fix: #2482 Infinity and NaN serialise to null (#2487)

* fix: #2482 Infinity and NaN serialise to null

* feat: add safeNumbers option

* include test for default behavior

* change option name to specialNumbers

* refactor to be more dry

* pr feedback

* remove string option

docs/options.md

@@ -204,6 +204,19 @@ Defines how date-time strings are parsed and validated. By default Ajv only allo
 This option makes JTD validation and parsing more permissive and non-standard. The date strings without time part will be accepted by Ajv, but will be rejected by other JTD validators.
 :::
 
+### specialNumbers <Badge text="JTD only" />
+
+Defines how special case numbers `Infinity`, `-Infinity` and `NaN` are handled.
+
+Option values:
+
+- `"fast"` - (default): Do not treat special numbers differently to normal numbers. This is the fastest method but also can produce invalid JSON if the data contains special numbers.
+- `"null"` - Special numbers will be serialized to `null` which is the correct behavior according to the JSON spec and is also the same behavior as `JSON.stringify`.
+
+::: warning The default behavior can produce invalid JSON
+Using `specialNumbers: "fast" or undefined` can produce invalid JSON when there are any special case numbers in the data.
+:::
+
 ### int32range <Badge text="JTD only" />
 
 Can be used to disable range checking for `int32` and `uint32` types.

lib/compile/jtd/serialize.ts

@@ -228,8 +228,19 @@ function serializeString({gen, data}: SerializeCxt): void {
   gen.add(N.json, _`${useFunc(gen, quote)}(${data})`)
 }
 
-function serializeNumber({gen, data}: SerializeCxt): void {
-  gen.add(N.json, _`"" + ${data}`)
+function serializeNumber({gen, data, self}: SerializeCxt): void {
+  const condition = _`${data} === Infinity || ${data} === -Infinity || ${data} !== ${data}`
+
+  if (self.opts.specialNumbers === undefined || self.opts.specialNumbers === "fast") {
+    gen.add(N.json, _`"" + ${data}`)
+  } else {
+    // specialNumbers === "null"
+    gen.if(
+      condition,
+      () => gen.add(N.json, _`null`),
+      () => gen.add(N.json, _`"" + ${data}`)
+    )
+  }
 }
 
 function serializeRef(cxt: SerializeCxt): void {

lib/core.ts

@@ -107,6 +107,7 @@ export interface CurrentOptions {
   timestamp?: "string" | "date" // JTD only
   parseDate?: boolean // JTD only
   allowDate?: boolean // JTD only
+  specialNumbers?: "fast" | "null" // JTD only
   $comment?:
     | true
     | ((comment: string, schemaPath?: string, rootSchema?: AnySchemaObject) => unknown)

spec/jtd-schema.spec.ts

@@ -146,6 +146,53 @@ describe("JSON Type Definition", () => {
     }
   })
 
+  describe("serialize special numeric values", () => {
+    describe("fast", () => {
+      const ajv = new _AjvJTD({specialNumbers: "fast"})
+
+      it(`should serialize Infinity to literal`, () => {
+        const serialize = ajv.compileSerializer({type: "float64"})
+        const res = serialize(Infinity)
+        assert.equal(res, "Infinity")
+        assert.throws(() => JSON.parse(res))
+      })
+      it(`should serialize -Infinity to literal`, () => {
+        const serialize = ajv.compileSerializer({type: "float64"})
+        const res = serialize(-Infinity)
+        assert.equal(res, "-Infinity")
+        assert.throws(() => JSON.parse(res))
+      })
+      it(`should serialize NaN to literal`, () => {
+        const serialize = ajv.compileSerializer({type: "float64"})
+        const res = serialize(NaN)
+        assert.equal(res, "NaN")
+        assert.throws(() => JSON.parse(res))
+      })
+    })
+    describe("to null", () => {
+      const ajv = new _AjvJTD({specialNumbers: "null"})
+
+      it(`should serialize Infinity to null`, () => {
+        const serialize = ajv.compileSerializer({type: "float64"})
+        const res = serialize(Infinity)
+        assert.equal(res, "null")
+        assert.equal(JSON.parse(res), null)
+      })
+      it(`should serialize -Infinity to null`, () => {
+        const serialize = ajv.compileSerializer({type: "float64"})
+        const res = serialize(-Infinity)
+        assert.equal(res, "null")
+        assert.equal(JSON.parse(res), null)
+      })
+      it(`should serialize NaN to null`, () => {
+        const serialize = ajv.compileSerializer({type: "float64"})
+        const res = serialize(NaN)
+        assert.equal(res, "null")
+        assert.equal(JSON.parse(res), null)
+      })
+    })
+  })
+
   describe("parse", () => {
     let ajv: AjvJTD
     before(() => (ajv = new _AjvJTD()))