From 3bc37952d12be5f61f012f968245322588a1786d Mon Sep 17 00:00:00 2001
From: Shadowfacts <me@shadowfacts.net>
Date: Thu, 31 Oct 2019 21:59:55 -0400
Subject: [PATCH] Add option to convert images in article content to data URIs

---
 lib/frenzy/pipeline/scrape_stage.ex | 111 ++++++++++++++++++++--------
 1 file changed, 81 insertions(+), 30 deletions(-)

diff --git a/lib/frenzy/pipeline/scrape_stage.ex b/lib/frenzy/pipeline/scrape_stage.ex
index c6d2363..8593738 100644
--- a/lib/frenzy/pipeline/scrape_stage.ex
+++ b/lib/frenzy/pipeline/scrape_stage.ex
@@ -5,7 +5,7 @@ defmodule Frenzy.Pipeline.ScrapeStage do
 
   @impl Stage
   def apply(opts, %{url: url} = item_params) do
-    case get_article_content(url, opts["extractor"]) do
+    case get_article_content(url, opts) do
       {:ok, content} ->
         {:ok, %{item_params | content: content}}
 
@@ -18,24 +18,36 @@ defmodule Frenzy.Pipeline.ScrapeStage do
   @impl Stage
   def validate_opts(opts) when is_map(opts) do
     # todo: figure out why this errors when an empty map is provided
-    case opts["extractor"] do
+    opts =
+      case opts["extractor"] do
+        nil ->
+          {:ok, %{opts | extractor: "builtin"}}
+
+        extractor when not is_binary(extractor) ->
+          {:error, "extractor must be a string"}
+
+        "builtin" ->
+          {:ok, opts}
+
+        extractor ->
+          try do
+            String.to_existing_atom("Elixir." <> extractor)
+            {:ok, opts}
+          rescue
+            ArgumentError ->
+              {:error, "extractor must be \"builtin\" or a module that exists"}
+          end
+      end
+
+    case opts["convert_to_data_uris"] do
       nil ->
-        {:ok, %{opts | extractor: "builtin"}}
+        {:ok, %{opts | convert_to_data_uris: true}}
 
-      extractor when not is_binary(extractor) ->
-        {:error, "extractor must be a string"}
-
-      "builtin" ->
+      value when is_boolean(value) ->
         {:ok, opts}
 
-      extractor ->
-        try do
-          String.to_existing_atom("Elixir." <> extractor)
-          {:ok, opts}
-        rescue
-          ArgumentError ->
-            {:error, "extractor must be \"builtin\" or a module that exists"}
-        end
+      _ ->
+        {:error, "convert_to_data_uris must be a boolean"}
     end
   end
 
@@ -43,14 +55,14 @@ defmodule Frenzy.Pipeline.ScrapeStage do
   def validate_opts(_), do: {:error, "options must be a map"}
 
   @spec get_article_content(String.t(), String.t()) :: {:ok, String.t()} | {:error, String.t()}
-  defp get_article_content(url, extractor) when is_binary(url) and url != "" do
+  defp get_article_content(url, opts) when is_binary(url) and url != "" do
     Logger.debug("Getting article from #{url}")
 
     url
     |> HTTPoison.get()
     |> case do
       {:ok, response} ->
-        handle_response(url, response, extractor)
+        handle_response(url, response, opts)
 
       {:error, %HTTPoison.Error{reason: reason}} ->
         {:error, "HTTPoison error: #{reason}"}
@@ -61,8 +73,8 @@ defmodule Frenzy.Pipeline.ScrapeStage do
 
   @spec handle_response(String.t(), HTTPoison.Response.t(), String.t()) ::
           {:ok, String.t()} | {:error, String.t()}
-  defp handle_response(url, %HTTPoison.Response{status_code: 200, body: body}, extractor) do
-    case extractor do
+  defp handle_response(url, %HTTPoison.Response{status_code: 200, body: body}, opts) do
+    case opts["extractor"] do
       "builtin" ->
         {:ok, Readability.article(body)}
 
@@ -72,9 +84,15 @@ defmodule Frenzy.Pipeline.ScrapeStage do
     end
     |> case do
       {:ok, html} ->
-        html = Floki.map(html, rewrite_image_urls(URI.parse(url)))
+        convert_to_data_uris =
+          case opts["convert_to_data_uris"] do
+            nil -> true
+            value -> value
+          end
 
-        case extractor do
+        html = Floki.map(html, rewrite_image_urls(convert_to_data_uris, URI.parse(url)))
+
+        case opts["extractor"] do
           "builtin" ->
             {:ok, Readability.readable_html(html)}
 
@@ -120,21 +138,54 @@ defmodule Frenzy.Pipeline.ScrapeStage do
   # Generates a helper function for the article with the given URI that takes an HTML element and,
   # if it's an <img> element whose src attribute does not have a hostname, adds the hostname and
   # scheme to the element.
-  defp rewrite_image_urls(%URI{host: host, scheme: scheme}) do
+  defp rewrite_image_urls(convert_to_data_uris, %URI{host: host, scheme: scheme}) do
     fn
-      {"img", [{"src", src} | attrs]} = elem ->
-        case URI.parse(src) do
-          %URI{host: nil, path: path} ->
-            new_src = URI.to_string(%URI{path: path, host: host, scheme: scheme})
+      {"img", attrs} ->
+        new_attrs =
+          Enum.map(attrs, fn
+            {"src", src} ->
+              case URI.parse(src) do
+                %URI{host: nil, path: path} ->
+                  new_src =
+                    URI.to_string(%URI{path: path, host: host, scheme: scheme})
+                    |> image_to_data_uri(convert_to_data_uris)
 
-            {"img", [{"src", new_src} | attrs]}
+                  {"src", new_src}
 
-          _ ->
-            elem
-        end
+                _ ->
+                  {"src", image_to_data_uri(convert_to_data_uris, src)}
+              end
+
+            attr ->
+              attr
+          end)
+
+        {"img", new_attrs}
 
       elem ->
         elem
     end
   end
+
+  @content_type_allowlist ["image/jpeg", "image/png", "image/heic", "image/heif", "image/tiff"]
+
+  # convert images to data URIs so that they're stored by clients as part of the body
+  defp image_to_data_uri(true, src) do
+    case HTTPoison.get(src) do
+      {:ok, %HTTPoison.Response{status_code: 200, body: body, headers: headers}} ->
+        {"Content-Type", content_type} =
+          Enum.find(headers, fn {header, _value} -> header == "Content-Type" end)
+
+        if content_type in @content_type_allowlist do
+          "data:#{content_type};base64,#{Base.encode64(body)}"
+        else
+          src
+        end
+
+      _ ->
+        src
+    end
+  end
+
+  defp image_to_data_uri(false, src), do: src
 end