Fix ICECandidate types (#174)

Author: roznawsk

lib/ex_webrtc/ice_candidate.ex

@@ -5,14 +5,14 @@ defmodule ExWebRTC.ICECandidate do
 
   @type t() :: %__MODULE__{
           candidate: binary(),
-          sdp_mid: non_neg_integer() | nil,
+          sdp_mid: binary() | nil,
           sdp_m_line_index: non_neg_integer() | nil,
           username_fragment: binary() | nil
         }
 
   defstruct [:candidate, :username_fragment, :sdp_mid, :sdp_m_line_index]
 
-  @spec to_json(t()) :: %{String.t() => String.t()}
+  @spec to_json(t()) :: %{String.t() => String.t() | non_neg_integer() | nil}
   def to_json(%__MODULE__{} = c) do
     %{
       "candidate" => c.candidate,
@@ -22,7 +22,7 @@ defmodule ExWebRTC.ICECandidate do
     }
   end
 
-  @spec from_json(%{String.t() => String.t()}) :: t()
+  @spec from_json(%{String.t() => String.t() | non_neg_integer() | nil}) :: t()
   def from_json(%{
         "candidate" => c,
         "sdpMid" => mid,

lib/ex_webrtc/peer_connection.ex

@@ -1193,7 +1193,7 @@ defmodule ExWebRTC.PeerConnection do
   def handle_info({:ex_ice, _from, {:new_candidate, candidate}}, state) do
     candidate = %ICECandidate{
       candidate: "candidate:" <> candidate,
-      sdp_mid: 0,
+      sdp_mid: "0",
       sdp_m_line_index: 0
       # username_fragment: "vx/1"
     }