From 13f001e3171613dc28844db94249923f881c6830 Mon Sep 17 00:00:00 2001
From: cozis <francesco.cozzuto@gmail.com>
Date: Sat, 20 Jun 2026 09:45:59 +0200
Subject: [PATCH] file_system: add setFileLength

---
 src/file_system.zig | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/src/file_system.zig b/src/file_system.zig
index 7dcc7d2..5f24578 100644
--- a/src/file_system.zig
+++ b/src/file_system.zig
@@ -488,6 +488,21 @@ pub fn fileSize(self: *FileSystem, open_file: *OpenFile) usize {
     return open_file.entity.bytes.items.len;
 }
 
+// Resize the file like ftruncate(2): shrinking discards the tail, growing
+// zero-fills. The offset is left in place except where it would fall past the
+// new end, which we clamp so a later read/write can't slice out of bounds.
+pub fn setFileLength(self: *FileSystem, open_file: *OpenFile, gpa: Allocator, length: usize) Allocator.Error!void {
+    _ = self;
+    const current = open_file.entity.bytes.items.len;
+    if (length < current) {
+        open_file.entity.bytes.shrinkRetainingCapacity(length);
+    } else if (length > current) {
+        try open_file.entity.bytes.appendNTimes(gpa, 0, length - current);
+    }
+    if (open_file.cursor > length)
+        open_file.cursor = length;
+}
+
 pub const SeekError = error{
     NegativeOffset,
     Overflow,