continuwuity/src/utils/content_disposition.rs

use infer::MatcherType;

use crate::debug_info;

const ATTACHMENT: &str = "attachment";
const INLINE: &str = "inline";
const APPLICATION_OCTET_STREAM: &str = "application/octet-stream";
const IMAGE_SVG_XML: &str = "image/svg+xml";

/// Returns a Content-Disposition of `attachment` or `inline`, depending on the
/// *parsed* contents of the file uploaded via format magic keys using `infer`
/// crate (basically libmagic without needing libmagic).
///
/// This forbids trusting what the client or remote server says the file is from
/// their `Content-Type` and we try to detect it ourselves. Also returns
/// `attachment` if the Content-Type does not match what we detected.
///
/// TODO: add a "strict" function for comparing the Content-Type with what we
/// detected: `file_type.mime_type() != content_type`
#[tracing::instrument(skip(buf))]
pub(crate) fn content_disposition_type(buf: &[u8], content_type: &Option<String>) -> &'static str {
	let Some(file_type) = infer::get(buf) else {
		return ATTACHMENT;
	};

	debug_info!("MIME type: {}", file_type.mime_type());

	match file_type.matcher_type() {
		MatcherType::Image | MatcherType::Audio | MatcherType::Text | MatcherType::Video => {
			if file_type.mime_type().contains("xml") {
				ATTACHMENT
			} else {
				INLINE
			}
		},
		_ => ATTACHMENT,
	}
}

/// overrides the Content-Type with what we detected
///
/// SVG is special-cased due to the MIME type being classified as `text/xml` but
/// browsers need `image/svg+xml`
#[tracing::instrument(skip(buf))]
pub(crate) fn make_content_type(buf: &[u8], content_type: &Option<String>) -> &'static str {
	let Some(file_type) = infer::get(buf) else {
		debug_info!("Failed to infer the file's contents");
		return APPLICATION_OCTET_STREAM;
	};

	let Some(claimed_content_type) = content_type else {
		return file_type.mime_type();
	};

	if claimed_content_type.contains("svg") && file_type.mime_type().contains("xml") {
		return IMAGE_SVG_XML;
	}

	file_type.mime_type()
}

/// sanitises the file name for the Content-Disposition using
/// `sanitize_filename` crate
#[tracing::instrument]
pub(crate) fn sanitise_filename(filename: String) -> String {
	let options = sanitize_filename::Options {
		truncate: false,
		..Default::default()
	};

	sanitize_filename::sanitize_with_options(filename, options)
}

/// creates the final Content-Disposition based on whether the filename exists
/// or not.
///
/// if filename exists:
/// `Content-Disposition: attachment/inline; filename=filename.ext`
///
/// else: `Content-Disposition: attachment/inline`
#[tracing::instrument(skip(file))]
pub(crate) fn make_content_disposition(
	file: &[u8], content_type: &Option<String>, content_disposition: Option<String>,
) -> String {
	let filename = content_disposition.map_or_else(String::new, |content_disposition| {
		let (_, filename) = content_disposition
			.split_once("filename=")
			.unwrap_or(("", ""));

		if filename.is_empty() {
			String::new()
		} else {
			sanitise_filename(filename.to_owned())
		}
	});

	if !filename.is_empty() {
		// Content-Disposition: attachment/inline; filename=filename.ext
		format!("{}; filename={}", content_disposition_type(file, content_type), filename)
	} else {
		// Content-Disposition: attachment/inline
		String::from(content_disposition_type(file, content_type))
	}
}

#[cfg(test)]
mod tests {
	#[test]
	fn string_sanitisation() {
		const SAMPLE: &str =
			"🏳️‍⚧️this\\r\\n įs \r\\n ä \\r\nstrïng 🥴that\n\r ../../../../../../../may be\r\n malicious🏳️‍⚧️";
		const SANITISED: &str = "🏳️‍⚧️thisrn įs n ä rstrïng 🥴that ..............may be malicious🏳️‍⚧️";

		let options = sanitize_filename::Options {
			windows: true,
			truncate: true,
			replacement: "",
		};

		// cargo test -- --nocapture
		println!("{}", SAMPLE);
		println!("{}", sanitize_filename::sanitize_with_options(SAMPLE, options.clone()));
		println!("{:?}", SAMPLE);
		println!("{:?}", sanitize_filename::sanitize_with_options(SAMPLE, options.clone()));

		assert_eq!(SANITISED, sanitize_filename::sanitize_with_options(SAMPLE, options.clone()));
	}
}