This info file describes the C++ family of socket classes.

Copyright (C) 1992,1993,1994 Gnanasekaran Swaminathan <gs4t@virginia.edu>

Permission is granted to make and distribute verbatim copies of this document provided the copyright notice and this permission notice are preserved on all copies.

Socket++ Library
****************

Socket++ is a family of C++ classes that gives the same interface as the iostream classes for input and output for communication between processes.

This documentation describes Version: 12Jan97 1.11 of socket++ library.

Socket++ Library Copyright Notice
*********************************

Copyright (C) 1992,1993,1994 Gnanasekaran Swaminathan

Permission is granted to use at your own risk and distribute this software in source and binary forms provided the above copyright notice and this paragraph are preserved on all copies. This software is provided "as is" with no express or implied warranty.

Acknowledgments
***************

Gordon Joly <G.Joly@cs.ucl.ac.uk> for reporting bugs in pipestream class implementation and providing an ftp site for the socket++ library at cs.ucl.ac.uk:~ftp/coside/gnu/socket++-1.x.tar.gz He also knows how to make the socket++ library a shared library.

Jim Anderson for reporting a bug in sockinet.C

Carl Gay <cgay@skinner.cs.uoregon.edu> for reporting a bug and a fix in sockinet.C

Oliver Imbusch <flabes@parystec.de> for reporting a bug in Makefile.in and suggesting several enhancements for sockbuf class.

Dierk Wendt <wendt@lambda.hella.de> for reporting errors in the socket++ documentation.

Per Bothner <bothner@cygnus.com> for configure, config.sub, config.shared and move-if-change files that are used to generate Makefile. These files are taken from his libg++-2.4 and hence, these files are governed by the Copyright Notice found in the file LICENCE in libg++.

Overview of Socket++ Library
****************************

Socket++ library defines a family of C++ classes that can be used more effectively than directly calling the underlying low-level system functions. One distinct advantage of the socket++ is that it has the same interface as that of the iostream so that the users can perform type-safe input output. See your local IOStream library documentation for more information on iostreams.

streambuf counterpart of the socket++ is sockbuf. sockbuf is an endpoint for communication with yet another sockbuf or simply a socket descriptor. sockbuf has also methods that act as interfaces for most of the commonly used system calls that involve sockets. See sockbuf Class, for more information on the socket buffer class.

For each communication domain, we derive a new class from sockbuf that has some additional methods that are specific to that domain. At present, only UNIX and INET domains are supported. sockunixbuf class and sockinetbuf class define the UNIX and INET domain of sockets respectively. See sockunixbuf Class, for UNIX sockets and see sockinetbuf Class, for INET sockets.

We also have domain specific socket address classes that are derived from a common base class called sockAddr. sockunixaddr class is used for UNIX domain addresses and sockinetaddr class is used for INET domain addresses. For more information on address classes see sockAddr Class, sockunixaddr Class, and sockinetaddr Class.

     Note: sockAddr is not spelled sockaddr in order to prevent name clash with the struct sockaddr declared in <sys/socket.h>.

We noted earlier that socket++ provides the same interface as the iostream library. For example, in the internet domain, we have isockinet, osockinet, and iosockinet classes that are counterparts to istream, ostream, and iostream classes of IOStream library. For more details on iosockstream classes see sockstream Classes.

The services of pipe(), socketpair(), and popen() system calls are provided by the pipestream class. See pipestream Classes.

sockbuf Class
*************

sockbuf class is derived from streambuf class of the iostream library. You can simultaneously read and write into a sockbuf just like you can listen and talk through a telephone. To accomplish the above goal, we maintain two independent buffers for reading and writing.

Constructors
============

sockbuf constructors sets up an endpoint for communication. A sockbuf object so created can be read from and written to in linebuffered mode. To change mode, refer to streambuf class in your IOStream library.

     Note: If you are using AT&T IOStream library, then the linebuffered mode is permanently turned off. Thus, you need to explicitly flush a socket stream. You can flush a socket stream buffer in one of the following four ways:

              // os is a socket ostream
              os << "this is a test" << endl;
              os << "this is a test\n" << flush;
              os << "this is a test\n"; os.flush ();
              os << "this is a test\n"; os->sync ();

sockbuf objects are created as follows where

  - s and so are sockbuf objects

  - sd is an integer which is a socket descriptor

  - af and proto are integers which denote domain number and protocol number respectively

  - ty is a sockbuf::type and must be one of sockbuf::sock_stream, sockbuf::sock_dgram, sockbuf::sock_raw, sockbuf::sock_rdm, and sockbuf::sock_seqpacket

sockbuf s(sd);
sockbuf s;
     Set socket descriptor of s to sd (defaults to -1). sockbuf destructor will close sd.

sockbuf s(af, ty, proto);
     Set socket descriptor of s to ::socket(af, int(ty), proto);

sockbuf so(s);
     Set socket descriptor of so to the socket descriptor of s.

s.open(ty, proto)
     does nothing and returns simply 0, the null pointer to sockbuf.

s.is_open()
     returns a non-zero number if the socket descriptor is open else return 0.

s = so;
     return a reference s after assigning s with so.

Destructor
==========

sockbuf::~sockbuf() flushes output and closes its socket if no other sockbuf is referencing it and _S_DELETE_DONT_CLOSE flag is not set. It also deletes its read and write buffers.

In what follows,

  - s is a sockbuf object

  - how is of type sockbuf::shuthow and must be one of sockbuf::shut_read, sockbuf::shut_write, and sockbuf::shut_readwrite

sockbuf::~sockbuf()
     flushes output and closes its socket if no other sockbuf object is referencing it before deleting its read and write buffers. If the _S_DELETE_DONT_CLOSE flag is set, then the socket is not closed.

s.close()
     closes the socket even if it is referenced by other sockbuf objects and _S_DELETE_DONT_CLOSE flag is set.

s.shutdown(how)
     shuts down read if how is sockbuf::shut_read, shuts down write if how is sockbuf::shut_write, and shuts down both read and write if how is sockbuf::shut_readwrite.

Reading and Writing
===================

sockbuf class offers several ways to read and write and tailors the behavior of several virtual functions of streambuf for socket communication.

In case of error, sockbuf::error(const char*) is called.

In what follows,

  - s is a sockbuf object

  - buf is buffer of type char*

  - bufsz is an integer and is less than sizeof(buf)

  - msgf is an integer and denotes the message flag

  - sa is of type sockAddr

  - msgh is a pointer to struct msghdr

  - wp is an integer and denotes time in seconds

  - c is a char

s.is_open()
     returns a non-zero number if the socket descriptor is open else return 0.

s.is_eof()
     returns a non-zero number if the socket has seen EOF while reading else return 0.

s.write(buf, bufsz)
     returns an int which must be equal to bufsz if bufsz chars in the buf are written successfully. It returns 0 if there is nothing to write or if, in case of timeouts, the socket is not ready for write Timeouts.

s.send(buf, bufsz, msgf)
     same as sockbuf::write described above but allows the user to control the transmission of messages using the message flag msgf. If msgf is sockbuf::msg_oob and the socket type of s is sockbuf::sock_stream, s sends the message in OUT-OF-BAND mode. If msgf is sockbuf::msg_dontroute, s sends the outgoing packets without routing. If msgf is 0, which is the default case, sockbuf::send behaves exactly like sockbuf::write.

s.sendto(sa, buf, bufsz, msgf)
     same as sockbuf::send but works on unconnected sockets. sa specifies the TO address for the message.

s.sendmsg(msgh, msgf)
     same as sockbuf::send but sends a struct msghdr object instead.

s.sys_write(buf, bufsz)
     calls sockbuf::write and returns the result. Unlike sockbuf::write sockbuf::sys_write is declared as a virtual function.

s.read(buf, bufsz)
     returns an int which is the number of chars read into the buf. In case of EOF, return EOF. Here, bufsz indicates the size of the buf. In case of timeouts, return 0 Timeouts.

s.recv(buf, bufsz, msgf)
     same as sockbuf::read described above but allows the user to receive OUT-OF-BAND data if msgf is sockbuf::msg_oob or to preview the data waiting to be read if msgf is sockbuf::msg_peek. If msgf is 0, which is the default case, sockbuf::recv behaves exactly like sockbuf::read.

s.recvfrom(sa, buf, bufsz, msgf)
     same as sockbuf::recv but works on unconnected sockets. sa specifies the FROM address for the message.

s.recvmsg(msgh, msgf)
     same as sockbuf::recv but reads a struct msghdr object instead.

s.sys_read(buf, bufsz)
     calls sockbuf::read and returns the result. Unlike sockbuf::read sockbuf::sys_read is declared as a virtual function.

s.is_readready(wp_sec, wp_usec)
     returns a non-zero int if s has data waiting to be read from the communication channel. If wp_sec >= 0, it waits for wp_sec 10^6 + wp_usec microseconds before returning 0 in case there are no data waiting to be read. If wp_sec < 0, then it waits until a datum arrives at the communication channel. wp_usec defaults to 0.

          Please Note: The data waiting in sockbuf's own buffer is different from the data waiting in the communication channel.

s.is_writeready(wp_sec, wp_usec)
     returns a non-zero int if data can be written onto the communication channel of s. If wp_sec >= 0, it waits for wp_sec 10^6 + wp_usec microseconds before returning 0 in case no data can be written. If wp_sec < 0, then it waits until the communication channel is ready to accept data. wp_usec defaults to 0.

          Please Note: The buffer of the sockbuf class is different from the buffer of the communication channel buffer.

s.is_exceptionpending(wp_sec, wp_usec)
     returns non-zero int if s has any exception events pending. If wp_sec >= 0, it waits for wp_sec 10^6 + wp_usec microseconds before returning 0 in case s does not have any exception events pending. If wp_sec < 0, then it waits until an expception event occurs. wp_usec defaults to 0.

          Please Note: The exceptions that sockbuf::is_exceptionpending is looking for are different from the C++ exceptions.

s.flush_output()
     flushes the output buffer and returns the number of chars flushed. In case of error, return EOF. sockbuf::flush_output is a protected member function and it is not available for general public.

s.doallocate()
     allocates free store for read and write buffers of s and returns 1 if allocation is done and returns 0 if there is no need. sockbuf::doallocate is a protected virtual member function and it is not available for general public.

s.underflow()
     returns the unread char in the buffer as an unsigned char if there is any. Else returns EOF if s cannot allocate space for the buffers, cannot read or peer is closed. sockbuf::underflow is a protected virtual member function and it is not available for general public.

s.overflow(c)
     if c==EOF, call and return the result of flush_output(), else if c=='\n' and s is linebuffered, call flush_output() and return c unless flush_output() returns EOF, in which case return EOF. In any other case, insert char c into the buffer and return c as an unsigned char. sockbuf::overflow is a protected member virtual function and it is not available for general public.

          Node: linebuffered mode does not work with AT&T IOStream library. Use explicit flushing to flush sockbuf.

s.sync()
     calls flush_output() and returns the result. Useful if the user needs to flush the output without writing newline char into the write buffer.

s.xsputn(buf, bufsz)
     write bufsz chars into the buffer and returns the number of chars successfully written. Output is flushed if any char in buf[0..bufsz-1] is '\n'.

s.recvtimeout(wp)
     sets the recv timeout to wp seconds. If wp is -1, it is a block and if wp is 0, it is a poll.

     It affects all read functions. If the socket is not read ready within wp seconds, the read call will return 0. It also affects sockbuf::underflow. sockbuf::underflow will not set the _S_EOF_SEEN flag if it is returning EOF because of timeout.

     sockbuf::recvtimeout returns the old recv timeout value.

s.sendtimeout(wp)
     sets the send timeout to wp seconds. If wp is -1, it is a block and if wp is 0, it is a poll.

     It affects all write functions. If the socket is not write ready within wp seconds, the write call will return 0.

     sockbuf::sendtimeout returns the old send timeout value.

Establishing connections
========================

A name must be bound to a sockbuf if processes want to refer to it and use it for communication. Names must be unique. A UNIX name is a 3-tuple, <PROTOCOL, LOCAL PATH, PEER PATH>. An INET name is a 5-tuple, <PROTOCOL, LOCAL ADDR, LOCAL PORT, PEER ADDR, PEER PORT>. sockbuf::bind is used to specify the local half of the name---<LOCAL PATH> for UNIX and <LOCAL ADDR, LOCAL PORT> for INET. sockbuf::connect and sockbuf::accept are used to specify the peer half of the name---<PEER PATH> for UNIX and <PEER ADDR, PEER PORT> for INET.

In what follows,

  - s and so are sockbuf objects

  - sa is a sockAddr object

  - nc is an integer denoting the number of connections to allow

s.bind(sa)
     binds sockAddr sa as the local half of the name for s. It returns 0 on success and returns the errno on failure.

s.connect(sa)
     sockbuf::connect uses sa to provide the peer half of the name for s and to establish the connection itself. sockbuf::connect also provides the local half of the name automatically and hence, the user should not use sockbuf::bind to bind any local half of the name. It returns 0 on success and returns the errno on failure.

s.listen(nc)
     makes s ready to accept connections. nc specifies the maximum number of outstanding connections that may be queued and must be at least 1 and less than or equal to sockbuf::somaxconn which is usually 5 on most systems.

sockbuf so = s.accept(sa)
sockbuf so = s.accept()
     accepts connections and returns the peer address in sa. s must be a listening sockbuf. See sockbuf::listen above.

Getting and Setting Socket Options
==================================

Socket options are used to control a socket communication. New options can be set and old value of the options can be retrived at the protocol level or at the socket level by using setopt and getopt member functions. In addition, you can also use special member functions to get and set specific options.

In what follows,

  - s is a sockbuf object

  - opval is an integer and denotes the option value

  - op is of type sockbuf::option and must be one of

       * sockbuf::so_error used to retrieve and clear error status

       * sockbuf::so_type used to retrieve type of the socket

       * sockbuf::so_debug is used to specify recording of debugging information

       * sockbuf::so_reuseaddr is used to specify the reuse of local address

       * sockbuf::so_keepalive is used to specify whether to keep connections alive or not

       * sockbuf::so_dontroute is used to specify whether to route messages or not

       * sockbuf::so_broadcast is used to specify whether to broadcast sockbuf::sock_dgram messages or not

       * sockbuf::so_oobinline is used to specify whether to inline OUT-OF-BAND data or not.

       * sockbuf::so_linger is used to specify for how long to linger before shutting down

       * sockbuf::so_sndbuf is used to retrieve and to set the size of the send buffer (communication channel buffer not sockbuf's internal buffer)

       * sockbuf::so_rcvbuf is used to retrieve and to set the size of the recv buffer (communication channel buffer not sockbuf's internal buffer)

s.getopt(op, &opval, sizeof(opval), oplevel)
     gets the option value of the sockbuf::option op  at the option level oplevel in opval. It returns the actual size of the buffer opval used. The default value of the oplevel is sockbuf::sol_socket.

s.setopt(op, &opval, sizeof(opval), oplevel)
     sets the option value of the sockbuf::option op  at the option level oplevel to opval. The default value of the oplevel is sockbuf::sol_socket.

s.gettype()
     gets the socket type of s. The return type is sockbuf::type.

s.clearerror()
     gets and clears the error status of the socket.

s.debug(opval)
     if opval is not -1, set the sockbuf::so_debug option value to opval. In any case, return the old option value of sockbuf::so_debug option. The default value of opval is -1.

s.reuseaddr(opval)
     if opval is not -1, set the sockbuf::so_reuseaddr option value to opval. In any case, return the old option value of sockbuf::so_reuseaddr option. The default value of opval is -1.

s.dontroute(opval)
     if opval is not -1, set the sockbuf::so_dontroute option value to opval. In any case, return the old option value of sockbuf::so_dontroute option. The default value of opval is -1.

s.oobinline(opval)
     if opval is not -1, set the sockbuf::so_oobinline option value to opval. In any case, return the old option value of sockbuf::so_oobinline option. The default value of opval is -1.

s.broadcast(opval)
     if opval is not -1, set the sockbuf::so_broadcast option value to opval. In any case, return the old option value of sockbuf::so_broadcast option. The default value of opval is -1.

s.keepalive(opval)
     if opval is not -1, set the sockbuf::so_keepalive option value to opval. In any case, return the old option value of sockbuf::so_keepalive option. The default value of opval is -1.

s.sendbufsz(opval)
     if opval is not -1, set the new send buffer size to opval. In any case, return the old buffer size of the send buffer. The default value of opval is -1.

s.recvbufsz(opval)
     if opval is not -1, set the new recv buffer size to opval. In any case, return the old buffer size of the recv buffer. The default value of opval is -1.

s.linger(tim)
     if tim is positive, set the linger time to tim seconds. If tim is 0, set the linger off. In any case, return the old linger time if it was set earlier. Otherwise return -1. The default value of tim is -1.

Time Outs While Reading and Writing
===================================

Time outs are very useful in handling data of unknown sizes and formats while reading and writing. For example, how does one communicate with a socket that sends chunks of data of unknown size and format? If only sockbuf::read is used without time out, it will block indefinitely. In such cases, time out facility is the only answer.

The following idiom is recommended. See Pitfalls for a complete example.

         int old_tmo = s.recvtimeout (2) // set time out (2 seconds here)
         for (;;) { // read or write
             char buf[256];
             int rval = s.read (buf, 256);
             if (rval == 0 || rval == EOF) break;
             // process buf here
         }
         s.recvtimeout (old_tmo); // reset time out

In what follows,

  - s is a sockbuf object

  - wp is waiting period in seconds

s.recvtimeout(wp)
     sets the recv timeout to wp seconds. If wp is -1, it is a block and if wp is 0, it is a poll.

     It affects all read functions. If the socket is not read ready within wp seconds, the read call will return 0. It also affects sockbuf::underflow. sockbuf::underflow will not set the _S_EOF_SEEN flag if it is returning EOF because of timeout.

     sockbuf::recvtimeout returns the old recv timeout value.

s.sendtimeout(wp)
     sets the send timeout to wp seconds. If wp is -1, it is a block and if wp is 0, it is a poll.

     It affects all write functions. If the socket is not write ready within wp seconds, the write call will return 0.

     sockbuf::sendtimeout returns the old send timeout value.

sockAddr Class
**************

Class sockAddr is an abstract base class for all socket address classes. That is, domain specific socket address classes are all derived from sockAddr class.

     Note: sockAddr is not spelled sockaddr in order to prevent name clash with struct sockaddr declared in <sys/socket.h>.

Non-abstract derived classes must have definitions for the following functions.

sockAddr::operator void* ()
     should simply return this.

sockAddr::size()
     should return sizeof(*this). The return type is int.

sockAddr::family()
     should return address family (domain name) of the socket address. The return type is int

sockinetbuf Class
*****************

sockinetbuf class is derived from sockbuf class and inherits most of the public functions of sockbuf. See sockbuf Class, for more information on sockbuf. In addition, it provides methods for getting sockinetaddr of local and peer connections. See sockinetaddr Class, for more information on sockinetaddr.

Methods
=======

In what follows,

  - ty denotes the type of the socket connection and is of type sockbuf::type

  - proto denotes the protocol and is of type int

  - si, ins are sockbuf objects and are in INET domain

  - adr denotes an INET address in host byte order and is of type unsigned long

  - serv denotes a service like "nntp" and is of type char*

  - proto denotes a protocol like "tcp" and is of type char*

  - thostname is of type char* and denotes the name of a host like "kelvin.acc.virginia.edu" or "128.143.24.31".

  - portno denotes a port in host byte order and is of type int

sockinetbuf ins(ty, proto)
     Constructs a sockinetbuf object ins whose socket communication type is ty and protocol is proto. proto defaults to 0.

sockinetbuf ins(si)
     Constructs a sockinetbuf object ins which uses the same socket as si uses.

ins = si
     performs the same function as sockbuf::operator=. See sockbuf Class, for more details.

ins.open(ty, proto)
     create a new sockinetbuf whose type and protocol are ty and proto respectively and assign it to ins.

sockinetaddr sina = ins.localaddr()
     returns the local INET address of the sockinetbuf object ins. The call will make sense only after a call to either sockbuf::bind or sockbuf::connect.

sockinetaddr sina = ins.peeraddr()
     returns the peer INET address of the sockinetbuf object ins. The call will make sense only after a call to sockbuf::connect.

const char* hn = ins.localhost()
     returns the local INET thostname of the sockinetbuf object ins. The call will make sense only after a call to either sockbuf::bind or sockbuf::connect.

const char* hn = ins.peerhost()
     returns the peer INET thostname of the sockinetbuf object ins. The call will make sense only after a call to sockbuf::connect.

int pn = ins.localport()
     returns the local INET port number of the sockinetbuf object ins in host byte order. The call will make sense only after a call to either sockbuf::bind or sockbuf::connect.

int pn = ins.peerport()
     returns the peer INET port number of the sockinetbuf object ins in local host byte order. The call will make sense only after a call to sockbuf::connect.

ins.bind ()
     binds ins to the default address INADDR_ANY and the default port. It returns 0 on success and returns the errno on failure.

ins.bind (adr, portno)
     binds ins to the address adr and the port portno. It returns 0 on success and returns the errno on failure.

ins.bind (adr, serv, proto)
     binds ins to the address, adr and the port corresponding to the service serv and the protocol proto>. It returns 0 on success and returns the errno on failure.

ins.bind (thostname, portno)
     binds ins to the address corresponding to the hostname thostname and the port portno. It returns 0 on success and returns the errno on failure.

ins.bind (thostname, serv, proto)
     binds ins to the address corresponding to the hostname thostname and the port corresponding to the service serv and the protocol proto>. It returns 0 on success and returns the errno on failure.

ins.connect (adr, portno)
     connects ins to the address adr and the port portno. It returns 0 on success and returns the errno on failure.

ins.connect (adr, serv, proto)
     connects ins to the address, adr and the port corresponding to the service serv and the protocol proto>. It returns 0 on success and returns the errno on failure.

ins.connect (thostname, portno)
     connects ins to the address corresponding to the hostname thostname and the port portno. It returns 0 on success and returns the errno on failure.

ins.connect (thostname, serv, proto)
     connects ins to the address corresponding to the hostname thostname and the port corresponding to the service serv and the protocol proto>. It returns 0 on success and returns the errno on failure.

INET Datagram Sockets
=====================

The following two programs illustrates how to use sockinetbuf class for datagram connection in INET domain. tdinread.cc also shows how to use isockinet class and tdinwrite.cc shows how to use osockinet class.

tdinread.cc
-----------

     // reads data sent by tdinwrite.cc
     #include <sockinet.h>

     int main(int ac, char** av)
     {
             isockinet  is (sockbuf::sock_dgram);
             is->bind();

             cout << "localhost = " << so.localhost() << endl
                  << "localport = " << so.localport() << endl;

             char         buf[256];
             int          n;

             is >> n;
             cout << av[0] << ": ";
             while(n--) {
                     is >> buf;
                     cout << buf << ' ';
             }
             cout << endl;

             return 0;
     }

tdinwrite.cc
------------

     // sends data to tdinread.cc
     #include <sockinetbuf.h>
     #include <stdlib.h>

     int main(int ac, char** av)
     {
             if (ac < 3) {
                     cerr << "USAGE: " << av[0] << " thostname port-number "
                          << "data ... " << endl;
                     return 1;
             }

             osockinet os (sockbuf::sock_dgram);
             os->connect (av[1], atoi(av[2]));

             cout << "local: " << so.localport() << ' '
                               << so.localhost() << endl
                  << "peer:  " << so.peerport() << ' '
                               << so.peerhost() << endl;

             os << ac-3; av += 3;
             while(*av) os << *av++ << ' ';
             os << endl;

             return 0;
     }

INET Stream Sockets
===================

The following two programs illustrates the use of sockinetbuf class for stream connection in INET domain. It also shows how to use iosockinet class.

tsinread.cc
-----------

     // receives strings from tsinwrite.cc and sends the strlen
     // of each string back to tsinwrite.cc
     #include        <sockinet.h>

     int main()
     {
             sockinetbuf     si(sockbuf::sock_stream);
             si.bind();

             cout << si.localhost() << ' ' << si.localport() << endl;
             si.listen();

             iosockinet s = si.accept();
             char          buf[1024];

             while (s >> buf) {
                     cout << buf << ' ';
                     s << ::strlen(buf) << endl;
             }
             cout << endl;

             return 0;
     }

tsinwrite.cc
------------

     // sends strings to tsinread.cc and gets back their length
     // usage: tsinwrite hostname portno
     //        see the output of tsinread for what hostname and portno to use

     #include        <sockinet.h>
     #include        <stdlib.h>

     int main(int ac, char** av)
     {
             iosockinet sio (sockbuf::sock_stream);
             sio->connect (av[1], atoi (av[2]));

             sio << "Hello! This is a test\n" << flush;

             // terminate the while loop in tsinread.cc
             si.shutdown(sockbuf::shut_write);

             int len;
             while (s >> len) cout << len << ' ';
             cout << endl;

             return 0;
     }

sockinetaddr Class
******************

Class sockinetaddr is derived from sockAddr declared in <sockstream.h> and from sockaddr_in declared in <netinet/in.h>. Always use a sockinetaddr object for an address with INET domain of sockets. See Connection Establishment.

In what follows,

  - adr denotes an INET address in host byte order and is of type unsigned long

  - serv denotes a service like "nntp" and is of type char*

  - proto denotes a protocol like "tcp" and is of type char*

  - thostname is of type char* and denotes the name of a host like "kelvin.acc.virginia.edu" or "128.143.24.31".

  - portno denotes a port in host byte order and is of type int

sockinetaddr sina
     Constructs a sockinetaddr object sina with default address INADDR_ANY and default port number 0.

sockinetaddr sina(adr, portno)
     Constructs a sockinetaddr object sina setting inet address to adr and the port number to portno. portno defaults to 0.

sockinetaddr sina(adr, serv, proto)
     Constructs a sockinetaddr object sina setting inet address to adr and the port number corresponding to the service serv and the protocol proto. The protocol defaults to "tcp".

sockinetaddr sina(thostname, portno)
     Constructs a sockinetaddr object sina setting inet address to the address of thostname and the port number to portno. portno defaults to 0.

sockinetaddr sina(thostname, serv, proto)
     Constructs a sockinetaddr object sina setting inet address to the address of thostname and the port number corresponding to the service serv and the protocol proto. The protocol defaults to "tcp".

void* a = sina
     returns the address of the sockaddr_in part of sockinetaddr object sina as void*.

int sz = sina.size()
     returns the sizeof sockaddr_in part of sockinetaddr object sina.

int af = sina.family()
     returns sockinetbuf::af_inet if all is well.

int pn = sina.getport()
     returns the port number of the sockinetaddr object sina in host byte order.

const char* hn = getthostname()
     returns the host name of the sockinetaddr object sina.

sockunixbuf Class
*****************

sockunixbuf class is derived from sockbuf class declared in <sockstream.h> and hence, inherits most of the public member functions of sockbuf. See sockbuf Class, for more information on sockbuf.

Methods
=======

In what follows,

  - ty denotes the socket type and is of type sockbuf::type

  - proto denotes the protocol number and is of type int

  - su is a sockbuf and must be in UNIX domain

  - path is the UNIX path name like "/tmp/unix_socket"

sockunixbuf uns(ty, proto)
     Constructs a sockunixbuf object uns with ty as its type and proto as its protocol number. proto defaults to 0.

sockunixbuf uns = su
     Constructs a sockunixbuf object uns which uses the same socket as is used by su.

uns = su
     sockunixbuf object uns closes its current socket if no other sockbuf is referring to it and uses the socket that sockbuf object su is using.

uns.open(ty, proto)
     create a sockunixbuf object with ty as its type and proto as its protocol and assign the sockunixbuf object so created to *this. It returns this. proto defaults to 0.

uns.bind(path)
     binds uns to the UNIX pathname path. It returns 0 on success and returns the errno on failure.

uns.connect(path)
     connects uns to the UNIX pathname path. It returns 0 on success and returns the errno on failure.

UNIX Datagram Sockets
=====================

The following two programs illustrates how to use sockunixbuf class for datagram connection in UNIX domain. tdunread.cc also shows how to use isockunix class and tdunwrite.cc shows how to use osockunix class.

tdunread.cc
-----------

     // reads data sent by tdunwrite.cc
     #include <sockunix.h>
     #include <unistd.h>
     #include <errno.h>

     int main(int ac, char** av)
     {
             if (ac != 2) {
                     cerr << "USAGE: " << av[0] << " socket_path_name\n";
                     return 1;
             }

             // isockunix builds the sockunixbuf object
             isockunix 	su (sockbuf::sock_dgram);

             su->bind(av[1]);

             cout << "Socket name = " << av[1] << endl;

             if (chmod(av[1], 0777) == -1) {
                     perror("chmod");
                     return 1;
             }

             char buf[1024];
             int i;
             su >> i;
             cout << av[0] << ": " << i << " strings: ";
             while (i--) {
                     su >> buf;
                     cout  << buf << ' ';
             }
             cout << endl;

             unlink(av[1]);
             return 0;
     }

tdunwrite.cc
------------

     // sends data to tdunread.cc
     #include <sockunix.h>

     int main(int ac, char** av)
     {
             if (ac < 2) {
                     cerr << "USAGE: " << av[0]
                          << " socket_path_name data...\n";
                     return 1;
             }

             osockunix	su (sockbuf::sock_dgram);

     	su->connect (av[1]);

             su << ac << ' ';
             while (*av) { su << av[i] << ' '; av++; }
             su << endl;

             return 0;
     }

UNIX Stream Sockets
===================

The following two programs illustrates how to use sockunixbuf class for stream connection in UNIX domain. It also shows how to use iosockunix class.

tsunread.cc
-----------

     // exchanges char strings with tsunwrite.cc
     #include <sockunix.h>
     #include <unistd.h>
     #include <errno.h>

     int main(int ac, char** av)
     {
             if (ac != 2) {
                     cerr << "USAGE: " << av[0] << " socket_path_name\n";
                     return 1;
             }

             sockunixbuf  su(sockbuf::sock_stream);
             su.bind(av [1]);

             cout << "Socket name = " << av[1] << endl;

             if (chmod(av[1], 0777) == -1) {
                     perror("chmod");
                     return 1;
             }

             su.listen(3);

             iosockunix ioput = su.accept ();
             char       buf[1024];

             ioput << av[0] << ' ' << av[1] << endl;
             while ( ioput >> buf ) cout << av[0] << ": " << buf << endl;
             unlink(av[1]);
             return 0;
     }

tsunwrite.cc
------------

     // exchanges char strings with tsunread.cc
     #include <sockunix.h>

     int main(int ac, char** av)
     {
             if (ac < 2) {
                     cerr << "USAGE: " << av[0]
                          << " socket_path_name data...\n";
                     return 1;
             }

             iosockunix oput (sockbuf::sock_stream);
             oput->connect (av [1]);

             char buf[128];

             oput >> buf;
             cout << buf << ' ';
             oput >> buf;
             cout << buf << endl;

             while (*av) oput << *av++ << ' ';
             oput << endl;

             return 0;
     }

sockunixaddr Class
******************

Class sockunixaddr is derived from class sockAddr declared in <sockstream.h> and from struct sockaddr_un declared in <sys/un.h>. Always use sockunixaddr objects for addresses with UNIX domain of sockets. See Connection Establishment.

In what follows,

  - path is the UNIX path name like "/tmp/unix_socket"

sockunixaddr suna(path)
     Constructs a sockunixaddr object suna with path as the UNIX path name.

void* a = suna
     returns the address of the sockaddr_un part of sockunixaddr object suna as void*.

int sz = suna.size()
     returns the sizeof sockaddr_un part of sockunixaddr object suna.

int af = suna.family()
     returns sockunixbuf::af_unix if all is well.

sockstream Classes
******************

sockstream classes are designed in such a way that they provide the same interface as their stream counterparts do. We have isockstream derived from istream and osockstream derived from ostream. We also have iosockstream which is derived from iostream.

Each domain also has its own set of stream classes. For example, unix domain has isockunix, osockunix, and iosockunix derived from isockstream, osockstream, and iosockstream respectively. Similarly, inet domain has isockinet, osockinet, and iosockinet.

iosockstreams
=============

isockstream Class
-----------------

Since isockstream is publicly derived from istream, most of the public functions of istream are also available in isockstream.

isockstream redefines rdbuf() defined in its virtual base class ios. Since, ios::rdbuf() is not virtual, care must be taken to call the correct rdbuf() through a reference or a pointer to an object of class isockstream.

In what follows,

  - sb is a sockbuf object

  - sbp is a pointer to a sockbuf object

isockstream is(sb)
     Constructs an isockstream object is with sb as its sockbuf.

isockstream is(sbp)
     Constructs an isockstream object is with *sbp as its sockbuf.

sbp = is.rdbuf()
     returns a pointer to the sockbuf of the isockstream object is.

isockstream::operator -> ()
     returns a pointer to the isockstream's sockbuf so that the user can use isockstream object as a sockbuf object.

              is->connect (sa); // same as is.rdbuf()->connect (sa);

osockstream Class
-----------------

Since osockstream is publicly derived from ostream, most of the public functions of ostream are also available in osockstream.

osockstream redefines rdbuf() defined in its virtual base class ios. Since, ios::rdbuf() is not virtual, care must be taken to call the correct rdbuf() through a reference or a pointer to an object of class osockstream.

In what follows,

  - sb is a sockbuf object

  - sbp is a pointer to a sockbuf object

osockstream os(sb)
     Constructs an osockstream object os with sb as its sockbuf.

osockstream os(sbp)
     Constructs an osockstream object os with *sbp as its sockbuf.

sbp = os.rdbuf()
     returns a pointer to the sockbuf of the osockstream object os.

osockstream::operator -> ()
     returns a pointer to the osockstream's sockbuf so that the user can use osockstream object as a sockbuf object.

              os->connect (sa); // same as os.rdbuf()->connect (sa);

iosockstream Class
------------------

Since iosockstream is publicly derived from iostream, most of the public functions of iostream are also available in iosockstream.

iosockstream redefines rdbuf() defined in its virtual base class ios. Since, ios::rdbuf() is not virtual, care must be taken to call the correct rdbuf() through a reference or a pointer to an object of class iosockstream.

In what follows,

  - sb is a sockbuf object

  - sbp is a pointer to a sockbuf object

iosockstream io(sb)
     Constructs an iosockstream object io with sb as its sockbuf.

iosockstream io(sbp)
     Constructs an iosockstream object io with *sbp as its sockbuf.

sbp = io.rdbuf()
     returns a pointer to the sockbuf of the iosockstream object io.

iosockstream::operator -> ()
     returns a pointer to the iosockstream's sockbuf so that the user can use iosockstream object as a sockbuf object.

              io->connect (sa); // same as io.rdbuf()->connect (sa);

iosockinet Stream Classes
=========================

We discus only isockinet class here. osockinet and iosockinet are similar and are left out. However, they are covered in the examples that follow.

isockinet
---------

isockinet is used to handle interprocess communication in INET domain. It is derived from isockstream class and it uses a sockinetbuf as its stream buffer. See iosockstream, for more details on isockstream. See sockinetbuf Class, for information on sockinetbuf.

In what follows,

  - ty is a sockbuf::type and must be one of sockbuf::sock_stream, sockbuf::sock_dgram, sockbuf::sock_raw, sockbuf::sock_rdm, and sockbuf::sock_seqpacket

  - proto denotes the protocol number and is of type int

  - sb is a sockbuf object and must be in INET domain

  - sinp is a pointer to an object of sockinetbuf

isockinet is (ty, proto)
     constructs an isockinet object is whose sockinetbuf buffer is of the type ty and has the protocol number proto. The default protocol number is 0.

isockinet is (sb)
     constructs a isockinet object is whose sockinetbuf is sb. sb must be in INET domain.

isockinet is (sinp)
     constructs a isockinet object is whose sockinetbuf is sinp.

sinp = is.rdbuf ()
     returns a pointer to the sockinetbuf of isockinet object is.

isockinet::operator ->
     returns sockinetbuf of sockinet so that the sockinet object acts as a smart pointer to sockinetbuf.

                  is->localhost (); // same as is.rdbuf ()->localhost ();

iosockinet examples
-------------------

The first pair of examples demonstrates datagram socket connections in the INET domain. First, tdinread prints its local host and local port on stdout and waits for input in the connection. tdinwrite is started with the local host and local port of tdinread as arguments. It sends the string "How do ye do!" to tdinread which in turn reads the string and prints on its stdout.

     // tdinread.cc
     #include <sockinet.h>

     int main ()
     {
         char buf[256];
         isockinet is (sockbuf::sock_dgram);
         is->bind ();

         cout << is->localhost() << ' ' << is->localport() << endl;

         is.getline (buf);
         cout << buf << endl;

         return 0;
     }

     // tdinwrite.cc--tdinwrite hostname portno
     #include <sockinet.h>
     #include <stdlib.h>

     int main (int ac, char** av)
     {
         osockinet os (sockbuf::sock_dgram);
         os->connect (av[1], atoi(av[2]));
         os << "How do ye do!" << endl;
         return 0;
     }

The next example communicates with an nntp server through a sockbuf::sock_stream socket connection in INET domain. After establishing a connection to the nntp server, it sends a "HELP" command and gets back the HELP message before sending the "QUIT" command.

     // tnntp.cc
     #include <sockinet.h>

     int main ()
     {
         char  buf[1024];
         iosockinet io (sockbuf::sock_stream);
         io->connect ("murdoch.acc.virginia.edu", "nntp", "tcp");
         io.getline (buf, 1024); cout << buf << endl;
         io << "HELP\r\n" << flush;
         io.getline (buf, 1024); cout << buf << endl;
         while (io.getline (buf, 1024))
             if (buf[0] == '.' && buf[1] == '\r') break;
             else if (buf[0] == '.' && buf[1] == '.') cout << buf+1 << endl;
             else cout << buf << endl;
         io << "QUIT\r\n" << flush;
         io.getline (buf, 1024); cout << buf << endl;
         return 0;
     }

iosockunix Classes
==================

We discuss only isockunix here. osockunix and iosockunix are similar.

isockunix class
---------------

isockunix is used to handle interprocess communication in UNIX domain. It is derived from isockstream class and it uses a sockunixbuf as its stream buffer. See iosockstream, for more details on isockstream. See sockunixbuf Class, for information on sockunixbuf.

In what follows,

  - ty is a sockbuf::type and must be one of sockbuf::sock_stream, sockbuf::sock_dgram, sockbuf::sock_raw, sockbuf::sock_rdm, and sockbuf::sock_seqpacket

  - proto denotes the protocol number and is of type int

  - sb is a sockbuf object and must be in UNIX domain

  - sinp is a pointer to an object of sockunixbuf

isockunix is (ty, proto)
     constructs an isockunix object is whose sockunixbuf buffer is of the type ty and has the protocol number proto. The default protocol number is 0.

isockunix is (sb)
     constructs a isockunix object is whose sockunixbuf is sb. sb must be in UNIX domain.

isockunix is (sinp)
     constructs a isockunix object is whose sockunixbuf is sinp.

sinp = is.rdbuf ()
     returns a pointer to the sockunixbuf of isockunix object is.

isockunix::operator ->
     returns sockunixbuf of sockunix so that the sockunix object acts as a smart pointer to sockunixbuf.

                  is->localhost (); // same as is.rdbuf ()->localhost ();

iosockunix examples
-------------------

tsunread listens for connections. When tsunwrite requests connection, tsunread accepts it and waits for input. tsunwrite sends the string "Hello!!!" to tsunread. tsunread reads the string sent by tsunwrite and prints on its stdout.

     // tsunread.cc
     #include <sockunix.h>
     #include <unistd.h>

     int main ()
     {
         sockunixbuf sunb (sockbuf::sock_stream);
         sunb.bind ("/tmp/socket+-");
         sunb.listen (2);
         isockunix is = sunb.accept ();
         char buf[32];
         is >> buf; cout << buf << endl;
         unlink ("/tmp/socket+-");
         return 0;
     }

     // tsunwrite.cc
     #include <sockunix.h>
     int main ()
     {
         osockunix os (sockbuf::sock_stream);
         os->connect ("/tmp/socket++");
         os << "Hello!!!\n" << flush;
         return 0;
     }

pipestream Classes
******************

pipestream stream classes provide the services of the UNIX system calls pipe and socketpair and the C library function popen. ipipestream, opipestream, and iopipestream are obtained by simply deriving from isockstream, osockstream and iosockstream respectively. See sockstream Classes for details.

In what follows,

  - ip is an ipipestream object

  - op is an opipestream object

  - iop is an iopipestream object

  - cmd is a char* denoting an executable like "wc"

  - ty is of type sockbuf::type indicating the type of the connection

  - proto is an int denoting a protocol number

ipipestream ip(cmd)
     construct an ipipestream object ip such that the output of the command cmd is available as input through ip.

opipestream op(cmd)
     construct an opipestream object op such that the input for the command cmd can be send through op.

iopipestream iop(cmd)
     construct an iopipestream object iop such that the input and the output to the command cmd can be sent and received through iop.

iopipestream iop(ty, proto)
     construct a iopipestream object iop whose socket is a socketpair of type ty with protocol number proto. ty defaults to sockbuf::sock_stream and proto defaults to 0. Object iop can be used either as a pipe or as a socketpair.

iop.pid ()
     return the process id of the child if the current process is the parent or return 0. If the process has not forked yet, return -1.

iopipestream::fork ()
     fork() is a static function of class iopipestream. fork() forks the current process and appropriately sets the cpid field of the iopipestream objects that have not forked yet.

pipestream as pipe
==================

pipe is used to communicate between parent and child processes in the UNIX domain.

The following example illustrates how to use iopipestream class as a pipe. The parent sends the string "I am the parent" to the child and receives the string "I am the child" from child. The child, in turn, receives the string "I am the parent" from parent and sends the string "I am the child" to the parent. Note the same iopipestream object is used for input and output in each process.

     #include <pipestream.h>

     int main()
     {
             iopipestream p;
             if ( p.fork() ) {
                     char buf[128];
                     p << "I am the parent\n" << flush;
                     cout << "parent: ";
                     while(p >> buf)
                             cout << buf << ' ';
                     cout << endl;
             }else {
                     char buf[128];
                     p.getline(buf, 127);
                     cout << "child: " << buf << endl;
                     p << "I am the child\n" << flush;
             }
             return 0;
     }

pipestream as socketpair
========================

Like pipes, socketpairs also allow communication between parent and child processes. But socketpairs are more flexible than pipes in the sense that they let the users choose the socket type and protocol.

The following example illustrates the use of iopipestream class as a socketpair whose type is sockbuf::sock_dgram. The parent sends the string "I am the parent" to the child and receives the string "I am the child" from the child. The child, in turn, receives and sends the strings "I am the parent" and "I am the child" respectively from and to the parent. Note in the following example that the same iopipestream object is used for both the input and the output in each process.

     #include <pipestream.h>

     int main()
     {
             iopipestream p(sockbuf::sock_dgram);
             if ( iopipestream::fork() ) {
                     char buf[128];
                     p << "I am the parent\n" << flush;
                     p.getline(buf, 127);
                     cout << "parent: " << buf << endl;
             }else {
                     char buf[128];
                     p.getline(buf, 127);
                     cout << "child: " << buf << endl;
                     p << "I am the child\n" << flush;
             }
             return 0;
     }

pipestream as popen
===================

popen is used to call an executable and send inputs and outputs to that executable. For example, the following example executes "/bin/date", gets its output, and prints it to stdout.

     #include <pipestream.h>

     int main ()
     {
         char buf[128];
         ipipestream p("/bin/date");

         p.getline (buf, 127);
         cout << buf << endl;
         return 0;
     }

Here is an example that prints "Hello World!!" on stdout. It uses opipestream object.

     #include <pipestream.h>

     int main ()
     {
         opipestream p("/bin/cat");
         p << "Hello World!!\n" << endl;
         return 0;
     }

The following example illustrates the use of iopipestream for both input and output.

     #include <pipestream.h>

     int main()
     {
             char buf[128];
             iopipestream p("lpc");
             p << "help\nquit\n" << flush;
             while ( p.getline(buf, 127) ) cout << buf << endl;
             return 0;
     }

Fork Class
**********

You can effectively use the Fork wrapper class to create child processes. You can use the Fork class, instead of directly using the system call fork (), if you desire the following:

  * Avoid zombie processes

  * Optionally kill child processes when the parent process terminates.

  * Want to know the reason for abnormal termination of child processes.

In what follows,

  - killchild is an integer.

  - reason is an integer.

  - signo is a valid signal.

  - f is a Fork object.

Fork f(killchild, reason)
     constructs a Fork object f. The constructor creates a child process. When the parent process terminates, it will kill the child process if killchild is not 0. Otherwise, the parent process will wait until all its child processes die. If reason is not 0, then it gives the reason for a child process's death on the stderr.

f.is_child ()
     returns 1 if the current process is the child process following the fork in constructing the Fork object f. Otherwise, return 0.

f.is_parent ()
     returns 1 if the current process is the parent process following the fork in constructing the Fork object f. Otherwise, return 0.

f.process_id ()
     returns the process id of the child process, if the current process is the parent process. Returns 0, if the current process is the child process. Returns -1, if fork failed.

Fork::suicide_signal (signo)
     is a static function. Upon the reciept of the signal signo, the current process will kill all its child processes created through Fork::Fork(int, int) irrespective of the value of the killchild flag used in the construction of the Fork objects. signo defaults to SIGTERM signal.

Fork Example
============

The following example illustrates the use of the Fork class to create child processes. First, we set up SIGTERM signal handler to kill all the child processes, by callling Fork::suicide_signal (). Second, we create several child and grandchild processes.

You can kill the top most parent process and all its children by sending a SIGTERM signal to the top most parent process.

     // tfork.C
     #include <iostream.h>
     #include <Fork.h>

     static void print (char* name, pid_t child)
     {
       if (child)
         cerr << "Parent " << getppid () << "; "
           << name << ' ' << getpid () << "; Child " << child << ";\n";
     }

     int main (int ac, char** av)
     {
       Fork::suicide_signal (SIGTERM);

       Fork a(0, 1);

       print ("a", a.process_id ());

       if (a.is_child ()) {
         sleep (3000);
       } else if (a.is_parent ()) {
         Fork b (1, 1);
         print ("b", b.process_id ());
         {
           Fork c (b.is_parent (), 1);
           if (b.is_child ())
     	print ("cchild", c.process_id ());
           else
     	print ("cparent", c.process_id ());
           if (c.is_child ()) {
     	sleep (3000);
     	return 0;
           }
         }
         if (b.is_child ()) {
           sleep (120);
           return 0x8;
         }
       }

       return 0;
     }

Class protocol
**************

protocol class is the base class for all the other application protocol classes like echo, smtp, etc. protocol is derived publicly from iosockstream. It uses protocolbuf class, a nested class of protocol,  as its stream buffer.

The protocol class is an abstract class and thus, you cannot instantiate an object of protocol.

Class protocol::protocolbuf
===========================

protocol::protocolbuf class is publicly derived from sockinetbuf and thus, it inherits all the latter's public member functions. In addition, the protocolbuf defines the following member functions.

In what follows,

  - p is an object of a non-abstract class derived from protocolbuf.

  - pname is the transport protocol name which is either protocol::tcp or protocol::udp.

  - addr is an unsigned long denoting the valid address of a machine in host byte order.

  - host is a char string denoting the name of a machine like "kelvin.seas.virginia.edu".

  - portno is an int and denotes the port number in host byte order.

protocol::protocolbuf::protocolbuf (pname)
     constructs protocolbuf object with the transport protocol set to pname.

p.protocol_name ()
     returns the name of the transport protocol of p as a char string.

p.rfc_name ()
     returns the name of the application protocol name of p as a char string. protocolbuf::rfc_name () is a pure virtual function; thus, any class derived from protocol::protocolbuf should provide a definition for protocolbuf::rfc_name ().

p.rfc_doc ()
     returns the RFC document name of the application protocol of p as a char string. protocolbuf::rfc_doc () is a pure virtual function; thus, any class derived from protocol::protocolbuf should provide a definition for protocolbuf::rfc_doc ().

p.serve_clients (portno)
     converts p into a server. Use the port specified in /etc/services for the application if portno < 0. Use a default port if 0 <= portno <= 1024. Otherwise, use portno as the port to accept clients requesting service. protocolbuf::serve_clients() is pure virtual function; thus, any class derived from protocol::protocolbuf should provide a definition for protocolbuf::serve_clients().

     Please do not change the meaning of portno when you derive your own class.

p.bind ()
     same as p.serve_clients (-1). It returns 0 on success and returns the errno on failure.

p.connect ()
     connects to the local host's server for the application. p acts as the client. It returns 0 on success and returns the errno on failure.

p.connect (addr)
     connects to the server running at the machine with address, addr. p acts as the client. It returns 0 on success and returns the errno on failure.

p.connect (host)
     connects to the server running at the machine, host. p acts as the client. It returns 0 on success and returns the errno on failure.

p.connect (host, portno)
     connects to the server servicing clients at portno at the machine, host. Unlike this connect call, the other variants of connect uses the port specified in the /etc/services file. It returns 0 on success and returns the errno on failure.

Echo Class
**********

The echo class implements RFC 862. An echo object, as a client, will get back what ever data it sends to an echo server. Similarly, an echo object, as a server, will echo back the data it receives from its client.

The echo class is derived from protocol class, and uses echo::echobuf as its stream buffer. echo::echobuf is in turn is derived from protocol::protcolbuf.

In what follows,

  - e is a echo object.

  - pname is a transport protocol name and must be either protocol::tcp or protocol::udp.

echo e (pname)
     constructs the echo object, e with pname as its transport protocol name.

echo::operator -> ()
     an echo object is a smart pointer for the underlying echobuf.

tsecho.C
--------

     // echo server. Serves clients at port 4000.
     #include <echo.h>
     #include <stdlib.h>

     int main ()
     {
       echo server (protocol::tcp);
       server->serve_clients (4000);
       return 1;
     }

tcecho.C
--------

     // echo client. Sends "mary had a litte lamb" to the server
     #include <echo.h>
     #include <stdlib.h>

     int main ()
     {
       echo e(protocol::tcp);

       e->connect ("kelvin.seas.virginia.edu", 4000);

       cout << e->rfc_name () << ' ' << e->rfc_doc () << endl;

       e << "mary had a little lamb\r\n" << flush;

       char buf [256];
       e.getline (buf, 255);

       cout << "got back: " << buf << endl;
       return 0;
     }

SMTP Class
**********

The smtp class, which is derived from protocol class, implements RFC 821. It can be used only as a client. Server function is not yet implemented.

smtp uses smtp::smtpbuf as its underlying stream buffer. Also, like the protocol class, smtp is a smart pointer class for it is smtp::smtpbuf.

In what follows,

  - s is an smtp object.

  - sb is an smtp::smtpbuf object.

  - io is a pointer to an ostream.

  - buf is a char buffer of length buflen.

  - str, str0, str1, ... are all char strings.

smtp s (io)
     constructs an smtp client, s. Any response the client gets from the server is sent to the ostream, io.

sb.get_response ()
     gets the server response and sends it to io of the smtpbuf.

sb.send_cmd (str0, str1, str2)
     concatenates strings str0, str1, and str2 and sends the concatenated string to the server before getting its response.

sb.send_buf (buf, buflen)
     sends the contents of the buf to the server.

sb.helo ()

sb.help (str)

sb.quit ()

sb.turn ()

sb.rset ()

sb.noop ()

sb.data ()

sb.vrfy (str)

sb.expn (str)
     implements the respective SMTP commands. See RFC 821 for the meaning of each.

sb.mail (str)
     sends the mail command to the server. str is the the reverse path or the FROM address.

sb.rcpt (str)
     sends the recipient command to the server. str is the forward path or the TO address.

sb.data (buf, buflen)
     sends the contents of the buffer, buf as the mail data to the recipient previously established through smtpbuf::rcpt() calls.

sb.data (filename)
     sends the contents of the file, filename as the mail data to the recipient previously established through smtpbuf::rcpt() calls.

tcsmtp.C
--------

     // smtp client.
     // The president sends a message to gs4t@virginia.edu.
     #include <smtp.h>
     #include <stdio.h>
     #include <pwd.h>
     #include <unistd.h>

     int main ()
     {
       smtp client (&cout);

       // establish connection
       client->connect ("fulton.seas.virginia.edu");
       client->helo ();

       // get help
       client->help ();

       // setup the FROM address
       client->mail ("president@whitehouse.gov");

       // setup the TO address
       client->rcpt ("gs4t@virginia.edu");

       // send the message
       client->data ();
       client << "Hi Sekar, I appoint you as the director of NASA\r\n" << flush;
       client << "    -Bill, Hill, and Chel\r\n" << flush;
       cout << client; // get the server response.

       // finally quit
       client->quit ();

       return 0;
     }

Error Handling
**************

Each class in the Socket++ library uses error(const char*) member function to report any errors that may occur during a system call. It first calls perror() to report the error message for the errno set by the system call. It then calls sock_error (const char* nm, const char* errmsg) where nm is the name of the class.

The sock_error() function simply prints the nm and the errmsg on the STDERR.

Pitfalls
********

Deadlocks in datagram sockets are the most common mistakes that novices make. To alleviate the problem, sockbuf class provides timeout facilities that can be used effectively to avoid deadlocks.

Consider the following simple tsmtp example which sends the HELP command to a smtp server and gets back the help message. Suppose it does not know the size of the help message nor the format of the message. In such cases, the timeout facilities of sockbuf class provides the required tools.

The example terminates the help message reception if the there is no input activity from the smtp server for 10 seconds.

tsmtp.cc
--------

     #include <sockinet.h>

     int main()
     {
     	iosockinet   sio(sockbuf::sock_stream);

     	sio->connect("kelvin.seas.virginia.edu", "smtp", "tcp");

     	char buf[512];
     	sio.getline(buf, 511); cout << buf << endl;
     	sio << "HELO kelvin\n" << flush;
     	sio.getline(buf, 511); cout << buf << endl;

     	sio << "HELP\n" << flush;

             // set the receive timeout to 10 seconds
             int tmo = sio->recvtimeout(10);

     	while ( sio.getline(buf, 511) ) cout << buf << endl;
     		// if the above while loop terminated due to timeout
     		// clear the state of sio.
     	if ( !sio->is_eof() )
     		sio.clear();
     	sio->recvtimeout(tmo); // reset the receive timeout time

     	sio << "QUIT\n" << flush;
     	sio.getline(buf, 511); cout << buf << endl;
             return 0;
     }