From cae3d272d346e4eef1a449ab17811e4e7e1407b8 Mon Sep 17 00:00:00 2001
From: Pk11 <pk11@outlook.jp>
Date: Sun, 9 Apr 2023 13:38:35 -0500
Subject: [PATCH] Only reserve space in trimmed NDS files for RSA key if it
 exists (#804)

---
 arm9/source/gamecart/gamecart.c | 11 ++++++++++-
 arm9/source/utils/gameutil.c    | 17 +++++++++++++----
 2 files changed, 23 insertions(+), 5 deletions(-)

diff --git a/arm9/source/gamecart/gamecart.c b/arm9/source/gamecart/gamecart.c
index df83bbe..0ca8077 100644
--- a/arm9/source/gamecart/gamecart.c
+++ b/arm9/source/gamecart/gamecart.c
@@ -254,7 +254,7 @@ u32 InitCartRead(CartData* cdata) {
         if (nds_header->device_capacity >= 15) return 1; // too big, not valid
         if (cdata->cart_size == 0)
             cdata->cart_size = (128 * 1024) << nds_header->device_capacity;
-        cdata->data_size = nds_header->ntr_rom_size + 0x88;
+        cdata->data_size = nds_header->ntr_rom_size;
         cdata->arm9i_rom_offset = 0;
 
         // TWL header
@@ -273,6 +273,15 @@ u32 InitCartRead(CartData* cdata) {
                 NTR_CmdReadHeader(cdata->storage);
                 if (!NTR_Secure_Init(cdata->storage, NULL, Cart_GetID(), 1)) return 1;
             }
+        } else {
+            // Check if immediately after the reported cart size
+            // is the magic number string 'ac' (auth code).
+            // If found, add 0x88 bytes for the download play RSA key.
+            u16 rsaMagic;
+            ReadCartBytes(&rsaMagic, cdata->data_size, 2, cdata, false);
+            if(rsaMagic == 0x6361) {
+                cdata->data_size += 0x88;
+            }
         }
 
         // store encrypted secure area
diff --git a/arm9/source/utils/gameutil.c b/arm9/source/utils/gameutil.c
index 72b7010..3c9da9b 100644
--- a/arm9/source/utils/gameutil.c
+++ b/arm9/source/utils/gameutil.c
@@ -3296,12 +3296,21 @@ u64 GetGameFileTrimmedSize(const char* path) {
         trimsize = GetAnyFileTrimmedSize(path);
     } else if (filetype & GAME_NDS) {
         TwlHeader hdr;
-        if (fvx_qread(path, &hdr, 0, sizeof(TwlHeader), NULL) != FR_OK)
+        if (fvx_qread(path, &hdr, 0, sizeof(TwlHeader), NULL) != FR_OK) {
             return 0;
-        if (hdr.unit_code != 0x00) // DSi or NDS+DSi
+        } if (hdr.unit_code != 0x00) { // DSi or NDS+DSi
             trimsize = hdr.ntr_twl_rom_size;
-        else if (hdr.ntr_rom_size) // regular NDS
-            trimsize = hdr.ntr_rom_size + 0x88;
+        } else if (hdr.ntr_rom_size) { // regular NDS
+            trimsize = hdr.ntr_rom_size;
+
+            // Check if immediately after the reported cart size
+            // is the magic number string 'ac' (auth code).
+            // If found, add 0x88 bytes for the download play RSA key.
+            u16 rsaMagic;
+            if(fvx_qread(path, &rsaMagic, trimsize, 2, NULL) == FR_OK && rsaMagic == 0x6361) {
+                trimsize += 0x88;
+            }
+        }
     } else {
         u8 hdr[0x200];
         if (fvx_qread(path, &hdr, 0, 0x200, NULL) != FR_OK)