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toJson, jsonTo, json (de)serialization for custom types; remove d…
…ependency on strtabs thanks to a hooking mechanism (#14563) * json custom serialization; application for strtabs * serialize using nesting * make toJson more feature complete * add since * Revert "Improve JSON serialisation of strtabs (#14549)" This reverts commit 7cb4ef2. * better approach via mixin * toJson, jsonTo * fix test * address comments * move to jsonutils * doc * cleanups * also test for js * also test for vm
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,126 @@ | ||
| ##[ | ||
| This module implements a hookable (de)serialization for arbitrary types. | ||
| Design goal: avoid importing modules where a custom serialization is needed; | ||
| see strtabs.fromJsonHook,toJsonHook for an example. | ||
| ]## | ||
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| import std/[json,tables,strutils] | ||
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| #[ | ||
| xxx | ||
| use toJsonHook,fromJsonHook for Table|OrderedTable | ||
| add Options support also using toJsonHook,fromJsonHook and remove `json=>options` dependency | ||
| future direction: | ||
| add a way to customize serialization, for eg allowing missing | ||
| or extra fields in JsonNode, field renaming, and a way to handle cyclic references | ||
| using a cache of already visited addresses. | ||
| ]# | ||
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| proc isNamedTuple(T: typedesc): bool {.magic: "TypeTrait".} | ||
| proc distinctBase(T: typedesc): typedesc {.magic: "TypeTrait".} | ||
| template distinctBase[T](a: T): untyped = distinctBase(type(a))(a) | ||
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| proc checkJsonImpl(cond: bool, condStr: string, msg = "") = | ||
| if not cond: | ||
| # just pick 1 exception type for simplicity; other choices would be: | ||
| # JsonError, JsonParser, JsonKindError | ||
| raise newException(ValueError, msg) | ||
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| template checkJson(cond: untyped, msg = "") = | ||
| checkJsonImpl(cond, astToStr(cond), msg) | ||
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| proc fromJson*[T](a: var T, b: JsonNode) = | ||
| ## inplace version of `jsonTo` | ||
| #[ | ||
| adding "json path" leading to `b` can be added in future work. | ||
| ]# | ||
| checkJson b != nil, $($T, b) | ||
| when compiles(fromJsonHook(a, b)): fromJsonHook(a, b) | ||
| elif T is bool: a = to(b,T) | ||
| elif T is Table | OrderedTable: | ||
| a.clear | ||
| for k,v in b: | ||
| a[k] = jsonTo(v, typeof(a[k])) | ||
| elif T is enum: | ||
| case b.kind | ||
| of JInt: a = T(b.getBiggestInt()) | ||
| of JString: a = parseEnum[T](b.getStr()) | ||
| else: checkJson false, $($T, " ", b) | ||
| elif T is Ordinal: a = T(to(b, int)) | ||
| elif T is pointer: a = cast[pointer](to(b, int)) | ||
| elif T is distinct: | ||
| when nimvm: | ||
| # bug, potentially related to https://github.com/nim-lang/Nim/issues/12282 | ||
| a = T(jsonTo(b, distinctBase(T))) | ||
| else: | ||
| a.distinctBase.fromJson(b) | ||
| elif T is string|SomeNumber: a = to(b,T) | ||
| elif T is JsonNode: a = b | ||
| elif T is ref | ptr: | ||
| if b.kind == JNull: a = nil | ||
| else: | ||
| a = T() | ||
| fromJson(a[], b) | ||
| elif T is array: | ||
| checkJson a.len == b.len, $(a.len, b.len, $T) | ||
| for i, val in b.getElems: | ||
| fromJson(a[i], val) | ||
| elif T is seq: | ||
| a.setLen b.len | ||
| for i, val in b.getElems: | ||
| fromJson(a[i], val) | ||
| elif T is object | tuple: | ||
| const isNamed = T is object or isNamedTuple(T) | ||
| when isNamed: | ||
| checkJson b.kind == JObject, $(b.kind) # we could customize whether to allow JNull | ||
| var num = 0 | ||
| for key, val in fieldPairs(a): | ||
| num.inc | ||
| if b.hasKey key: | ||
| fromJson(val, b[key]) | ||
| else: | ||
| # we could customize to allow this | ||
| checkJson false, $($T, key, b) | ||
| checkJson b.len == num, $(b.len, num, $T, b) # could customize | ||
| else: | ||
| checkJson b.kind == JArray, $(b.kind) # we could customize whether to allow JNull | ||
| var i = 0 | ||
| for val in fields(a): | ||
| fromJson(val, b[i]) | ||
| i.inc | ||
| else: | ||
| # checkJson not appropriate here | ||
| static: doAssert false, "not yet implemented: " & $T | ||
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| proc jsonTo*(b: JsonNode, T: typedesc): T = | ||
| ## reverse of `toJson` | ||
| fromJson(result, b) | ||
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| proc toJson*[T](a: T): JsonNode = | ||
| ## serializes `a` to json; uses `toJsonHook(a: T)` if it's in scope to | ||
| ## customize serialization, see strtabs.toJsonHook for an example. | ||
| when compiles(toJsonHook(a)): result = toJsonHook(a) | ||
| elif T is Table | OrderedTable: | ||
| result = newJObject() | ||
| for k, v in pairs(a): result[k] = toJson(v) | ||
| elif T is object | tuple: | ||
| const isNamed = T is object or isNamedTuple(T) | ||
| when isNamed: | ||
| result = newJObject() | ||
| for k, v in a.fieldPairs: result[k] = toJson(v) | ||
| else: | ||
| result = newJArray() | ||
| for v in a.fields: result.add toJson(v) | ||
| elif T is ref | ptr: | ||
| if a == nil: result = newJNull() | ||
| else: result = toJson(a[]) | ||
| elif T is array | seq: | ||
| result = newJArray() | ||
| for ai in a: result.add toJson(ai) | ||
| elif T is pointer: result = toJson(cast[int](a)) | ||
| elif T is distinct: result = toJson(a.distinctBase) | ||
| elif T is bool: result = %(a) | ||
| elif T is Ordinal: result = %(a.ord) | ||
| else: result = %a |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,44 @@ | ||
| discard """ | ||
| targets: "c cpp js" | ||
| """ | ||
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| import std/jsonutils | ||
| import std/json | ||
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| proc testRoundtrip[T](t: T, expected: string) = | ||
| let j = t.toJson | ||
| doAssert $j == expected, $j | ||
| doAssert j.jsonTo(T).toJson == j | ||
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| import tables | ||
| import strtabs | ||
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| template fn() = | ||
| block: # toJson, jsonTo | ||
| type Foo = distinct float | ||
| testRoundtrip('x', """120""") | ||
| when not defined(js): | ||
| testRoundtrip(cast[pointer](12345)): """12345""" | ||
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| # causes workaround in `fromJson` potentially related to | ||
| # https://github.com/nim-lang/Nim/issues/12282 | ||
| testRoundtrip(Foo(1.5)): """1.5""" | ||
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| block: | ||
| testRoundtrip({"z": "Z", "y": "Y"}.toOrderedTable): """{"z":"Z","y":"Y"}""" | ||
| when not defined(js): # pending https://github.com/nim-lang/Nim/issues/14574 | ||
| testRoundtrip({"z": (f1: 'f'), }.toTable): """{"z":{"f1":102}}""" | ||
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| block: | ||
| testRoundtrip({"name": "John", "city": "Monaco"}.newStringTable): """{"mode":"modeCaseSensitive","table":{"city":"Monaco","name":"John"}}""" | ||
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| block: # complex example | ||
| let t = {"z": "Z", "y": "Y"}.newStringTable | ||
| type A = ref object | ||
| a1: string | ||
| let a = (1.1, "fo", 'x', @[10,11], [true, false], [t,newStringTable()], [0'i8,3'i8], -4'i16, (foo: 0.5'f32, bar: A(a1: "abc"), bar2: A.default)) | ||
| testRoundtrip(a): | ||
| """[1.1,"fo",120,[10,11],[true,false],[{"mode":"modeCaseSensitive","table":{"y":"Y","z":"Z"}},{"mode":"modeCaseSensitive","table":{}}],[0,3],-4,{"foo":0.5,"bar":{"a1":"abc"},"bar2":null}]""" | ||
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| static: fn() | ||
| fn() |