concat-stream

$ npm install concat-stream

var concat = require('concat-stream')
var fs = require('fs')

var read = fs.createReadStream('readme.md')
var write = concat(function(data) {})

read.pipe(write)

var write = concat(function(data) {})
write.write([1,2,3])
write.write([4,5,6])
write.end()
// data will be [1,2,3,4,5,6] in the above callback

var write = concat(function(data) {})
write.write(new Buffer('hello '))
write.write(new Buffer('world'))
write.end()
// data will be a buffer that toString()s to 'hello world' in the above callback