Using frame-stream to add a header to a stream (i.e. add only one frame to the start of the stream)

_stream_header.md

Example showing how to add a header to a stream. Uses frame-stream to add a single frame containing the header. The rest of the data is left on the stream. Can be used to add metadata to the start of a stream.

test.js

"use strict";

let frame = require('frame-stream');

function write_header(s, header)
{
    var out_stream = frame.encode();
    out_stream._pushFrameData = function (bufs)
    {
        for (let buf of bufs)
        {
            s.write(buf);
        }
    };
    out_stream.end(header);
}

function read_header(s, max_size, cb)
{
    if (!cb)
    {
        cb = max_size;
        max_size = 0;
    }

    let in_stream = frame.decode(
    {
        maxSize: max_size
    });

    function done(v)
    {
        if (v)
        {
            throw v;
        }
    }

    s.on('readable', function onread()
    {
        let data = this.read();

        if (data)
        {
            let buffer = in_stream.buffer;

            try
            {
                in_stream.push = done;
                in_stream._transform(data, null, done);
            }
            catch (v)
            {
                s.removeListener('readable', onread);

                if (v instanceof Buffer)
                {
                    let rest = buffer ? Buffer.concat([buffer, data]) : data;
                    s.unshift(rest.slice(in_stream.opts.lengthSize + v.length));
                    return cb(null, v);
                }

                cb(v);
            }
        }
    });
}

var net = require('net'),
    server = net.createServer(function (socket)
    {
        read_header(socket, function (err, header)
        {
            if (err)
            {
                socket.on('readable', function ()
                {
                    this.read();
                });

                return console.error(err);
            }
            console.log('header:', header.toString('utf8'));
            socket.pipe(process.stdout);
        });

        socket.on('end', function ()
        {
            server.close();
        });
    });

server.listen(40000);

var socket = net.connect(40000, function ()
{
    this.cork();
    write_header(this, 'hello there');
    this.end('following data');
    this.uncork();
});