diff --git a/common/alloc/buffer.go b/common/alloc/buffer.go
index 9acb42c1..acf1e6e6 100644
--- a/common/alloc/buffer.go
+++ b/common/alloc/buffer.go
@@ -9,6 +9,7 @@ const (
 	defaultOffset = 16
 )
 
+// A Writer that writes contents into the given buffer.
 type BytesWriter func([]byte) int
 
 // Buffer is a recyclable allocation of a byte array. Buffer.Release() recycles