Adds a FileFormatCheck for checking if a file format is squashfs

This will be used to ensure a squashfs file that is selected is sane

Source/Common/CMakeLists.txt

@@ -1,8 +1,9 @@
 set(NAME Common)
 set(SRCS
   ArgumentLoader.cpp
-  EnvironmentLoader.cpp
   Config.cpp
+  EnvironmentLoader.cpp
+  FileFormatCheck.cpp
   StringUtil.cpp)
 
 add_library(${NAME} STATIC ${SRCS})

Source/Common/FileFormatCheck.cpp

@@ -0,0 +1,65 @@
+#include <fstream>
+#include <string>
+
+namespace FEX::FormatCheck {
+  bool IsSquashFS(std::string const &Filename) {
+    // If it is a regular file then we need to check if it is a valid archive
+    struct SquashFSHeader {
+      uint32_t magic;
+      uint32_t inode_count;
+      uint32_t mtime;
+      uint32_t block_size;
+      uint32_t fragment_entry_count;
+      uint16_t compression_id;
+      uint16_t block_log;
+      uint16_t flags;
+      uint16_t id_count;
+      uint16_t version_major;
+      uint16_t version_minor;
+      uint64_t More[8]; // More things that don't matter to us
+    };
+
+    SquashFSHeader Header{};
+    std::fstream File(Filename, std::ios::in);
+
+    if (!File.is_open()) {
+      return false;
+    }
+
+    if (!File.seekg(0, std::fstream::end)) {
+      return false;
+    }
+
+    auto FileSize = File.tellg();
+    if (File.fail()) {
+      return false;
+    }
+
+    if (FileSize <= 0) {
+      return false;
+    }
+
+    if (!File.seekg(0, std::fstream::beg)) {
+      return false;
+    }
+
+    if (FileSize < sizeof(SquashFSHeader)) {
+      return false;
+    }
+
+    if (!File.read(reinterpret_cast<char*>(&Header), sizeof(SquashFSHeader))) {
+      return false;
+    }
+
+    // Make sure the cookie matches
+    if (Header.magic == 0x73717368) {
+      // Sanity check the version
+      uint32_t version = (uint32_t)Header.version_major << 16 | Header.version_minor;
+      if (version >= 0x00040000) {
+        // Everything is sane, we can add it
+        return true;
+      }
+    }
+    return false;
+  }
+}

Source/Common/FileFormatCheck.h

@@ -0,0 +1,7 @@
+#pragma once
+
+#include <string>
+
+namespace FEX::FormatCheck {
+  bool IsSquashFS(std::string const &Filename);
+}