added a global store for domains not supporting 100-continue

it's a pretty naive implementation, as it grows unbounded, and isn't
thread safe, mostly due to negligent cost of fake fetch.

lib/httpx/plugins/expect.rb

@@ -10,6 +10,10 @@ module HTTPX
     module Expect
       EXPECT_TIMEOUT = 2
 
+      def self.no_expect_store
+        @no_expect_store ||= []
+      end
+
       def self.extra_options(options)
         Class.new(options.class) do
           def_option(:expect_timeout) do |seconds|
@@ -29,6 +33,18 @@ module HTTPX
       end
 
       module RequestMethods
+        def initialize(*)
+          super
+          return if @body.empty?
+
+          threshold = @options.expect_threshold_size
+          return if threshold && !@body.unbounded_body? && @body.bytesize < threshold
+
+          return if Expect.no_expect_store.include?(origin)
+
+          @headers["expect"] = "100-continue"
+        end
+
         def response=(response)
           if response && response.status == 100 &&
              !@headers.key?("expect") &&
@@ -42,28 +58,18 @@ module HTTPX
             # so we have to reactivate it again.
             @headers["expect"] = "100-continue"
             @informational_status = 100
+            Expect.no_expect_store.delete(origin)
           end
           super
         end
       end
 
-      module RequestBodyMethods
-        def initialize(*, options)
-          super
-          return if @body.nil?
-
-          threshold = options.expect_threshold_size
-          return if threshold && !unbounded_body? && @body.bytesize < threshold
-
-          @headers["expect"] = "100-continue"
-        end
-      end
-
       module ConnectionMethods
         def send(request)
           request.once(:expect) do
             @timers.after(@options.expect_timeout) do
               if request.state == :expect && !request.expects?
+                Expect.no_expect_store << request.origin
                 request.headers.delete("expect")
                 consume
               end

test/support/requests/plugins/expect.rb

@@ -20,12 +20,16 @@ module Requests
         server = Expect100Server.new
         th = Thread.new { server.start }
         begin
+          http = HTTPX.plugin(:expect)
           uri = build_uri("/delay?delay=4", server.origin)
-          response = HTTPX.plugin(:expect).post(uri, body: "helloworld")
+          response = http.post(uri, body: "helloworld")
           verify_status(response, 200)
           body = response.body.to_s
           assert body == "echo: helloworld"
           verify_header(response.instance_variable_get(:@request).headers, "expect", "100-continue")
+
+          next_request = http.build_request(:post, build_uri("/", server.origin), body: "helloworld")
+          verify_header(next_request.headers, "expect", "100-continue")
         ensure
           server.shutdown
           th.join
@@ -53,12 +57,16 @@ module Requests
         server = Expect100Server.new
         th = Thread.new { server.start }
         begin
+          http = HTTPX.plugin(:expect)
           uri = build_uri("/no-expect", server.origin)
-          response = HTTPX.plugin(:expect).post(uri, body: "helloworld")
+          response = http.post(uri, body: "helloworld")
           verify_status(response, 200)
           body = response.body.to_s
           assert body == "echo: helloworld"
           verify_no_header(response.instance_variable_get(:@request).headers, "expect")
+
+          next_request = http.build_request(:post, build_uri("/", server.origin), body: "helloworld")
+          verify_no_header(next_request.headers, "expect")
         ensure
           server.shutdown
           th.join