Introduce forceCanonical function to create canonical encoding

Author: qnikst

scls-cbor/src/Cardano/SCLS/CBOR/Canonical/Encoder.hs

@@ -15,11 +15,13 @@ module Cardano.SCLS.CBOR.Canonical.Encoder (
   encodeAsMap,
   SomeEncodablePair (..),
   mkEncodablePair,
+  forceCanonical,
 ) where
 
 import Cardano.SCLS.CBOR.Canonical (CanonicalEncoding (getRawEncoding), assumeCanonicalEncoding)
 import Codec.CBOR.ByteArray.Sliced qualified as BAS
 import Codec.CBOR.Encoding qualified as E
+import Codec.CBOR.FlatTerm (fromFlatTerm, toFlatTerm)
 import Codec.CBOR.Term
 import Codec.CBOR.Write (toStrictByteString)
 import Data.Array.Byte qualified as Prim
@@ -38,6 +40,7 @@ import Data.Text (Text)
 import Data.Text.Lazy qualified as TL
 import Data.Traversable (mapAccumL)
 import Data.Word
+import GHC.Stack (HasCallStack)
 import GHC.TypeLits
 
 -- | Encode data to CBOR corresponding with the SCLS format.
@@ -361,3 +364,23 @@ in the canonical format
 toCanonicalTagged :: proxy (v :: Symbol) -> Word64 -> Term -> CanonicalEncoding
 toCanonicalTagged v 258 (TList ns) = toCanonicalCBOR v (Set.fromList ns)
 toCanonicalTagged v t term = assumeCanonicalEncoding (E.encodeTag64 t) <> toCanonicalCBOR v term
+
+{- |
+  Converts any CBOR encoding to its canonical form by first decoding it to a generic
+  CBOR 'Term' and then re-encoding it canonically according to the Cardano specification.
+
+  **When to use:**
+
+  Use this function as a last resort when you have a CBOR encoding ('E.Encoding') that may not
+  be in canonical form and you need to ensure canonicalization. It is primarily intended for
+  situations where you do not have a more direct or efficient way to produce canonical CBOR.
+
+  **Caveats:**
+
+  This function is slow because it fully decodes the input encoding and then re-encodes it.
+  Avoid using it in performance-critical code paths.
+-}
+forceCanonical :: (HasCallStack) => proxy (v :: Symbol) -> E.Encoding -> CanonicalEncoding
+forceCanonical p x = case fromFlatTerm decodeTerm (toFlatTerm x) of
+  Left e -> error $ "forceCanonical: unable to decode term, generated by Encoding: " <> show e
+  Right y -> toCanonicalCBOR p y