Allow changing placeholder image host.

README.md

@@ -54,6 +54,23 @@ Rails.application.configure do
 end
 ```
 
+You can even change placeholder image host, if for example you prefer [fillmurray](https://fillmurray.com):
+
+```ruby
+Rails.application.configure do
+  config.middleware.use ImagePlaceholder::Middleware, size_pattern: { /.*/ => '320/320' }, host: 'fillmurray.com'
+end
+```
+
+Last but not least, this middleware can be used with any Rack application:
+
+```ruby
+# config.ru
+use ImagePlaceholder::Middleware, size_pattern: { /.*/ => '320/320' }, host: 'fillmurray.com'
+run YourRackApp
+```
+
+
 ## Development
 
 After checking out the repo, run `bin/setup` to install dependencies. Then, run `rake spec` to run the tests. You can also run `bin/console` for an interactive prompt that will allow you to experiment.

config.ru

@@ -1,4 +1,4 @@
 require 'image_placeholder'
 
-use ImagePlaceholder::Middleware, size_pattern: { /.*/ => 320 }
+use ImagePlaceholder::Middleware, size_pattern: { /.*/ => '320/320' }, host: 'fillmurray.com'
 run Rack::File.new(File.expand_path(File.join(__dir__, 'spec/support')))

lib/image_placeholder/middleware.rb

@@ -2,10 +2,11 @@
 
 module ImagePlaceholder
   class Middleware
-    def initialize(app, image_extensions: %w(jpg png), size_pattern: {/.*/ => 100})
+    def initialize(app, image_extensions: %w(jpg png), size_pattern: {/.*/ => 100}, host: 'via.placeholder.com')
       @app = app
       @image_extensions = image_extensions
       @size_pattern = size_pattern
+      @host = host
     end
 
     def call(env)
@@ -22,7 +23,7 @@ def call(env)
     private
 
     def serve_placeholder_image(size = 100)
-      net_response  = Net::HTTP.get_response(URI("https://via.placeholder.com/#{size}"))
+      net_response  = Net::HTTP.get_response(URI("https://#{@host}/#{size}"))
       rack_response = Rack::Response.new(net_response.body, net_response.code.to_i)
       safe_headers  = net_response.to_hash
                         .reject { |key, _| hop_by_hop_header_fields.include?(key.downcase) }

spec/middleware_spec.rb

@@ -78,6 +78,7 @@ def app
       Rack::Lint.new(
         Middleware.new(
           Rack::File.new(static_path),
+          host: 'via.placeholder.com',
           image_extensions: %w(jpg),
           size_pattern: {
             %r{/uploads/.*/s_[0-9]+\.[a-z]{3}$} => 200,