reset connection builder by default when Faraday::Connection#build is called

lib/faraday/builder.rb

@@ -25,11 +25,12 @@ module Faraday
     end
 
     def build(options = {}, &block)
-      if options[:reset]
+      inner = @handlers.shift
+      if !options[:keep]
         @handlers.clear
       end
       block.call(self)
-      run(self.class.inner_app)
+      run(inner || self.class.inner_app)
     end
 
     def [](index)

test/connection_test.rb

@@ -219,6 +219,36 @@ class TestConnection < Faraday::TestCase
     end
   end
 
+  def test_allows_rebuilding_of_connection_handlers
+    conn  = Faraday::Connection.new
+    conn.to_app
+    inner = conn.builder.handlers[0]
+    mware = conn.builder.handlers[1].call({})
+    assert_kind_of Faraday::Adapter::NetHttp, mware
+
+    conn.build do |b|
+      b.adapter :test
+    end
+    mware = conn.builder.handlers[1].call({})
+    assert_kind_of Faraday::Adapter::Test, mware
+    assert_equal   inner,                  conn.builder.handlers[0]
+  end
+
+  def test_allows_extending_of_existing_connection_handlers
+    conn  = Faraday::Connection.new
+    conn.to_app
+    mware = conn.builder.handlers[1].call({})
+    assert_kind_of Faraday::Adapter::NetHttp, mware
+    assert_equal   2,                         conn.builder.handlers.size
+
+    conn.build :keep => true do |b|
+      b.adapter :test
+    end
+    mware = conn.builder.handlers[1].call({})
+    assert_kind_of Faraday::Adapter::Test, mware
+    assert_equal   3,                      conn.builder.handlers.size
+  end
+
   def test_sets_default_adapter_if_none_set
     conn  = Faraday::Connection.new
     assert_equal 0, conn.builder.handlers.size