual URL you want to fetch
    let url = "http://example.com/some-compressed-resource";
    let data = fetch_and_decompress(url)?;

    // Use the decompressed data as needed...

    Ok(())
}

In this code snippet, we first create a reqwest::Client with .gzip(false).deflate(false) to disable automatic decompression. Then, we check the Content-Encoding header to see which compression method was used (if any), and we manually decompress the response using GzDecoder for gzip or DeflateDecoder for deflate. Finally, we return the decompressed data as a Vec<u8>.

Remember that the above example uses the blocking API from reqwest. If you're using async, you'll need to adjust the code to work with .await and the async counterparts of the reqwest and flate2 functions.