Adapt the Livebook XML parsing to add a mini-parser to allow us to in…

…terface with the AWS API

lib/flame_ec2/ec2_api.ex

@@ -5,6 +5,7 @@ defmodule FlameEC2.EC2Api do
 
   alias FlameEC2.BackendState
   alias FlameEC2.Config
+  alias FlameEC2.EC2Api.XML
   alias FlameEC2.Templates
 
   require Logger
@@ -28,12 +29,12 @@ defmodule FlameEC2.EC2Api do
           url: uri,
           method: :post,
           form: params,
-          headers: [{:accept, "application/json"}],
           aws_sigv4: Map.put_new(credentials, :service, "ec2")
         ]
         |> Req.new()
         |> Req.request()
         |> raise_or_response!()
+        |> Map.fetch!(:body)
         |> Map.fetch!("RunInstancesResponse")
         |> Map.fetch!("instancesSet")
         |> Map.fetch!("item")
@@ -132,11 +133,27 @@ defmodule FlameEC2.EC2Api do
   end
 
   defp raise_or_response!({:ok, %Req.Response{} = resp}) do
-    resp.body
+    if xml?(resp) do
+      update_in(resp.body, &XML.decode!/1)
+    else
+      resp
+    end
   end
 
   defp raise_or_response!({:error, exception}) do
     Logger.error("Failed to create instance with exception: #{inspect(exception)}")
     raise exception
   end
+
+  # Adapted from https://github.com/livebook-dev/livebook/blob/v0.14.5/lib/livebook/file_system/s3/client.ex
+  defp xml?(response) do
+    guess_xml? = String.starts_with?(response.body, "<?xml")
+
+    case FlameEC2.EC2Api.Utils.fetch_content_type(response) do
+      {:ok, content_type} when content_type in ["text/xml", "application/xml"] -> true
+      # Apparently some requests return XML without content-type
+      :error when guess_xml? -> true
+      _otherwise -> false
+    end
+  end
 end

lib/flame_ec2/ec2_api/utils.ex

@@ -0,0 +1,18 @@
+defmodule FlameEC2.EC2Api.Utils do
+  @moduledoc false
+  # Adapted from https://github.com/livebook-dev/livebook/blob/v0.14.5/lib/livebook/utils.ex
+
+  @doc """
+  Retrieves content type from response headers.
+  """
+  @spec fetch_content_type(Req.Response.t()) :: {:ok, String.t()} | :error
+  def fetch_content_type(%Req.Response{} = res) do
+    case res.headers["content-type"] do
+      [value] ->
+        {:ok, value |> String.split(";") |> hd()}
+
+      _other ->
+        :error
+    end
+  end
+end

lib/flame_ec2/ec2_api/xml.ex

@@ -0,0 +1,90 @@
+defmodule FlameEC2.EC2Api.XML do
+  # Adapted from https://github.com/livebook-dev/livebook/blob/v0.14.5/lib/livebook/file_system/s3/xml.ex
+  @moduledoc false
+  import Record
+
+  @text "__text"
+
+  defrecord(:xmlElement, extract(:xmlElement, from_lib: "xmerl/include/xmerl.hrl"))
+  defrecord(:xmlText, extract(:xmlText, from_lib: "xmerl/include/xmerl.hrl"))
+
+  @doc """
+  Decodes a XML into a map.
+
+  Raises in case of errors.
+  """
+  def decode!(xml) do
+    xml_str = :unicode.characters_to_list(xml)
+    opts = [{:hook_fun, &hook_fun/2}]
+    {element, []} = :xmerl_scan.string(xml_str, opts)
+    element
+  end
+
+  # Callback hook_fun for xmerl parser
+  defp hook_fun(element, global_state) when Record.is_record(element, :xmlElement) do
+    tag = xmlElement(element, :name)
+    content = xmlElement(element, :content)
+
+    value =
+      case List.foldr(content, :none, &content_to_map/2) do
+        %{@text => text} = v ->
+          case String.trim(text) do
+            "" -> Map.delete(v, @text)
+            trimmed -> Map.put(v, @text, trimmed)
+          end
+
+        v ->
+          v
+      end
+
+    {%{Atom.to_string(tag) => value}, global_state}
+  end
+
+  defp hook_fun(text, global_state) when Record.is_record(text, :xmlText) do
+    text = xmlText(text, :value)
+    {:unicode.characters_to_binary(text), global_state}
+  end
+
+  # Convert the content of an Xml node into a map.
+  # When there is more than one element with the same tag name, their
+  # values get merged into a list.
+  # If the content is only text then that is what gets returned.
+  # If the content is a mix between text and child elements, then the
+  # elements are processed as described above and all the text parts
+  # are merged under the `__text' key.
+
+  defp content_to_map(x, :none) do
+    x
+  end
+
+  defp content_to_map(x, acc) when is_map(x) and is_map(acc) do
+    [{tag, value}] = Map.to_list(x)
+
+    if Map.has_key?(acc, tag) do
+      update_fun = fn
+        l when is_list(l) -> [value | l]
+        v -> [value, v]
+      end
+
+      Map.update!(acc, tag, update_fun)
+    else
+      Map.put(acc, tag, value)
+    end
+  end
+
+  defp content_to_map(x, %{@text => text} = acc) when is_binary(x) and is_map(acc) do
+    %{acc | @text => <<x::binary, text::binary>>}
+  end
+
+  defp content_to_map(x, acc) when is_binary(x) and is_map(acc) do
+    Map.put(acc, @text, x)
+  end
+
+  defp content_to_map(x, acc) when is_binary(x) and is_binary(acc) do
+    <<x::binary, acc::binary>>
+  end
+
+  defp content_to_map(x, acc) when is_map(x) and is_binary(acc) do
+    Map.put(x, @text, acc)
+  end
+end