Do not raise ValueError at early end of binary stream

preserves.nimble

@@ -1,6 +1,6 @@
 # Package
 
-version = "20230823"
+version = "20230825"
 author        = "Emery Hemingway"
 description   = "data model and serialization format"
 license       = "Unlicense"

src/preserves.nim

@@ -631,12 +631,10 @@ proc encode*[E](pr: Preserve[E]): seq[byte] =
   s.write pr
   result = cast[seq[byte]](move s.data)
 
+
 proc decodePreserves*(s: Stream; E = void): Preserve[E] =
   ## Decode a Preserves value from a binary-encoded stream.
-  if s.atEnd: raise newException(ValueError, "End of Preserves stream")
-  proc assertStream(check: bool) =
-    if not check:
-      raise newException(ValueError, "invalid Preserves stream")
+  if s.atEnd: raise newException(IOError, "End of Preserves stream")
   const endMarker = 0x84
   let tag = s.readUint8()
   case tag
@@ -715,7 +713,7 @@ proc decodePreserves*(s: Stream; E = void): Preserve[E] =
     for _ in 1..len:
       result.int = (result.int shl 8) + s.readUint8().BiggestInt
   of endMarker:
-    assertStream(false)
+    raise newException(ValueError, "invalid Preserves stream")
   else:
     case 0xf0 and tag
     of 0x90:
@@ -731,7 +729,7 @@ proc decodePreserves*(s: Stream; E = void): Preserve[E] =
       for i in 1..<len:
         result.int = (result.int shl 8) or s.readUint8().BiggestInt
     else:
-      assertStream(false)
+      raise newException(ValueError, "invalid Preserves stream")
 
 proc decodePreserves*(s: string; E = void): Preserve[E] =
   ## Decode a string of binary-encoded Preserves.