Add bigint_to_string option to encode big integer to string

README.md

@@ -152,6 +152,16 @@ iex> Poison.encode!(%{:foo => "foo1", "foo" => "foo2"}, strict_keys: true)
 ** (Poison.EncodeError) duplicate key found: :foo
 ```
 
+### 64bit Integers
+
+Some programming languages such as Javascript do not support 64bit integers.
+You can pass the `bigint_to_string: true` option to convert it to string type.
+
+```iex
+iex> Poison.encode!(4_294_967_296, %{bigint_to_string: true})
+"\"4294967296\""
+```
+
 ## Benchmarking
 
 ```sh-session

lib/poison/encoder.ex

@@ -86,13 +86,15 @@ defprotocol Poison.Encoder do
   @typep indent :: non_neg_integer
   @typep offset :: non_neg_integer
   @typep strict_keys :: boolean
+  @typep bigint_to_string :: boolean
 
   @type options :: %{
           optional(:escape) => escape,
           optional(:pretty) => pretty,
           optional(:indent) => indent,
           optional(:offset) => offset,
-          optional(:strict_keys) => strict_keys
+          optional(:strict_keys) => strict_keys,
+          optional(:bigint_to_string) => bigint_to_string
         }
 
   @spec encode(t, options) :: iodata
@@ -221,8 +223,13 @@ defimpl Poison.Encoder, for: BitString do
 end
 
 defimpl Poison.Encoder, for: Integer do
-  def encode(integer, _options) do
-    Integer.to_string(integer)
+  def encode(integer, options) do
+    if Map.get(options, :bigint_to_string, false) &&
+         (integer > 0xFFFFFFFF || integer < -0x80000000) do
+      integer |> Integer.to_string() |> Poison.Encoder.encode(options)
+    else
+      Integer.to_string(integer)
+    end
   end
 end
 

test/poison/encoder_test.exs

@@ -14,6 +14,17 @@ defmodule Poison.EncoderTest do
     assert to_json(42) == "42"
   end
 
+  test "BigInteger to string" do
+    assert to_json(0xFFFFFFFF + 1) == "#{0xFFFFFFFF + 1}"
+    assert to_json(-0x80000000 - 1) == "#{-0x80000000 - 1}"
+
+    assert to_json(0xFFFFFFFF + 1, bigint_to_string: true) ==
+             ~s("#{0xFFFFFFFF + 1}")
+
+    assert to_json(-0x80000000 - 1, bigint_to_string: true) ==
+             ~s("#{-0x80000000 - 1}")
+  end
+
   test "Float" do
     assert to_json(99.99) == "99.99"
     assert to_json(9.9e100) == "9.9e100"