diff --git a/rust/Cargo.toml b/rust/Cargo.toml
index ed14de2..dd08d57 100644
--- a/rust/Cargo.toml
+++ b/rust/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "freenet-stdlib"
-version = "0.3.2"
+version = "0.3.3"
 edition = "2021"
 rust-version = "1.80"
 publish = true
diff --git a/rust/src/memory/buf.rs b/rust/src/memory/buf.rs
index c637bb7..46d9e4a 100644
--- a/rust/src/memory/buf.rs
+++ b/rust/src/memory/buf.rs
@@ -184,6 +184,27 @@ impl<'instance> BufferMut<'instance> {
     }
 }
 
+impl std::io::Write for BufferMut<'_> {
+    fn write(&mut self, buf: &[u8]) -> std::io::Result<usize> {
+        let last_write = (*self.write_ptr) as usize;
+        let free = self.buffer.len() - last_write;
+        let n = buf.len().min(free);
+        if n == 0 && !buf.is_empty() {
+            return Err(std::io::Error::new(
+                std::io::ErrorKind::WriteZero,
+                "buffer full",
+            ));
+        }
+        self.buffer[last_write..last_write + n].copy_from_slice(&buf[..n]);
+        *self.write_ptr = (last_write + n) as u32;
+        Ok(n)
+    }
+
+    fn flush(&mut self) -> std::io::Result<()> {
+        Ok(())
+    }
+}
+
 #[inline(always)]
 pub(crate) fn compute_ptr<T>(ptr: *mut T, linear_mem_space: &WasmLinearMem) -> *mut T {
     let mem_start_ptr = linear_mem_space.start_ptr;
@@ -200,13 +221,15 @@ fn from_raw_builder<'a>(builder_ptr: *mut BufferBuilder, mem: WasmLinearMem) ->
     unsafe {
         #[cfg(feature = "trace")]
         {
-            let contract_mem = std::slice::from_raw_parts(mem.start_ptr, mem.size as usize);
-            tracing::trace!(
-                "*mut BufferBuilder <- offset: {}; in mem: {:?}",
-                builder_ptr as usize,
-                &contract_mem[builder_ptr as usize
-                    ..builder_ptr as usize + std::mem::size_of::<BufferBuilder>()]
-            );
+            if !mem.start_ptr.is_null() && mem.size > 0 {
+                let contract_mem = std::slice::from_raw_parts(mem.start_ptr, mem.size as usize);
+                tracing::trace!(
+                    "*mut BufferBuilder <- offset: {}; in mem: {:?}",
+                    builder_ptr as usize,
+                    &contract_mem[builder_ptr as usize
+                        ..builder_ptr as usize + std::mem::size_of::<BufferBuilder>()]
+                );
+            }
             // use std::{fs::File, io::Write};
             // let mut f = File::create(std::env::temp_dir().join("dump.mem")).unwrap();
             // f.write_all(contract_mem).unwrap();
@@ -340,6 +363,94 @@ fn __frnt__initiate_buffer(capacity: u32) -> i64 {
     buffer as i64
 }
 
+#[cfg(test)]
+mod test_io_write {
+    use super::*;
+    use std::io::Write;
+
+    /// Create a BufferMut backed by host memory (no WASM runtime needed).
+    /// Uses `__frnt__initiate_buffer` which allocates in host memory during tests,
+    /// and a null-base WasmLinearMem so compute_ptr is a no-op on absolute pointers.
+    unsafe fn host_buffer_mut(capacity: u32) -> BufferMut<'static> {
+        let builder_ptr = __frnt__initiate_buffer(capacity) as *mut BufferBuilder;
+        let linear_mem = WasmLinearMem {
+            start_ptr: std::ptr::null(),
+            size: 0,
+        };
+        BufferMut::from_ptr(builder_ptr, linear_mem)
+    }
+
+    /// Call std::io::Write::write (not BufferMut::write which has different signature)
+    fn io_write(buf: &mut BufferMut<'_>, data: &[u8]) -> std::io::Result<usize> {
+        Write::write(buf, data)
+    }
+
+    #[test]
+    fn write_trait_basic() {
+        let mut buf = unsafe { host_buffer_mut(32) };
+        let n = io_write(&mut buf, b"hello").unwrap();
+        assert_eq!(n, 5);
+        assert_eq!(buf.read_bytes(5), b"hello");
+    }
+
+    #[test]
+    fn write_trait_fills_exactly() {
+        let mut buf = unsafe { host_buffer_mut(4) };
+        let n = io_write(&mut buf, b"abcd").unwrap();
+        assert_eq!(n, 4);
+        assert_eq!(buf.read_bytes(4), b"abcd");
+    }
+
+    #[test]
+    fn write_trait_partial_when_near_full() {
+        let mut buf = unsafe { host_buffer_mut(4) };
+        io_write(&mut buf, b"ab").unwrap();
+        // Only 2 bytes free, writing 3 should write 2
+        let n = io_write(&mut buf, b"xyz").unwrap();
+        assert_eq!(n, 2);
+        assert_eq!(buf.read_bytes(4), b"abxy");
+    }
+
+    #[test]
+    fn write_trait_error_when_full() {
+        let mut buf = unsafe { host_buffer_mut(2) };
+        io_write(&mut buf, b"ab").unwrap();
+        let err = io_write(&mut buf, b"c").unwrap_err();
+        assert_eq!(err.kind(), std::io::ErrorKind::WriteZero);
+    }
+
+    #[test]
+    fn write_trait_empty_slice_ok() {
+        let mut buf = unsafe { host_buffer_mut(4) };
+        let n = io_write(&mut buf, b"").unwrap();
+        assert_eq!(n, 0);
+    }
+
+    #[test]
+    fn write_all_trait() {
+        let mut buf = unsafe { host_buffer_mut(16) };
+        buf.write_all(b"hello world").unwrap();
+        assert_eq!(buf.read_bytes(11), b"hello world");
+    }
+
+    #[test]
+    fn write_all_insufficient_space() {
+        let mut buf = unsafe { host_buffer_mut(4) };
+        let err = buf.write_all(b"hello").unwrap_err();
+        assert_eq!(err.kind(), std::io::ErrorKind::WriteZero);
+    }
+
+    #[test]
+    fn bincode_serialize_into() {
+        let data: Vec<u32> = vec![1, 2, 3, 4, 5];
+        let size = bincode::serialized_size(&data).unwrap() as usize;
+        let mut buf = unsafe { host_buffer_mut(size as u32) };
+        bincode::serialize_into(&mut buf, &data).unwrap();
+        let result: Vec<u32> = bincode::deserialize(buf.read_bytes(size)).unwrap();
+        assert_eq!(result, data);
+    }
+}
+
 #[cfg(all(test, any(unix, windows), feature = "wasmer-tests"))]
 mod test {
     use super::*;