Compute the number of object properties to serialize.

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Changed
+- The length of objects is now pre-computed, reducing the size of the encoded
+  object and speeding up the decoing process. Thanks to Karchnu for his contribution.
+
 ## [0.2.1] - 2020-09-29
 
 ### Fixed

README.md

@@ -54,7 +54,7 @@ house = House.from_cbor(cbor)
 house.address                 # => "Crystal Road 1234"
 house.location                # => #<Location:0x10cd93d80 @latitude=12.3, @longitude=34.5>
 bytes = house.to_cbor         # => Bytes[...]
-CBOR::Diagnostic.to_s(bytes)  # => {_ "address": "Crystal Road 1234", "location": {_ "lat": 12.3, "lng": 34.5}}
+CBOR::Diagnostic.to_s(bytes)  # => {"address": "Crystal Road 1234", "location": {"lat": 12.3, "lng": 34.5}}
 
 data_array = [data]
 cbor_array = data_array.to_cbor # => Bytes[...]
@@ -63,7 +63,7 @@ CBOR::Diagnostic.to_s(cbor)     # => [{"address": "Crystal Road 1234", "location
 houses = Array(House).from_cbor(cbor_array)
 houses.size                  # => 1
 bytes = houses.to_cbor       # => Bytes[...]
-CBOR::Diagnostic.to_s(bytes) # => [{_ "address": "Crystal Road 1234", "location": {_ "lat": 12.3, "lng": 34.5}}]
+CBOR::Diagnostic.to_s(bytes) # => [{"address": "Crystal Road 1234", "location": {"lat": 12.3, "lng": 34.5}}]
 ```
 
 ## Installation
@@ -158,7 +158,7 @@ end
 
 a = A.from_cbor({"a" => 1, "b" => 2}.to_cbor) # => A(@cbor_unmapped={"b" => 2}, @a=1)
 bytes = a.to_cbor                             # => Bytes[...]
-CBOR::Diagnostic.to_s(bytes)                  # => {_ "a": 1, "b": 2}
+CBOR::Diagnostic.to_s(bytes)                  # => {"a": 1, "b": 2}
 ```
 
 ### Class annotation `CBOR::Serializable::Options`

spec/cbor/serializable_spec.cr

@@ -66,7 +66,7 @@ end
 
 describe CBOR::Serializable do
   describe "rfc examples" do
-    describe %(example {_ "a": 1, "b": [_ 2, 3]}) do
+    describe %(example {"a": 1, "b": [2, 3]}) do
       it "decodes from cbor" do
         result = ExampleA.from_cbor(Bytes[0xbf, 0x61, 0x61, 0x01, 0x61, 0x62, 0x9f, 0x02, 0x03, 0xff, 0xff])
 
@@ -75,7 +75,7 @@ describe CBOR::Serializable do
       end
     end
 
-    describe %(example {_ "Fun": true, "Amt": -2}) do
+    describe %(example {"Fun": true, "Amt": -2}) do
       it "decodes from cbor" do
         result = ExampleB.from_cbor(Bytes[0xbf, 0x63, 0x46, 0x75, 0x6e, 0xf5, 0x63, 0x41, 0x6d, 0x74, 0x21, 0xff])
 
@@ -84,7 +84,7 @@ describe CBOR::Serializable do
       end
     end
 
-    describe %(example ["a", {_ "b": "c"}]) do
+    describe %(example ["a", {"b": "c"}]) do
       it "decodes from cbor" do
         result = Array(String | ExampleC).from_cbor(Bytes[0x82, 0x61, 0x61, 0xbf, 0x61, 0x62, 0x61, 0x63, 0xff])
 
@@ -137,7 +137,7 @@ describe CBOR::Serializable do
 
       it "encodes to CBOR" do
         cbor = House.from_cbor(bytes).to_cbor
-        CBOR::Diagnostic.to_s(cbor).should eq(%({_ "address": "Crystal Road 1234", "location": {_ "lat": 12.3, "lng": 34.5}}))
+        CBOR::Diagnostic.to_s(cbor).should eq(%({"address": "Crystal Road 1234", "location": {"lat": 12.3, "lng": 34.5}}))
       end
     end
 
@@ -168,7 +168,7 @@ describe CBOR::Serializable do
       it "encodes to CBOR" do
         cbor = Array(House).from_cbor(bytes).to_cbor
 
-        CBOR::Diagnostic.to_s(cbor).should eq(%([{_ "address": "Crystal Road 1234", "location": {_ "lat": 12.3, "lng": 34.5}}]))
+        CBOR::Diagnostic.to_s(cbor).should eq(%([{"address": "Crystal Road 1234", "location": {"lat": 12.3, "lng": 34.5}}]))
       end
     end
 
@@ -185,7 +185,7 @@ describe CBOR::Serializable do
         res.a.should eq(1)
         res.cbor_unmapped.should eq({"b" => 2})
 
-        CBOR::Diagnostic.to_s(res.to_cbor).should eq(%({_ "a": 1, "b": 2}))
+        CBOR::Diagnostic.to_s(res.to_cbor).should eq(%({"a": 1, "b": 2}))
       end
     end
   end

src/cbor/serializable.cr

@@ -243,6 +243,10 @@ module CBOR
       raise ::CBOR::SerializationError.new("Unknown CBOR attribute: #{key}", self.class.to_s, nil)
     end
 
+    protected def get_cbor_unmapped
+      {} of String => ::CBOR::Type
+    end
+
     protected def on_to_cbor(cbor : ::CBOR::Encoder)
     end
 
@@ -268,9 +272,28 @@ module CBOR
           {% end %}
         {% end %}
 
-        cbor.object do
-          {% for name, value in properties %}
+        # Compute the size of the final list of properties to serialize.
+        # This allows a more compact encoding, and a faster decoding.
+        nb_properties_to_serialize = 0
+        {% for name, value in properties %}
             _{{name}} = @{{name}}
+          {% unless value[:emit_null] %}
+            unless _{{name}}.nil?
+              nb_properties_to_serialize += 1
+            end
+          {% else %}
+            nb_properties_to_serialize += 1
+          {% end %}
+        {% end %}
+
+        nb_properties_to_serialize += get_cbor_unmapped.size
+
+
+        {% if properties.size > 0 %}
+          cbor.write_object_start nb_properties_to_serialize
+
+          {% for name, value in properties %}
+              _{{name}} = @{{name}}
 
             {% unless value[:emit_null] %}
               unless _{{name}}.nil?
@@ -279,22 +302,22 @@ module CBOR
               # Write the key of the map
               cbor.write({{value[:key]}})
 
-              {% if value[:converter] %}
-                if _{{name}}
-                  {{ value[:converter] }}.to_cbor(_{{name}}, cbor)
-                else
-                  cbor.write(nil, use_undefined: value[:nil_as_undefined])
-                end
-              {% else %}
-                _{{name}}.to_cbor(cbor)
-              {% end %}
+            {% if value[:converter] %}
+              if _{{name}}
+                {{ value[:converter] }}.to_cbor(_{{name}}, cbor)
+              else
+                cbor.write(nil, use_undefined: value[:nil_as_undefined])
+              end
+            {% else %}
+              _{{name}}.to_cbor(cbor)
+            {% end %}
 
             {% unless value[:emit_null] %}
               end
             {% end %}
           {% end %}
           on_to_cbor(cbor)
-        end
+        {% end %}
       {% end %}
     end
 
@@ -310,6 +333,10 @@ module CBOR
         end
       end
 
+      protected def get_cbor_unmapped
+        cbor_unmapped
+      end
+
       protected def on_to_cbor(cbor : ::CBOR::Encoder)
         cbor_unmapped.each do |key, value|
           cbor.write(key)