simple example complete

.gitignore

@@ -1 +1,5 @@
-.vscode/
+*vsidx
+*.opendb
+.vs
+out
+CMakePresets.json

.vscode/c_cpp_properties.json

@@ -11,7 +11,8 @@
                 "_UNICODE"
             ],
             "windowsSdkVersion": "10.0.22621.0",
-            "intelliSenseMode": "windows-msvc-x64"
+            "intelliSenseMode": "windows-msvc-x64",
+            "configurationProvider": "ms-vscode.cmake-tools"
         }
     ],
     "version": 4

System_Calls/readme.md

@@ -79,3 +79,13 @@ Below are the system calls that can be used to access network functionality.
 
     freeaddrinfo(servinfo); // free the linked list
     ```
+
+* **socket() :**
+
+  * Purpose :
+
+    Assign a *file descriptor* for accessing OS resources to access network. Defines the type connection it would make to other host.
+
+  * Function Prototype :
+
+    

examples/tcp_client.c

@@ -0,0 +1,95 @@
+/*
+* client.c -- a stream socket client demo
+*/
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <errno.h>
+#include <string.h>
+#include <netdb.h>
+#include <sys/types.h>
+#include <netinet/in.h>
+#include <sys/socket.h>
+
+#include <arpa/inet.h>
+
+#define PORT "3490"    // the port client will be connecting to
+
+#define MAXDATASIZE 100  // max number of bytes we can get at once
+
+//get sockaddr, IPv4 or IPv6:
+void *get_in_addr(struct sockaddr *sa){
+    
+    if(sa->sa_family == AF_INET){
+        return &(((struct sockaddr_in*)sa)->sin_addr);
+    }
+
+    return &(((struct sockaddr_in6*)sa)->sin6_addr);
+}
+
+int main(int argc, char *argv[]){
+    int sockfd, numbytes;
+    char buf[MAXDATASIZE];
+    struct addrinfo hints, *servinfo, *p;
+    int rv;
+    char s[INET6_ADDRSTRLEN];
+
+    if(argc != 2){
+        fprintf(stderr, "usage: client hostname\n");
+        exit(1);
+    }
+
+
+    memset(&hints, 0, sizeof hints);
+    hints.ai_family = AF_UNSPEC;
+    hints.ai_socktype = SOCK_STREAM;
+
+    if((rv = getaddrinfo(argv[1], PORT, &hints, &servinfo)) != 0){
+        fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
+        return 1;
+    }
+
+    // loop through all the results and connect to the first we can
+    for( p = servinfo; p != NULL ; p = p->ai_next){
+        if((sockfd = socket(p->ai_family, p->ai_socktype,
+                        p->ai_protocol)) == -1){
+            perror("client: socket");
+            continue;
+        }
+
+        if(connect(sockfd, p->ai_addr, p->ai_addlen) == -1){
+            close(sockfd);
+            perror("client: connect");
+            continue;
+        }
+
+        break;
+    }
+
+    if( p == NULL ){
+        fprintf(stderr, "client: failed to connect\n");
+        return 2;
+    }
+
+
+    inet_ntop(p->ai_family, get_in_addr((struct sockaddr *)p->ai_addr),
+                s, sizeof s);
+
+    printf("client: connecting to %s\n", s);
+
+    freeaddrinfo(servinfo); // all done with this structure
+
+    if((numbytes = recv(sockfd, buf, MAXDATASIZE-1, 0)) == -1){
+        perror("recv");
+        exit(1);
+    }
+
+    buf[numbytes] = '\0';
+
+    printf("client: received '%s' \n", buf);
+
+    close(sockfd);
+
+    return 0;
+}

examples/tcp_server.c

@@ -0,0 +1,135 @@
+/*
+*	server.c  --  a stream socket server demo
+*/
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <errno.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <netdb.h>
+#include <arpa/inet.h>
+#include <sys/wait.h>
+#include <signal.h>
+
+#define PORT "3490"		// the port users will be connecting to
+
+#define BACKLOG 10		// how many pending connections queue will hold
+
+void sigchld_handler(int s) {
+	
+	// waitpid() might overwrite errno, so we save and restore it:
+
+	int saved_errno = errno;
+
+	while (waitpid(-1, NULL, WNOHANG) > 0);
+
+	errno = saved_errno;
+}
+
+
+// get sockaddr, IPv4 or IPv6:
+void* get_in_addr(struct sockaddr* sa) {
+
+	if (sa->sa_family == AF_INET) {
+		return &(((struct sockaddr_in*)sa)->sin_addr);
+	}
+
+	return &(((struct sockaddr_in6*)sa)->sin6_addr);
+}
+
+int main(int argc, char* argv[]) {
+
+	int sockfd, new_fd; // listen on sock_fd, new connection on new_fd
+	struct addrinfo hints, * servinfo, * p;
+	struct sockaddr_storage their_addr; // connector's address information
+	socklen_t sin_size;
+	struct sigaction sa;
+	int yes = 1;
+	char s[INET6_ADDRSTRLEN];
+	int rv;
+
+	memset(&hints, 0, sizeof hints);
+	hints.ai_family = AF_UNSPEC;
+	hints.ai_socktype = SOCK_STREAM;
+	hints.ai_flags = AI_PASSIVE; // use my IP
+
+	if ((rv = getaddrinfo(NULL, PORT, &hints, &servinfo)) != 0) {
+		fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
+		return 1;
+	}
+
+	// loop through all the results and bind to the first we can
+	for (p = servinfo; p != NULL; p = p->ai_next) {
+		if ((sockfd = socket(p->ai_family, p->ai_socktype, p->ai_protocol)) == -1) {
+			perror("server: socket");
+			continue;
+		}
+
+		if (setsocket(sockfd, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof(int)) == -1) {
+			perror("setsockopt");
+			exit(1);
+		}
+
+		if (bind(sockfd, p->ai_addr, p->ai_addlen) == -1) {
+			close(sockfd);
+			perror("server: bind");
+			continue;
+		}
+
+		break;
+	}
+
+	freeaddrinfo(servinfo);	  // all done with this structure
+
+	if( p == NULL ){
+		fprintf(stderr, "server: failed to bind\n");
+		exit(1);
+	}
+
+	if(listen(sockfd, BACKLOG) == -1){
+		perror("listen");
+		exit(1);
+	}
+
+	sa.sa_handler = sigchld_handler; // reap all dead processes
+	sigemptyset(&sa.sa_mask);
+	sa.sa_flags = SA_RESTART;
+	if(sigaction(SIGCHLD, &sa, NULL) == -1){
+		perror("sigaction");
+		exit(1);
+	}
+
+	printf("server: waiting for connections...\n");
+
+	while(1){	// main accept() loop
+		sin_size = sizeof their_addr;
+		new_fd = accept(sockfd, (struct sockaddr *)&their_addr, &sin_size);
+		if(new_fd == -1){
+			perror("accept");
+			continue;
+		}
+
+		inet_ntop(their_addr.ss_family,
+					get_in_addr((struct sockaddr *)&their_addr),
+					s, sizeof s);
+
+		printf("server: got connection from %s\n", s);
+
+		if(!fork()){ // this is the child process
+			close(sockfd);	// child doesn't need the listener
+			if( send(new_fd, "Hello, world!", 13, 0) == -1)
+				perror("send");
+
+			close(new_fd);
+			exit(0);
+		}
+
+		close(new_fd);  // parent doesn't need this
+	}
+
+	return 0;
+}

examples/udp_client.c

@@ -0,0 +1,67 @@
+/*
+* udp_client -- a datagram "client" demo
+*/
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <errno.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+#include <netdb.h>
+
+#define SERVERPORT "4950"  // the port users will be connecting to
+
+int main(int argc, char* argv[]){
+
+    int sockfd;
+    struct addrinfo hints, *servinfo, *p;
+    int rv;
+    int numbytes;
+
+    if( argc != 3){
+        fprintf(stderr, "usage: talker hostname message\n");
+        exit(1);
+    }
+
+    memset(&hints, 0, sizeof hints);
+    hints.ai_family = AF_INET6; // set to AF_INET to use IPv4
+    hints.ai_socktype = SOCK_DGRAM;
+
+    if((rv = getaddrinfo(argv[1], SERVERPORT, &hints, &servinfo)) != 0){
+        fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
+        return 1;
+    }
+
+    // loop throught all the results and make a socket
+    for( p = servinfo; p != NULL ; p = p->ai_next){
+        if((sockfd = socket(p->ai_family, p->ai_socktype,
+                p->ai_protocol)) == -1){
+            perror("talker: socket");
+            continue;
+        }
+
+        break;
+    }
+
+    if( p == NULL ){
+        fprintf(stderr, "talker: failed to create socket\n");
+        return 2;
+    }
+
+    if((numbytes = sendto(sockfd, argv[2], strlen(argv[2]), 0,
+        p->ai_addr, p->ai_addrlen)) == -1 ){
+        perror("talker: sendto");
+        exit(1);
+    }
+
+    freeaddrinfo(servinfo);
+
+    printf("talker: sent %d bytes to %s\n", numbytes, argv[1]);
+    close(sockfd);
+
+    return 0;
+}

examples/udp_server.c

@@ -0,0 +1,97 @@
+/*
+* listener.c -- a datagram sockets "server" demo
+*/
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <errno.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+#include <netdb.h>
+
+#define MYPORT "4950"   // the port users will be connecting to
+
+#define MAXBUFLEN 100
+
+// get sockaddr, IPv4 or IPv6:
+void *get_in_addr(struct sockaddr *sa){
+    if( sa->sa_family == AF_INET){
+        return &(((struct sockaddr_in*)sa)->sin_addr);
+    }
+
+    return &(((struct sockaddr_in6*)sa)->sin6_addr);
+}
+
+int main(int argc, char* argv[] ){
+
+    int sockfd;
+    struct addrinfo hints, *servinfo, *p;
+    int rv;
+    int numbytes;
+    struct sockaddr_storage their_addr;
+    char buf[MAXBUFLEN];
+    socklen_t addr_len;
+    char s[INET6_ADDRSTRLEN];
+
+    memset(&hints, 0, sizeof hints);
+    hints.ai_family = AF_INET6; // set to AF_INET to use IPv4
+    hints.ai_socktype = SOCK_DGRAM;
+    hints.ai_flags = AI_PASSIVE;  // use my IP
+
+    if((rv = getaddrinfo(NULL, MYPORT, &hints, &servinfo)) != 0){
+        fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
+        return 1;
+    }
+
+    // loop through all the results and bind to the first we can
+    for(p = servinfo ; p != NULL ; p = p->ai_next){
+        if((sockfd = socket(p->ai_family, p->ai_socktype,
+                        p->ai_protocol)) == -1 ){
+
+            perror("listener: socket");
+            continue;                    
+        }
+
+        if( bind(sockfd, p->ai_addr, p->ai_addrlen) == -1){
+            close(sockfd);
+            perror("listener: bind");
+            continue;
+        }
+
+        break;
+    }
+
+    if( p == NULL ){
+        fprintf(stderr, "listener: failed to bind socket\n");
+        return 2;
+    }
+
+    freeaddrinfo(servinfo);
+
+    printf("listener: waiting to recvfrom...\n");
+
+    addr_len = sizeof their_addr;
+    if((numbytes = recvfrom(sockfd, buf, MAXBUFLEN-1, 0,
+        (struct sockaddr *)&their_addr, &addr_len)) == -1){
+        
+        perror("recvfrom");
+        exit(1);
+    }
+
+    printf("listener: got packet from %s\n",
+        inet_ntop(their_addr.ss_family,
+        get_in_addr((struct sockaddr *)&their_addr),
+        s, sizeof s));
+
+    
+    printf("listener: packet is %d bytes long\n", numbytes);
+    buf[numbytes] = '\0';
+    printf("listener: packet contains \"%s\"\n", buf);
+
+    close(sockfd);
+    return 0;
+}