From 5acce15ed907d29a5575668a09e7d94cf7a36b3f Mon Sep 17 00:00:00 2001
From: Ben Harris <bjh21@bjh21.me.uk>
Date: Tue, 30 May 2023 16:55:22 +0200
Subject: [PATCH] js: pass preferences file from JS to C on the heap, not the
 stack

The C stack used by Emscripten is quite small, so passing more than a
few klilobytes of data on it tends to cause an overflow.  Current
versions of puzzles will only generate tiny preferences files, but this
might change in future and in any case Puzzles shouldn't crash just
because the preferences in local storage have got corrupted.

To fix this, we now have JavaScript allocate a suitable amount of C heap
memory using malloc() and stick the preferences file in there.

This could plausibly fail if the preferences file were really big, but
that's unlikely since browsers generally limit an origin to about 5 MB
of local storage.  In any case, if malloc() does fail, we'll just ignore
the preferences file, which is probably the right thing to do.
---
 cmake/platforms/emscripten.cmake | 3 +++
 emcclib.js                       | 8 +++++++-
 emccpre.js                       | 2 +-
 3 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/cmake/platforms/emscripten.cmake b/cmake/platforms/emscripten.cmake
index d74217f..b7e9c7d 100644
--- a/cmake/platforms/emscripten.cmake
+++ b/cmake/platforms/emscripten.cmake
@@ -49,6 +49,9 @@ set(emcc_export_list
   _rescale_puzzle
   # Callback for loading user preferences
   _prefs_load_callback
+  # Functions for allocating and freeing C memory
+  _malloc
+  _free
   # Main program, run at initialisation time
   _main)
 
diff --git a/emcclib.js b/emcclib.js
index bd4762d..d8ef57f 100644
--- a/emcclib.js
+++ b/emcclib.js
@@ -827,7 +827,13 @@ mergeInto(LibraryManager.library, {
             var prefsdata =
                 localStorage.getItem(location.pathname + " preferences");
             if (prefsdata !== undefined && prefsdata !== null) {
-                prefs_load_callback(me, prefsdata);
+                var lenbytes = lengthBytesUTF8(prefsdata) + 1;
+                var dest = _malloc(lenbytes);
+                if (dest != 0) {
+                    stringToUTF8(prefsdata, dest, lenbytes);
+                    prefs_load_callback(me, dest);
+                    _free(dest);
+                }
             }
         } catch (error) {
             // Log the error but otherwise pretend the settings were
diff --git a/emccpre.js b/emccpre.js
index a114ce1..842a392 100644
--- a/emccpre.js
+++ b/emccpre.js
@@ -693,7 +693,7 @@ function initPuzzle() {
                                    ['number','number']);
     timer_callback = Module.cwrap('timer_callback', 'void', ['number']);
     prefs_load_callback = Module.cwrap('prefs_load_callback', 'void',
-                                       ['number','string']);
+                                       ['number','number']);
 
     if (resizable_div !== null) {
         var resize_handle = document.getElementById("resizehandle");