# end
#
# var bob = new Person("Bob", 1986)
-# var alice = new Person("Alice", 1978, bob)
-#
# assert bob.serialize_to_json(pretty=true, plain=true) == """
#{
# "name": "Bob",
# "next_of_kin": null
#}"""
#
+# var alice = new Person("Alice", 1978, bob)
# assert alice.serialize_to_json(pretty=true, plain=true) == """
#{
# "name": "Alice",
# "next_of_kin": null
# }
#}"""
+#
+# # You can also build JSON objects as a `Map`
+# var charlie = new Map[String, nullable Serializable]
+# charlie["name"] = "Charlie"
+# charlie["year_of_birth"] = 1968
+# charlie["next_of_kin"] = alice
+# assert charlie.serialize_to_json(pretty=true, plain=true) == """
+#{
+# "name": "Charlie",
+# "year_of_birth": 1968,
+# "next_of_kin": {
+# "name": "Alice",
+# "year_of_birth": 1978,
+# "next_of_kin": {
+# "name": "Bob",
+# "year_of_birth": 1986,
+# "next_of_kin": null
+# }
+# }
+#}"""
# ~~~
#
-# ## JSON to Nit objects
+# ## Read JSON to create Nit objects
+#
+# The `JsonDeserializer` supports reading JSON code with or without metadata.
+# It can create Nit objects from a remote service returning JSON data
+# or to read local configuration files as Nit objects.
+# However, it needs to know which Nit class to recreate from each JSON object.
+# The class is either declared or inferred:
#
-# The `JsonDeserializer` support reading JSON code with minimal metadata
-# 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.
+# 1. The JSON object defines a `__class` key with the name of the Nit class as value.
+# This attribute is generated by the `JsonSerializer` with other metadata,
+# it can also be specified by other external tools.
+# 2. A refinement of `JsonDeserializer::class_name_heuristic` identifies the Nit class.
+# 3. If all else fails, `JsonDeserializer` uses the static type of the attribute.
#
# ### Usage Example
#
# ~~~nitish
# import json::serialization
#
-# class MeetupConfig
+# class Triangle
# serialize
#
-# var description: String
-# var max_participants: nullable Int
-# var answers: Array[FlatString]
+# var corners = new Array[Point]
+# redef var to_s is serialize_as("name")
# end
#
-# var json_code = """
-# {"__class": "MeetupConfig", "description": "My Awesome Meetup", "max_participants": null, "answers": ["Pepperoni", "Chicken"]}"""
-# var deserializer = new JsonDeserializer(json_code)
+# class Point
+# serialize
+#
+# var x: Int
+# var y: Int
+# end
#
-# var meet = deserializer.deserialize
+# # Metadata on each JSON object tells the deserializer what is its Nit type,
+# # and it supports special types such as generic collections.
+# var json_with_metadata = """{
+# "__class": "Triangle",
+# "corners": {"__class": "Array[Point]",
+# "__items": [{"__class": "Point", "x": 0, "y": 0},
+# {"__class": "Point", "x": 3, "y": 0},
+# {"__class": "Point", "x": 2, "y": 2}]},
+# "name": "some triangle"
+# }"""
#
-# # Check for errors
+# var deserializer = new JsonDeserializer(json_with_metadata)
+# var object = deserializer.deserialize
# assert deserializer.errors.is_empty
+# assert object != null
+# print object
#
-# assert meet isa MeetupConfig
-# assert meet.description == "My Awesome Meetup"
-# assert meet.max_participants == null
-# assert meet.answers == ["Pepperoni", "Chicken"]
+# # However most non-Nit services won't add the metadata and instead produce plain JSON.
+# # Without a "__class", the deserializer relies on `class_name_heuristic` and the static type.
+# # The type of the root object to deserialize can be specified by calling
+# # its deserialization constructor `from_deserializer`.
+# var plain_json = """{
+# "corners": [{"x": 0, "y": 0},
+# {"x": 3, "y": 0},
+# {"x": 2, "y": 2}],
+# "name": "the same triangle"
+# }"""
+#
+# deserializer = new JsonDeserializer(plain_json)
+# object = new Triangle.from_deserializer(deserializer)
+# assert deserializer.errors.is_empty # If false, `obj` is invalid
+# print object
+# ~~~
+#
+# ### Missing attributes and default values
+#
+# When reading JSON, some attributes expected by Nit classes may be missing.
+# The JSON object may come from an external API using optional attributes or
+# from a previous version of your program without the attributes.
+# When an attribute is not found, the deserialization engine acts in one of three ways:
+#
+# 1. If the attribute has a default value or if it is annotated by `lazy`,
+# the engine leave the attribute to the default value. No error is raised.
+# 2. If the static type of the attribute is nullable, the engine sets
+# the attribute to `null`. No error is raised.
+# 3. Otherwise, the engine raises an error and does not set the attribute.
+# The caller must check for `errors` and must not read from the attribute.
+#
+# ~~~nitish
+# import json::serialization
+#
+# class MyConfig
+# serialize
+#
+# var width: Int # Must be in JSON or an error is raised
+# var height = 4
+# var volume_level = 8 is lazy
+# var player_name: nullable String
+# var tmp_dir: nullable String = "/tmp" is lazy
+# end
+#
+# # ---
+# # JSON object with all expected attributes -> OK
+# var plain_json = """
+# {
+# "width": 11,
+# "height": 22,
+# "volume_level": 33,
+# "player_name": "Alice",
+# "tmp_dir": null
+# }"""
+# var deserializer = new JsonDeserializer(plain_json)
+# var obj = new MyConfig.from_deserializer(deserializer)
+#
+# assert deserializer.errors.is_empty
+# assert obj.width == 11
+# assert obj.height == 22
+# assert obj.volume_level == 33
+# assert obj.player_name == "Alice"
+# assert obj.tmp_dir == null
+#
+# # ---
+# # JSON object missing optional attributes -> OK
+# plain_json = """
+# {
+# "width": 11
+# }"""
+# deserializer = new JsonDeserializer(plain_json)
+# obj = new MyConfig.from_deserializer(deserializer)
+#
+# assert deserializer.errors.is_empty
+# assert obj.width == 11
+# assert obj.height == 4
+# assert obj.volume_level == 8
+# assert obj.player_name == null
+# assert obj.tmp_dir == "/tmp"
+#
+# # ---
+# # JSON object missing the mandatory attribute -> Error
+# plain_json = """
+# {
+# "player_name": "Bob",
+# }"""
+# deserializer = new JsonDeserializer(plain_json)
+# obj = new MyConfig.from_deserializer(deserializer)
+#
+# # There's an error, `obj` is partial
+# assert deserializer.errors.length == 1
+#
+# # Still, we can access valid attributes
+# assert obj.player_name == "Bob"
# ~~~
module serialization
# Depth-first path in the serialized object tree.
private var path = new Array[Map[String, nullable Object]]
+ # Names of the attributes from the root to the object currently being deserialized
+ var attributes_path = new Array[String]
+
# Last encountered object reference id.
#
# See `id_to_object`.
self.root = root
end
- redef fun deserialize_attribute(name)
+ redef fun deserialize_attribute(name, static_type)
do
- assert not path.is_empty # This is an internal error, abort
+ if path.is_empty then
+ # The was a parsing error or the root is not an object
+ if not root isa Error then
+ errors.add new Error("Deserialization Error: parsed JSON value is not an object.")
+ end
+ deserialize_attribute_missing = false
+ return null
+ end
+
var current = path.last
if not current.keys.has(name) then
- errors.add new Error("Deserialization Error: JSON object has not attribute '{name}'.")
+ # Let the generated code / caller of `deserialize_attribute` raise the missing attribute error
+ deserialize_attribute_missing = true
return null
end
var value = current[name]
- return convert_object(value)
+ attributes_path.add name
+ var res = convert_object(value, static_type)
+ attributes_path.pop
+
+ deserialize_attribute_missing = false
+ return res
end
# This may be called multiple times by the same object from constructors
cache[id] = new_object
end
- # Convert from simple Json object to Nit object
- private fun convert_object(object: nullable Object): nullable Object
+ # Convert the simple JSON `object` to a Nit object
+ private fun convert_object(object: nullable Object, static_type: nullable String): nullable Object
do
if object isa JsonParseError then
errors.add object
if class_name == null then
# Fallback to custom heuristic
class_name = class_name_heuristic(object)
+
+ if class_name == null and static_type != null then
+ # Fallack to the static type, strip the `nullable` prefix
+ var prefix = "nullable "
+ if static_type.has(prefix) then
+ class_name = static_type.substring_from(prefix.length)
+ else class_name = static_type
+ end
end
if class_name == null then
# Simple JSON array without serialization metadata
if object isa Array[nullable Object] then
+ # Can we use the static type?
+ if static_type != null then
+ var prefix = "nullable "
+ var class_name = if static_type.has(prefix) then
+ static_type.substring_from(prefix.length)
+ else static_type
+
+ opened_array = object
+ var value = deserialize_class(class_name)
+ opened_array = null
+ return value
+ end
+
+ # This branch should rarely be used:
+ # when an array is the root object which is accepted but illegal in standard JSON,
+ # or in strange custom deserialization hacks.
+
var array = new Array[nullable Object]
var types = new HashSet[String]
var has_nullable = false
return typed_array
end
- # Uninferable type, return as `Array[nullable Object]`
+ # Uninferrable type, return as `Array[nullable Object]`
return array
end
return object
end
+ # Current array open for deserialization, used by `SimpleCollection::from_deserializer`
+ private var opened_array: nullable Array[nullable Object] = null
+
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`
+ # User customizable heuristic to infer 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.
+ # Use the content of `json_object` to identify what Nit class it should be deserialized into.
+ # Or use `self.attributes_path` indicating where the deserialized object will be stored,
+ # is is less reliable as some objects don't have an associated attribute:
+ # the root/first deserialized object and collection elements.
+ #
+ # Return the class name as a `String` when it can be inferred,
+ # or `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.
# serialize
#
# var error: String
+ # var related_data: MyData
# end
#
# class MyJsonDeserializer
#
# redef fun class_name_heuristic(json_object)
# do
+ # # Infer the Nit class from the content of the JSON object.
# if json_object.keys.has("error") then return "MyError"
# if json_object.keys.has("data") then return "MyData"
+ #
+ # # Infer the Nit class from the attribute where it will be stored.
+ # # This line duplicates a previous line, and would only apply when
+ # # `MyData` is within a `MyError`.
+ # if attributes_path.not_empty and attributes_path.last == "related_data" then return "MyData"
+ #
# return null
# end
# end
#
- # var json = """{"data": "some other data"}"""
+ # var json = """{"data": "some data"}"""
# var deserializer = new MyJsonDeserializer(json)
# var deserialized = deserializer.deserialize
# assert deserialized isa MyData
#
- # json = """{"error": "some error message"}"""
+ # json = """{"error": "some error message",
+ # "related_data": {"data": "some other data"}"""
# deserializer = new MyJsonDeserializer(json)
# deserialized = deserializer.deserialize
# assert deserialized isa MyError
return res
end
- redef fun accept_json_serializer(v) do v.stream.write(to_json)
+ redef fun accept_json_serializer(v)
+ do
+ v.stream.write "\""
+ for i in [0 .. self.length[ do
+ var char = self[i]
+ if char == '\\' then
+ v.stream.write "\\\\"
+ else if char == '\"' then
+ v.stream.write "\\\""
+ else if char < ' ' then
+ if char == '\n' then
+ v.stream.write "\\n"
+ else if char == '\r' then
+ v.stream.write "\\r"
+ else if char == '\t' then
+ v.stream.write "\\t"
+ else
+ v.stream.write char.escape_to_utf16
+ end
+ else
+ v.stream.write char.to_s
+ end
+ end
+ v.stream.write "\""
+ end
end
redef class Serializable
return stream.to_s
end
+ # Serialize `self` to plain JSON
+ #
+ # Compatibility alias for `serialize_to_json(plain=true)`.
+ fun to_json: String do return serialize_to_json(plain=true)
+
+ # Serialize `self` to plain pretty JSON
+ #
+ # Compatibility alias for `serialize_to_json(plain=true, pretty=true)`.
+ fun to_pretty_json: String do return serialize_to_json(plain=true, pretty=true)
+
# Refinable service to customize the serialization of this class to JSON
#
# This method can be refined to customize the serialization by either
# Utility to serialize a normal Json array
private fun serialize_to_pure_json(v: JsonSerializer)
do
- v.stream.write "["
- v.indent_level += 1
- var is_first = true
- for e in self do
- if is_first then
- is_first = false
- else v.stream.write ","
- v.new_line_and_indent
+ v.stream.write "["
+ v.indent_level += 1
+ var is_first = true
+ for e in self do
+ if is_first then
+ is_first = false
+ else v.stream.write ","
+ v.new_line_and_indent
- if not v.try_to_serialize(e) then
- assert e != null # null would have been serialized
- v.warn("element of type {e.class_name} is not serializable.")
- end
+ if not v.try_to_serialize(e) then
+ assert e != null # null would have been serialized
+ v.warn("element of type {e.class_name} is not serializable.")
end
- v.indent_level -= 1
- v.new_line_and_indent
- v.stream.write "]"
+ end
+ v.indent_level -= 1
+ v.new_line_and_indent
+ v.stream.write "]"
end
end
v.notify_of_creation self
init
- var arr = v.path.last["__items"].as(SequenceRead[nullable Object])
- for o in arr do
- var obj = v.convert_object(o)
- self.add obj
+ var open_array: nullable SequenceRead[nullable Object] = v.opened_array
+ if open_array == null then
+ # With metadata
+ var arr = v.path.last.get_or_null("__items")
+ if not arr isa SequenceRead[nullable Object] then
+ # If there is nothing, we consider that it is an empty collection.
+ if arr != null then v.errors.add new Error("Deserialization Error: invalid format in {self.class_name}")
+ return
+ end
+ open_array = arr
+ end
+
+ # Try to get the name of the single parameter type assuming it is E.
+ # This does not work in non-generic subclasses,
+ # when the first parameter is not E, or
+ # when there is more than one parameter. (The last one could be fixed)
+ var class_name = class_name
+ var items_type = null
+ var bracket_index = class_name.index_of('[')
+ if bracket_index != -1 then
+ var start = bracket_index + 1
+ var ending = class_name.last_index_of(']')
+ items_type = class_name.substring(start, ending-start)
+ end
+
+ # Fill array
+ for o in open_array do
+ var obj = v.convert_object(o, items_type)
+ if obj isa E then
+ add obj
+ else v.errors.add new AttributeTypeError(self, "items", obj, "E")
end
end
end
v.notify_of_creation self
init
- var length = v.deserialize_attribute("__length").as(Int)
- var keys = v.path.last["__keys"].as(SequenceRead[nullable Object])
- var values = v.path.last["__values"].as(SequenceRead[nullable Object])
+ var length = v.deserialize_attribute("__length")
+ var keys = v.path.last.get_or_null("__keys")
+ var values = v.path.last.get_or_null("__values")
+
+ # Length is optional
+ if length == null and keys isa SequenceRead[nullable Object] then length = keys.length
+
+ # Consistency check
+ if not length isa Int or length < 0 or
+ not keys isa SequenceRead[nullable Object] or
+ not values isa SequenceRead[nullable Object] or
+ keys.length != values.length or length != keys.length then
+
+ # If there is nothing or length == 0, we consider that it is an empty Map.
+ if (length != null and length != 0) or keys != null or values != null then
+ v.errors.add new Error("Deserialization Error: invalid format in {self.class_name}")
+ end
+ return
+ end
+
for i in length.times do
var key = v.convert_object(keys[i])
var value = v.convert_object(values[i])
+
+ if not key isa K then
+ v.errors.add new AttributeTypeError(self, "keys", key, "K")
+ continue
+ end
+
+ if not value isa V then
+ v.errors.add new AttributeTypeError(self, "values", value, "V")
+ continue
+ end
+
+ if has_key(key) then
+ v.errors.add new Error("Deserialization Error: duplicated key '{key or else "null"}' in {self.class_name}, previous value overwritten")
+ end
+
self[key] = value
end
end
nitlanguage / nit.git / blobdiff