From 706e016ef8a8c1d611002859acefbd7e3ca9cbd7 Mon Sep 17 00:00:00 2001
From: Sergey Pepyakin <sergei@parity.io>
Date: Wed, 3 Jul 2019 18:06:59 +0200
Subject: [PATCH] Fix shrinking.

---
 src/memory/mmap_bytebuf.rs | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/src/memory/mmap_bytebuf.rs b/src/memory/mmap_bytebuf.rs
index d9e7ed8..ee6478e 100644
--- a/src/memory/mmap_bytebuf.rs
+++ b/src/memory/mmap_bytebuf.rs
@@ -153,7 +153,9 @@ impl ByteBuf {
                         )
                         .as_slice();
                     let dst = new_mmap.as_slice_mut();
-                    dst[..src.len()].copy_from_slice(src);
+                    let amount = src.len().min(dst.len());
+                    dst[..amount].copy_from_slice(&src[..amount]);
+
                 }
 
                 Some(new_mmap)
@@ -197,3 +199,17 @@ impl ByteBuf {
         Ok(())
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::ByteBuf;
+
+    const PAGE_SIZE: usize = 4096;
+
+    // This is not required since wasm memories can only grow but nice to have.
+    #[test]
+    fn byte_buf_shrink() {
+        let mut byte_buf = ByteBuf::new(PAGE_SIZE * 3).unwrap();
+        byte_buf.realloc(PAGE_SIZE * 2).unwrap();
+    }
+}