lib/net/protocol.rb (rbuf_fill): avoid exception with read_nonblock

Exceptions are noisy in debug output and waste allocations.
Use "exception: false" introduced in 2.1 to return symbols for
common errors instead.

Follow-up commits will be prepared to reduce EOFError exceptions
to further quiet debug output and IO.select may be replaced by
io/wait methods if available to reduce allocations.

[ruby-core:68787] [Feature #11044]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@50219 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,8 @@
+Sat Apr 11 04:46:42 2015  Eric Wong  <e@80x24.org>
+
+	* lib/net/protocol.rb (rbuf_fill): avoid exception with read_nonblock
+	  [ruby-core:68787] [Feature #11044]
+
 Fri Apr 10 23:57:44 2015  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* dir.c (need_normalization): use getattrlist() if fgetattrlist()

lib/net/protocol.rb

@@ -149,23 +149,21 @@ module Net # :nodoc:
     BUFSIZE = 1024 * 16
 
     def rbuf_fill
-      begin
-        @rbuf << @io.read_nonblock(BUFSIZE)
-      rescue IO::WaitReadable
-        if IO.select([@io], nil, nil, @read_timeout)
-          retry
-        else
-          raise Net::ReadTimeout
-        end
-      rescue IO::WaitWritable
+      case rv = @io.read_nonblock(BUFSIZE, exception: false)
+      when String
+        return @rbuf << rv
+      when :wait_readable
+        IO.select([@io], nil, nil, @read_timeout) or raise Net::ReadTimeout
+        # continue looping
+      when :wait_writable
         # OpenSSL::Buffering#read_nonblock may fail with IO::WaitWritable.
         # http://www.openssl.org/support/faq.html#PROG10
-        if IO.select(nil, [@io], nil, @read_timeout)
-          retry
-        else
-          raise Net::ReadTimeout
-        end
-      end
+        IO.select(nil, [@io], nil, @read_timeout) or raise Net::ReadTimeout
+        # continue looping
+      when nil
+        # callers do not care about backtrace, so avoid allocating for it
+        raise EOFError, 'end of file reached', []
+      end while true
     end
 
     def rbuf_consume(len)