Decode from non-seekable streams

preserves.nimble

@@ -1,6 +1,6 @@
 # Package
 
-version = "20240426"
+version = "20240506"
 author        = "Emery Hemingway"
 description   = "data model and serialization format"
 license       = "Unlicense"

src/preserves/private/decoding.nim

@@ -15,11 +15,12 @@ proc readVarint(s: Stream): uint =
     c = uint s.readUint8
   result = result or (c shl shift)
 
-proc decodePreserves*(s: Stream): Value =
+proc decodePreserves*(s: Stream): Value {.gcsafe.}
+
+proc decodePreserves(s: Stream; tag: uint8): Value =
   ## Decode a Preserves value from a binary-encoded stream.
   if s.atEnd: raise newException(IOError, "End of Preserves stream")
   const endMarker = 0x84
-  let tag = s.readUint8()
   case tag
   of 0x80: result = Value(kind: pkBoolean, bool: false)
   of 0x81: result = Value(kind: pkBoolean, bool: true)
@@ -99,30 +100,38 @@ proc decodePreserves*(s: Stream): Value =
   of 0xb4:
     result = Value(kind: pkRecord)
     var label = decodePreserves(s)
-    while s.peekUint8() != endMarker:
-      result.record.add decodePreserves(s)
+    var tag = s.readUint8()
+    while tag != endMarker:
+      result.record.add decodePreserves(s, tag)
+      tag = s.readUint8()
     result.record.add(move label)
-    discard s.readUint8()
   of 0xb5:
     result = Value(kind: pkSequence)
-    while s.peekUint8() != endMarker:
-      result.sequence.add decodePreserves(s)
-    discard s.readUint8()
+    var tag = s.readUint8()
+    while tag != endMarker:
+      result.sequence.add decodePreserves(s, tag)
+      tag = s.readUint8()
   of 0xb6:
     result = Value(kind: pkSet)
-    while s.peekUint8() != endMarker:
-      incl(result, decodePreserves(s))
-    discard s.readUint8()
+    var tag = s.readUint8()
+    while tag != endMarker:
+      incl(result, decodePreserves(s, tag))
+      tag = s.readUint8()
   of 0xb7:
     result = Value(kind: pkDictionary)
-    while s.peekUint8() != endMarker:
-      result[decodePreserves(s)] = decodePreserves(s)
-    discard s.readUint8()
+    var tag = s.readUint8()
+    while tag != endMarker:
+      result[decodePreserves(s, tag)] = decodePreserves(s)
+      tag = s.readUint8()
   of endMarker:
     raise newException(ValueError, "invalid Preserves stream")
   else:
     raise newException(ValueError, "invalid Preserves tag byte 0x" & tag.toHex(2))
 
+proc decodePreserves*(s: Stream): Value {.gcsafe.} =
+  ## Decode a Preserves value from a binary-encoded stream.
+  s.decodePreserves s.readUint8()
+
 proc decodePreserves*(s: string): Value =
   ## Decode a string of binary-encoded Preserves.
   decodePreserves(s.newStringStream)