fix ub when writing

fuzz/Cargo.toml

@@ -12,8 +12,15 @@ libfuzzer-sys = "0.4"
 simdnbt = { path = "../simdnbt" }
 
 [[bin]]
-name = "fuzz_target_1"
-path = "fuzz_targets/fuzz_target_1.rs"
+name = "borrow_read"
+path = "fuzz_targets/borrow_read.rs"
+test = false
+doc = false
+bench = false
+
+[[bin]]
+name = "owned_write"
+path = "fuzz_targets/owned_write.rs"
 test = false
 doc = false
 bench = false

fuzz/fuzz_targets/borrow_read.rs

@@ -0,0 +1,11 @@
+#![no_main]
+
+use std::io::Cursor;
+
+use libfuzzer_sys::fuzz_target;
+
+fuzz_target!(|data: &[u8]| {
+    if let Ok(simdnbt::borrow::Nbt::Some(r)) = simdnbt::borrow::read(&mut Cursor::new(data)) {
+        r.as_compound().to_owned();
+    }
+});

fuzz/fuzz_targets/owned_write.rs

@@ -6,6 +6,6 @@ fuzz_target!(|data: &[u8]| {
     if let Ok(simdnbt::borrow::Nbt::Some(r)) =
         simdnbt::borrow::read(&mut std::io::Cursor::new(data))
     {
-        r.as_compound().to_owned();
+        simdnbt::owned::BaseNbt::write_unnamed(&r.as_compound().to_owned().into(), &mut Vec::new());
     }
 });

simdnbt/benches/compare.rs

@@ -1,9 +1,10 @@
 use std::{
     fs::File,
+    hint::black_box,
     io::{Cursor, Read},
 };
 
-use criterion::{black_box, criterion_group, criterion_main, Criterion, Throughput};
+use criterion::{criterion_group, criterion_main, Criterion, Throughput};
 use flate2::read::GzDecoder;
 
 fn bench_read_file(filename: &str, c: &mut Criterion) {

simdnbt/benches/compare_hypixel.rs

@@ -1,10 +1,11 @@
 use std::{
     collections::HashMap,
     fs::File,
+    hint::black_box,
     io::{Cursor, Read},
 };
 
-use criterion::{black_box, criterion_group, criterion_main, Criterion, Throughput};
+use criterion::{criterion_group, criterion_main, Criterion, Throughput};
 use flate2::read::GzDecoder;
 
 pub fn bench_read_file(filename: &str, c: &mut Criterion) {

simdnbt/benches/nbt_borrow.rs

@@ -1,9 +1,10 @@
 use std::{
     fs::File,
+    hint::black_box,
     io::{Cursor, Read},
 };
 
-use criterion::{black_box, criterion_group, criterion_main, Criterion, Throughput};
+use criterion::{criterion_group, criterion_main, Criterion, Throughput};
 use flate2::read::GzDecoder;
 
 fn bench_file(filename: &str, c: &mut Criterion) {

simdnbt/benches/nbt_owned.rs

@@ -1,9 +1,10 @@
 use std::{
     fs::File,
+    hint::black_box,
     io::{Cursor, Read},
 };
 
-use criterion::{black_box, criterion_group, criterion_main, Criterion, Throughput};
+use criterion::{criterion_group, criterion_main, Criterion, Throughput};
 use flate2::read::GzDecoder;
 
 fn bench_file(filename: &str, c: &mut Criterion) {

simdnbt/src/fastvec.rs

@@ -271,10 +271,13 @@ impl<'orig, T> FastVecFromVec<'orig, T> {
     }
 }
 impl<T> Drop for FastVecFromVec<'_, T> {
+    /// Move the FastVec contents back into the original Vec.
     fn drop(&mut self) {
-        // we intentionally don't drop the fastvec since the allocation is moved into
-        // the vec
-        *self.original = unsafe { ManuallyDrop::take(&mut self.fastvec).into_vec() };
+        // we intentionally don't drop anything here
+        unsafe {
+            let new_vec = ManuallyDrop::take(&mut self.fastvec).into_vec();
+            (self.original as *mut Vec<T>).write(new_vec);
+        }
     }
 }
 

simdnbt/src/owned/mod.rs

@@ -810,4 +810,13 @@ mod tests {
 
         assert_ne!(nbt, modified_nbt);
     }
+
+    #[test]
+    fn write_compound() {
+        let nbt = BaseNbt {
+            name: "".into(),
+            tag: NbtCompound { values: vec![] },
+        };
+        BaseNbt::write_unnamed(&nbt, &mut Vec::new());
+    }
 }