Use dupIO to avoid unwanted sharing when encoding (fixes #318)

This calls dupIO before evaluating each token in the token stream.

Author: adamgundry

cborg/cborg.cabal

@@ -59,6 +59,11 @@ flag optimize-gmp
   manual: False
   description: Use optimized code paths for integer-gmp
 
+flag dupIO
+  default: False
+  manual: True
+  description: Use dupIO to avoid unwanted sharing when encoding
+
 --------------------------------------------------------------------------------
 -- Library
 
@@ -100,6 +105,10 @@ library
     primitive               >= 0.5     && < 0.10,
     text                    >= 1.1     && < 1.3 || >= 2.0 && <2.2
 
+  if flag(dupIO)
+    cpp-options:            -DDUPIO
+    build-depends: dupIO >= 0.1.0 && < 0.2
+
   if flag(optimize-gmp)
     cpp-options:            -DOPTIMIZE_GMP
     if impl(ghc >= 9.0)

cborg/src/Codec/CBOR/Write.hs

@@ -75,6 +75,10 @@ import qualified Codec.CBOR.ByteArray.Sliced           as BAS
 import           Codec.CBOR.Encoding
 import           Codec.CBOR.Magic
 
+#if defined(DUPIO)
+import qualified Data.Dup                              as Dup
+#endif
+
 --------------------------------------------------------------------------------
 
 -- | Turn an 'Encoding' into a lazy 'L.ByteString' in CBOR binary
@@ -110,7 +114,13 @@ buildStep vs1 k (BI.BufferRange op0 ope0) =
     go vs1 op0
   where
     go vs !op
-      | op `plusPtr` bound <= ope0 = case vs of
+      | op `plusPtr` bound <= ope0 = do
+#if defined(DUPIO)
+        dup_vs <- Dup.dupIO vs
+        case dup_vs of
+#else
+        case vs of
+#endif
           TkWord     x vs' -> PI.runB wordMP     x op >>= go vs'
           TkWord64   x vs' -> PI.runB word64MP   x op >>= go vs'