X-Git-Url: http://nitlanguage.org

diff --git a/lib/json/serialization.nit b/lib/json/serialization.nit
index 7332b83..3707b19 100644
--- a/lib/json/serialization.nit
+++ b/lib/json/serialization.nit
@@ -14,30 +14,159 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-# Handles serialization and deserialization of objects to/from Json.
+# Handles serialization and deserialization of objects to/from JSON
+#
+# ## Nity JSON
+#
+# `JsonSerializer` write Nit objects that subclass `Serializable` to JSON,
+# and `JsonDeserializer` can read them. They both use meta-data added to the
+# generated JSON to recreate the Nit instances with the exact original type.
+#
+# For more information on Nit serialization, see: ../serialization/README.md
+#
+# ## Plain JSON
+#
+# The attribute `JsonSerializer::plain_json` triggers generating plain and
+# clean JSON. This format is easier to read for an human and a non-Nit program,
+# but it cannot be fully deserialized. It can still be read by services from
+# `json::static` and `json::dynamic`.
+#
+# A shortcut to this service is provided by `Serializable::to_plain_json`.
+#
+# ### Usage Example
+#
+# ~~~nitish
+# import json::serialization
+#
+# class Person
+#     serialize
+#
+#     var name: String
+#     var year_of_birth: Int
+#     var next_of_kin: nullable Person
+# end
+#
+# var bob = new Person("Bob", 1986)
+# var alice = new Person("Alice", 1978, bob)
+#
+# assert bob.to_plain_json == """
+# {"name": "Bob", "year_of_birth": 1986, "next_of_kin": null}"""
+#
+# assert alice.to_plain_json == """
+# {"name": "Alice", "year_of_birth": 1978, "next_of_kin": {"name": "Bob", "year_of_birth": 1986, "next_of_kin": null}}"""
+# ~~~
+#
+# ## JSON to Nit objects
+#
+# The `JsonDeserializer` support reading JSON code with minimal meta-data
+# to easily create Nit object from client-side code or configuration files.
+# Each JSON object must define the `__class` attribute with the corresponding
+# Nit class and the expected attributes with its name in Nit followed by its value.
+#
+# ### Usage Example
+#
+# ~~~nitish
+# import json::serialization
+#
+# class MeetupConfig
+#     serialize
+#
+#     var description: String
+#     var max_participants: nullable Int
+#     var answers: Array[FlatString]
+# end
+#
+# var json_code = """
+# {"__class": "MeetupConfig", "description": "My Awesome Meetup", "max_participants": null, "answers": ["Pepperoni", "Chicken"]}"""
+# var deserializer = new JsonDeserializer(json_code)
+#
+# var meet = deserializer.deserialize
+# assert meet isa MeetupConfig
+# assert meet.description == "My Awesome Meetup"
+# assert meet.max_participants == null
+# assert meet.answers == ["Pepperoni", "Chicken"]
+# ~~~
 module serialization
 
-import ::serialization
+import ::serialization::caching
 private import ::serialization::engine_tools
 import static
 
 # Serializer of Nit objects to Json string.
 class JsonSerializer
-	super Serializer
+	super CachingSerializer
 
 	# Target writing stream
 	var stream: Writer
 
+	# Write plain JSON? easier to read but does not support Nit deserialization
+	#
+	# If `false`, the default, serialize to support deserialization:
+	#
+	# * Write meta-data, including the types of the serialized objects so they can
+	#   be deserialized to their original form using `JsonDeserializer`.
+	# * Use references when an object has already been serialized so to not duplicate it.
+	# * Support cycles in references.
+	# * Preserve the Nit `Char` type as an object because it does not exist in JSON.
+	# * The generated JSON is standard and can be read by non-Nit programs.
+	#   However, some Nit types are not represented by the simplest possible JSON representation.
+	#   With the added meta-data, it can be complex to read.
+	#
+	# If `true`, serialize for other programs:
+	#
+	# * Nit objects are serialized to pure and standard JSON so they can
+	#   be easily read by non-Nit programs and humans.
+	# * Nit objects are serialized for every references, so they can be duplicated.
+	#   It is easier to read but it creates a larger output.
+	# * Does not support cycles, will replace the problematic references by `null`.
+	# * Does not serialize the meta-data needed to deserialize the objects
+	#   back to regular Nit objects.
+	# * Keys of Nit `HashMap` are converted to their string reprensentation using `to_s`.
+	var plain_json = false is writable
+
+	# List of the current open objects, the first is the main target of the serialization
+	#
+	# Used only when `plain_json == true` to detect cycles in serialization.
+	private var open_objects = new Array[Object]
+
+	# Has the first attribute of the current object already been serialized?
+	#
+	# Used only when `plain_json == true`.
+	private var first_attribute = false
+
 	redef fun serialize(object)
 	do
 		if object == null then
 			stream.write "null"
-		else object.serialize_to_json(self)
+		else
+			if plain_json then
+				for o in open_objects do
+					if object.is_same_serialized(o) then
+						# Cycle detected
+						stream.write "null"
+						return
+					end
+				end
+
+				open_objects.add object
+			end
+
+			first_attribute = true
+			object.serialize_to_json self
+			first_attribute = false
+
+			if plain_json then open_objects.pop
+		end
 	end
 
 	redef fun serialize_attribute(name, value)
 	do
-		stream.write ", \""
+		if not plain_json or not first_attribute then
+			stream.write ", "
+			first_attribute = false
+		end
+
+		stream.write "\""
 		stream.write name
 		stream.write "\": "
 		super
@@ -45,9 +174,9 @@ class JsonSerializer
 
 	redef fun serialize_reference(object)
 	do
-		if refs_map.has_key(object) then
+		if not plain_json and cache.has_object(object) then
 			# if already serialized, add local reference
-			var id = ref_id_for(object)
+			var id = cache.id_for(object)
 			stream.write "\{\"__kind\": \"ref\", \"__id\": "
 			stream.write id.to_s
 			stream.write "\}"
@@ -56,38 +185,20 @@ class JsonSerializer
 			serialize object
 		end
 	end
-
-	# Map of references to already serialized objects.
-	private var refs_map = new StrictHashMap[Serializable,Int]
-
-	# Get the internal serialized reference for this `object`.
-	private fun ref_id_for(object: Serializable): Int
-	do
-		if refs_map.has_key(object) then
-			return refs_map[object]
-		else
-			var id = refs_map.length
-			refs_map[object] = id
-			return id
-		end
-	end
 end
 
 # Deserializer from a Json string.
 class JsonDeserializer
-	super Deserializer
+	super CachingDeserializer
 
 	# Json text to deserialize from.
 	private var text: Text
 
 	# Root json object parsed from input text.
-	var root: nullable Jsonable is noinit
+	private var root: nullable Jsonable is noinit
 
 	# Depth-first path in the serialized object tree.
-	var path = new Array[JsonObject]
-
-	# Map of references to already deserialized objects.
-	private var id_to_object = new StrictHashMap[Int, Object]
+	private var path = new Array[JsonObject]
 
 	# Last encountered object reference id.
 	#
@@ -102,10 +213,14 @@ class JsonDeserializer
 
 	redef fun deserialize_attribute(name)
 	do
-		assert not path.is_empty
+		assert not path.is_empty # This is an internal error, abort
 		var current = path.last
 
-		assert current.keys.has(name)
+		if not current.keys.has(name) then
+			errors.add new Error("Deserialization Error: JSON object has not attribute '{name}'.")
+			return null
+		end
+
 		var value = current[name]
 
 		return convert_object(value)
@@ -117,37 +232,76 @@ class JsonDeserializer
 	do
 		var id = just_opened_id
 		if id == null then return # Register `new_object` only once
-		id_to_object[id] = new_object
+		cache[id] = new_object
 	end
 
 	# Convert from simple Json object to Nit object
 	private fun convert_object(object: nullable Object): nullable Object
 	do
+		if object isa JsonParseError then
+			errors.add object
+			return null
+		end
+
 		if object isa JsonObject then
-			assert object.keys.has("__kind")
-			var kind = object["__kind"]
+			var kind = null
+			if object.keys.has("__kind") then
+				kind = object["__kind"]
+			end
 
 			# ref?
 			if kind == "ref" then
-				assert object.keys.has("__id")
+				if not object.keys.has("__id") then
+					errors.add new Error("Serialization Error: JSON object reference does not declare a `__id`.")
+					return object
+				end
+
 				var id = object["__id"]
-				assert id isa Int
+				if not id isa Int then
+					errors.add new Error("Serialization Error: JSON object reference declares a non-integer `__id`.")
+					return object
+				end
+
+				if not cache.has_id(id) then
+					errors.add new Error("Serialization Error: JSON object reference has an unknown `__id`.")
+					return object
+				end
 
-				assert id_to_object.has_key(id)
-				return id_to_object[id]
+				return cache.object_for(id)
 			end
 
 			# obj?
-			if kind == "obj" then
-				assert object.keys.has("__id")
-				var id = object["__id"]
-				assert id isa Int
+			if kind == "obj" or kind == null then
+				var id = null
+				if object.keys.has("__id") then
+					id = object["__id"]
+
+					if not id isa Int then
+						errors.add new Error("Serialization Error: JSON object declaration declares a non-integer `__id`.")
+						return object
+					end
+
+					if cache.has_id(id) then
+						errors.add new Error("Serialization Error: JSON object with `__id` {id} is deserialized twice.")
+						# Keep going
+					end
+				end
 
-				assert object.keys.has("__class")
-				var class_name = object["__class"]
-				assert class_name isa String
+				var class_name = object.get_or_null("__class")
+				if class_name == null then
+					# Fallback to custom heuristic
+					class_name = class_name_heuristic(object)
+				end
 
-				assert not id_to_object.has_key(id) else print "Error: Object with id '{id}' of {class_name} is deserialized twice."
+				if class_name == null then
+					errors.add new Error("Serialization Error: JSON object declaration does not declare a `__class`.")
+					return object
+				end
+
+				if not class_name isa String then
+					errors.add new Error("Serialization Error: JSON object declaration declares a non-string `__class`.")
+					return object
+				end
 
 				# advance on path
 				path.push object
@@ -164,44 +318,165 @@ class JsonDeserializer
 
 			# char?
 			if kind == "char" then
-				assert object.keys.has("__val")
+				if not object.keys.has("__val") then
+					errors.add new Error("Serialization Error: JSON `char` object does not declare a `__val`.")
+					return object
+				end
+
 				var val = object["__val"]
-				assert val isa String
 
-				if val.length != 1 then print "Error: expected a single char when deserializing '{val}'."
+				if not val isa String or val.is_empty then
+					errors.add new Error("Serialization Error: JSON `char` object does not declare a single char in `__val`.")
+					return object
+				end
 
 				return val.chars.first
 			end
 
-			print "Malformed Json string: unexpected Json Object kind '{kind or else "null"}'"
-			abort
+			errors.add new Error("Serialization Error: JSON object has an unknown `__kind`.")
+			return object
 		end
 
+		# Simple JSON array without serialization metadata
 		if object isa Array[nullable Object] then
-			# special case, isa Array[nullable Serializable]
-			var array = new Array[nullable Serializable]
-			for e in object do array.add e.as(nullable Serializable)
+			var array = new Array[nullable Object]
+			var types = new HashSet[String]
+			var has_nullable = false
+			for e in object do
+				var res = convert_object(e)
+				array.add res
+
+				if res != null then
+					types.add res.class_name
+				else has_nullable = true
+			end
+
+			if types.length == 1 then
+				var array_type = types.first
+
+				var typed_array
+				if array_type == "FlatString" then
+					if has_nullable then
+						typed_array = new Array[nullable FlatString]
+					else typed_array = new Array[FlatString]
+				else if array_type == "Int" then
+					if has_nullable then
+						typed_array = new Array[nullable Int]
+					else typed_array = new Array[Int]
+				else if array_type == "Float" then
+					if has_nullable then
+						typed_array = new Array[nullable Float]
+					else typed_array = new Array[Float]
+				else
+					# TODO support all array types when we separate the constructor
+					# `from_deserializer` from the filling of the items.
+
+					if not has_nullable then
+						typed_array = new Array[Object]
+					else
+						# Unsupported array type, return as `Array[nullable Object]`
+						return array
+					end
+				end
+
+				assert typed_array isa Array[nullable Object]
+
+				# Copy item to the new array
+				for e in array do typed_array.add e
+				return typed_array
+			end
+
+			# Uninferable type, return as `Array[nullable Object]`
 			return array
 		end
 
 		return object
 	end
 
-	redef fun deserialize do return convert_object(root)
+	redef fun deserialize
+	do
+		errors.clear
+		return convert_object(root)
+	end
+
+	# User customizable heuristic to get the name of the Nit class to deserialize `json_object`
+	#
+	# This method is called only when deserializing an object without the metadata `__class`.
+	# Return the class name as a `String` when it can be inferred.
+	# Return `null` when the class name cannot be found.
+	#
+	# If a valid class name is returned, `json_object` will then be deserialized normally.
+	# So it must contain the attributes of the corresponding class, as usual.
+	#
+	# ~~~nitish
+	# class MyData
+	#     serialize
+	#
+	#     var data: String
+	# end
+	#
+	# class MyError
+	#     serialize
+	#
+	#     var error: String
+	# end
+	#
+	# class MyJsonDeserializer
+	#     super JsonDeserializer
+	#
+	#     redef fun class_name_heuristic(json_object)
+	#     do
+	#         if json_object.keys.has("error") then return "MyError"
+	#         if json_object.keys.has("data") then return "MyData"
+	#         return null
+	#     end
+	# end
+	#
+	# var json = """{"data": "some other data"}"""
+	# var deserializer = new MyJsonDeserializer(json)
+	# var deserialized = deserializer.deserialize
+	# assert deserialized isa MyData
+	#
+	# json = """{"error": "some error message"}"""
+	# deserializer = new MyJsonDeserializer(json)
+	# deserialized = deserializer.deserialize
+	# assert deserialized isa MyError
+	# ~~~
+	protected fun class_name_heuristic(json_object: JsonObject): nullable String
+	do
+		return null
+	end
 end
 
 redef class Serializable
 	private fun serialize_to_json(v: JsonSerializer)
 	do
-		var id = v.ref_id_for(self)
-		v.stream.write "\{\"__kind\": \"obj\", \"__id\": "
-		v.stream.write id.to_s
-		v.stream.write ", \"__class\": \""
-		v.stream.write class_name
-		v.stream.write "\""
+		var id = v.cache.new_id_for(self)
+		v.stream.write "\{"
+		if not v.plain_json then
+			v.stream.write "\"__kind\": \"obj\", \"__id\": "
+			v.stream.write id.to_s
+			v.stream.write ", \"__class\": \""
+			v.stream.write class_name
+			v.stream.write "\""
+		end
 		core_serialize_to(v)
 		v.stream.write "\}"
 	end
+
+	# Serialize this object to plain JSON
+	#
+	# This is a shortcut using `JsonSerializer::plain_json`,
+	# see its documentation for more information.
+	fun to_plain_json: String
+	do
+		var stream = new StringWriter
+		var serializer = new JsonSerializer(stream)
+		serializer.plain_json = true
+		serializer.serialize self
+		stream.close
+		return stream.to_s
+	end
 end
 
 redef class Int
@@ -219,9 +494,13 @@ end
 redef class Char
 	redef fun serialize_to_json(v)
 	do
-		v.stream.write "\{\"__kind\": \"char\", \"__val\": "
-		v.stream.write to_s.to_json
-		v.stream.write "\}"
+		if v.plain_json then
+			v.stream.write to_s.to_json
+		else
+			v.stream.write "\{\"__kind\": \"char\", \"__val\": "
+			v.stream.write to_s.to_json
+			v.stream.write "\}"
+		end
 	end
 end
 
@@ -256,74 +535,88 @@ redef class SimpleCollection[E]
 	redef fun serialize_to_json(v)
 	do
 		# Register as pseudo object
-		var id = v.ref_id_for(self)
-		v.stream.write """{"__kind": "obj", "__id": """
-		v.stream.write id.to_s
-		v.stream.write """, "__class": """"
-		v.stream.write class_name
-		v.stream.write """", "__length": """
-		v.stream.write length.to_s
-		v.stream.write """, "__items": """
+		if not v.plain_json then
+			var id = v.cache.new_id_for(self)
+			v.stream.write """{"__kind": "obj", "__id": """
+			v.stream.write id.to_s
+			v.stream.write """, "__class": """"
+			v.stream.write class_name
+			v.stream.write """", "__items": """
+		end
+
 		serialize_to_pure_json v
-		v.stream.write "\}"
+
+		if not v.plain_json then
+			v.stream.write "\}"
+		end
 	end
 
 	redef init from_deserializer(v: Deserializer)
 	do
+		super
 		if v isa JsonDeserializer then
 			v.notify_of_creation self
 			init
 
-			var length = v.deserialize_attribute("__length").as(Int)
 			var arr = v.path.last["__items"].as(SequenceRead[nullable Object])
-			for i in length.times do
-				var obj = v.convert_object(arr[i])
+			for o in arr do
+				var obj = v.convert_object(o)
 				self.add obj
 			end
 		end
 	end
 end
 
-redef class Array[E]
-	redef fun serialize_to_json(v)
-	do
-		if class_name == "Array[nullable Serializable]" then
-			# Using class_name to get the exact type,
-			# we do not want Array[Int] or anything else here.
-
-			serialize_to_pure_json v
-		else super
-	end
-end
-
 redef class Map[K, V]
 	redef fun serialize_to_json(v)
 	do
 		# Register as pseudo object
-		var id = v.ref_id_for(self)
+		var id = v.cache.new_id_for(self)
+
+		if v.plain_json then
+			v.stream.write "\{"
+			var first = true
+			for key, val in self do
+				if not first then
+					v.stream.write ", "
+				else first = false
+
+				if key == null then key = "null"
+
+				v.stream.write key.to_s.to_json
+				v.stream.write ": "
+				if not v.try_to_serialize(val) then
+					v.warn("element of type {val.class_name} is not serializable.")
+					v.stream.write "null"
+				end
+			end
+			v.stream.write "\}"
+		else
+			v.stream.write """{"__kind": "obj", "__id": """
+			v.stream.write id.to_s
+			v.stream.write """, "__class": """"
+			v.stream.write class_name
+			v.stream.write """", "__length": """
+			v.stream.write length.to_s
 
-		v.stream.write """{"__kind": "obj", "__id": """
-		v.stream.write id.to_s
-		v.stream.write """, "__class": """"
-		v.stream.write class_name
-		v.stream.write """", "__length": """
-		v.stream.write length.to_s
-		v.stream.write """, "__keys": """
+			v.stream.write """, "__keys": """
+			keys.serialize_to_pure_json v
 
-		keys.serialize_to_pure_json v
+			v.stream.write """, "__values": """
+			values.serialize_to_pure_json v
 
-		v.stream.write """, "__values": """
-		values.serialize_to_pure_json v
-		v.stream.write "\}"
+			v.stream.write "\}"
+		end
 	end
 
 	# Instantiate a new `Array` from its serialized representation.
 	redef init from_deserializer(v: Deserializer)
 	do
-		init
+		super
 
 		if v isa JsonDeserializer then
 			v.notify_of_creation self
+			init
 
 			var length = v.deserialize_attribute("__length").as(Int)
 			var keys = v.path.last["__keys"].as(SequenceRead[nullable Object])