encoding: sort dictionaries by encoded keys

src/preserves/private/encoding.nim

@@ -1,7 +1,7 @@
 # SPDX-FileCopyrightText: ☭ Emery Hemingway
 # SPDX-License-Identifier: Unlicense
 
-import std/[assertions, endians, streams]
+import std/[algorithm, assertions, endians, streams]
 import bigints
 import ./values
 
@@ -96,10 +96,22 @@ proc write*(str: Stream; pr: Value) =
       str.write(val)
     str.write(0x84'u8)
   of pkDictionary:
+    var
+      keyIndices = newSeqOfCap[(string, int)](pr.dict.len)
+      keyBuffer = newStringStream()
+    for i in 0..pr.dict.high:
+      keyBuffer.write(pr.dict[i][0])
+      keyIndices.add((keyBuffer.data.move, i))
+      keyBuffer.setPosition(0)
+        # add each encoded key and its index to the seq
+    sort(keyIndices) do (a, b: (string, int)) -> int:
+      cmp(a[0], b[0])
+        # sort the seq by encoded keys
     str.write(0xb7'u8)
-    for (key, value) in pr.dict.items:
-      str.write(key)
-      str.write(value)
+    for (keyBytes, i) in keyIndices:
+      str.write(keyBytes)
+      str.write(pr.dict[i][1])
+        # encode the values in sorted key order
     str.write(0x84'u8)
   of pkEmbedded:
     # str.write(0x86'u8)