improve interest calculation

do not check buffer before going to the parsers, which also take that account

for http2, use the http2 connection send buffer (instead of the connection buffer) to figure out whether it's waiting on a WINDOW_UPDATE, which is more correct and efficient

on http1, the logic is the same, but the code is simplified, as the checks become the same regardless of whether request or @requests.first is picked up

lib/httpx/connection.rb

@@ -230,9 +230,6 @@ module HTTPX
         return @io.interests if connecting?
       end
 
-      # if the write buffer is full, we drain it
-      return :w unless @write_buffer.empty?
-
       return @parser.interests if @parser
 
       nil

lib/httpx/connection/http1.rb

@@ -31,14 +31,9 @@ module HTTPX
     end
 
     def interests
-      # this means we're processing incoming response already
-      return :r if @request
+      request = @request || @requests.first
 
-      return if @requests.empty?
-
-      request = @requests.first
-
-      return unless request
+      return unless request && request.current_context?
 
       return :w if request.interests == :w || !@buffer.empty?
 

lib/httpx/connection/http2.rb

@@ -52,9 +52,6 @@ module HTTPX
     end
 
     def interests
-      # waiting for WINDOW_UPDATE frames
-      return :r if @buffer.full?
-
       if @connection.state == :closed
         return unless @handshake_completed
 
@@ -65,6 +62,19 @@ module HTTPX
         return @buffer.empty? ? :r : :rw
       end
 
+      unless @contexts.key?(Fiber.current)
+        return :w unless @pings.empty?
+
+        return
+      end
+
+      unless @connection.send_buffer.empty?
+        return :rw unless @buffer.empty?
+
+        # waiting for WINDOW_UPDATE frames
+        return :r
+      end
+
       return :w if !@pending.empty? && can_buffer_more_requests?
 
       return :w unless @drains.empty?
@@ -72,10 +82,10 @@ module HTTPX
       if @buffer.empty?
         return if @streams.empty? && @pings.empty?
 
-        return :r
+        :r
+      else
+        :w
       end
-
-      :rw
     end
 
     def close