FIX: Hide excerpt of binary files in GitHub onebox (#15639)

Oneboxer did not know if a file is binary or not and always tried to
show an excerpt of the file.

lib/onebox/mixins/git_blob_onebox.rb

@@ -169,6 +169,12 @@ module Onebox
             else
               contents = URI.parse(self.raw_template(m)).open(read_timeout: timeout).read
 
+              if contents.encoding == Encoding::BINARY
+                @raw = nil
+                @binary = true
+                return
+              end
+
               contents_lines = contents.lines           #get contents lines
               contents_lines_size = contents_lines.size #get number of lines
 
@@ -211,6 +217,7 @@ module Onebox
             #     as *side effects* of the `raw` method! They must all appear
             #     AFTER the call to `raw`! Don't get bitten by this like I did!
             content: raw,
+            binary: @binary,
             lang: "lang-#{@lang}",
             lines: @selected_lines_array ,
             has_lines: !@selected_lines_array.nil?,

lib/onebox/templates/githubblob.mustache

@@ -1,5 +1,6 @@
 <h4><a href="{{link}}" target="_blank" rel="noopener">{{title}}</a></h4>
 
+{{^binary}}
   {{^has_lines}}
     {{#model_file}}
       <iframe class="render-viewer" width="{{width}}" height="{{height}}" src="{{content}}" sandbox="allow-scripts allow-same-origin allow-top-navigation ">
@@ -48,6 +49,11 @@
       </code>
     </pre>
   {{/has_lines}}
+{{/binary}}
+
+{{#binary}}
+  This file is binary. <a href="{{link}}" target="_blank" rel="noopener">show original</a>
+{{/binary}}
 
 {{#truncated}}
   This file has been truncated. <a href="{{link}}" target="_blank" rel="noopener">show original</a>

spec/lib/onebox/engine/github_blob_onebox_spec.rb

@@ -5,6 +5,7 @@ require "rails_helper"
 describe Onebox::Engine::GithubBlobOnebox do
   before do
     @link = "https://github.com/discourse/onebox/blob/master/lib/onebox/engine/github_blob_onebox.rb"
+    @uri = URI.parse(@link)
     stub_request(:get, "https://raw.githubusercontent.com/discourse/onebox/master/lib/onebox/engine/github_blob_onebox.rb")
       .to_return(status: 200, body: onebox_response(described_class.onebox_name))
   end
@@ -20,5 +21,16 @@ describe Onebox::Engine::GithubBlobOnebox do
     it "includes blob contents" do
       expect(html).to include("module Oneboxer")
     end
+
+    it "does not include blob contents if it is binary" do
+      # stub_request if the response must be binary (ASCII-8BIT)
+      uri = mock('object')
+      uri.stubs(:open).returns(File.open("#{Rails.root}/spec/fixtures/pdf/small.pdf", "rb"))
+      URI.stubs(:parse).with(@link).returns(@uri)
+      URI.stubs(:parse).with('https://raw.githubusercontent.com/discourse/onebox/master/lib/onebox/engine/github_blob_onebox.rb').returns(uri)
+
+      expect(html).not_to include('/Pages')
+      expect(html).to include('This file is binary.')
+    end
   end
 end