added first session UDP echo server and client

.gitignore

@@ -0,0 +1 @@
+*.o

session1/udp_echo/Makefile

@@ -0,0 +1,14 @@
+TARGETS = echo_server echo_client
+
+CC = gcc
+CFLAGS = -g -D$(DEFINES)
+
+all: $(TARGETS) Makefile
+clean:
+	rm -f $(TARGETS)
+	rm -f *.o *.~
+
+echo_server: echo_server.o
+echo_client: echo_client.o	
+
+.PHONY: all clean

session1/udp_echo/echo_client.c

@@ -0,0 +1,67 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <errno.h>
+#include <string.h>
+
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+
+
+void handle_error(char *msg)
+{
+	fprintf(stderr, "%s: %s\n", msg, strerror(errno));
+
+	exit(EXIT_FAILURE);
+}
+
+
+int main(int argc, char *argv[])
+{
+	int fd;
+	char *lineptr = NULL;
+	ssize_t linelen = 0;
+
+	struct sockaddr_in sa = { .sin_family = AF_INET };
+
+	if (argc != 3) {
+		printf("usage: %s DEST-IP PORT\n", argv[0]);
+		exit(-1);
+	}
+
+	if (!inet_aton(argv[1], &sa.sin_addr))
+		fprintf(stderr, "Failed to parse destination IP address\n");
+
+	sa.sin_port = atoi(argv[2]);
+	if (!sa.sin_port)
+		fprintf(stderr, "Failed to parse port number");
+
+	fd = socket(AF_INET, SOCK_DGRAM, 0);
+	if (fd < 0)
+		handle_error("Failed to create socket");
+
+	if (connect(fd, (struct sockaddr *) &sa, sizeof(sa)))
+		handle_error("Failed to connect socket");
+
+	while (!feof(stdin)) {
+		size_t len = getline(&lineptr, &linelen, stdin);
+		if (len > 0) {
+			if (send(fd, lineptr, len+1, 0) == -1)
+				handle_error("Failed to send");
+
+#ifdef ECHO
+			if (recv(fd, lineptr, linelen, 0) == -1)
+				handle_error("Failed to recv");
+
+			fprintf(stdout, "%s", lineptr);
+#endif
+		}
+	}
+
+	if (close(fd))
+		handle_error("Failed to close socket");
+
+	free(lineptr);
+
+	return 0;
+}

session1/udp_echo/echo_server.c

@@ -0,0 +1,65 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <errno.h>
+#include <string.h>
+
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+
+
+void handle_error(char *msg)
+{
+	fprintf(stderr, "%s: %s\n", msg, strerror(errno));
+
+	exit(EXIT_FAILURE);
+}
+
+
+int main(int argc, char *argv[])
+{
+	int fd;
+	char line[1024];
+	ssize_t msglen;
+	socklen_t salen;
+
+	struct sockaddr_in sa = { .sin_family = AF_INET };
+
+	if (argc != 2) {
+		printf("usage: %s PORT\n", argv[0]);
+		exit(-1);
+	}
+
+	sa.sin_port = atoi(argv[1]);
+	if (!sa.sin_port)
+		fprintf(stderr, "Failed to parse port number");
+
+
+	fd = socket(AF_INET, SOCK_DGRAM, 0);
+	if (fd < 0)
+		handle_error("Failed to create socket");
+
+	if (bind(fd, (struct sockaddr *) &sa, sizeof(sa)))
+		handle_error("Failed to bind socket");
+
+	while (1) {
+		salen = sizeof(sa);
+
+		msglen = recvfrom(fd, &line, sizeof(line), 0, (struct sockaddr *) &sa, &salen)
+		if (msglen == -1)
+			handle_error("Failed to recv");
+
+#ifdef ECHO
+		if (sendto(fd, &line, msglen, 0,
+			(struct sockaddr *) &sa, salen) == -1)
+			handle_error("Failed to send");
+#else
+		fprintf(stdout, "%s", line);
+#endif
+	}
+
+	if (close(fd))
+		handle_error("Failed to close socket");
+
+	return 0;
+}