Use frozen string literals

lib/net/http.rb

@@ -1615,7 +1615,7 @@ def connect
                                       write_timeout: @write_timeout,
                                       continue_timeout: @continue_timeout,
                                       debug_output: @debug_output)
-          buf = "CONNECT #{conn_address}:#{@port} HTTP/#{HTTPVersion}\r\n"
+          buf = +"CONNECT #{conn_address}:#{@port} HTTP/#{HTTPVersion}\r\n"
           buf << "Host: #{@address}:#{@port}\r\n"
           if proxy_user
             credential = ["#{proxy_user}:#{proxy_pass}"].pack('m0')

lib/net/http/generic_request.rb

@@ -316,7 +316,7 @@ def encode_multipart_form_data(out, params, opt)
     boundary ||= SecureRandom.urlsafe_base64(40)
     chunked_p = chunked?
 
-    buf = String.new
+    buf = +''
     params.each do |key, value, h={}|
       key = quote_string(key, charset)
       filename =
@@ -401,7 +401,7 @@ def write_header(sock, ver, path)
     if /[\r\n]/ =~ reqline
       raise ArgumentError, "A Request-Line must not contain CR or LF"
     end
-    buf = String.new
+    buf = +''
     buf << reqline << "\r\n"
     each_capitalized do |k,v|
       buf << "#{k}: #{v}\r\n"

lib/net/http/response.rb

@@ -648,7 +648,7 @@ def procdest(dest, block)
     if block
       Net::ReadAdapter.new(block)
     else
-      dest || String.new
+      dest || +''
     end
   end