ethereum: fix bug with rlp encoding of zero bytes

Null bytes in lists were getting eaten during concatenation. To avoid
this, we track encoded item widths (which are always 1 or higher) and
+can them all together.

This likely did not affect any of the other Ethereum code, considering
it nearly always measures atoms, and the null byte would be seen as
no bytes in that case.

pkg/arvo/lib/ethereum.hoon

@@ -76,12 +76,17 @@
           (encode-length wid.b.in 0x80)
         ::
             %l
-          =/  out=@
-            %+  roll  l.in
-            |=  [ni=item en=@]
-            (cat 3 (encode ni) en)
-          %^  cat  3  out
-          (encode-length (met 3 out) 0xc0)
+          ::  we +can because b+1^0x0 encodes to 0x00
+          ::
+          =/  l=(list byts)
+            %+  turn  l.in
+            |=  ni=item
+            =+  (encode ni)
+            [(max 1 (met 3 -)) -]
+          %+  can  3
+          %+  snoc  (flop l)
+          =-  (met 3 -)^-
+          (encode-length (roll (turn l head) add) 0xc0)
         ==
     ::
     ++  encode-length

pkg/arvo/tests/lib/ethereum/rlp.hoon

@@ -36,6 +36,14 @@
       :+  "set of three"
         0xc7c0.c1c0.c3c0.c1c0
       l+[l+~ l+[l+~ ~] l+[l+~ l+[l+~ ~] ~] ~]
+    ::
+      :+  "list with zero byte"
+        0xc311.0022
+      l+~[b+1^0x11 b+1^0x0 b+1^0x22]
+    ::
+      :+  "list of zero bytes"
+        0xc300.0000
+      l+~[b+1^0x0 b+1^0x0 b+1^0x0]
   ==
 ::
 |%
@@ -48,8 +56,8 @@
   %+  weld
     %+  category  "encode"
     %+  expect-eq
-      !>  dat
-      !>  (encode rlp)
+      !>  `@ux`dat
+      !>  `@ux`(encode rlp)
   %+  category  "decode"
   %+  expect-eq
     !>  rlp