Limit hash keys to certain types.

src/cbor.cr

@@ -5,13 +5,21 @@ require "./cbor/**"
 module CBOR
   VERSION = "0.1.0"
 
+  # Represents CBOR Hash Keys: everything except Nil, hashs, arrays.
+  alias HashKeyType = Int8  | Int16  | Int32  | Int64  | Int128 |
+                      UInt8 | UInt16 | UInt32 | UInt64 |
+                      Float32 | Float64 |
+                      String |
+                      Bool |
+                      Bytes
+
   # Represents CBOR types
   alias Type = Nil |
                Bool |
                String |
                Bytes |
                Array(Type) |
-               Hash(Type, Type) |
+               Hash(HashKeyType,  Type) |
                Int8 |
                UInt8 |
                Int16 |

src/cbor/decoder.cr

@@ -7,6 +7,34 @@ class CBOR::Decoder
     @current_token = @lexer.next_token
   end
 
+  # This is similar to read_value but with a focus on a key for a hash.
+  def read_key : HashKeyType
+    v = case token = @current_token
+    when Token::StringT
+      finish_token!
+      token.value.as(String)
+    when Token::IntT
+      finish_token!
+      token.value
+    when Token::FloatT
+      finish_token!
+      token.value
+    when Token::BytesT
+      finish_token!
+      token.value.as(Bytes)
+    when Token::SimpleValueT
+      finish_token!
+      token.value.to_t
+    else
+      puts "hash key with a #{token.class.to_s} value"
+      unexpected_token(token)
+    end
+    if v.nil?
+      raise ""
+    end
+    v
+  end
+
   def read_value : Type
     case token = @current_token
     when Token::TagT
@@ -34,8 +62,11 @@ class CBOR::Decoder
       arr
     when Token::MapT
       finish_token!
-      map = Hash(Type, Type).new
-      consume_sequence(token.size) { map[read_value] = read_value }
+      map = Hash(HashKeyType, Type).new
+      consume_sequence(token.size) {
+        key = read_key
+        map[key] = read_value
+      }
       map
     else
       unexpected_token(token)