send tcp

Author: Your Name

simple_examples/tcp.c

@@ -1,6 +1,9 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>
+#include <limits.h>
+#include <string.h>
+#include <time.h>
 
 #include <netdb.h>
 #include <sys/socket.h>
@@ -9,12 +12,34 @@
 #include <netinet/in.h>
 #include <netinet/tcp.h>
 
+#define D_PORT 80
+
+struct pseudohdr{
+	unsigned int src;
+	unsigned int dst;
+	unsigned char filler; /* always null */
+	unsigned char proto; /* always 0x6 */
+	unsigned short len; /* len of real tcp hdr + data */
+};
+
+unsigned short in_cksum(unsigned short *addr, size_t len);
+
 int main(int argc, char *argv[])
 {
 	struct addrinfo *hints, *answ, *tmp;
+	struct pseudohdr *psehdr;
 	struct tcphdr *send_frame;
+	void *final_frame;
 	int sock, ret;
 	ssize_t send_cnt;
+	unsigned short s_port, d_port = htons(D_PORT);
+	unsigned int seq_num, ack_num;
+	time_t t;
+	srand((unsigned int)time(&t));
+	s_port = htons((rand() % USHRT_MAX - 2048 + 1) + 2048);
+	d_port = htons(D_PORT);
+	seq_num = htonl(rand() % UINT_MAX + 1);
+	ack_num = 0;
 	if (argc < 2) {
 		fprintf(stderr, "need host name\n");
 		exit(1);
@@ -27,6 +52,15 @@ int main(int argc, char *argv[])
 		perror("malloc");
 		exit(1);
 	}
+	if ( (psehdr = calloc(1, sizeof(struct pseudohdr))) == NULL) {
+		perror("malloc");
+		exit(1);
+	}
+	if ( (final_frame = calloc(1, sizeof(struct tcphdr) +
+					sizeof(struct pseudohdr))) == NULL) {
+		perror("malloc");
+		exit(1);
+	}
 	hints->ai_family = AF_INET;
 	hints->ai_socktype = SOCK_RAW;
 	hints->ai_protocol = IPPROTO_TCP;
@@ -57,11 +91,73 @@ int main(int argc, char *argv[])
 		exit(1);
 	}
 	*/
+	/* get my ip address */
+	connect(sock, tmp->ai_addr, tmp->ai_addrlen);
+	struct sockaddr_in addr;
+	socklen_t len = sizeof(struct sockaddr_in);
+	getsockname(sock, (struct sockaddr *)&addr, &len);
+	printf("tcp from address: %s\n", inet_ntoa(addr.sin_addr));
+
+	/* filling pseudo hdr */
+	psehdr->src = addr.sin_addr.s_addr;
+	psehdr->dst = ((struct sockaddr_in *)tmp->ai_addr)->sin_addr.s_addr;
+	psehdr->filler = 0;
+	psehdr->proto = IPPROTO_TCP;
+	psehdr->len = htons(20);
+
+	/* prepare tcp hdr */
+	send_frame->source = s_port;
+	send_frame->dest = d_port;
+	send_frame->seq = seq_num;
+	send_frame->ack_seq = ack_num;
+	send_frame->doff = 5;
+	send_frame->fin = 0;
+	send_frame->syn = 1;
+	send_frame->rst = 0;
+	send_frame->psh = 0;
+	send_frame->ack = 0;
+	send_frame->urg = 0;
+	send_frame->window = 0xffff;
+	send_frame->check = 0;
+
+	/* collect all frame (pseudo and real hdr) for computing checksum */
+	memcpy(final_frame, psehdr, sizeof(struct pseudohdr));
+	memcpy(final_frame + sizeof(struct pseudohdr), send_frame,
+			sizeof(struct tcphdr));
+	send_frame->check = in_cksum(final_frame, sizeof(struct tcphdr)+
+			sizeof(struct pseudohdr));
+
+	/* send tcp hdr */
 	send_cnt = sendto(sock, send_frame, sizeof(struct tcphdr), 0,
 			tmp->ai_addr, tmp->ai_addrlen);
 	if (send_cnt == -1) {
 		perror("sendto");
 		exit(1);
+	} else {
+		printf("was send %d bytes\n", send_cnt);
 	}
 	return 0;
 }
+
+unsigned short in_cksum(unsigned short *addr, size_t len)
+{
+	int nleft = len;
+	int sum = 0;
+	unsigned short *w = addr;
+	unsigned short answer = 0;
+	
+	while (nleft > 1)  {
+		sum += *w++;
+		nleft -= 2;
+	}
+	
+	if (nleft == 1) {
+		*(unsigned char *)(&answer) += *(unsigned char *)w;
+		sum += answer;
+	}
+	
+	sum = (sum >> 16) + (sum & 0xffff);	/* add hi 16 to low 16 */
+	sum += (sum >> 16);			/* add carry */
+	answer = ~sum;				/* truncate to 16 bits */
+	return(answer);
+}