gistfile1.js

var fs = require('fs');

var in = fs.openSync('/path/to/file', 'r');
var out = /* ... a net.Stream instance from somewhere ... */

var sent = 0, err = 0;
do {
    try {
        err = fs.sendfileSync(out.fd, in.fd, sent, 0);
        sent += err;
    } catch (e) {
        if (e.errno !== process.EAGAIN) {
            throw e;
        }

        continue;
    }
} while (err > 0);