[Go] [Rust] update language bindings to return value API

ARCHITECTURE.md

@@ -48,6 +48,23 @@ subroutines.
       - https://github.com/rust-lang/rust/pull/76986
       - https://github.com/rust-lang/rfcs/pull/2884
 
+### Error codes, and Result
+
+In low-level C, everything is return through status codes.
+
+In Rust, status is communicated through `Result<Output, Error>`
+In particular for verification, Errors are used if the protocol is not followed:
+- wrong input length
+- point not on curve
+- point not in subgroup
+- zero point
+
+However if all those exceptional rules are followed, but verification still fails,
+the failure is communicated through a boolean.
+
+Similarly in Go, errors are used to communicate breaking protocol rules
+and the result of verification is communicated through a bool.
+
 ## Code organization
 
 TBD

bindings/c_typedefs.nim

@@ -175,18 +175,18 @@ proc toCparam*(name: string, typ: NimNode): string =
       typ.treeRepr()
     let sTyp = $typ[2]
     if sTyp in TypeMap:
-      "const " & TypeMap[sTyp] & " "  & name & "[], ptrdiff_t " & name & "_len"
+      "const " & TypeMap[sTyp] & " "  & name & "[], size_t " & name & "_len"
     else:
-      "const " & sTyp & " " & name & "[], ptrdiff_t " & name & "_len"
+      "const " & sTyp & " " & name & "[], size_t " & name & "_len"
   elif typ.kind == nnkVarTy and typ[0].kind == nnkCall:
     typ[0][0].expectKind(nnkOpenSymChoice)
     doAssert typ[0][0][0].eqIdent"[]"
     doAssert typ[0][1].eqIdent"openArray"
     let sTyp = $typ[0][2]
     if sTyp in TypeMap:
-      TypeMap[sTyp] & " " & name & "[], ptrdiff_t " & name & "_len"
+      TypeMap[sTyp] & " " & name & "[], size_t " & name & "_len"
     else:
-      sTyp & " " & name & "[], ptrdiff_t " & name & "_len"
+      sTyp & " " & name & "[], size_t " & name & "_len"
   elif typ.kind == nnkPtrTy and typ[0].kind == nnkCall:
     typ[0][0].expectKind(nnkOpenSymChoice)
     doAssert typ[0][0][0].eqIdent"[]"