Rescue IO::WaitReadable instead of EAGAIN for blocking read (#2121)

* Add test for waiting with an open client connection

* Rescue IO::WaitReadable instead of EAGAIN for blocking read
On Windows, `read_nonblock` raises `Errno::EWOULDBLOCK` if a blocking read would occur, which is a different value from `Errno::EAGAIN`. Both of these errors are extended by `IO::WaitReadable` which is Ruby's recommended exception class for retrying `read_nonblock`.

History.md

@@ -13,6 +13,7 @@
   * Windows update extconf.rb for use with ssp and varied Ruby/MSYS2 combinations (#2069)
   * Preserve `BUNDLE_GEMFILE` env var when using `prune_bundler` (#1893)
   * Send 408 request timeout even when queue requests is disabled (#2119)
+  * Rescue IO::WaitReadable instead of EAGAIN for blocking read (#2121)
 
 * Refactor
   * Remove unused loader argument from Plugin initializer (#2095)

lib/puma/client.rb

@@ -153,7 +153,7 @@ module Puma
 
       begin
         data = @io.read_nonblock(CHUNK_SIZE)
-      rescue Errno::EAGAIN
+      rescue IO::WaitReadable
         return false
       rescue SystemCallError, IOError, EOFError
         raise ConnectionError, "Connection error detected during read"
@@ -349,7 +349,7 @@ module Puma
 
       begin
         chunk = @io.read_nonblock(want)
-      rescue Errno::EAGAIN
+      rescue IO::WaitReadable
         return false
       rescue SystemCallError, IOError
         raise ConnectionError, "Connection error detected during read"

test/test_puma_server.rb

@@ -754,4 +754,17 @@ EOF
     # it is set to a reasonable number.
     assert_operator request_body_wait, :>=, 900
   end
+
+  def test_open_connection_wait
+    server_run app: ->(_) { [200, {}, ["Hello"]] }
+    s = send_http nil
+    sleep 0.1
+    s << "GET / HTTP/1.0\r\n\r\n"
+    assert_equal 'Hello', s.readlines.last
+  end
+
+  def test_open_connection_wait_no_queue
+    @server = Puma::Server.new @app, @events, queue_requests: false
+    test_open_connection_wait
+  end
 end