added support for connection: close, by:

* sending info on whether the session is in persistent mode to the
request;
* on parser, set keep-alive when persistent, at all times;
* when not persistent, set keep-alive on all requests til the last;
* on error recovery, when resetting to 1 request at a time, still keep
alive to all requests til the last;
* on next error recovery, set connection: close

lib/httpx/connection/http1.rb

@@ -78,6 +78,7 @@ module HTTPX
         break if idx >= requests_limit
         next if request.state == :done
 
+        request.headers["connection"] ||= request.options.persistent || idx < requests_limit - 1 ? "keep-alive" : "close"
         handle(request)
       end
     end
@@ -206,7 +207,14 @@ module HTTPX
     def disable_pipelining
       return if @requests.empty?
 
-      @requests.each { |r| r.transition(:idle) }
+      @requests.each do |r|
+        r.transition(:idle)
+
+        # when we disable pipelining, we still want to try keep-alive.
+        # only when keep-alive with one request fails, do we fallback to
+        # connection: close.
+        r.headers["connection"] = "close" if @max_concurrent_requests == 1
+      end
       # server doesn't handle pipelining, and probably
       # doesn't support keep-alive. Fallback to send only
       # 1 keep alive request.
@@ -216,7 +224,7 @@ module HTTPX
 
     def set_request_headers(request)
       request.headers["host"] ||= request.authority
-      request.headers["connection"] ||= "keep-alive"
+      request.headers["connection"] ||= request.options.persistent ? "keep-alive" : "close"
       if !request.headers.key?("content-length") &&
          request.body.bytesize == Float::INFINITY
         request.chunk!

lib/httpx/session.rb

@@ -197,7 +197,7 @@ module HTTPX
 
     def build_request(verb, uri, options)
       rklass = @options.request_class
-      request = rklass.new(verb, uri, @options.merge(options))
+      request = rklass.new(verb, uri, @options.merge(options).merge(persistent: @persistent))
       request.on(:response, &method(:on_response).curry[request])
       request.on(:promise, &method(:on_promise))
       request

test/http_test.rb

@@ -36,7 +36,7 @@ class HTTPTest < Minitest::Test
     assert log_output.match(%r{HEADLINE: "GET .+ HTTP/1\.1"})
     assert log_output.match(%r{HEADER: Accept: */*})
     assert log_output.match(/HEADER: Host: \w+/)
-    assert log_output.match(/HEADER: Connection: keep\-alive/)
+    assert log_output.match(/HEADER: Connection: close/)
     # assert response headers
     assert log_output.match(%r{HEADLINE: 200 HTTP/1\.1})
     assert log_output.match(/HEADER: content\-type: \w+/)