added comments and mach-o binary support to infer

CHANGELOG.md

@@ -4,6 +4,10 @@ Dates are given in YYYY-MM-DD format - for example, the 15th of October 2021 is
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/), and this project adheres to
 [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## Unreleased
+### Added
+- When using the [`infer`] backend, fif is now able to detect [Mach-O](https://en.wikipedia.org/wiki/Mach-O) binaries
+
 ## v0.5.0 - 2022-01-01
 ### Changed
 - The Minimum Supported Rust Version (MSRV) is now **1.54.0**.

Cargo.lock

@@ -80,9 +80,9 @@ checksum = "baf1de4339761588bc0619e3cbc0120ee582ebb74b53b4efbf79117bd2da40fd"
 
 [[package]]
 name = "clap"
-version = "3.0.7"
+version = "3.0.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "12e8611f9ae4e068fa3e56931fded356ff745e70987ff76924a6e0ab1c8ef2e3"
+checksum = "8c506244a13c87262f84bf16369740d0b7c3850901b6a642aa41b031a710c473"
 dependencies = [
  "atty",
  "bitflags",
@@ -754,9 +754,9 @@ dependencies = [
 
 [[package]]
 name = "siphasher"
-version = "0.3.8"
+version = "0.3.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ba1eead9e94aa5a2e02de9e7839f96a007f686ae7a1d57c7797774810d24908a"
+checksum = "a86232ab60fa71287d7f2ddae4a7073f6b7aac33631c3015abb556f08c6d0a3e"
 
 [[package]]
 name = "smallvec"

src/mime_db.rs

@@ -42,28 +42,56 @@ cfg_if! {
 			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: https://www.renpy.org/)
 				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: https://h3adsh0tzz.com/2020/01/macho-file-format/
+				// 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,
@@ -83,8 +111,8 @@ cfg_if! {
 					// - 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
+					// - if it does, the nested `any` will short circuit and immediately return true, causing the parent `any` to
-					//   the same
+					//   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 :(

src/parameters.rs

@@ -7,7 +7,7 @@ use std::collections::BTreeSet;
 use std::path::PathBuf;
 
 use cfg_if::cfg_if;
-use clap::{Parser, ArgEnum};
+use clap::{ArgEnum, Parser};
 
 use crate::utils::{CLAP_LONG_VERSION, CLAP_VERSION};
 use crate::String as StringType;

src/tests/mod.rs

@@ -351,6 +351,7 @@ fn accepts_good_args() {
 /// Ensures that output from the `-V` and `--version` flags is formatted properly.
 fn check_version_output() {
 	use std::string::String;
+
 	use assert_cmd::Command;
 	use regex::Regex;
 
@@ -364,7 +365,6 @@ fn check_version_output() {
 		output
 	);
 
-
 	// test `--version` matches the format of "fif x.y.z (OS, example backend, commit #1234abc)"
 	let mut cmd = Command::cargo_bin("fif").unwrap();
 	let output = cmd.arg("--version").ok().unwrap().stdout;