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// SPDX-FileCopyrightText: 2021-2022 Lynnesbian
// SPDX-License-Identifier: GPL-3.0-or-later
//! Backend-neutral Mime database abstraction.
use cfg_if::cfg_if;
use mime::Mime;
/// A thin wrapper around either [`Infer`] or [`xdg-mime::SharedMimeInfo`], depending on which [cargo features]
/// fif was compiled with. By default, fif uses an [`Infer`]-based implementation on Windows, and an
/// [`xdg-mime`]-based one everywhere else. This behaviour can be changed at compile time by using the aforementioned
/// [cargo features].
/// [cargo features]:
/// [`Infer`]:
/// [`xdg-mime::SharedMimeInfo`]:
/// [`xdg-mime`]:
pub trait MimeDb {
/// Initialise the database.
fn init() -> Self;
/// Given a slice of bytes, returns the inferred MIME type, if any.
fn get_type(&self, data: &[u8]) -> Option<Mime>;
cfg_if! {
if #[cfg(any(all(unix, feature = "infer-backend"), all(not(unix), not(feature = "xdg-mime-backend"))))] {
use std::str::FromStr;
/// The [`Infer`]( implementation of [`MimeDb`].
pub struct InferDb {
db: infer::Infer,
fn open_document_check(buf: &[u8], kind: &str) -> bool {
let mime = format!("application/vnd.oasis.opendocument.{}", kind);
let mime = mime.as_bytes();
buf.len() > 38 + mime.len() && buf.starts_with(b"PK\x03\x04") && buf[38..mime.len() + 38] == mime[..]
impl MimeDb for InferDb {
fn init() -> Self {
let mut info = infer::Infer::new();
// In addition to the file inferences provided by Infer, I've also added a few of my own below. Some of them
// replace Infer's existing ones, some of them are less than perfect, and still others are for relatively
// obscure formats, so I'm not really sure whether or not they should be contributed upstream.
// OpenDocument Text (used by e.g. LibreOffice Writer)
info.add("application/vnd.oasis.opendocument.text", "odt", |buf| {
open_document_check(buf, "text")
// OpenDocument Spreadsheet (LibreOffice Calc)
info.add("application/vnd.oasis.opendocument.spreadsheet", "ods", |buf| {
open_document_check(buf, "spreadsheet")
// OpenOffice Presentation (LibreOffice Impress)
info.add("application/vnd.oasis.opendocument.presentation", "odp", |buf| {
open_document_check(buf, "presentation")
// Ren'Py Archive (Ren'Py:
info.add("application/x-rpa", "rpa", |buf| {
buf.len() >= 34 && buf.starts_with(b"RPA-") && buf[7] == b' ' && buf[24] ==b' '
// Mach-O Binaries (The executable format used by macOS)
// my source for most of this info is this article:
// like linux's ELF binaries, mach-o binaries do not typically have an extension, but if they did, it'd
// probably be something like ".macho", so, that'll do i guess. fif doesn't actually use the extensions
// specified here anyway.
info.add("application/x-mach-binary", "macho", |buf| {
// a 32-bit mach-o header occupies 28 bits of space, so any input smaller than that cannot be a mach-o
// binary, even if it starts with the magic numbers.
// the three magic numbers that can appear are 0xFEEDFACF, 0xFEEDFACE, and 0xCAFEBABE. the code below
// checks for all three of these, in both big and little endian order.
// java class files also start with 0xCAFEBABE. since infer doesn't support detecting these files,
// collisions are not an issue. if, however, infer does gain support for identifying java class files, the
// 0xCAFEBABE check should be removed, as java bytecode files are far more prevalent than 32-bit universal
// mach-o binaries [citation needed].
buf.len() >= 28 && [b"\xFE\xED\xFA\xCF", b"\xFE\xED\xFA\xCE", b"\xCA\xFE\xBA\xBE", b"\xCF\xFA\xED\xFE",
b"\xCE\xFA\xED\xFE", b"\xBE\xBA\xFE\xCA"].iter().any(|magic_numbers| buf.starts_with(&magic_numbers[..]))
// info.add("application/x-msi", "msi", |buf| {
// TODO: find a way to detect MSI files properly - this just detects those weird windows OLE files and therefore
// also picks up on .doc files
// buf.starts_with(b"\xd0\xcf\x11\xe0\xa1\xb1\x1a\xe1")
// });
// Scalable Vector Graphics
info.add("image/svg+xml", "svg", |buf| {
// before doing the moderately expensive SVG check, we should make sure that the input is actually SGML-ish,
// by which i mean, starts with anywhere from zero to ∞-1 whitespace characters, and then a less than sign,
// and then there's some other stuff we don't care about right now
// so, here comes our fancy pants """""SGML-ish validator"""""
for c in buf {
match c {
// whitespace (according to
b'\t' | b'\r' | b'\n' | b'\x20' => continue,
b'<' => break,
_ => return false,
// finally, to check whether or not the file is an SVG:
// - split the buffer up into chunks separated by the less than sign
// - check to see if this chunk starts with any of these identifiers:
let identifiers: Vec<&[u8]> = vec![b"svg", b"SVG", b"!DOCTYPE svg", b"!DOCTYPE SVG"];
// - if it does, the nested `any` will short circuit and immediately return true, causing the parent `any` to
// do the same
// - and finally, if none of the chunks match, we'll return false
// TODO: this is kind of messy, i'd like to clean it up somehow :(
.split(|c| *c == b'<')
.any(|buf| identifiers.iter().any(|id| buf.starts_with(id)))
Self { db: info }
fn get_type(&self, data: &[u8]) -> Option<Mime> {
if let Some(mime) = self.db.get(data) {
match Mime::from_str(mime.mime_type()) {
Err(_) => None,
Ok(m) => Some(m),
} else { None }
} else {
/// The [`xdg-mime`]( implementation of [`MimeDb`].
pub struct XdgDb {
db: xdg_mime::SharedMimeInfo,
impl MimeDb for XdgDb {
fn init() -> Self {
Self { db: xdg_mime::SharedMimeInfo::new() }
fn get_type(&self, data: &[u8]) -> Option<Mime> {
self.db.get_mime_type_for_data(data).map(|m| m.0)