Media Types

Get MIME type from string

The following example shows how to parse a MIME type from a string using the mime crate. FromStrError produces a default MIME type in an unwrap_or clause.

use mime::{Mime, APPLICATION_OCTET_STREAM};

fn main() {
    let invalid_mime_type = "i n v a l i d";
    let default_mime = invalid_mime_type
        .parse::<Mime>()
        .unwrap_or(APPLICATION_OCTET_STREAM);

    println!(
        "MIME for {:?} used default value {:?}",
        invalid_mime_type, default_mime
    );

    let valid_mime_type = "TEXT/PLAIN";
    let parsed_mime = valid_mime_type
        .parse::<Mime>()
        .unwrap_or(APPLICATION_OCTET_STREAM);

    println!(
        "MIME for {:?} was parsed as {:?}",
        valid_mime_type, parsed_mime
    );
}

Get MIME type from filename

The following example shows how to return the correct MIME type from a given filename using the mime crate. The program will check for file extensions and match against a known list. The return value is mime:Mime.

use mime::Mime;

fn find_mimetype (filename : &String) -> Mime{

    let parts : Vec<&str> = filename.split('.').collect();

    let res = match parts.last() {
            Some(v) =>
                match *v {
                    "png" => mime::IMAGE_PNG,
                    "jpg" => mime::IMAGE_JPEG,
                    "json" => mime::APPLICATION_JSON,
                    &_ => mime::TEXT_PLAIN,
                },
            None => mime::TEXT_PLAIN,
        };
    return res;
}

fn main() {
    let filenames = vec!("foobar.jpg", "foo.bar", "foobar.png");
    for file in filenames {
	    let mime = find_mimetype(&file.to_owned());
	 	println!("MIME for {}: {}", file, mime);
	 }

}

Parse the MIME type of a HTTP response

When receiving a HTTP reponse from reqwest the MIME type or media type may be found in the Content-Type header. reqwest::header::HeaderMap::get retrieves the header as a reqwest::header::HeaderValue, which can be converted to a string. The mime crate can then parse that, yielding a mime::Mime value.

The mime crate also defines some commonly used MIME types.

Note that the reqwest::header module is exported from the http crate.

use error_chain::error_chain;
use mime::Mime;
use std::str::FromStr;
use reqwest::header::CONTENT_TYPE;

 error_chain! {
    foreign_links {
        Reqwest(reqwest::Error);
        Header(reqwest::header::ToStrError);
        Mime(mime::FromStrError);
    }
 }

#[tokio::main]
async fn main() -> Result<()> {
    let response = reqwest::get("https://www.rust-lang.org/logos/rust-logo-32x32.png").await?;
    let headers = response.headers();

    match headers.get(CONTENT_TYPE) {
        None => {
            println!("The response does not contain a Content-Type header.");
        }
        Some(content_type) => {
            let content_type = Mime::from_str(content_type.to_str()?)?;
            let media_type = match (content_type.type_(), content_type.subtype()) {
                (mime::TEXT, mime::HTML) => "a HTML document",
                (mime::TEXT, _) => "a text document",
                (mime::IMAGE, mime::PNG) => "a PNG image",
                (mime::IMAGE, _) => "an image",
                _ => "neither text nor image",
            };

            println!("The reponse contains {}.", media_type);
        }
    };

    Ok(())
}