Example NetBIOS server code

1   /*
2    * Example NetBIOS server
3    */

4   #include <stdio.h>
5   #include <signal.h>
6   #include <stropts.h>
7   #include <xti.h>
8   #include <fcntl.h>
9   #include <sys/nb/nbtpi.h>

10  #define SRV_NAME  "NB-XTI-DEMO-SERV"
11  #define RFCNBPATH "/dev/nbcots"
12  #define NBEPATH   "/dev/netbeui"
13  #define DISCONNECT -1

14  extern int t_errno;
15  void run_server(int);
16  int conn_fd;
17  char *netpath = RFCNBPATH;

18  main(int argc, char *argv[])
19  {
20      int listen_fd;
21      struct t_bind *bind;
22      struct t_call *call;
23      struct nbaddr srv_addr;
24      struct nbaddr client_addr;

25      /* ensure child processes do not become zombies */

26      signal(SIGCHLD, SIG_IGN);

27      if ((listen_fd =
28                 t_open(netpath, O_RDWR, (struct t_info *) NULL)) < 0) {
29          t_error("t_open failed for listen_fd");
30          exit(1);
31      }

32      if ((bind = (struct t_bind *)t_alloc(listen_fd, T_BIND, T_ADDR))
33                                                              == NULL) {
34          t_error("t_alloc of t_bind structure failed");
35          exit(2);
36      }

37      bind->qlen = 5;
38      bind->addr.len = sizeof(srv_addr);
39      bind->addr.buf = (char *)&srv_addr;

40      srv_addr.nb_type = NB_UNIQUE;
41      memcpy(srv_addr.nb_name, SRV_NAME, NB_NAMELEN);

42      if (t_bind(listen_fd, bind, bind) < 0) {
43          t_error("t_bind failed for listen_fd");
44          exit(3);
45      }

46      if (memcmp(srv_addr.nb_name, SRV_NAME, NB_NAMELEN) != 0) {
47          fprintf(stderr, "t_bind bound wrong address\n");
48          exit(4);
49      }

50      if ((call = (struct t_call *)t_alloc(listen_fd, T_CALL, T_ADDR))
51                                                            == NULL) {
52          t_error("t_alloc failed");
53          exit(5);
54      }
55      call->addr.len = sizeof(srv_addr);
56      call->addr.buf = (char *)&client_addr;

57      while (1) {
58          if (t_listen(listen_fd, call) < 0) {
59              t_error("t_listen failed for listen_fd");
60              exit(6);
61          }
62          if ((conn_fd = accept_call(listen_fd, call)) != DISCONNECT)
63              run_server(listen_fd);
64      }
65  }

66  int
67  accept_call(int listen_fd, struct t_call *call)
68  {
69      int resfd;

70      if ((resfd = t_open(netpath, O_RDWR, (struct t_info *) NULL))
71                                                               < 0) {
72          t_error("t_open for responding fd failed");
73          exit(7);
74      }

75      if (t_bind(resfd, (struct t_bind *) NULL,
76                        (struct t_bind *) NULL) < 0) {
77          t_error("t_bind for responding fd failed");
78          exit(8);
79      }

80      if (t_accept(listen_fd, resfd, call) < 0) {
81          if (t_errno == TLOOK) {
82              if (t_rcvdis(listen_fd, (struct t_discon *) NULL) < 0) {
83                  t_error("t_rcvdis failed for listen_fd");
84                  exit(9);
85              }
86              if (t_close(resfd) < 0) {
87                  t_error("t_close failed for responding fd");
88                  exit(10);
89              }
90              return(DISCONNECT);
91          }
92          t_error("t_accept failed");
93          exit(11);
94      }

95      return(resfd);
96  }

97  connrelease()
98  {
99      exit(0);
100 }

101 void
102 run_server(int listen_fd)
103 {
104     int nbytes;
105     FILE *logfp;

106     struct {
107         unsigned short  length;
108         char            buf[1024];
109     } msg;

110     switch (fork()) {

111     case -1:
112         perror("fork failed");
113         exit(12);

114     default:                   /* parent */
115         /* close conn_fd and go up to listen again */
116         if (t_close(conn_fd) < 0) {
117             t_error("t_close failed for conn_fd");
118             exit(13);
119         }
120         return;

121     case 0:                    /* child */
122         /* close listen_fd and do service */
123         if (t_close(listen_fd) < 0) {
124             t_error("t_close failed for listen_fd");
125             exit(14);
126         }
127         if ((logfp = fopen("logfile", "r")) == NULL) {
128             perror("cannot open logfile");
129             exit(15);
130         }

131         signal(SIGPOLL, connrelease);

132         if (ioctl(conn_fd, I_SETSIG, S_INPUT) < 0) {
133             perror("ioctl I_SETSIG failed");
134             exit(16);
135         }

136         if (t_look(conn_fd) != 0) {
137             fprintf(stderr, "t_look returned unexpected event");
138             exit(17);
139         }

140         while ((nbytes = fread(msg.buf, 1, 1024, logfp)) > 0) {
141             msg.length = nbytes;
142             if (t_snd(conn_fd, &msg, nbytes +
143                                 sizeof(msg.length), 0) < 0) {
144                 t_error("t_snd failed");
145                 exit(18);
146             }
147         }

148         msg.length = 0;

149     if (t_snd(conn_fd, &msg, 2, 0) < 0) {
150         t_error("can't send 0 bytes");
151         exit(19);
152     }

153     pause();   /* until disconnect indication arrives */
154     }
155 }

line 16

declares the variable that will identify the transport endpoint to be used by the child process (to be spawned later) when it communicates with the client. The variable happens to be global in this example to avoid passing it around as a parameter. It is referenced both by main and run_server.

line 17

assigns the device name of the transport to be used. Use the value NBEPATH instead of RFCNBPATH to access NetBEUI.

line 20

declares the variable to be used by the parent process to identify the transport endpoint that the parent process will use to listen for incoming connection requests.

lines 27-28

open a connection-oriented full-duplex transport endpoint in non-blocking mode. The third argument is set to NULL in this example, indicating that the server does not care to examine any of the transport provider's attributes.

lines 32-33

allocate the struct t_bind data structure to be used in the call to t_bind.

line 37

sets the depth of the queue for incoming connection requests to five.

line 39

points addr.buf to the NetBIOS name structure.

lines 40-41

assign the server's well-known NetBIOS name. The name is termed ``well-known'' because all clients on the network are expected to know this name. The server expects to be the only one on the network with this name, so it assigns the name type a value of NB_UNIQUE.

line 42

binds the server's name and the length of the connection request queue to the transport endpoint. These are specified in the second argument (first occurrence of bind). The third argument points to the same bind data structure specified in the second argument. The transport provider will return in bind->qlen the actual value of the connection request queue length it can support, if that is less than the requested value.

lines 50-51

allocate the struct t_call data structure to be used in the call to t_listen.

lines 55-56

set up the call data structure. call->add.buf will point to the name of the client trying to connect to the server. This value will be filled in by the call to t_listen on line 58.

lines 57-65

loop forever listening for connection requests on one transport endpoint, accepting them on different transport endpoint, then spawning a child process to communicate with the client.

lines 62-63

accept the connection with the client on the new transport endpoint, conn_fd. The server parent process will continue to listen for incoming connection requests on listen_fd, while the child process spawned in run_server will respond to the client. The functions accept_call and run_server are application-level functions, not XTI functions.

lines 66-96

open a new transport endpoint, let the transport bind any valid name to it, then accept the incoming connection request on that endpoint.

line 70

opens a new transport endpoint.

line 75

lets the transport select a NetBIOS name to bind to the endpoint.

line 80

accepts on resfd the connection request received earlier on listen_fd. By accepting the connection request on a file descriptor different from the one on which the connection request was received, the server can fork a child process to handle the client request, while the (parent) server continues to listen for new clients trying to connect on the original file descriptor.

lines 81-91

respond to an asynchronous event. The server assumes the client is now trying to disconnect. The server responds by consuming the disconnect event (line 82) and shutting down the transport endpoint on which it intended to accept the connection (line 86).

An alternative is to call t_look after line 81 to determine precisely what asynchronous event has occurred. The server can then respond appropriately. See the manual page for t_look for a description of the asynchronous events returned by this function.

line 90

returns DISCONNECT to indicate that the connection request was aborted by the client.

line 95

returns the value of the transport endpoint on which the connection request has been accepted.

lines 97-100

declare the signal handler that is set in line 131. If an unexpected input message arrives at the transport endpoint, this handler will be executed. The handler simply exits, tearing down the transport endpoint the server is listening on. The exit also kills all of the child processes that are communicating with clients, thus tearing down their transport endpoints. Clients will receive the T_DISCONNECT asynchronous event at their local transport endpoint.

lines 106-109

declare the variable to hold the next chunk of data to be read from the log file and transmitted to a client.

line 110

spawns a child process to communicate with the client.

lines 114-120

close conn_fd. The parent process executes these lines because it will not be using this transport endpoint. The transport endpoint associated with conn_fd is not destroyed, however, because the child process will leave it open to communicate with the client. The parent returns to the calling function to continue to listen for connections on listen_fd.

lines 121-125

close listen_fd. The child process executes these lines because it will not be using this transport endpoint. The transport endpoint associated with listen_fd is not destroyed, however, because the parent process will leave it open to listen for the next incoming connection request from a client.

lines 127-130

open the log file for reading. The child process executes these lines.

lines 131-155

list the remaining instructions to be executed by the child process.

line 131

sets connrelease as the SIGPOLL signal handler.

line 132

establishes that a SIGPOLL signal will be generated if an unexpected message arrives at the transport endpoint denoted by conn_fd.

lines 140-147

read from the log file in 1K chunks and send both the data and the number of bytes read to the client.

lines 148-152

signal the end of the file by sending a message with the length field set to zero.

line 153

waits until the SIGPOLL signal is generated. This will occur when the client receives the message with the length field set to zero, because the client will send a disconnect indication to the server by calling t_rcvdis. The signal handler connrelease will then be called, which calls exit to terminate the process.