FSP - File Service Protocol Suite Code

209 lines (161 with data), 10.1 kB

                                    Interested parties about FSP please email
                                                               to Radim Kolar
                                                           hsn at sendmail.cz
                                                        visit our homepage on
                                                  http://fsp.sourceforge.net/
                                                                 and join us!
    
        For more than 7 years benefits of FSP protocol were unnoticed
        and FSP software was not maintained...

    FSP today

        Written by Radim Kolar

        Protocol related

	FSP uses UDP datagrams and it is reliable even when there is
	high number of packet loss. It is usable on WiFi network with
	60%-80% packet loss.

	FSP can very quickly addapt to changing line condition. This
	is excelent for wireless packet networks where network condition
	changes wildly based on receiver location and disturbance.
	Unlike TCP based protocols, FSP has a fast restart when
	line condition improves - It do not needs any RTT for retuning
	self. FSP goes immediatly back to maximum possible speed.
	
	Maximum FSP speed is by design lower than maximum speed of TCP
	based protocols because it has only 1 packet in the network.
	TCP protocol has about 3 packets. Design of FSP protocol
	makes impossible to send more than 1 packet into network.
	This is nice method for bandwidth protection, better handling
	traffic spikes and for sever protection against denial of
	service attacks on server.

	FSP server do not sends any data out unless is asked for. This
	solves problem with transfering duplicate data when using TCP
	protocol on overloaded lines. About 30% are dupes, thrown out
	by client. Note: TCP stacks from BSD family has this dupe
	ratio much lower.

        Embedded devices

	FSP protocol is very easy to implement; client core has about
	one page of C code. It is ideal for embedded devices for
	file-transfer tasks, like firmware downloading. Because of its
	simplicity, there is a little chance to writing buggy
	implementation.

	FSP is also good for remote booting. It is simplier, faster
	and more reliable than TFTP and supports directory listings.

	FSP protocol can be used as wire-protocol even without using
	any layer 2 stuff. It operates in degraded mode with extra
	features disabled.

	Stealth operation

	UDP ports are not often port scanned today, only one exception
	is scanning for Windows/Samba file sharing service. Nobody
	will notice that you are running a fsp server.

	FSP uses UDP which is unnoticed by many firewalls. FSP server
	runs on 21 port by default, if you move it to port 53 (dns)
	even strictly configured firewall can be worked around.

	You want to run anonymous archive and want to keep lamers out.

        Busy sites

	You want to share something without ruining your valueable
	bandwidth or latency. FSP protocol is slower than TCP based
	protocol it means that more bandwith will be left for your own use.
	Important point is that starting data sharing via FSP do not
	considerably raises your network latency because FSP can
	have just 1 packet floating in network. In ideal condition you will
	not notice increased latency at all.

	You have overloaded archive site. It is historicaly proven fact
	that FSP handles overloaded lines or sites better than anything else.
	FSP is very suitable for distributing updates to very large number
	of subscribers because it can easily handle traffic spikes without
	breaking connections and it can be very easily distributed between
	multiple servers because it is more or less connectionless.

	You do want to share large data files (movies, ISO images) on
	slow (or you do not want to waste valuable bandwidth) lines.
	Ideal for sharing files on modem lines.

        FSP daemon is a very light server.

    What is the purpose of FSP (V2.8.1):

        Written by A.J.Doherty@reading.ac.uk
    
        FSP is a set of programs that implements a public-access archive
        similar to an anonymous-FTP archive.  It is not meant to be a
        replacement for FTP; it is only meant to do what anonymous-FTP
        does, but in a manner more acceptable to the provider of the
        service and more friendly to the clients. 

        Providing anonymous-FTP service can be costly --- each active
        session consumes one process slot in the OS and one stream socket
        entry in the network sub-system.  The servers can also run
        concurrently, adding to the system load.  A popular archive site
        can easily be overwhelmed as a result.  Some were forced to
        shutdown and some impose inconvenient access restrictions. 

        Unlike FTP, FSP is connection-less and virtually state-less.  One
        server handles requests from all clients machines.  Each active
        client machine takes up 16-bytes in a dynamically extensible
        table.  Since only one server exists on a server machine at any
        time, the load added to the server machine is no more than one. 

        In exchange for allowing site operators to keep their sites open
        and do away with cumbersome access restrictions, this is what the
        clients accept with FSP: 

         1) Lower transfer rate.  The maximum rate is 1 kbyte per UDP
            message round-trip time between the client and the server.
        
        In addition to the potential for more abundant sites and more
        accessible sites, this is what the clients gain with FSP:

         1) Robustness.  Since FSP is connectionless, fluctuations in
            the network will not abort a FSP transaction.  Furthermore,
            the 16-bytes of data for each client can be regenerated at
            any point during any transaction.  Thus, if the server goes
            down at any point during a transaction, the transaction will
            resume when the server is restarted.  (like NFS) 

         2) Friendlier user interface.  FSP does not have its own command
            interpretor like FTP.  Since it is connectionless, there is
            no reason to carry much information from one command to the
            next, and the commands can all be made into individual Unix
            programs.  For instance, there is one program you run to list
            the directory and another you run to download a file. 

         3) Client protection.  FSP oversees a directory structure similar
            to that of an anonymous-FTP.  However, a directory created
            via FSP transaction is owned by the client machine that issued
            the creation request.  The client can create and delete files
            and subdirectories in that directory.  In addition, the client
            can enable any of the four attributes for that directory: 

                A) Give all other clients the permission to create files.

                B) Give all other clients the permission to delete files
                   or subdirectories.

                C) Give all other clients the permission to read files.
                   (this is true by default)

                D) Give all other clients the permission to create sub-
                   directories.

            Note: A subdirectory can be deleted if it is empty and the
                  client owns the subdirectory.

         4) Server protection.  FSP server does not spawn sub-programs.
            It will accept only paths that are downward relative to its
            designated working directory.  On systems with symbolic links,
            the server will follow symbolic links, but it does not follow
            uplinks ("..").  Clients cannot create symbolic links and
            care should be taken so that other users on the server machine
            cannot create symbolic links in the server's work space. 

            It is also fairly difficult to formulate an attack to force a
            shutdown of a FSP site by actions of a rogue site.  About the
            only way to disrupt a FSP service is to flood the FSP site
            with network packets.  FSP server prevents itself from
            'counter-flooding' by filtering for legitimate requests using
            the following method:

                A) Each request message contains a key.  For each client,
                   server database contains the keys to be used for the
                   next client request and for the previous client request.

                B) If the next request does not contain a key that matches
                   either of the two keys, it is accepted only if at least
                   one minute has elapsed since the last time a request
                   is accepted.  If the key does match the old key
                   (retransmit by client) it is accepted if the elapse time
                   is greater than 3 seconds.

                C) Every request message accepted is acknowledged with
                   one reply message.  The reply message contains a new
                   key to used for the next request.  The new key is
                   computed by the server with a pseudo-random number
                   generator. 

            Flooding is a blatant violation of network etiquette because
            a site can be subjected to flooding attack whether it has FSP
            running or not, and flooding congests every link and gateway
            between the rogue client and the server.  As a further measure
            of protection, the server loads a table of rogue clients on
            startup.  The server will not respond to requests from any of
            those clients.

    ***********************************************************************

    This is a free software.  Be creative; make your own macros and tools
    and let me know of any bugs and suggestions. 
   
    ***********************************************************************
    
    Source code uses several BSD-like licenses; Whole FSP is distributed
    under 2-point BSD license, also known as MIT X11 License.