Add flavor feature: reader will skip null fields

README.md

@@ -87,6 +87,7 @@ You can use `useDefaultSerializationIn` to add serializers of a flavor to a spec
   requireAllFields = true
   omitOptionalFields = true
   allowUnknownFields = true
+  skipNullFields = false
 ```
 
 ```Nim

json_serialization/format.nim

@@ -24,20 +24,23 @@ template flavorUsesAutomaticObjectSerialization*(T: type DefaultFlavor): bool =
 template flavorOmitsOptionalFields*(T: type DefaultFlavor): bool = false
 template flavorRequiresAllFields*(T: type DefaultFlavor): bool = false
 template flavorAllowsUnknownFields*(T: type DefaultFlavor): bool = false
+template flavorSkipNullFields*(T: type DefaultFlavor): bool = false
 
 # We create overloads of these traits to force the mixin treatment of the symbols
 type DummyFlavor* = object
 template flavorUsesAutomaticObjectSerialization*(T: type DummyFlavor): bool = true
 template flavorOmitsOptionalFields*(T: type DummyFlavor): bool = false
 template flavorRequiresAllFields*(T: type DummyFlavor): bool = false
 template flavorAllowsUnknownFields*(T: type DummyFlavor): bool = false
+template flavorSkipNullFields*(T: type DummyFlavor): bool = false
 
 template createJsonFlavor*(FlavorName: untyped,
                            mimeTypeValue = "application/json",
                            automaticObjectSerialization = false,
                            requireAllFields = true,
                            omitOptionalFields = true,
-                           allowUnknownFields = true) {.dirty.} =
+                           allowUnknownFields = true,
+                           skipNullFields = false) {.dirty.} =
   type FlavorName* = object
 
   template Reader*(T: type FlavorName): type = Reader(Json, FlavorName)
@@ -49,3 +52,4 @@ template createJsonFlavor*(FlavorName: untyped,
   template flavorOmitsOptionalFields*(T: type FlavorName): bool = omitOptionalFields
   template flavorRequiresAllFields*(T: type FlavorName): bool = requireAllFields
   template flavorAllowsUnknownFields*(T: type FlavorName): bool = allowUnknownFields
+  template flavorSkipNullFields*(T: type FlavorName): bool = skipNullFields

json_serialization/lexer.nim

@@ -580,7 +580,11 @@ proc scanString*[T](lex: var JsonLexer, val: var T, limit: int)
 proc scanValue*[T](lex: var JsonLexer, val: var T)
                    {.gcsafe, raises: [IOError].}
 
+proc tokKind*(lex: var JsonLexer): JsonValueKind
+               {.gcsafe, raises: [IOError].}
+
 template parseObjectImpl*(lex: JsonLexer,
+                         skipNullFields: static[bool],
                          actionInitial: untyped,
                          actionClosing: untyped,
                          actionComma: untyped,
@@ -645,7 +649,13 @@ template parseObjectImpl*(lex: JsonLexer,
         error(lex, errColonExpected, actionError)
 
       lex.advance
-      actionValue
+      when skipNullFields:
+        if lex.tokKind() == JsonValueKind.Null:
+          lex.scanNull()
+        else:
+          actionValue
+      else:
+        actionValue
       if not lex.ok: actionError
     else:
       error(lex, errStringExpected, actionError)
@@ -657,7 +667,7 @@ proc scanObject*[T](lex: var JsonLexer, val: var T)
   when T isnot (string or JsonVoid or JsonObjectType):
     {.fatal: "`scanObject` only accepts `string` or `JsonVoid` or `JsonObjectType`".}
 
-  parseObjectImpl(lex):
+  parseObjectImpl(lex, false):
     # initial action
     when T is string:
       val.add '{'

json_serialization/parser.nim

@@ -211,7 +211,7 @@ proc parseNumber*(r: var JsonReader, val: var JsonNumber)
     r.raiseParserError(errNumberExpected)
   r.lex.scanNumber(val)
   r.checkError
-  
+
 proc toInt*(r: var JsonReader, val: JsonNumber, T: type SomeSignedInt, portable: bool): T
       {.gcsafe, raises: [JsonReaderError].}=
   if val.sign == JsonSign.Neg:
@@ -291,14 +291,20 @@ proc parseFloat*(r: var JsonReader, T: type SomeFloat): T
 
 proc parseAsString*(r: var JsonReader, val: var string)
        {.gcsafe, raises: [IOError, JsonReaderError].} =
+  mixin flavorSkipNullFields
+  type
+    Reader = typeof r
+    Flavor = Reader.Flavor
+  const skipNullFields = flavorSkipNullFields(Flavor)
+
   case r.tokKind
   of JsonValueKind.String:
     escapeJson(r.parseString(), val)
   of JsonValueKind.Number:
     r.lex.scanNumber(val)
     r.checkError
   of JsonValueKind.Object:
-    parseObjectImpl(r.lex):
+    parseObjectImpl(r.lex, skipNullFields):
       # initial action
       val.add '{'
     do: # closing action
@@ -355,7 +361,7 @@ proc parseValue*(r: var JsonReader, val: var JsonValueRef)
                   {.gcsafe, raises: [IOError, JsonReaderError].} =
   r.lex.scanValue(val)
   r.checkError
-  
+
 template parseArray*(r: var JsonReader; body: untyped) =
   if r.tokKind != JsonValueKind.Array:
     r.raiseParserError(errBracketLeExpected)
@@ -375,9 +381,15 @@ template parseArray*(r: var JsonReader; idx: untyped; body: untyped) =
   do: r.raiseParserError() # error action
 
 template parseObject*(r: var JsonReader, key: untyped, body: untyped) =
+  mixin flavorSkipNullFields
+  type
+    Reader = typeof r
+    Flavor = Reader.Flavor
+  const skipNullFields = flavorSkipNullFields(typeof Flavor)
+
   if r.tokKind != JsonValueKind.Object:
     r.raiseParserError(errCurlyLeExpected)
-  parseObjectImpl(r.lex): discard # initial action
+  parseObjectImpl(r.lex, skipNullFields): discard # initial action
   do: discard # closing action
   do: discard # comma action
   do: # key action
@@ -388,9 +400,15 @@ template parseObject*(r: var JsonReader, key: untyped, body: untyped) =
     r.raiseParserError()
 
 template parseObjectCustomKey*(r: var JsonReader, keyAction: untyped, body: untyped) =
+  mixin flavorSkipNullFields
+  type
+    Reader = typeof r
+    Flavor = Reader.Flavor
+  const skipNullFields = flavorSkipNullFields(Flavor)
+
   if r.tokKind != JsonValueKind.Object:
     r.raiseParserError(errCurlyLeExpected)
-  parseObjectImpl(r.lex): discard # initial action
+  parseObjectImpl(r.lex, skipNullFields): discard # initial action
   do: discard # closing action
   do: discard # comma action
   do: # key action
@@ -414,6 +432,12 @@ proc readJsonNodeField(r: var JsonReader, field: var JsonNode)
   field = r.parseJsonNode()
 
 proc parseJsonNode(r: var JsonReader): JsonNode =
+  mixin flavorSkipNullFields
+  type
+    Reader = typeof r
+    Flavor = Reader.Flavor
+  const skipNullFields = flavorSkipNullFields(Flavor)
+
   case r.tokKind
   of JsonValueKind.String:
     result = JsonNode(kind: JString, str: r.parseString())
@@ -428,7 +452,7 @@ proc parseJsonNode(r: var JsonReader): JsonNode =
         r.toInt(val, typeof(result.num), JsonReaderFlag.portableInt in r.lex.flags))
   of JsonValueKind.Object:
     result = JsonNode(kind: JObject)
-    parseObjectImpl(r.lex): discard # initial action
+    parseObjectImpl(r.lex, skipNullFields): discard # initial action
     do: discard # closing action
     do: discard # comma action
     do: # key action

tests/test_json_flavor.nim

@@ -51,6 +51,9 @@ type
     three: JsonNumber[string]
     four: JsonValueRef[uint64]
 
+  ListOnly = object
+    list: JsonString
+
 Container.useDefaultSerializationIn StringyJson
 
 createJsonFlavor OptJson
@@ -71,8 +74,21 @@ const
     }
   }
 }
+
+"""
+  jsonTextWithNullFields = """
+{
+  "list": null
+}
 """
 
+createJsonFlavor NullyFields,
+  skipNullFields = true,
+  requireAllFields = false
+
+Container.useDefaultSerializationIn NullyFields
+ListOnly.useDefaultSerializationIn NullyFields
+
 suite "Test JsonFlavor":
   test "basic test":
     let c = Container(name: "c", x: -10, y: 20, list: @[1'i64, 2, 25])
@@ -104,3 +120,15 @@ suite "Test JsonFlavor":
     check:
       ww == vv
       xx == """{"two":-789.0009e-19,"three":999.776000e33,"four":{"apple":[1,true,"three"],"banana":{"chip":123,"z":null,"v":false}}}"""
+
+  test "object with null fields":
+    expect JsonReaderError:
+      let x = Json.decode(jsonTextWithNullFields, Container)
+      discard x
+
+    let x = NullyFields.decode(jsonTextWithNullFields, Container)
+    check x.list.len == 0
+
+    # field should not processed at all
+    let y = NullyFields.decode(jsonTextWithNullFields, ListOnly)
+    check y.list.string.len == 0