Communication

Handling multiple TCP Connections in C++

C/C++ Users Journal, v.14, No. 5, May 1996, pp. 17-23.
The article described the TCP API class library contained in the present tcp_relay code in much more detail.

comp.sources.misc

vol 47, issue 103

"Async relaying of TCP packets by a Finite Automaton [small example]" [plain text file]

The USENET article posted on comp.lang.c++ on Wed Feb 1 09:11:48 CST 1995

• a variable-bit coding of sequences of integers (including Arithmetic compression ),
• a trick of sharing a stream buffer (a "file") among several streams,
• handling of extended file names, e.g.,
  EndianOut stream("| compress > /tmp/aa.Z");
  FILE * fp = fopen("tcp://localhost:7","r");
  fstream fp("| cat | cat",ios::in|ios::out);
  This function is also available separately, see below
• explicit endian specification in dealing with integer streams
• TCP streams
• TCP transactor, a shell RPC-like tool
• a primitive Logging service
• a Vocabulary package, (poly/homo)morphic dictionaries with a dynamic "inheritance" path, an embedded OO system

There are also a few convenience functions/classes. The code is written in a portable way and rather commented; verification tests are provided as well.

The README file [plain text file]

Complete source code archive [.tar.gz, 77K]

Layered I/O statement

Opening of extended file names

TCPStream - a C++ standard iostream over a TCP channel

Executing a shell command feeding from a named FIFO pipe is trivial, except for one pitfall, as an article "Scripting daemons through pipes; e.g.: newsreader in sh? (yes!)" explains. The article also shows off a few sh-agents talking (and talking back) to daemons and other UNIX-interactive programs.

• exec_with_piped.c, the scripting tool itself
• nntp_scripting.sh, a shell news agent -- an example of using exec_with_piped to script a remote NNTP daemon (accessed via telnet)

"The most primitive and nearly universal database interface",
exec_with_piped as a database "bridge" that lets applications or scripts access an SQL server without ODBC drivers, Embedded SQL, etc.

The functionality of TCPStreams is identical to that of an fstream: the only difference is that it may take really a while for an i/o operation on a TCP channel to finish. It is unreasonable to make the whole application wait. Thus an application is given a chance to tell a TCP buffer being created that it does not want the network i/o to block. Application does it by deriving and instantiating a NetCallback object. If the currently registered NetCallback::async_io_hint() returns true, a newly created TCP socket is turned into a (POSIX) non-blocking mode; when the stream wants to flush/fill its buffer and the operation can't be completed immediately, the stream calls NetCallback::yield(). When this function returns, the stream gives another try to the input/output operation.

With the TCPStream, you can check your POP3 mail like this:

   TCPstream link;
   link.connect(SocketAddr("hostname",110));
   if( !link.is_open() || !link )
      _error("Failed to establish the connection");
   link << "USER " << user_name << endl;
   int resp_code; char buffer[100];
   link >> resp_code;
   if( ! link.get(buffer,sizeof(buffer)-1,'\r').good() )
      _error("error reading a response line from the link");
   if( resp_code >= 300 )
      _error("bummer");
   ...etc...

TCP streams are helpful on a server side as well. See vTCPstream_server.cc for a sample (forking) server.

Advanced i/o and Arithmetic Compression classlib
the package that contains the TCPStream class and its implementation

HTTP Virtual File System
one project that made use of the TCPStream class

This code is to perform a single transaction -- a request/reply exchange -- with a "server" on the other end of a TCP pipe. The tool establishes a connection to a server, sends a request, listens to the reply, and prints it on its standard output.

Examples:

     tcp-trans localhost:79 user-name
will emulate finger

     tcp-trans proxyhost:80 "GET http://some.host/ HTTP/1.1"
         "Host: some.host:80" "User-Agent: $LOGNAME" ""
will fetch the root web page off some.host using a web proxy

     tcp-trans some.host:25 "expn <postmaster>" "quit"
reveals the real person behind the postmaster

     tcp-trans some.host:13
prints the current timestamp off the some.host
 

source code archive off this site [.cc, 4K]

Requires

TCPStream - a C++ standard iostream over a TCP channel

This is a source code archive that accompanies a DDJ article "Distributing Data Using TLT30G". TLT30G is a software system for distributing files from a central location to a number of clients over unidirectional, noisy, and generally slow communication links. The code archive is a self-contained implementation of a particular transport layer of the TLT30G broadcasting system. This Link Access Plugin implements transmission of TLT30G's segments as UDP datagrams over a TCP/IP network. Of all the protocols of the TCP/IP suite, UDP fits best for a packet-oriented broadcast without any feedback.

The code in the archive below defines and implements basic network classes (IPaddress, SocketAddr), UDP classes (UDPsocket, UDPsocketIn, UDPsocketOut), datagram streams to assemble and disassemble a UDP datagram, and the TLT30G's LAP interface itself.
 

Distributing Data Using TLT30G

Dr.Dobb's Journal, #289, September 1998, pp.34-40, 92-93.

Speaking in Iostreams-ese

C/C++ Users Journal, v.15, No. 5, May 1997, pp. 47-55.

Keywords: Finite Automaton, FSM, HTTP, Scheme, CGI, Computation, WWW, Push

tail-f.scm script's description

A USENET article explaining the technique [plain text file],
posted on comp.lang.scheme, comp.programming, comp.infosystems.www.authoring.cgi, comp.infosystems.www.misc newsgroups on Tue Mar 25 13:17:13 CST 1997.