# Handles serialization and deserialization of objects to/from JSON
#
-# ## Nity JSON
+# ## Writing JSON with metadata
#
# `JsonSerializer` write Nit objects that subclass `Serializable` to JSON,
-# and `JsonDeserializer` can read them. They both use meta-data added to the
+# and `JsonDeserializer` can read them. They both use metadata 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
+# ## Writing 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`.
+# A shortcut to these writing services is provided by `Serializable::serialize_to_json`.
#
# ### Usage Example
#
# import json::serialization
#
# class Person
-# auto_serializable
+# serialize
#
# var name: String
# var year_of_birth: Int
# 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 bob.serialize_to_json(pretty=true, plain=true) == """
+#{
+# "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}}"""
+# assert alice.serialize_to_json(pretty=true, plain=true) == """
+#{
+# "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 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.
+#
+# ### 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
+#
+# # Check for errors
+# assert deserializer.errors.is_empty
+#
+# 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
private 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
+ # Write plain JSON? Standard JSON without metadata for deserialization
#
# If `false`, the default, serialize to support deserialization:
#
- # * Write meta-data, including the types of the serialized objects so they can
+ # * Write metadata, 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.
+ # With the added metadata, it can be complex to read.
#
# If `true`, serialize for other programs:
#
# * 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
+ # * Does not serialize the metadata needed to deserialize the objects
# back to regular Nit objects.
- # * Keys of Nit `HashMap` are converted to their string reprensentation using `to_s`.
+ # * Keys of Nit `HashMap` are converted to their string representation using `to_s`.
var plain_json = false is writable
+ # Write pretty JSON for human eyes?
+ #
+ # Toggles skipping lines between attributes of an object and
+ # properly indent the written JSON.
+ var pretty_json = false is writable
+
+ # Current indentation level used for writing `pretty_json`
+ private var indent_level = 0
+
# 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.
if plain_json then
for o in open_objects do
if object.is_same_serialized(o) then
- # Cycle detected
+ # Cycle, can't be managed in plain json
+ warn "Cycle detected in serialized object, replacing reference with 'null'."
stream.write "null"
return
end
end
first_attribute = true
- object.serialize_to_json self
+ object.accept_json_serializer self
first_attribute = false
if plain_json then open_objects.pop
redef fun serialize_attribute(name, value)
do
if not plain_json or not first_attribute then
- stream.write ", "
+ stream.write ","
first_attribute = false
end
+ new_line_and_indent
stream.write "\""
stream.write name
stream.write "\": "
redef fun serialize_reference(object)
do
- if not plain_json and 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)
- stream.write "\{\"__kind\": \"ref\", \"__id\": "
+ var id = cache.id_for(object)
+ stream.write "\{"
+ indent_level += 1
+ new_line_and_indent
+ stream.write "\"__kind\": \"ref\", \"__id\": "
stream.write id.to_s
+ indent_level -= 1
+ new_line_and_indent
stream.write "\}"
else
# serialize here
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
+ # Write a new line and indent it, only if `pretty_json`
+ private fun new_line_and_indent
do
- if refs_map.has_key(object) then
- return refs_map[object]
- else
- var id = refs_map.length
- refs_map[object] = id
- return id
+ if pretty_json then
+ stream.write "\n"
+ for i in indent_level.times do stream.write "\t"
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.
- private var root: nullable Jsonable is noinit
+ private var root: nullable Object is noinit
# Depth-first path in the serialized object tree.
- private 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[Map[String, nullable Object]]
# Last encountered object reference id.
#
init do
var root = text.parse_json
- if root isa JsonObject then path.add(root)
+ if root isa Map[String, nullable Object] then path.add(root)
self.root = root
end
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)
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 JsonObject then
- assert object.keys.has("__kind")
- var kind = object["__kind"]
+ if object isa JsonParseError then
+ errors.add object
+ return null
+ end
+
+ if object isa Map[String, nullable Object] then
+ 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
- assert id_to_object.has_key(id)
- return id_to_object[id]
+ if not cache.has_id(id) then
+ errors.add new Error("Serialization Error: JSON object reference has an unknown `__id`.")
+ return object
+ end
+
+ 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
+
+ if class_name == null then
+ errors.add new Error("Serialization Error: JSON object declaration does not declare a `__class`.")
+ return object
+ end
- assert not id_to_object.has_key(id) else print "Error: Object with id '{id}' of {class_name} is deserialized twice."
+ 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
# 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 == "ASCIIFlatString" or array_type == "UnicodeFlatString" 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: Map[String, nullable Object]): nullable String
+ do
+ return null
+ end
+end
+
+redef class Text
+
+ # Deserialize a `nullable Object` from this JSON formatted string
+ #
+ # Warning: Deserialization errors are reported with `print_error` and
+ # may be returned as a partial object or as `null`.
+ #
+ # This method is not appropriate when errors need to be handled programmatically,
+ # manually use a `JsonDeserializer` in such cases.
+ fun from_json_string: nullable Object
+ do
+ var deserializer = new JsonDeserializer(self)
+ var res = deserializer.deserialize
+ if deserializer.errors.not_empty then
+ print_error "Deserialization Errors: {deserializer.errors.join(", ")}"
+ end
+ return res
+ end
+
+ redef fun accept_json_serializer(v) do v.stream.write(to_json)
end
redef class Serializable
- private fun serialize_to_json(v: JsonSerializer)
+
+ # Serialize `self` to JSON
+ #
+ # Set `plain = true` to generate standard JSON, without deserialization metadata.
+ # Use this option if the generated JSON will be read by other programs or humans.
+ # Use the default, `plain = false`, if the JSON is to be deserialized by a Nit program.
+ #
+ # Set `pretty = true` to generate pretty JSON for human eyes.
+ # Use the default, `pretty = false`, to generate minified JSON.
+ #
+ # This method should not be refined by subclasses,
+ # instead `accept_json_serializer` can customize the serialization of an object.
+ #
+ # See: `JsonSerializer`
+ fun serialize_to_json(plain, pretty: nullable Bool): String
+ do
+ var stream = new StringWriter
+ var serializer = new JsonSerializer(stream)
+ serializer.plain_json = plain or else false
+ serializer.pretty_json = pretty or else false
+ serializer.serialize self
+ stream.close
+ return stream.to_s
+ end
+
+ # Refinable service to customize the serialization of this class to JSON
+ #
+ # This method can be refined to customize the serialization by either
+ # writing pure JSON directly on the stream `v.stream` or
+ # by using other services of `JsonSerializer`.
+ #
+ # Most of the time, it is preferable to refine the method `core_serialize_to`
+ # which is used by all the serialization engines, not just JSON.
+ protected fun accept_json_serializer(v: JsonSerializer)
do
- var id = v.ref_id_for(self)
+ var id = v.cache.new_id_for(self)
v.stream.write "\{"
+ v.indent_level += 1
if not v.plain_json then
+ v.new_line_and_indent
v.stream.write "\"__kind\": \"obj\", \"__id\": "
v.stream.write id.to_s
v.stream.write ", \"__class\": \""
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
+ v.indent_level -= 1
+ v.new_line_and_indent
+ v.stream.write "\}"
end
end
redef class Int
- redef fun serialize_to_json(v) do v.stream.write(to_s)
+ redef fun accept_json_serializer(v) do v.stream.write to_s
end
redef class Float
- redef fun serialize_to_json(v) do v.stream.write(to_s)
+ redef fun accept_json_serializer(v) do v.stream.write to_s
end
redef class Bool
- redef fun serialize_to_json(v) do v.stream.write(to_s)
+ redef fun accept_json_serializer(v) do v.stream.write to_s
end
redef class Char
- redef fun serialize_to_json(v)
+ redef fun accept_json_serializer(v)
do
if v.plain_json then
- v.stream.write to_s.to_json
+ to_s.accept_json_serializer v
else
v.stream.write "\{\"__kind\": \"char\", \"__val\": "
- v.stream.write to_s.to_json
+ to_s.accept_json_serializer v
v.stream.write "\}"
end
end
end
-redef class String
- redef fun serialize_to_json(v) do v.stream.write(to_json)
-end
-
redef class NativeString
- redef fun serialize_to_json(v) do to_s.serialize_to_json(v)
+ redef fun accept_json_serializer(v) do to_s.accept_json_serializer(v)
end
redef class Collection[E]
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 ", "
+ 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
end
+ v.indent_level -= 1
+ v.new_line_and_indent
v.stream.write "]"
end
end
redef class SimpleCollection[E]
- redef fun serialize_to_json(v)
+ redef fun accept_json_serializer(v)
do
# Register as pseudo object
if not v.plain_json then
- var id = v.ref_id_for(self)
- v.stream.write """{"__kind": "obj", "__id": """
+ var id = v.cache.new_id_for(self)
+ v.stream.write """{"""
+ v.indent_level += 1
+ v.new_line_and_indent
+ 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": """
+ v.stream.write """","""
+ v.new_line_and_indent
+ v.stream.write """"__items": """
end
serialize_to_pure_json v
if not v.plain_json then
+ v.indent_level -= 1
+ v.new_line_and_indent
v.stream.write "\}"
end
end
- redef init from_deserializer(v: Deserializer)
+ redef init from_deserializer(v)
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 v.plain_json or 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)
+ redef fun accept_json_serializer(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 "\{"
+ v.indent_level += 1
var first = true
for key, val in self do
if not first then
- v.stream.write ", "
+ v.stream.write ","
else first = false
+ v.new_line_and_indent
- if key == null then key = "null"
-
- v.stream.write key.to_s.to_json
+ var k = key or else "null"
+ k.to_s.accept_json_serializer v
v.stream.write ": "
if not v.try_to_serialize(val) then
+ assert val != null # null would have been serialized
v.warn("element of type {val.class_name} is not serializable.")
v.stream.write "null"
end
end
+ v.indent_level -= 1
+ v.new_line_and_indent
v.stream.write "\}"
else
- v.stream.write """{"__kind": "obj", "__id": """
+ v.stream.write "\{"
+ v.indent_level += 1
+ v.new_line_and_indent
+ 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 ","
+ v.new_line_and_indent
+ v.stream.write """"__keys": """
keys.serialize_to_pure_json v
- v.stream.write """, "__values": """
+ v.stream.write ","
+ v.new_line_and_indent
+ v.stream.write """"__values": """
values.serialize_to_pure_json v
+ v.indent_level -= 1
+ v.new_line_and_indent
v.stream.write "\}"
end
end
- # Instantiate a new `Array` from its serialized representation.
- redef init from_deserializer(v: Deserializer)
+ redef init from_deserializer(v)
do
super
nitlanguage / nit.git / blobdiff