http server issue

[xr]

The official answer is

var http = require('http');
var through = require('through');

var server = http.createServer(function (req, res) {
    if (req.method === 'POST') {
        req.pipe(through(function (buf) {
            this.queue(buf.toString().toUpperCase());
        })).pipe(res);
    }
    else res.end('send me a POST\n');
});
server.listen(parseInt(process.argv[2]));

which could pass the http server task. but if I separate the through function like:
var tr = through(write).. like the following code.

var http = require('http');
var through = require('through');
var tr = through(function (buf) {
    this.queue(buf.toString().toUpperCase());
});
var server = http.createServer(function (req, res) {
    if (req.method === 'POST') {
        req.pipe(tr).pipe(res);
    }
    else res.end('send me a POST\n');
});
server.listen(parseInt(process.argv[2]));

It failed, give me the error like:

ACTUAL                             EXPECTED
------                             --------
"ON"                               "ON"                          
"THEM"                             "THEM"                        
"ON"                           !== "BUT,"                        
"THEM"                         !== "MASTER"                      
"BUT,"                         !== "OF"                          
"MASTER"                       !== "BUT,"                        
"OF"                           !== "MASTER"                      
"BUT,"                         !== "OF"                          
"MASTER"                       !== "SNAKES,"                     
"OF"                           !== "WE"                          
"SNAKES,"                          "SNAKES,"                     
"WE"                           !== "CAN"                         
"SNAKES,"                      !== "WE"                          
"CAN"                              "CAN"                         
"WE"                           !== "SLOUGHCHANGE"                
"CAN"                          !== "IN"                          
"SLOUGHCHANGE"                     "SLOUGHCHANGE"                
"IN"                           !== "THE"                         
"SLOUGHCHANGE"                 !== "IN"                          
"THE"                          !== "NIP"                         
"IN"                           !== "THE"                         
"NIP"                          !== "OF"                          
"THE"                          !== "NIP"                         
"OF"                           !== "A"                           
"NIP"                          !== "OF"                          
"A"                            !== "NAPPLE"                      
"OF"                           !== "A"                           
"NAPPLE"                       !== "SOLONGAS"                    
"A"                            !== "NAPPLE"                      
"SOLONGAS"                     !== "WE"                          
"NAPPLE"                       !== "SOLONGAS"                    
"WE"                           !== "CAN"                         
"SOLONGAS"                     !== "WE"                          
"CAN"                          !== "ALLSEE"                      
"WE"                           !== "CAN"                         
"ALLSEE"                       !== "FOR"                         
"CAN"                          !== "ALLSEE"                      
"FOR"                          !== ""                            
""                             !== null                          
# FAIL

Could anybody tell me why?

[xr]

I think the solution is here. no bother nodeschool/discussions#124 (comment)