LibCore: Add offsets to binary signature matching

Some file signatures are at an offset into the file, so we need to be
able to specify an offset to start matching bytes at.

Userland/Libraries/LibCore/MimeData.cpp

@@ -85,38 +85,38 @@ String guess_mime_type_based_on_filename(const StringView& path)
     return "text/plain";
 }
 
-#define ENUMERATE_HEADER_CONTENTS                                                                                                             \
-    __ENUMERATE_MIME_TYPE_HEADER(bmp, "image/bmp", 2, 'B', 'M')                                                                               \
-    __ENUMERATE_MIME_TYPE_HEADER(bzip2, "application/x-bzip2", 3, 'B', 'Z', 'h')                                                              \
-    __ENUMERATE_MIME_TYPE_HEADER(elf, "extra/elf", 4, 0x7F, 'E', 'L', 'F')                                                                    \
-    __ENUMERATE_MIME_TYPE_HEADER(flac, "extra/flac", 4, 0x66, 0x4C, 0x61, 0x43)                                                               \
-    __ENUMERATE_MIME_TYPE_HEADER(gif_87, "image/gif", 6, 'G', 'I', 'F', '8', '7', 'a')                                                        \
-    __ENUMERATE_MIME_TYPE_HEADER(gif_89, "image/gif", 6, 'G', 'I', 'F', '8', '9', 'a')                                                        \
-    __ENUMERATE_MIME_TYPE_HEADER(gzip, "application/gzip", 2, 0x1F, 0x8B)                                                                     \
-    __ENUMERATE_MIME_TYPE_HEADER(jpeg, "image/jpeg", 4, 0xFF, 0xD8, 0xFF, 0xDB)                                                               \
-    __ENUMERATE_MIME_TYPE_HEADER(jpeg_huh, "image/jpeg", 4, 0xFF, 0xD8, 0xFF, 0xEE)                                                           \
-    __ENUMERATE_MIME_TYPE_HEADER(jpeg_jfif, "image/jpeg", 12, 0xFF, 0xD8, 0xFF, 0xE0, 0x00, 0x10, 'J', 'F', 'I', 'F', 0x00, 0x01)             \
-    __ENUMERATE_MIME_TYPE_HEADER(midi, "audio/midi", 4, 0x4D, 0x54, 0x68, 0x64)                                                               \
-    __ENUMERATE_MIME_TYPE_HEADER(pbm, "image/x-portable-bitmap", 3, 0x50, 0x31, 0x0A)                                                         \
-    __ENUMERATE_MIME_TYPE_HEADER(pgm, "image/x-portable-graymap", 3, 0x50, 0x32, 0x0A)                                                        \
-    __ENUMERATE_MIME_TYPE_HEADER(png, "image/png", 8, 0x89, 'P', 'N', 'G', 0x0D, 0x0A, 0x1A, 0x0A)                                            \
-    __ENUMERATE_MIME_TYPE_HEADER(ppm, "image/x-portable-pixmap", 3, 0x50, 0x33, 0x0A)                                                         \
-    __ENUMERATE_MIME_TYPE_HEADER(sevenzip, "application/x-7z-compressed", 6, 0x37, 0x7A, 0xBC, 0xAF, 0x27, 0x1C)                              \
-    __ENUMERATE_MIME_TYPE_HEADER(shell, "text/x-shellscript", 10, '#', '!', '/', 'b', 'i', 'n', '/', 's', 'h', '\n')                          \
-    __ENUMERATE_MIME_TYPE_HEADER(sqlite, "extra/sqlite", 16, 'S', 'Q', 'L', 'i', 't', 'e', ' ', 'f', 'o', 'r', 'm', 'a', 't', ' ', '3', 0x00) \
-    __ENUMERATE_MIME_TYPE_HEADER(tiff, "image/tiff", 4, 'I', 'I', '*', 0x00)                                                                  \
-    __ENUMERATE_MIME_TYPE_HEADER(tiff_bigendian, "image/tiff", 4, 'M', 'M', 0x00, '*')
+#define ENUMERATE_HEADER_CONTENTS                                                                                                                \
+    __ENUMERATE_MIME_TYPE_HEADER(bmp, "image/bmp", 0, 2, 'B', 'M')                                                                               \
+    __ENUMERATE_MIME_TYPE_HEADER(bzip2, "application/x-bzip2", 0, 3, 'B', 'Z', 'h')                                                              \
+    __ENUMERATE_MIME_TYPE_HEADER(elf, "extra/elf", 0, 4, 0x7F, 'E', 'L', 'F')                                                                    \
+    __ENUMERATE_MIME_TYPE_HEADER(flac, "extra/flac", 0, 4, 0x66, 0x4C, 0x61, 0x43)                                                               \
+    __ENUMERATE_MIME_TYPE_HEADER(gif_87, "image/gif", 0, 6, 'G', 'I', 'F', '8', '7', 'a')                                                        \
+    __ENUMERATE_MIME_TYPE_HEADER(gif_89, "image/gif", 0, 6, 'G', 'I', 'F', '8', '9', 'a')                                                        \
+    __ENUMERATE_MIME_TYPE_HEADER(gzip, "application/gzip", 0, 2, 0x1F, 0x8B)                                                                     \
+    __ENUMERATE_MIME_TYPE_HEADER(jpeg, "image/jpeg", 0, 4, 0xFF, 0xD8, 0xFF, 0xDB)                                                               \
+    __ENUMERATE_MIME_TYPE_HEADER(jpeg_huh, "image/jpeg", 0, 4, 0xFF, 0xD8, 0xFF, 0xEE)                                                           \
+    __ENUMERATE_MIME_TYPE_HEADER(jpeg_jfif, "image/jpeg", 0, 12, 0xFF, 0xD8, 0xFF, 0xE0, 0x00, 0x10, 'J', 'F', 'I', 'F', 0x00, 0x01)             \
+    __ENUMERATE_MIME_TYPE_HEADER(midi, "audio/midi", 0, 4, 0x4D, 0x54, 0x68, 0x64)                                                               \
+    __ENUMERATE_MIME_TYPE_HEADER(pbm, "image/x-portable-bitmap", 0, 3, 0x50, 0x31, 0x0A)                                                         \
+    __ENUMERATE_MIME_TYPE_HEADER(pgm, "image/x-portable-graymap", 0, 3, 0x50, 0x32, 0x0A)                                                        \
+    __ENUMERATE_MIME_TYPE_HEADER(png, "image/png", 0, 8, 0x89, 'P', 'N', 'G', 0x0D, 0x0A, 0x1A, 0x0A)                                            \
+    __ENUMERATE_MIME_TYPE_HEADER(ppm, "image/x-portable-pixmap", 0, 3, 0x50, 0x33, 0x0A)                                                         \
+    __ENUMERATE_MIME_TYPE_HEADER(sevenzip, "application/x-7z-compressed", 0, 6, 0x37, 0x7A, 0xBC, 0xAF, 0x27, 0x1C)                              \
+    __ENUMERATE_MIME_TYPE_HEADER(shell, "text/x-shellscript", 0, 10, '#', '!', '/', 'b', 'i', 'n', '/', 's', 'h', '\n')                          \
+    __ENUMERATE_MIME_TYPE_HEADER(sqlite, "extra/sqlite", 0, 16, 'S', 'Q', 'L', 'i', 't', 'e', ' ', 'f', 'o', 'r', 'm', 'a', 't', ' ', '3', 0x00) \
+    __ENUMERATE_MIME_TYPE_HEADER(tiff, "image/tiff", 0, 4, 'I', 'I', '*', 0x00)                                                                  \
+    __ENUMERATE_MIME_TYPE_HEADER(tiff_bigendian, "image/tiff", 0, 4, 'M', 'M', 0x00, '*')
 
-#define __ENUMERATE_MIME_TYPE_HEADER(var_name, mime_type, pattern_size, ...) \
-    static const u8 var_name##_arr[pattern_size] = { __VA_ARGS__ };          \
+#define __ENUMERATE_MIME_TYPE_HEADER(var_name, mime_type, pattern_offset, pattern_size, ...) \
+    static const u8 var_name##_arr[pattern_size] = { __VA_ARGS__ };                          \
     static constexpr ReadonlyBytes var_name = ReadonlyBytes { var_name##_arr, pattern_size };
 ENUMERATE_HEADER_CONTENTS
 #undef __ENUMERATE_MIME_TYPE_HEADER
 
 Optional<String> guess_mime_type_based_on_sniffed_bytes(const ReadonlyBytes& bytes)
 {
-#define __ENUMERATE_MIME_TYPE_HEADER(var_name, mime_type, pattern_size, ...) \
-    if (bytes.starts_with(var_name))                                         \
+#define __ENUMERATE_MIME_TYPE_HEADER(var_name, mime_type, pattern_offset, pattern_size, ...)                       \
+    if (static_cast<ssize_t>(bytes.size()) >= pattern_offset && bytes.slice(pattern_offset).starts_with(var_name)) \
         return mime_type;
     ENUMERATE_HEADER_CONTENTS;
 #undef __ENUMERATE_MIME_TYPE_HEADER