fix: #2482 Infinity and NaN serialise to null

docs/options.md

@@ -204,6 +204,14 @@ 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. Use `specialNumbers: "null"` to serialize them to `null` which is correct behavior according to the JSON spec. If you wish to handle these values, however, and not lose the data you can use `specialNumbers: "string"` which will serialize them to strings. If this option is not set the values will be included as the original literal values.
+
+::: warning The default behavior can produce invalid JSON
+If `specialNumbers` is left undefined, the serializer will produce invalid JSON when there are any special case numbers in the data. This is, however, the fastest mode and so should be used unless you expect to encounter special case numbers.
+:::
+
 ### int32range <Badge text="JTD only" />
 
 Can be used to disable range checking for `int32` and `uint32` types.

lib/compile/jtd/serialize.ts

@@ -228,8 +228,17 @@ 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 || ${data} === -Infinity || Number.isNaN(${data})`
+  const addNumber = (): CodeGen => gen.add(N.json, _`"" + ${data}`)
+
+  if (self.opts.specialNumbers === "null") {
+    gen.if(condition, () => gen.add(N.json, _`null`), addNumber)
+  } else if (self.opts.specialNumbers === "string") {
+    gen.if(condition, () => gen.add(N.json, str`"${data}"`), addNumber)
+  } else {
+    addNumber()
+  }
 }
 
 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?: "string" | "null" // JTD only
   $comment?:
     | true
     | ((comment: string, schemaPath?: string, rootSchema?: AnySchemaObject) => unknown)

spec/jtd-schema.spec.ts

@@ -146,6 +146,76 @@ describe("JSON Type Definition", () => {
     }
   })
 
+  describe("serialize special numeric values", () => {
+    describe("default", () => {
+      const ajv = new _AjvJTD()
+
+      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("to string", () => {
+      const ajv = new _AjvJTD({specialNumbers: "string"})
+
+      it(`should serialize Infinity to string`, () => {
+        const serialize = ajv.compileSerializer({type: "float64"})
+        const res = serialize(Infinity)
+        assert.equal(res, '"Infinity"')
+        assert.equal(JSON.parse(res), "Infinity")
+      })
+      it(`should serialize -Infinity to string`, () => {
+        const serialize = ajv.compileSerializer({type: "float64"})
+        const res = serialize(-Infinity)
+        assert.equal(res, '"-Infinity"')
+        assert.equal(JSON.parse(res), "-Infinity")
+      })
+      it(`should serialize NaN to string`, () => {
+        const serialize = ajv.compileSerializer({type: "float64"})
+        const res = serialize(NaN)
+        assert.equal(res, '"NaN"')
+        assert.equal(JSON.parse(res), "NaN")
+      })
+    })
+  })
+
   describe("parse", () => {
     let ajv: AjvJTD
     before(() => (ajv = new _AjvJTD()))