Use Decimal to improve precision of multipleOf validation

README.md

@@ -8,7 +8,7 @@
 [![License](https://img.shields.io/hexpm/l/ex_json_schema.svg)](https://github.com/jonasschmidt/ex_json_schema/blob/master/LICENSE)
 [![Last Updated](https://img.shields.io/github/last-commit/jonasschmidt/ex_json_schema.svg)](https://github.com/jonasschmidt/ex_json_schema/commits/master)
 
-A JSON Schema validator with support for the draft 4, draft 6 and draft 7 specifications and zero dependencies. Passes the official [JSON Schema Test Suite](https://github.com/json-schema/JSON-Schema-Test-Suite).
+A JSON Schema validator with support for the draft 4, draft 6 and draft 7 specifications. Passes the official [JSON Schema Test Suite](https://github.com/json-schema/JSON-Schema-Test-Suite).
 
 ## Installation
 

lib/ex_json_schema/validator/multiple_of.ex

@@ -9,6 +9,7 @@ defmodule ExJsonSchema.Validator.MultipleOf do
   alias ExJsonSchema.Validator.Error
 
   @behaviour ExJsonSchema.Validator
+  @zero Decimal.new(0)
 
   @impl ExJsonSchema.Validator
   def validate(_, _, {"multipleOf", multiple_of}, data, _) do
@@ -19,28 +20,27 @@ defmodule ExJsonSchema.Validator.MultipleOf do
     []
   end
 
-  defp do_validate(_, 0) do
-    []
-  end
-
-  defp do_validate(0, _) do
-    # "Expected multipleOf to be > 1."
-    [%Error{error: %Error.MultipleOf{expected: 0}}]
+  defp do_validate(multiple_of, data) when is_number(multiple_of) and is_number(data) do
+    dec_multiple_of = dec(multiple_of)
+    dec_data = dec(data)
+
+    cond do
+      dec_multiple_of == @zero -> [%Error{error: %Error.MultipleOf{expected: 0}}]
+      dec_data == @zero -> []
+      Decimal.integer?(Decimal.div(dec_data, dec_multiple_of)) -> []
+      true -> [%Error{error: %Error.MultipleOf{expected: multiple_of}}]
+    end
   end
 
-  defp do_validate(_, data) when not is_number(data) do
+  defp do_validate(_, _) do
     []
   end
 
-  defp do_validate(multiple_of, data) when is_number(multiple_of) and is_number(data) do
-    if Float.ceil(data / multiple_of) == Float.floor(data / multiple_of) do
-      []
+  defp dec(number) do
+    if is_float(number) do
+      Decimal.from_float(number)
     else
-      [%Error{error: %Error.MultipleOf{expected: multiple_of}}]
+      Decimal.new(number)
     end
   end
-
-  defp do_validate(_, _) do
-    []
-  end
 end

mix.exs

@@ -33,6 +33,7 @@ defmodule ExJsonSchema.Mixfile do
 
   defp deps do
     [
+      {:decimal, "~> 2.0"},
       {:dialyxir, "~> 0.5", only: [:test], runtime: false},
       {:ex_doc, ">= 0.0.0", only: :dev, runtime: false},
       {:excoveralls, "~> 0.10", only: :test},

test/ex_json_schema/validator_test.exs

@@ -473,6 +473,25 @@ defmodule ExJsonSchema.ValidatorTest do
       [{"Expected value to be a multiple of 2.", "#"}],
       [%Error{error: %Error.MultipleOf{expected: 2}, path: "#"}]
     )
+
+    assert_validation_errors(
+      %{"multipleOf" => 0.1},
+      123.45,
+      [{"Expected value to be a multiple of 0.1.", "#"}],
+      [%Error{error: %Error.MultipleOf{expected: 0.1}, path: "#"}]
+    )
+
+    assert valid?(%{"multipleOf" => 5}, 0)
+  end
+
+  test "multiple of validator division by 0" do
+    assert ExJsonSchema.Validator.MultipleOf.validate(nil, nil, {"multipleOf", 0}, 5, nil) ==
+             [%Error{error: %Error.MultipleOf{expected: 0}}]
+  end
+
+  test "multiple of precision" do
+    assert valid?(%{"multipleOf" => 0.01}, 147.41)
+    assert valid?(%{"multipleOf" => 0.01}, 147.42)
   end
 
   test "validation errors for minimum length" do