added support for :expect_threshold_size, to disable expect: 100-continue based on body bytesize sent

lib/httpx/plugins/expect.rb

@@ -18,14 +18,27 @@ module HTTPX
 
             seconds
           end
+
+          def_option(:expect_threshold_size) do |bytes|
+            bytes = Integer(bytes)
+            raise Error, ":expect_threshold_size must be positive" unless bytes.positive?
+
+            bytes
+          end
         end.new(options).merge(expect_timeout: EXPECT_TIMEOUT)
       end
 
       module RequestBodyMethods
-        def initialize(*)
+        def initialize(*, options)
           super
           return if @body.nil?
 
+          if (threshold = options.expect_threshold_size)
+            unless unbounded_body?
+              return if @body.bytesize < threshold
+            end
+          end
+
           @headers["expect"] = "100-continue"
         end
       end

test/support/requests/plugins/expect.rb

@@ -13,6 +13,20 @@ module Requests
         verify_uploaded(body, "form", "foo" => "bar")
       end
 
+      def test_plugin_expect_100_form_params_under_threshold
+        uri = build_uri("/post")
+        session = HTTPX.plugin(:expect, expect_threshold_size: 4)
+        response = session.post(uri, body: "a" * 3)
+        verify_status(response, 200)
+        body = json_body(response)
+        verify_no_header(body["headers"], "Expect")
+
+        response = session.post(uri, body: "a" * 5)
+        verify_status(response, 200)
+        body = json_body(response)
+        verify_header(body["headers"], "Expect", "100-continue")
+      end
+
       # def test_plugin_expect_100_send_body_after_delay
       #   uri = build_uri("/delay/3")
       #   response = HTTPX.plugin(:expect).post(uri, form: { "foo" => "bar" })