♻️ Explicitly "throw :eof" for EOF in get_response

This feels a lot more self-documenting than returning nil then breaking
when nil is returned.  Also, it lets me refactor the return values for
the get_response_line/get_response_literal methods, or throw from even
deeper in the stack.

Author: nevans

lib/net/imap.rb

@@ -2222,24 +2222,26 @@ def get_tagged_response(tag, cmd, timeout = nil)
 
     def get_response
       buff = String.new
-      while true
-        get_response_line(buff) or break
-        break unless /\{(\d+)\}\r\n\z/n =~ buff
-        get_response_literal(buff, $1.to_i) or break
+      catch :eof do
+        while true
+          get_response_line(buff)
+          break unless /\{(\d+)\}\r\n\z/n =~ buff
+          get_response_literal(buff, $1.to_i)
+        end
       end
       return nil if buff.length == 0
       $stderr.print(buff.gsub(/^/n, "S: ")) if @@debug
       @parser.parse(buff)
     end
 
     def get_response_line(buff)
-      line = @sock.gets(CRLF) or return
+      line = @sock.gets(CRLF) or throw :eof
       buff << line
     end
 
     def get_response_literal(buff, literal_size)
       literal = String.new(capacity: literal_size)
-      @sock.read(literal_size, literal) or return
+      @sock.read(literal_size, literal) or throw :eof
       buff << literal
     end