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// SPDX-FileCopyrightText: 2021-2022 Lynnesbian
// SPDX-License-Identifier: GPL-3.0-or-later
//! File handling - scanning, detecting MIME types, and so on.
use std::collections::{BTreeSet, HashMap};
use std::fs::File;
use std::io::{self, Read, Seek, SeekFrom};
use std::path::Path;
use std::str::FromStr;
use cfg_if::cfg_if;
use itertools::{Either, Itertools};
use log::{debug, error};
use mime::Mime;
use mime_guess::from_ext;
use once_cell::sync::Lazy;
use parking_lot::RwLock;
use walkdir::{DirEntry, WalkDir};
use crate::findings::{Findings, ScanError};
use crate::mime_db::MimeDb;
use crate::parameters::ScanOpts;
use crate::utils::APPLICATION_ZIP;
use crate::{String, MIMEDB};
/// Cache of MIME types and their associated extensions, used by [`mime_extension_lookup()`]
static MIMEXT: Lazy<RwLock<HashMap<String, Option<Vec<String>>>>> = Lazy::new(|| RwLock::new(HashMap::new()));
/// The number of bytes to read initially when identifying a file's MIME type. Used in the [`mime_type`] function.
/// Rather than reading the entire file all at once into a [`BUF_SIZE`] buffer, it tends to be faster to read a small
/// chunk of the file and trying to identify that, proceeding with the larger buffer if that fails. Many file formats
/// can be identified with the first few dozen bytes, so the "happy path" will likely be taken in the majority of cases.
pub const INITIAL_BUF_SIZE: usize = 128;
/// The number of bytes to read if the file couldn't be identified from its first [`INITIAL_BUF_SIZE`] bytes. Used in
/// the [`mime_type`] function.
pub const BUF_SIZE: usize = 8192;
/// A [`Mime`] representing the "application/x-ole-storage" MIME type.
static APPLICATION_X_OLE_STORAGE: Lazy<Mime> = Lazy::new(|| Mime::from_str("application/x-ole-storage").unwrap());
cfg_if! {
if #[cfg(windows)] {
/// Determines whether or not a file is hidden by checking its win32 file attributes.
pub fn is_hidden(entry: &DirEntry) -> bool {
use std::os::windows::prelude::*;
const FILE_ATTRIBUTE_HIDDEN: u32 = 0x2; //
std::fs::metadata(entry.path()) // try to get metadata for file
false, // if getting metadata/attributes fails, assume it's not hidden
|f| f.file_attributes() & FILE_ATTRIBUTE_HIDDEN > 0,
} else {
/// Determines whether or not a file is hidden by checking for a leading full stop.
pub fn is_hidden(entry: &DirEntry) -> bool {
.map_or(false, |f| f.starts_with('.') && f != ".")
/// Returns `true` if a file matches the given criteria. This means checking whether the file's extension appears in
/// `exts` (if specified), potentially skipping over hidden files, and so on.
pub fn wanted_file(
entry: &DirEntry,
exts: Option<&BTreeSet<&str>>,
exclude: Option<&BTreeSet<&str>>,
scan_opts: &ScanOpts,
) -> bool {
if entry.depth() == 0 {
// the root directory should always be scanned.
return true;
if !scan_opts.hidden && is_hidden(entry) {
// skip hidden files and directories. this check is performed first because it's very lightweight.
return false;
if entry.file_type().is_dir() {
// always allow directories - there's no point doing file extension matching on something that isn't a file.
return true;
if let Some(ext) = entry.path().extension() {
// file has extension - discard invalid UTF-8 and normalise it to lowercase.
let ext = ext.to_string_lossy().to_lowercase();
let ext = ext.as_str();
if scan_opts.ignore_unknown_exts && from_ext(ext).is_empty() {
// unknown extension, skip.
return false;
if let Some(exts) = exts {
// only scan if the file has one of the specified extensions.
} else {
// no extensions specified - the file should be scanned unless its extension is on the exclude list.
exclude.map_or(true, |exclude| !exclude.contains(&ext))
} else {
// no file extension
/// Inspects the given entry, returning a [`Findings`] on success and a [`ScanError`] on failure.
/// In the event of an IO error, the returned [`ScanError`] will be of type [`ScanError::File`]. Otherwise, a
/// [`ScanError::Mime`] will be returned, meaning that the file was scanned successfully, but a MIME type could not be
/// determined.
pub fn scan_file(entry: &DirEntry, canonical_paths: bool) -> Result<Findings, ScanError> {
let path = entry.path();
// try to determine MIME type for this entry
let result = match mime_type(&*MIMEDB, path) {
// an error occurred while trying to read the file
Err(_) => return Err(ScanError::File(path)),
// the file was read successfully, but we were unable to determine its MIME type
Ok(None) => return Err(ScanError::Mime(path)),
// a MIME type was found!
Ok(Some(result)) => result,
// set of known extensions for the given MIME type
let known_exts = mime_extension_lookup(result.essence_str().into());
// file extension for this particular file
let entry_ext = path.extension();
let valid = match known_exts {
// there is a known set of extensions for this MIME type, and the file has an extension
Some(e) if entry_ext.is_some() => e.contains(&entry_ext.unwrap().to_string_lossy().to_lowercase().into()),
// either this file has no extension, or there is no known set of extensions for this MIME type :(
Some(_) | None => false,
let path = if canonical_paths {
match std::fs::canonicalize(path) {
Ok(path) => path,
Err(_) => return Err(ScanError::File(entry.path())),
} else {
path.to_path_buf() // :c
Ok(Findings {
file: path,
mime: result,
/// Takes a slice of [`DirEntry`]s and calls [`scan_file`] on each one, returning the results in a vector.
pub fn scan_from_walkdir(
entries: &[DirEntry],
canonical_paths: bool,
use_threads: bool,
) -> (Vec<Findings>, Vec<ScanError>) {
cfg_if! {
if #[cfg(feature = "multi-threaded")] {
use rayon::prelude::*;
const CHUNKS: usize = 32;
if use_threads && entries.len() > CHUNKS {
// split the entries into chunks of 32, and iterate over each chunk of entries in a separate thread
return entries
.flat_map_iter(|chunk| {
.iter() // iter over the chunk, which is a slice of DirEntry structs
.map(|entry| scan_file(entry, canonical_paths))
}).partition_map(|result| match result {
Ok(f) => Either::Left(f),
Err(e) => Either::Right(e),
} else {
// should always be false when multi-threading is disabled at compile time
// if we end up here, either
// - there were less than CHUNKS files to scan, or
// - the user specified that only one thread should be used, by specifying `-j 1`
// - fif was compiled without the `multi-threading` feature
.partition_map(|entry: &DirEntry| match scan_file(entry, canonical_paths) {
Ok(f) => Either::Left(f),
Err(e) => Either::Right(e),
/// Scans a given directory with [`WalkDir`], filters with [`wanted_file`], checks for errors, and returns a vector of
/// [`DirEntry`]s.
pub fn scan_directory(
dirs: &Path,
exts: Option<&BTreeSet<&str>>,
exclude: Option<&BTreeSet<&str>>,
scan_opts: &ScanOpts,
) -> Option<Vec<DirEntry>> {
let stepper = WalkDir::new(dirs).follow_links(scan_opts.follow_symlinks).into_iter();
let mut probably_fatal_error = false;
let entries: Vec<DirEntry> = stepper
.filter_entry(|e| wanted_file(e, exts, exclude, scan_opts)) // filter out unwanted files
.filter_map(|e| {
if let Err(err) = &e {
debug!("uh oh spaghettio!! {:#?}", e);
// log errors to stdout, and remove them from the iterator
let path = err.path().map_or("General error".into(), Path::to_string_lossy);
if err.depth() == 0 {
// if something goes wrong while trying to read the root directory, we're probably not going to get much done
probably_fatal_error = true;
// TODO: is there a way to just say `map_or(x, |y| y).thing()` instead of `map_or(x.thing(), |y| y.thing())`?
// i don't care whether i'm returning a walkdir error or an io error, i just care about whether or not it
// implements ToString (which they both do). map_or doesn't work on trait objects though :(
error!("{}: {}", path, err.io_error().map_or(err.to_string(), |e| e.to_string()));
return None;
// remove directories from the final list
.filter(|e| !e.file_type().is_dir())
// if fif is invoked without `-f` on a symlinked directory, it will recurse into the symlink (as desired) and ignore
// any symlinks inside the symlinked root directory. however, the root directory will still be added to `entries` as
// if it were a file to be scanned, and `scan_file` will fail to scan it, adding "Failed to read ~/whatever" to the
// output. to avoid this, we can remove all symlinks from `entries` if `-f` is not set. i know this is kind of
// confusing, but it's honestly kind of hard to explain... maybe a screenshot is better:
// adding the symlink filter removes the line that's being pointed to in the image. 0u0
.filter(|e| scan_opts.follow_symlinks || !e.file_type().is_symlink())
if probably_fatal_error {
} else {
/// Tries to identify the MIME type of a file from a given path.
pub fn mime_type<T: MimeDb>(db: &T, path: &Path) -> io::Result<Option<Mime>> {
let mut buffer = [0; INITIAL_BUF_SIZE];
let mut file = File::open(path)?;
// read a small amount to start with
let mut read = io::Result::Ok(0);
for _ in 0..3 {
// try to read the file up to 3 times, retrying if interrupted, bailing otherwise;
read = buffer);
match read {
Ok(_) => break,
Err(ref e) if e.kind() == io::ErrorKind::Interrupted => continue,
Err(_) => break,
let read = read?;
let r = db.get_type(&buffer);
if read < INITIAL_BUF_SIZE {
// the file is smaller than INITIAL_BUF_SIZE - there's no point reading it again
return Ok(r);
let r = r.filter(|mime|
// some MIME types should be investigated further, reading up to BUF_SIZE even if they've been determined already
// one such type is XML - there's many more specific types that can be determined by reading further (such as SVG)
mime != &mime::TEXT_XML
// another is ZIP - many file formats (DOCX, ODT, JAR...) are just ZIP files with particular data structures.
// determining that a file is in one of the MS office formats in particular requires looking quite far into the
// file.
&& mime != &*APPLICATION_ZIP
// doc/ppt/xls files are a subset of what's known as an "OLE2 compound document storage", at least according to
// shared-mime-info. if a pre-OOXML era MS office file is scanned and identified as x-ole-storage, reading further
// will allow it to be detected correctly as the appropriate filetype.
if r.is_some() {
return Ok(r);
// attempt to read up to BUF_SIZE bytes of the file.
let mut buffer = [0; BUF_SIZE];; buffer)?;
/// Returns a list of known extensions for this MIME type, if any.
/// This function uses the [`Mime`]'s "essence" rather than the [`Mime`] itself - [`mime_guess::get_mime_extensions`]
/// ignores the type suffix, treating "image/svg+xml" as "image/svg", and thus fails to find any extensions. Passing the
/// `essence_str` (which includes the suffix) fixes this.
pub fn mime_extension_lookup(essence: String) -> Option<Vec<String>> {
if let Some(exts) = {
return exts.clone();
let mut exts = mime_guess::get_mime_extensions_str(essence.as_str());
if exts.is_none() {
// no matches :c
// mime_guess' database isn't exactly perfect... there are a lot of times where the db will return "some/x-thing"
// but mime_guess only understands "some/thing", or vice-versa.
// so, if there appear to be no extensions, try replacing "some/x-thing" with "some/thing", or "some/thing" with
// "some/x-thing".
if essence.contains("/x-") {
// replace e.g. "application/x-gzip" with "application/gzip"
exts = mime_guess::get_mime_extensions_str(&essence.replace("/x-", "/"));
} else {
// replace e.g. "video/mp2t" with "video/x-mp2t"
exts = mime_guess::get_mime_extensions_str(&essence.replace('/', "/x-"));
let exts = match exts {
Some(exts) => {
let possible_exts: Vec<String> = exts.iter().map(|e| String::from(*e)).collect();
Some(if essence == mime::IMAGE_JPEG.essence_str() {
// possible_exts starts with "jpe", because it's alphabetically before "jpeg" and "jpg". however, jpg/jpeg are
// far more common than jpe, so it makes sense to suggest one of those rather than jpe. to do this, we can
// add "jpg" to the start of the possible_exts list, ensuring that it will be the extension suggested by fif.
[vec![String::from("jpg")], possible_exts].concat()
} else if essence == mime::TEXT_XML.essence_str() || essence == "application/xml" {
// a somewhat similar case arises with XML files - the first suggested extension is "asa", when it should
// (in my opinion) be "xml".
// there's also another problem: SVG files can easily be misidentified as XML files, because they usually
// *are* valid XML - the more whitespace and comments an SVG file begins with, the more bytes must be read
// before it's possible to determine that it's an SVG rather than an XML file. to "fix" this, we can add "svg"
// as a valid extension for XML files, ensuring that SVG files misidentified as XML will still be considered
// to have valid extensions.
// TODO: if a file is detected as application/xml, but it has an extension like "xht" which corresponds to
// "application/xhtml+xml", let it through - in other words, if it's identified as application/xml, but its
// extension is classed as application/*+xml, consider it OK
[vec![String::from("xml"), String::from("svg")], possible_exts].concat()
} else if essence == "application/msword" {
// classic office files considered harmful
vec![String::from("doc"), String::from("xls"), String::from("ppt")]
} else if essence == "application/zip" {
// neither xdg-mime nor infer seem to be able to detect office XML files properly...
vec![String::from("zip"), String::from("docx"), String::from("xlsx"), String::from("pptx")],
} else if essence == "application/x-ms-dos-executable" {
// .dll, .exe, and .scr files are given the same MIME type... but you definitely don't want to rename one to the
// other!
[vec![String::from("dll"), String::from("exe"), String::from("scr")], possible_exts].concat()
} else {
None => None,
MIMEXT.write().insert(essence, exts.clone());