crypto/cipher: update docs for the Stream interface

Specify what will happen if len(dst) != len(src).

Change-Id: I66afa3730f637753b825189687418f14ddec3629
Reviewed-on: https://go-review.googlesource.com/1754
Reviewed-by: Adam Langley <agl@golang.org>

diff --git a/src/crypto/cipher/cipher.go b/src/crypto/cipher/cipher.go
index 67afdb1e057a5637c4cf35452e11a108c089de19..7d27fde61d8fac2a0fd63548d35d0b8bf02a7493 100644 (file)
--- a/src/crypto/cipher/cipher.go
+++ b/src/crypto/cipher/cipher.go
@@ -29,6 +29,9 @@ type Block interface {
 type Stream interface {
        // XORKeyStream XORs each byte in the given slice with a byte from the
        // cipher's key stream. Dst and src may point to the same memory.
+       // If len(dst) < len(src), XORKeyStream should panic. It is acceptable
+       // to pass a dst bigger than src, and in that case, XORKeyStream will
+       // only update dst[:len(src)] and will not touch the rest of dst.
        XORKeyStream(dst, src []byte)
 }