From 4f9ad3a162d789318d55f9426ec13ddc201acf77 Mon Sep 17 00:00:00 2001
From: CasualPokePlayer <50538166+CasualPokePlayer@users.noreply.github.com>
Date: Tue, 29 Apr 2025 22:47:35 -0700
Subject: [PATCH] Allow truncation to work within VFileFromMemory (#3455)

* Allow truncation to work within VFileFromMemory/VFileFromConstMemory

Truncation here is limited to buffer size (allowing for shrinking but not growing the buffer size)

* Don't change VFileFromConstMemory; have VFileFromMemory write "expand" size until the buffer size

* 0 out "expanded" space
---
 src/util/vfs/vfs-mem.c | 25 ++++++++++++++++++++++---
 1 file changed, 22 insertions(+), 3 deletions(-)

diff --git a/src/util/vfs/vfs-mem.c b/src/util/vfs/vfs-mem.c
index 06189b886..05580f544 100644
--- a/src/util/vfs/vfs-mem.c
+++ b/src/util/vfs/vfs-mem.c
@@ -26,6 +26,7 @@ static ssize_t _vfmWriteNoop(struct VFile* vf, const void* buffer, size_t size);
 static void* _vfmMap(struct VFile* vf, size_t size, int flags);
 static void _vfmUnmap(struct VFile* vf, void* memory, size_t size);
 static void _vfmTruncate(struct VFile* vf, size_t size);
+static void _vfmTruncateNoExpand(struct VFile* vf, size_t size);
 static void _vfmTruncateNoop(struct VFile* vf, size_t size);
 static ssize_t _vfmSize(struct VFile* vf);
 static bool _vfmSync(struct VFile* vf, void* buffer, size_t size);
@@ -51,7 +52,7 @@ struct VFile* VFileFromMemory(void* mem, size_t size) {
 	vfm->d.write = _vfmWrite;
 	vfm->d.map = _vfmMap;
 	vfm->d.unmap = _vfmUnmap;
-	vfm->d.truncate = _vfmTruncateNoop;
+	vfm->d.truncate = _vfmTruncateNoExpand;
 	vfm->d.size = _vfmSize;
 	vfm->d.sync = _vfmSync;
 
@@ -236,8 +237,12 @@ ssize_t _vfmRead(struct VFile* vf, void* buffer, size_t size) {
 ssize_t _vfmWrite(struct VFile* vf, const void* buffer, size_t size) {
 	struct VFileMem* vfm = (struct VFileMem*) vf;
 
-	if (size + vfm->offset >= vfm->size) {
-		size = vfm->size - vfm->offset;
+	if (size + vfm->offset > vfm->size) {
+		vfm->size = size + vfm->offset;
+		if (vfm->size > vfm->bufferSize) {
+			vfm->size = vfm->bufferSize;
+			size = vfm->size - vfm->offset;
+		}
 	}
 
 	memcpy((void*) ((uintptr_t) vfm->mem + vfm->offset), buffer, size);
@@ -287,6 +292,20 @@ void _vfmTruncate(struct VFile* vf, size_t size) {
 	_vfmExpand(vfm, size);
 }
 
+void _vfmTruncateNoExpand(struct VFile* vf, size_t size) {
+	struct VFileMem* vfm = (struct VFileMem*) vf;
+
+	if (size > vfm->bufferSize) {
+		size = vfm->bufferSize;
+	}
+
+	if (size > vfm->size) {
+		memset((void*) ((uintptr_t) vfm->mem + vfm->size), 0, size - vfm->size);
+	}
+
+	vfm->size = size;
+}
+
 void _vfmTruncateNoop(struct VFile* vf, size_t size) {
 	// TODO: Return value?
 	UNUSED(vf);