From 95206944697f9c2422b12c446741057ae04bdd02 Mon Sep 17 00:00:00 2001
From: Vicki Pfau <vi@endrift.com>
Date: Tue, 29 Apr 2025 23:03:35 -0700
Subject: [PATCH] Util: Fix VFSMem truncation not affecting offsets

---
 src/util/test/vfs.c    | 31 ++++++++++++++++++++++++++++++-
 src/util/vfs/vfs-mem.c |  6 ++++++
 2 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/src/util/test/vfs.c b/src/util/test/vfs.c
index 2d1cfd56a..d0a4ef1b4 100644
--- a/src/util/test/vfs.c
+++ b/src/util/test/vfs.c
@@ -72,14 +72,33 @@ M_TEST_DEFINE(openNullMemChunkNonzero) {
 }
 
 M_TEST_DEFINE(resizeMem) {
-	uint8_t bytes[32];
+	uint8_t bytes[32] = {
+		0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
+		0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F,
+		0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
+		0x18, 0x19, 0x1A, 0x1B, 0x1C, 0x1D, 0x1E, 0x1F
+	};
 	struct VFile* vf = VFileFromMemory(bytes, 32);
 	assert_non_null(vf);
+	assert_int_equal(vf->seek(vf, 0, SEEK_END), 32);
 	assert_int_equal(vf->size(vf), 32);
+
 	vf->truncate(vf, 64);
 	assert_int_equal(vf->size(vf), 32);
+	assert_int_equal(bytes[15], 0x0F);
+	assert_int_equal(bytes[16], 0x10);
+	assert_int_equal(vf->seek(vf, 0, SEEK_CUR), 32);
+
 	vf->truncate(vf, 16);
+	assert_int_equal(vf->size(vf), 16);
+	assert_int_equal(vf->seek(vf, 0, SEEK_CUR), 16);
+
+	vf->truncate(vf, 64);
 	assert_int_equal(vf->size(vf), 32);
+	assert_int_equal(bytes[15], 0x0F);
+	assert_int_equal(bytes[16], 0x00);
+	assert_int_equal(vf->seek(vf, 0, SEEK_CUR), 16);
+
 	vf->close(vf);
 }
 
@@ -87,11 +106,16 @@ M_TEST_DEFINE(resizeConstMem) {
 	uint8_t bytes[32] = {0};
 	struct VFile* vf = VFileFromConstMemory(bytes, 32);
 	assert_non_null(vf);
+	assert_int_equal(vf->seek(vf, 0, SEEK_END), 32);
 	assert_int_equal(vf->size(vf), 32);
+
 	vf->truncate(vf, 64);
 	assert_int_equal(vf->size(vf), 32);
+	assert_int_equal(vf->seek(vf, 0, SEEK_CUR), 32);
+
 	vf->truncate(vf, 16);
 	assert_int_equal(vf->size(vf), 32);
+	assert_int_equal(vf->seek(vf, 0, SEEK_CUR), 32);
 	vf->close(vf);
 }
 
@@ -99,11 +123,16 @@ M_TEST_DEFINE(resizeMemChunk) {
 	uint8_t bytes[32] = {0};
 	struct VFile* vf = VFileMemChunk(bytes, 32);
 	assert_non_null(vf);
+	assert_int_equal(vf->seek(vf, 0, SEEK_END), 32);
 	assert_int_equal(vf->size(vf), 32);
+
 	vf->truncate(vf, 64);
 	assert_int_equal(vf->size(vf), 64);
+	assert_int_equal(vf->seek(vf, 0, SEEK_CUR), 32);
+
 	vf->truncate(vf, 16);
 	assert_int_equal(vf->size(vf), 16);
+	assert_int_equal(vf->seek(vf, 0, SEEK_CUR), 16);
 	vf->close(vf);
 }
 
diff --git a/src/util/vfs/vfs-mem.c b/src/util/vfs/vfs-mem.c
index 05580f544..048194e2d 100644
--- a/src/util/vfs/vfs-mem.c
+++ b/src/util/vfs/vfs-mem.c
@@ -290,6 +290,9 @@ void _vfmUnmap(struct VFile* vf, void* memory, size_t size) {
 void _vfmTruncate(struct VFile* vf, size_t size) {
 	struct VFileMem* vfm = (struct VFileMem*) vf;
 	_vfmExpand(vfm, size);
+	if (vfm->offset > vfm->size) {
+		vfm->offset = vfm->size;
+	}
 }
 
 void _vfmTruncateNoExpand(struct VFile* vf, size_t size) {
@@ -304,6 +307,9 @@ void _vfmTruncateNoExpand(struct VFile* vf, size_t size) {
 	}
 
 	vfm->size = size;
+	if (vfm->offset > vfm->size) {
+		vfm->offset = vfm->size;
+	}
 }
 
 void _vfmTruncateNoop(struct VFile* vf, size_t size) {