Linux program entry - Socket / inetd programming
Unix socket programing is basically a book name. Socket programing actually needs
When the degree of the foundation, I don't want to include the sea to the sea. If you need thorough research, you can buy this
The book is seen. Here I want to provide some simple writing on both ends of Server / Client, let you have a start.
Point, as a foundation for further research. Many more complicated content, I am not detailed here.
Ming, you can use this Xuankai, take it, and then familiarize yourself.
inetd provides a passive server service, that is, the server is started to be used, usually
exist. For example, FTP, Telnetd, POP3, IMAP, AUTH, etc. When these services are used,
No need to start. In addition, inetd converts socket into stdin / stdout, thus making network services
The design is greatly simplified, you can use Printf and FGETS to complete the complex network protocol.
Client Int Sock_connect (Char * Domain, INT Port) {INT White_sock
Struct Hostent * Site; Struct SockAddr_in Me; Site = GethostByName (Domain); if (Site == Null) Return -2; White_Sock = Socket (AF_INET, SOCK_STREAM, 0); if (White_Sock <0) Return -1; Memset & me, 0, SIZEOF (Struct SockAddr_in); Memcpy (& Me.SIN_ADDR, Site-> H_ADDR_List [0], Site-> H_LENGTH); Me.SIN_FAMILY = AF_INET; Me.SIN_PORT = HTONS (port); Return (Connect) White_sock, (struct socmeddr *) & me, sizeof (struct sockaddr)) <0)? -1: white_sock;}
The steps to connect to the servo end to the server side, first you have to find out the location of the other party, can
use:
gethostbyname ()
Next to build a socket, then use this socket to establish a connection.
Next, we use this simple Socket program to write a simple browser that reads the WWW web page (see
HTML SOURCE).
#include
GCC -O EX1 Client.c
carried out
./ex1 www.linux.org.tw server listen to a port
To build a network server, the first step is to "listen to the distance", that is, to listen.
The following is a method of building a service:
int DaemonSocket; struct sockaddr_in DaemonAddr; int BindSocket (void) {DaemonSocket = socket (AF_INET, SOCK_STREAM, 0); if (DaemonSocket == - 1) return 0; DaemonAddr.sin_family = AF_INET; DaemonAddr.sin_port = htons (DAEMON_PORT); IF (Bind (DaemonSocket, & Daemonaddr, Sizeof (Daemonaddr)) <0) {Printf ("can not bind! / n"); return 0;}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}}} NOT LISTEN! / N "); Return 0;} Return 1;} INCOMING CALL To see if there is a connection, you can use the following way:
INT INCOMING_CALL (Void) {FD_SET SOCK; STRUCT TIMEVAL TV; INT T; fd_zero (& Sock); fd_set (daemonpsignal (); if (! bindsocket ()) {Printf ("can not bind socket! / n"); exit 1);} Writelock ();} Printf ("Chess Daemon IS Up, Have Fun! / N"); Now = Time (NULL); DLOG ("--------------- ----------------------------- / n "); DLOG (" I am back!% s "" chess daemon comes To alive again./n ", asctime (constim"); do {if (incoming_call ()) {if (connectClient ()) {fd_set sock; struct TimeVal TV; int T; char BUF [128]; CHAR CC [2]; INT N; DAEMON_PRINTF ("Welcome to Chinese Chess Game Center! / N"); fd_zero (& Sock); fd_set (clientsocket, & sock); n = 0; do {tv.tv_sec = 60; tv.tv_usec = 0; T = SELECT (ClientSocket 1, & Sock, NULL, NULL, & TV); if (t <= 0 ||! Fd_isset (clientsocket, & sock); Read (ClientSocket, CC, 1 ); if (CC [0] == 13 || CC [0] == 10 || CC [0] == 0) {BUF [N] = 0; DLOG ("% S / N", BUF); IF (strncasecmp (buf, "exit", 4) == 0) {close (clientSocket); Break;} n = 0;} ELS e {buf [n] = cc [0]; n ;}} while (1);}}} while (1); return 1;}
Telnet Localhost 9901
In dealing with the Connect Client, in fact, fork or thread can be used to handle multiple connectors.
inetd protemming
Using inetd to do a network program design is a simple and stable design method, you don't need to consider
Miscellaneous socket programing. Your design work is almost completed after designing the communication agreement.
The tricks needed, only for simple text analysis skills.
Goodie inet service
First, let's write a service called Goodie.
Goodie.c #include
This program is very simple, isn't it?
Compile
GCC -O Goodie GoodIE.c
Set / etc / services and /etc/inetd.conf Add this line in / etc / services
Goodie 20001 / TCP
Its significance is that the Goodie This service is in Port 20001, TCP Agreement.
Next, add the following line in /etc/inetd.conf
Goodie Stream TCP NOWAIT ROOT / FULL_GOODIE_PATH_NAME / Goodie
The significance of each number
Service_name needs to be named in Services.
Sock_type has many kinds, mostly STREAM / DGRAM.
Proto generally uses TCP / UDP.
Flags has Wait / NOWAIT.
User is you specified that the program is to start with that user, this example is root, if
Safety is considered, you should use Nobody. In general, it is recommended that you use low privileges.
Do not open root use rights unless necessary.
Server_Path and Args, this is your location of your service and the number you want to join.
Next to restart inetd
KILLALL INETD inetd
This way we build a port 20001 Goodie Service.
Now let's check if your good can perform:
Telnet Localhost 20001
or
Telnet your_host_name 20001
Results of the
Trying 127.0.0.1 ... connect to localhost. Escape character is '^]'. Welcome to Goodie Service! Connection Closed by Foreign Host.
Very simple? Letter do not believe in you, Telnet / POP3 / IMAP / FTP is established by this way
Service.
We now create a little "Internet Agreement", this agreement allows us to enter "exit",
Outline, while other instructions are output and input the same string.
#include
{Char BUF [1024]; int OK; "Welcome to Goodie Service! / N"); fflush (stdout); ok = 0; do {while (Fgets (BUF, 1023, stdin) == null); if (StrncaseCMP (BUF, "exit", 4) == 0) OK = 1; Printf (buf); fflush (stdout);} while (!!);}
Results of the
Telnet Localhost 20001
or
Telnet your_host_name 20001 Trying 127.0.0.1 ... connection to localhost. escape character is '^]'. Welcome to Goodie Service!
Enter "Help"
Help Help
Enter "EXIT"
EXIT EXIT CONNECTION CLOSED by foreIGN Host.
Next, we will design a slightly complex communication agreement, which is more common to general purpose. #include
"BYE", "exit", null}; int getcmd (char * cmd) {INT N = 0; while (cmds [n]! = null) {
IF (strncasecmp (cmd, cmds [n], strlen (cmds [n])) == 0) return n; n ;} return -1;} void main (void) {charf [1024];
INT OK; Printf ("Welcome to Goodie Service! / N); fflush (stdout); ok = 0; do {while (fgets (buf, 1023, stdin) == null); Switch (getCmd (BUF)) { Case -1: Printf ("Unknown Command! / N"); Break; Case 0: Printf ("How May I Help You, SIR? / N"); Break; Case 1: Printf ("I Will Say% S" , & buf [3]); Break; Case 2: Printf ("How're you doing today? / n"); Break; Case 3: Printf ("Si Ya, Mate! / N"); OK = 1; Break Case 4: Printf ("Go Ahead! / N"); OK = 1; Break;} fflush (stdout);} while (!!);
} Telnet localhost 20001
or
Telnet your_host_name 20001
Try to enter "Help", "Say", "Hello", "BYE", "EXIT", etc., and others do not
The instructions in the command column.
When designing the inetd service program, pay special attention to the problem of buffer overflow, that is, the following
Status:
Char buffer_overflow [64]; fscanf (stdin, "% s", buffer_overflow);
Almost all security vulnerabilities have come.
You must not use this, no matter whether any reason, the same usage is not available. Cracker can pass through
Your Buffer is burst, then stuffed into his own program coming in.
Ok Station, Webmaster, Brian Lin
