BYOND Resource Cache format (#483)

thanks!

Author: itsmeow

README.md

@@ -190,6 +190,7 @@ Everything will immediately show up in ImHex's Content Store and gets bundled wi
 | ReFS | | [`patterns/refs.hexpat`](patterns/fs/refs.hexpat) | Microsoft Resilient File System |
 | RGBDS | | [`patterns/rgbds.hexpat`](patterns/rgbds.hexpat) | [RGBDS](https://rgbds.gbdev.io) object file format |
 | RPM | | [`patterns/rpm.hexpat`](patterns/rpm.hexpat) | [RPM](http://ftp.rpm.org/max-rpm/s1-rpm-file-format-rpm-file-format.html) package file format |
+| RSC | | [`patterns/rsc.hexpat`](patterns/rsc.hexpat) | BYOND Resource Cache file |
 | SDB | | [`patterns/sdb.hexpat`](patterns/sdb.hexpat) | [Shim DataBase](https://learn.microsoft.com/en-us/windows/win32/devnotes/application-compatibility-database) file format |
 | Shell Link | `application/x-ms-shortcut` | [`patterns/lnk.hexpat`](patterns/lnk.hexpat) | Windows Shell Link file format |
 | shp | | [`patterns/shp.hexpat`](patterns/shp.hexpat) | ESRI shape file |

patterns/rsc.hexpat

@@ -0,0 +1,83 @@
+#pragma author itsmeow
+#pragma description BYOND Resource Cache file
+
+import std.mem;
+import std.time;
+import std.hash;
+
+// Whether to validate CRC32 for RSCEntries or not.
+const bool check_crc = true;
+
+using time_t = std::time::EpochTime [[format("format_unix_time")]];
+fn format_unix_time(time_t t) {
+    return std::time::format(std::time::to_local(t), "%c");
+};
+
+// Based on alexkar598/rsc-tools
+// Copyright (c) alexkar598
+// Permissioned granted for use in pattern
+enum Type : u8 {
+  // Unknown file
+  Unknown = 0x0,
+  // Sequencer file (.mid, .midi, .mod, .s3m, .xm, .it, .oxm)
+  Sequencer = 0x1,
+  // Audio file (.wav, .ogg, .raw, .wma, .aiff, .mp3)
+  Audio = 0x2,
+  // Sprite sheet file (.dmi)
+  SpriteSheet = 0x3,
+  // Bitmap file (.bmp)
+  Bitmap = 0x5,
+  // Lossless image file (.png)
+  LosslessImage = 0x6,
+  // Archive file (.zip)
+  Archive = 0x9,
+  // Resource archive file (.rsc)
+  Resource = 0xa,
+  // Lossy image file (.jpg, .jpeg)
+  LossyImage = 0xb,
+  // Dynamic sprite sheet file (.ddmi)
+  DynamicSpriteSheet = 0xc,
+  // Animated image file (.gif)
+  AnimatedImage = 0xd,
+  // Font file (.ttf)
+  Font = 0xe,
+};
+
+struct RSCEntry {
+    u32 byteLength [[comment("Size of the entry, starting after this field")]];
+    u8 used [[comment("Whether or not this entry is used in the DMB. This is updated on a rebuild to 'skip' now unused entries")]];
+    if(used) {
+        u8 type_raw;
+        Type type = type_raw [[export]];
+        bool encrypted = (type_raw & 0b10000000) == 0b10000000 [[export, comment("Encrypted entries are unable to have their content decoded at this time")]];
+        u32 checksum_crc32 [[comment("CRC32 of content array with a poly of 0xaf and a XOR-in/init of 0xffffffff")]];
+        time_t modified [[comment("Unix/epoch timestamp of modification datetime")]];
+        time_t added [[comment("Unix/epoch timestamp of creation/addition to RSC datetime")]];
+        u32 contentLength [[comment("Length of the content array")]];
+        char filename[] [[comment("Name of the source file")]];
+              
+        u32 expectedContentLength = byteLength - 17 - sizeof(filename);
+        // Use the encoded length rather than computed length
+        // because this is what is used for checksum calculation
+        u8 content [contentLength];
+        if (contentLength < expectedContentLength) {
+            // continue to end of block
+            // RSC files can contain leftover data, much like a filesystem with unlinked files
+            padding [expectedContentLength - contentLength];
+        }
+        if (expectedContentLength != contentLength) {
+            u32 computedByteLength = contentLength + 17 + sizeof(filename);
+            std::warning(std::format("Length mismatch for RSCEntry at 0x{:x}: contentLength={} expectedContentLength={} byteLength={} computedByteLength={}", $, contentLength, expectedContentLength, byteLength, computedByteLength));
+        }
+        if (check_crc) {
+            u32 computed_checksum_crc32 = std::hash::crc32(content, 0xffffffff, 0xaf, 0, false, false) [[export]];
+            if(computed_checksum_crc32 != checksum_crc32) {
+                std::warning(std::format("Checksum mismatch at 0x{:x}: stored={} computed={}", $, checksum_crc32, computed_checksum_crc32));
+            }
+        }
+    } else {
+        u8 content [ byteLength ];
+    }
+};
+
+RSCEntry entries[while(!std::mem::eof())] @ 0x00;