Encode short byte-strings as hex text

src/preserves.nim

@@ -6,8 +6,8 @@ import std/[base64, endians, hashes, options, sets, sequtils, streams, tables, t
 
 from std/json import escapeJson, escapeJsonUnquoted
 from std/macros import hasCustomPragma, getCustomPragmaVal
-import ./preserves/private/dot
 from std/strutils import parseEnum
+import ./preserves/private/dot
 
 when defined(tracePreserves):
   template trace(args: varargs[untyped]) =
@@ -1070,15 +1070,22 @@ proc concat[E](result: var string; pr: Preserve[E]) =
   of pkString:
     result.add escapeJson(pr.string)
   of pkByteString:
-    for b in pr.bytes:
-      if b.char notin {'\20'..'\21', '#'..'[', ']'..'~'}:
+    if sequtils.any(pr.bytes, proc (b: byte): bool = b.char in {'\20'..'\21', '#'..'[', ']'..'~'}):
+      if pr.bytes.len > 64:
         result.add("#[") #]#
         result.add(base64.encode(pr.bytes))
         result.add(']')
-        return
-    result.add("#\"")
-    result.add(cast[string](pr.bytes))
-    result.add('"')
+      else:
+        const alphabet = "0123456789abcdef"
+        result.add("#x\"")
+        for b in pr.bytes:
+          result.add(alphabet[int(b shr 4)])
+          result.add(alphabet[int(b and 0xf)])
+        result.add('"')
+    else:
+      result.add("#\"")
+      result.add(cast[string](pr.bytes))
+      result.add('"')
   of pkSymbol:
     result.add(escapeJsonUnquoted(pr.symbol))
   of pkRecord: