From 9411ce53876f45d75febbe6ba0a96650bef357a0 Mon Sep 17 00:00:00 2001
From: toaster <rollerorbital@gmail.com>
Date: Thu, 18 Sep 2025 12:45:22 +0100
Subject: [PATCH] Environment::read/writeModuleName: Convert lumpnums to a
 netsafe form for transit

- Introduces new functions
    - W_LumpIntoNetSave
    - W_LumpFromNetSave
- Essentially shims the upper 16 bits to account for unimportant files
---
 src/acs/vm/ACSVM/Environment.cpp | 10 +++-
 src/w_wad.cpp                    | 87 ++++++++++++++++++++++++++++++++
 src/w_wad.h                      |  3 ++
 3 files changed, 98 insertions(+), 2 deletions(-)

diff --git a/src/acs/vm/ACSVM/Environment.cpp b/src/acs/vm/ACSVM/Environment.cpp
index 6461ec514..3a2af3c40 100644
--- a/src/acs/vm/ACSVM/Environment.cpp
+++ b/src/acs/vm/ACSVM/Environment.cpp
@@ -25,6 +25,7 @@
 #include "Script.hpp"
 #include "Serial.hpp"
 #include "Thread.hpp"
+#include "../../../w_wad.h"
 
 #include <iostream>
 #include <list>
@@ -596,7 +597,12 @@ namespace ACSVM
    ModuleName Environment::readModuleName(Serial &in) const
    {
       auto s = readString(in);
-      auto i = ReadVLN<std::size_t>(in);
+      size_t i = ReadVLN<std::size_t>(in);
+
+      if ((i = W_LumpFromNetSave(i)) == LUMPERROR)
+      {
+          CONS_Debug(DBG_GAMELOGIC, "lumpnum not found for ACS module '%s'\n", s->str);
+      }
 
       return {s, nullptr, i};
    }
@@ -768,7 +774,7 @@ namespace ACSVM
    void Environment::writeModuleName(Serial &out, ModuleName const &in) const
    {
       writeString(out, in.s);
-      WriteVLN(out, in.i);
+      WriteVLN<std::size_t>(out, W_LumpIntoNetSave(in.i));
    }
 
    //
diff --git a/src/w_wad.cpp b/src/w_wad.cpp
index b188c2a00..e69d4b36d 100644
--- a/src/w_wad.cpp
+++ b/src/w_wad.cpp
@@ -1634,6 +1634,93 @@ UINT8 W_LumpExists(const char *name)
 	return false;
 }
 
+// Thanks to the introduction of "client side WAD files",
+// a notion which is insanity in any other branch of DOOM,
+// any direct wadnum ID is not a guaranteed index (and
+// lumpnum_t, which has it in their upper bits, suffer too)
+// We can do an O(n) conversion back and forth, which is
+// better than nothing, but still kind of annoying to do.
+// It was either this or killing musicwads lmao ~toast 180925
+
+lumpnum_t W_LumpIntoNetSave(lumpnum_t lump)
+{
+	UINT32 wad = (lump >> 16);
+	if (lump == LUMPERROR // Bad already
+	|| wad < mainwads) // Same between client/server
+	{
+		// Give what we get.
+		return lump;
+	}
+
+	if (wad >= numwadfiles // Outside of range
+	|| !wadfiles[wad]->important) // Can't convert local lumpnum
+	{
+		// No good return result!
+		return LUMPERROR;
+	}
+
+	// Count previous local files the client might not have.
+	UINT32 i = (mainwads + musicwads), localoffset = 0;
+	for (; i < wad; i++)
+	{
+		if (wadfiles[i]->important)
+			continue;
+
+		localoffset++;
+	}
+
+	if (!localoffset)
+	{
+		// No local files, return unchanged.
+		return lump;
+	}
+
+	if (localoffset <= wad)
+	{
+		// Success, return with the conversion.
+		return ((wad - localoffset) << 16) | (lump & UINT16_MAX);
+	}
+
+	// Death!!
+	return LUMPERROR;
+}
+
+lumpnum_t W_LumpFromNetSave(lumpnum_t lump)
+{
+	UINT32 netwad = (lump >> 16);
+	if (lump == LUMPERROR // Bad already
+	|| netwad < mainwads) // Same between client/server
+	{
+		// Give what we get.
+		return lump;
+	}
+
+	// Count previous local files the server would ignore.
+	UINT32 i = (mainwads + musicwads), localoffset = 0;
+	for (; (i - localoffset) <= netwad && i < numwadfiles; i++)
+	{
+		if (wadfiles[i]->important)
+			continue;
+
+		localoffset++;
+	}
+
+	if (!localoffset)
+	{
+		// No local files, return unchanged.
+		return lump;
+	}
+
+	if (netwad + localoffset < numwadfiles)
+	{
+		// Success, return with the conversion.
+		return ((netwad + localoffset) << 16) | (lump & UINT16_MAX);
+	}
+
+	// Death!!
+	return LUMPERROR;
+}
+
 size_t W_LumpLengthPwad(UINT16 wad, UINT16 lump)
 {
 	if (!TestValidLump(wad, lump))
diff --git a/src/w_wad.h b/src/w_wad.h
index 06553ea28..7024826dc 100644
--- a/src/w_wad.h
+++ b/src/w_wad.h
@@ -188,6 +188,9 @@ lumpnum_t W_CheckNumForNameInBlock(const char *name, const char *blockstart, con
 lumpnum_t W_CheckNumForNameInFolder(const char *lump, const char *folder);
 UINT8 W_LumpExists(const char *name); // Lua uses this.
 
+lumpnum_t W_LumpIntoNetSave(lumpnum_t lump);
+lumpnum_t W_LumpFromNetSave(lumpnum_t lump);
+
 size_t W_LumpLengthPwad(UINT16 wad, UINT16 lump);
 size_t W_LumpLength(lumpnum_t lumpnum);