Add support for IEEE 754 NaN and ±infinity unpacking (#53)

lexmag · Dec 28, 2020 · 3b93d43 · 3b93d43
1 parent 7728859
commit 3b93d43
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Showing 3 changed files with 58 additions and 3 deletions.
diff --git a/lib/msgpax.ex b/lib/msgpax.ex
@@ -15,18 +15,23 @@ defmodule Msgpax do
   `false`                           | boolean       | `false`
   `-1`                              | integer       | `-1`
   `1.25`                            | float         | `1.25`
+  *N/A*                             | NaN           | `Msgpax.NaN`<sup>1</sup>
+  *N/A*                             | +infinity     | `Msgpax.Infinity`<sup>1</sup>
+  *N/A*                             | -infinity     | `Msgpax.NegInfinity`<sup>1</sup>
   `:ok`                             | string        | `"ok"`
   `Atom`                            | string        | `"Elixir.Atom"`
   `"str"`                           | string        | `"str"`
   `"\xFF\xFF"`                      | string        | `"\xFF\xFF"`
-  `#Msgpax.Bin<"\xFF">`             | binary        | `"\xFF"`<sup>1</sup>
+  `#Msgpax.Bin<"\xFF">`             | binary        | `"\xFF"`<sup>2</sup>
   `%{foo: "bar"}`                   | map           | `%{"foo" => "bar"}`
   `[foo: "bar"]`                    | map           | `%{"foo" => "bar"}`
   `[1, true]`                       | array         | `[1, true]`
   `#Msgpax.Ext<4, "02:12">`         | extension     | `#Msgpax.Ext<4, "02:12">`
   `#DateTime<2017-12-06 00:00:00Z>` | extension     | `#DateTime<2017-12-06 00:00:00Z>`
 
-  <sup>1</sup>To deserialize back to `Msgpax.Bin` structs see the `unpack/2` options.
+  <sup>1</sup>NaN and ±infinity are not enabled by default. See `unpack/2` for for more information.
+
+  <sup>2</sup>To deserialize back to `Msgpax.Bin` structs see the `unpack/2` options.
   """
 
   alias __MODULE__.Packer
@@ -199,6 +204,10 @@ defmodule Msgpax do
     * `:ext` - (module) a module that implements the `Msgpax.Ext.Unpacker`
       behaviour. For more information, see the docs for `Msgpax.Ext.Unpacker`.
 
+    * `:nonfinite_floats` - (boolean) if `true`, deserializes NaN and ±infinity to
+      "signalling" atoms (see the "Data conversion" section), otherwise errors.
+      Defaults to `false`.
+
   ## Examples
 
       iex> Msgpax.unpack(<<163, "foo">>)

diff --git a/lib/msgpax/unpacker.ex b/lib/msgpax/unpacker.ex
@@ -9,6 +9,7 @@ defmodule Msgpax.UnpackError do
             | {:invalid_format, integer}
             | :incomplete
             | {:ext_unpack_failure, module, Msgpax.Ext.t()}
+            | {:nonfinite_float, atom}
         }
 
   defexception [:reason]
@@ -26,13 +27,22 @@ defmodule Msgpax.UnpackError do
 
       {:ext_unpack_failure, module, struct} ->
         "module #{inspect(module)} could not unpack extension: #{inspect(struct)}"
+
+      {:nonfinite_float, value} ->
+        "encountered non-finite float value: #{inspect(value)}"
     end
   end
 end
 
 defmodule Msgpax.Unpacker do
   @moduledoc false
 
+  alias Msgpax.{
+    NaN,
+    Infinity,
+    NegInfinity
+  }
+
   def unpack(<<buffer::bits>>, options) do
     unpack(buffer, [], Map.new(options), [], 0, 1)
   end
@@ -63,6 +73,18 @@ defmodule Msgpax.Unpacker do
       quote(do: <<0xD2, value::32-signed>>),
       quote(do: <<0xD3, value::64-signed>>)
     ] => quote(do: value),
+    [
+      quote(do: <<0xCA, 0::1, 0xFF, 0::23>>),
+      quote(do: <<0xCB, 0::1, 0xFF, 0b111::3, 0::52>>)
+    ] => quote(do: unpack_float(Infinity, var!(options))),
+    [
+      quote(do: <<0xCA, 1::1, 0xFF, 0::23>>),
+      quote(do: <<0xCB, 1::1, 0xFF, 0b111::3, 0::52>>)
+    ] => quote(do: unpack_float(NegInfinity, var!(options))),
+    [
+      quote(do: <<0xCA, _sign::1, 0xFF, _fraction::23>>),
+      quote(do: <<0xCB, _sign::1, 0xFF, 0b111::3, _fraction::52>>)
+    ] => quote(do: unpack_float(NaN, var!(options))),
     # Negative fixint
     [quote(do: <<0b111::3, value::5>>)] => quote(do: value - 0b100000)
   }
@@ -186,6 +208,14 @@ defmodule Msgpax.Unpacker do
     content
   end
 
+  defp unpack_float(value, %{nonfinite_floats: true}) do
+    value
+  end
+
+  defp unpack_float(value, _options) do
+    throw({:nonfinite_float, value})
+  end
+
   defp unpack_ext(type, content, options) do
     if type < 128 do
       type

diff --git a/test/msgpax_test.exs b/test/msgpax_test.exs
@@ -104,8 +104,24 @@ defmodule MsgpaxTest do
     assert_format Atom, <<171>>, "Elixir.Atom"
   end
 
-  test "float" do
+  test "floats" do
     assert_format 42.1, <<203>>
+
+    for {packed, value} <- %{
+          # 32-bit.
+          <<202, 0x7FC00000::32>> => Msgpax.NaN,
+          <<202, 0x7F800000::32>> => Msgpax.Infinity,
+          <<202, 0xFF800000::32>> => Msgpax.NegInfinity,
+          # 64-bit.
+          <<203, 0x7FF8::16, 0::48>> => Msgpax.NaN,
+          <<203, 0x7FF0::16, 0::48>> => Msgpax.Infinity,
+          <<203, 0xFFF0::16, 0::48>> => Msgpax.NegInfinity
+        } do
+      assert Msgpax.unpack(packed) ==
+               {:error, %Msgpax.UnpackError{reason: {:nonfinite_float, value}}}
+
+      assert Msgpax.unpack(packed, nonfinite_floats: true) == {:ok, value}
+    end
   end
 
   test "positive fixint" do