Basic example raw af inet tcp server and client

IPv4 RAW_AF_INET TCP

• In this program, you are going to learn

• How to create a Socket ?

• How to bind a socket ?

• How to send a data ?

• How to recv a data ?

• How to use socket APIs ?

  • socket

  • bind

  • sendto

  • recvfrom

Topics in this section,

• program 1: tcp single server and single client : single data transfer

• program 2: tcp single server and single client : multiple data transfer

program 1 : tcp single server and single client : single data transfer

Topics in this section,

• IPV4 RAW_AF_INET TCP SOCKET FAQs

• Program1 : Step 1: Sequence Diagram for SERVER.c

• Program1 : Step 2: Program for Server.c

• Program1 : Step 3: Compile and Execute Server.c

• Program1 : Step 4: Sequence Diagram for CLIENT.c

• Program1 : Step 5: Program for Client.c

• Program1 : Step 6: Compile and Execute Client.c

• Summary

program 2 : tcp single server and single client : multiple data transfer

Topics in this section,

• IPV4 RAW_AF_INET TCP SOCKET FAQs

• Program2 : Step 1: Sequence Diagram for SERVER.c

• Program2 : Step 2: Program for Server.c

• Program2 : Step 3: Compile and Execute Server.c

• Program2 : Step 4: Sequence Diagram for CLIENT.c

• Program2 : Step 5: Program for Client.c

• Program2 : Step 6: Compile and Execute Client.c

• Summary

IPV4 RAW_AF_INET TCP SOCKET : FAQs

Let us answer few basic questions in this socket

What does socket(AF_INET, SOCK_RAW, IPPROTO_TCP) do?

See Answer

This call creates a raw socket in the AF_INET address family for direct access to TCP packets.

When is it appropriate to use SOCK_RAW sockets with TCP?

See Answer

It’s suitable for tasks like packet capturing, network monitoring, or implementing custom protocols where direct access to TCP packets is needed.

Can this socket be used for regular TCP communication?

See Answer

While technically possible, it’s not recommended for regular communication due to increased complexity and potential security risks.

How does a raw TCP socket differ from a regular TCP socket?

See Answer

A raw TCP socket provides direct access to the TCP layer, allowing for manual packet manipulation, whereas regular TCP sockets handle packet details internally.

What are some use cases for raw TCP sockets?

See Answer

Use cases include network sniffing, packet analysis, security auditing, and developing custom network protocols.

How can I capture and analyze TCP packets using raw sockets?

See Answer

You can use the raw socket to capture TCP packets and analyze them using packet analysis tools like Wireshark.

Is error checking needed after creating the socket?

See Answer

Yes, checking for errors ensures that the socket is created successfully before proceeding with further operations.

Why is it important to check the return value of sendto() and recvfrom() in socket programming?

See Answer

It detects issues such as network errors or closed connections.

Program1 : Step 1: Sequence Diagram for SERVER.c

Program1: step 2: program for server.c

• There are many functions used in socket. We can classify those functions based on functionalities.

  • Create Socket

  • Bind Socket

  • Recvfrom data_packet

  • Sendto data_packet

  • Close socket

• socket() is used to create a new socket. For example,

server_socket = socket(AF_INET, SOCK_RAW, IPPROTO_TCP);

• bind() is used to associate the socket with a specific address and port. For example,

ret = bind(server_socket, (struct sockaddr*)&server_addr, sizeof(server_addr));

• recvfrom is commonly used with sockets, where communication is connectionless. it provides information about the source (sender) of the data, including the sender’s IP address and port number. For example,

len  = recvfrom(server_socket, buffer, sizeof(buffer), 0, NULL, NULL);

• close is used to close the socket To free up system resources associated with the socket. For example,

(void)close(server_socket);

• See the full program below,

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <netinet/ip.h>
#include <netinet/tcp.h>
#include <ctype.h>

#define PORT 8080
#define BUFFER_SIZE 1024

void recv_data(
const char *packet, 
size_t length) 
{
    int header_size, i;
    char c;

    header_size = sizeof(struct iphdr) + 
    sizeof(struct tcphdr);
    
    printf("Receivedpacket:");

    for (i = header_size; i < length; ++i) {
        c = packet[i];
        if (isprint(c) || c == '\n' 
	|| c == '\r') {
            printf("%c", c);
	}
    }
    printf("\n");
}

void validate_convert_addr(
char *ip_str,
struct sockaddr_in *sock_addr)
{
  if (ip_str == NULL) {
   perror("Invalid ip_str\n");
   exit(EXIT_FAILURE);
 }

 if (sock_addr == NULL) {
   perror("Invalid sock_addr\n");
   exit(EXIT_FAILURE);
 }

 printf("IP Address: %s\n", ip_str);

 if (inet_pton(AF_INET, ip_str,
 &(sock_addr->sin_addr)) <= 0) {
    perror("Invalid address\n");
    exit(EXIT_FAILURE);
  }
}

int main(int argc, char *argv[]) 
{
    int server_socket;
    int len, ret;
    struct sockaddr_in 
    server_addr;
    char buffer[BUFFER_SIZE];

    if (argc != 2) {
        printf("%s<ip-addr>\n",
        argv[0]);
        exit(EXIT_FAILURE);
    }

    server_socket = socket(AF_INET, 
		    SOCK_RAW, 
		    IPPROTO_TCP);

    if (server_socket < 0) {
        perror("Socket creation failed");
        exit(EXIT_FAILURE);
    }

    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(PORT);
    validate_convert_addr(argv[1],
    &server_addr);

    ret = bind(server_socket, 
    (struct sockaddr*)&server_addr, 
    sizeof(server_addr)); 
    
    if (ret < 0) {
        perror("Bind failed");
        (void)close(server_socket);
        exit(EXIT_FAILURE);
    }

    printf("Serverlisten\n");

    len = recv(server_socket, 
    buffer, sizeof(buffer), 0);

    if (len < 0) {
        perror("Receive failed");
        (void)close(server_socket);
        exit(EXIT_FAILURE);
    }

    recv_data(buffer, len);

    (void)close(server_socket);

    return 0;
}

Program1 : Step 3: Compile and Execute Server.c

$ gcc -o server server.c

$ sudo ./server 127.0.0.1

IP Address: 127.0.0.1
Serverlisten
Receivedpacket:_Hello from client!

Program1 : Step 4: Sequence Diagram for CLIENT.c

Program1 : step 5: program for client.c

• There are many functions used in socket. We can classify those functions based on functionalities.

  • Create Socket

  • Sendto data_packet

  • Close socket

• socket is used to create a new socket. For example,

client_socket = socket(AF_INET, SOCK_RAW, IPPROTO_TCP);

• sendto is used to send the encoded message to the specified server address and port using a socket. For example,

ret = sendto(client_socket, buffer + 3, sizeof(struct iphdr) + sizeof(struct tcphdr) + len, 0, (struct sockaddr*)&server_addr, sizeof(server_addr));

• close is used to close the socket To free up system resources associated with the socket. For example,

(void)close(client_socket);

• See the full program below,

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <netinet/ip.h>
#include <netinet/tcp.h>

#define SERVER_IP "127.0.0.1"
#define PORT 8080
#define BUFFER_SIZE 1024

void craft_tcp_packet(
char *buffer, 
const char *data, 
size_t data_len) 
{
    struct iphdr *ip_header;
    struct tcphdr *tcp_header;
   
    ip_header = (struct iphdr *)buffer;
    ip_header->ihl = 5;                   
    ip_header->version = 4;               
    ip_header->tos = 0;                   
    ip_header->tot_len = sizeof(struct iphdr) + 
    sizeof(struct tcphdr) + data_len;
    ip_header->id = htons(54321);         
    ip_header->frag_off = 0;              
    ip_header->ttl = 255;                 
    ip_header->protocol = IPPROTO_TCP;    
    ip_header->check = 0;                 
    ip_header->saddr = INADDR_ANY;        
    ip_header->daddr = INADDR_ANY;     

    tcp_header = (struct tcphdr *)
    (buffer + sizeof(struct iphdr));
    tcp_header->source = htons(12345);    
    tcp_header->dest = htons(PORT);       
    tcp_header->seq = 0;                  
    tcp_header->ack_seq = 0;              
    tcp_header->doff = 5;                 
    tcp_header->fin = 0;                
    tcp_header->syn = 0;                  
    tcp_header->rst = 0;                  
    tcp_header->psh = 1;                  
    tcp_header->ack = 0;                  
    tcp_header->urg = 0;                  
    tcp_header->window = htons(5840);     
    tcp_header->check = 0;                
    tcp_header->urg_ptr = 0;              

    memcpy(buffer + 
    sizeof(struct iphdr) + 
    sizeof(struct tcphdr), data, 
    data_len);
}

void validate_convert_addr(
char *ip_str,
struct sockaddr_in *sock_addr)
{
  if (ip_str == NULL) {
   perror("Invalid ip_str\n");
   exit(EXIT_FAILURE);
 }

 if (sock_addr == NULL) {
   perror("Invalid sock_addr\n");
   exit(EXIT_FAILURE);
 }

 printf("IP Address: %s\n", ip_str);

 if (inet_pton(AF_INET, ip_str,
 &(sock_addr->sin_addr)) <= 0) {
    perror("Invalid address\n");
    exit(EXIT_FAILURE);
  }
}

int main(int argc, char *argv[]) 
{
    int client_socket;
    int i, len, ret;
    struct sockaddr_in 
    server_addr;
    char buffer[BUFFER_SIZE];
    const char *message = 
    "Hello from client!";

    if (argc != 2) {
        printf("%s<ip-addr>\n",
        argv[0]);
        exit(EXIT_FAILURE);
    }

    client_socket = socket(AF_INET, 
		    SOCK_RAW, 
		    IPPROTO_TCP);

    if (client_socket < 0) {
        perror("Socket creation failed");
        exit(EXIT_FAILURE);
    }

    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(PORT);
    validate_convert_addr(argv[1],
    &server_addr);

    len = strlen(message);

    craft_tcp_packet(buffer, 
    message, len);

    strcpy(buffer + 3, message);    
    
    ret = sendto(client_socket, buffer + 3, 
    sizeof(struct iphdr) + 
    sizeof(struct tcphdr) + len,
    0, (struct sockaddr *)&server_addr, 
    sizeof(server_addr));

    if (ret < 0) {
        perror("Send failed");
        (void)close(client_socket);
        exit(EXIT_FAILURE);
    }

    printf("Sentpacket:%s\n", message);

    (void)close(client_socket);

    return 0;
}

Program1 : Step 6: Compile and Execute Client.c

$ gcc -o client client.c

$ sudo ./client 127.0.0.1

IP Address: 127.0.0.1
Sentpacket:Hello from client!

Program2 : Step 1: Sequence Diagram for SERVER.c

Program2 : step 2: program for server.c

• There are many functions used in socket. We can classify those functions based on functionalities.

  • Create Socket

  • Bind Socket

  • Recvfrom data_packet

  • Close socket

• socket() is used to create a new socket. For example,

server_socket = socket(AF_INET, SOCK_RAW, IPPROTO_TCP);

• bind() is used to associate the socket with a specific address and port. For example,

ret = bind(server_socket, (struct sockaddr*)&server_addr, sizeof(server_addr));

• recvfrom is commonly used with sockets, where communication is connectionless. it provides information about the source (sender) of the data, including the sender’s IP address and port number. For example,

len  = recvfrom(server_socket, buffer, sizeof(buffer), 0, NULL, NULL);

• close is used to close the socket To free up system resources associated with the socket. For example,

(void)close(server_socket);

• See the full program below,

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <netinet/ip.h>
#include <netinet/tcp.h>
#include <ctype.h>

#define PORT 8081
#define BUFFER_SIZE 1024
#define NUM_MESSAGES 10

void recv_data(
const char *packet, 
size_t length) 
{
    int header_size, i;
    char c;

    header_size = sizeof(struct iphdr) + 
    sizeof(struct tcphdr);

    printf("Received: ");
    for (i = header_size; i < length; ++i) {
        c = packet[i];
        if (isprint(c) || c == '\n' || c == '\r') {
            printf("%c", c);
	}
    }
    printf("\n");
}

void validate_convert_addr(
char *ip_str,
struct sockaddr_in *sock_addr)
{
  if (ip_str == NULL) {
   perror("Invalid ip_str\n");
   exit(EXIT_FAILURE);
 }

 if (sock_addr == NULL) {
   perror("Invalid sock_addr\n");
   exit(EXIT_FAILURE);
 }

 printf("IP Address: %s\n", ip_str);

 if (inet_pton(AF_INET, ip_str,
 &(sock_addr->sin_addr)) <= 0) {
    perror("Invalid address\n");
    exit(EXIT_FAILURE);
  }
}

int main(int argc, char *argv[]) 
{
    int server_socket;
    int i, ret, len;
    struct sockaddr_in 
    server_addr;
    char buffer[BUFFER_SIZE];

    if (argc != 2) {
	printf("%s<ip-addr>",
	argv[0]);
	exit(EXIT_FAILURE);
    }

    server_socket = socket(AF_INET, 
		    SOCK_RAW, 
		    IPPROTO_TCP);

    if (server_socket < 0) {
        perror("Socket creation failed");
        exit(EXIT_FAILURE);
    }

    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(PORT);
    validate_convert_addr(argv[1], 
    &server_addr);

    ret = bind(server_socket, 
    (struct sockaddr*)&server_addr, 
    sizeof(server_addr)); 
 
    if (ret < 0) {
        perror("Bind failed");
        (void)close(server_socket);
        exit(EXIT_FAILURE);
    }

    printf("Server listening\n");

    i = 0;
    while (i < NUM_MESSAGES) {
        len = recv(server_socket, 
	buffer, sizeof(buffer), 0);

        if (len < 0) {
            perror("Receive failed");
	    break;
        }

        recv_data(buffer, len);
	++i;
    }
    
    (void)close(server_socket);

    return 0;
}

Program2 : Step 3: Compile and Execute Server.c

$ gcc -o server server.c

$ sudo ./server 127.0.0.1

IP Address: 127.0.0.1
Server listening
Received: _Hello from client!
Received: _Hello from client!
Received: _Hello from client!
Received: _Hello from client!
Received: _Hello from client!
Received: _Hello from client!
Received: _Hello from client!
Received: _Hello from client!
Received: _Hello from client!
Received: _Hello from client!

Program2 : Step 4: Sequence Diagram for CLIENT.c

Program2 : step 5: program for client.c

• There are many functions used in socket. We can classify those functions based on functionalities.

  • Create Socket

  • Sendto data_packet

  • Close socket

• socket is used to create a new socket. For example,

client_socket = socket(AF_INET, SOCK_RAW, IPPROTO_TCP);

• sendto is used to send the encoded message to the specified server address and port using a socket. For example,

ret = sendto(client_socket, buffer + 3, sizeof(struct iphdr) + sizeof(struct tcphdr) + len, 0, (struct sockaddr*)&server_addr, sizeof(server_addr));

• close is used to close the socket To free up system resources associated with the socket. For example,

(void)close(server_socket);

• See the full program below,

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <netinet/ip.h>
#include <netinet/tcp.h>

#define BUFFER_SIZE 1024
#define NUM_MESSAGES 10
#define PORT 8081

void validate_convert_addr(
char *ip_str,
struct sockaddr_in *sock_addr)
{
  if (ip_str == NULL) {
   perror("Invalid ip_str\n");
   exit(EXIT_FAILURE);
 }

 if (sock_addr == NULL) {
   perror("Invalid sock_addr\n");
   exit(EXIT_FAILURE);
 }

 printf("IP Address: %s\n", ip_str);

 if (inet_pton(AF_INET, ip_str,
 &(sock_addr->sin_addr)) <= 0) {
    perror("Invalid address\n");
    exit(EXIT_FAILURE);
  }
}

void craft_tcp_packet(
char *buffer, 
const char *data, 
size_t data_len) 
{
    struct iphdr *ip_header;
    struct tcphdr *tcp_header;
    int i;

    ip_header = (struct iphdr *)buffer;
    ip_header->ihl = 5;                   
    ip_header->version = 4;               
    ip_header->tos = 0;                   
    ip_header->tot_len = sizeof(struct iphdr) + 
    sizeof(struct tcphdr) 
    + data_len; 
    ip_header->id = htons(54321);         
    ip_header->frag_off = 0;              
    ip_header->ttl = 255;                 
    ip_header->protocol = IPPROTO_TCP;    
    ip_header->check = 0;                
    ip_header->saddr = INADDR_ANY;        
    ip_header->daddr = INADDR_ANY;  

    tcp_header = (struct tcphdr *)
    (buffer + sizeof(struct iphdr));
    tcp_header->source = htons(12345);    
    tcp_header->dest = htons(PORT) ;      
    tcp_header->seq = 0;                  
    tcp_header->ack_seq = 0;             
    tcp_header->doff = 5;                 
    tcp_header->fin = 0;                  
    tcp_header->syn = 0;                  
    tcp_header->rst = 0;                  
    tcp_header->psh = 1;                  
    tcp_header->ack = 0;                  
    tcp_header->urg = 0;                  
    tcp_header->window = htons(5840);     
    tcp_header->check = 0;                
    tcp_header->urg_ptr = 0;              
    
    memcpy(buffer + sizeof(struct iphdr) + 
    sizeof(struct tcphdr), data, data_len);
}

int main(int argc, char *argv[]) 
{
    int client_socket;
    int ret, i;
    int len;
    struct sockaddr_in 
    server_addr;
    char buffer[BUFFER_SIZE];
    const char *message = 
    "Hello from client!";

    if (argc != 2) {
	printf("%s<ip-addr>\n",
	argv[0]);
	exit(EXIT_FAILURE);
    }

    client_socket = socket(AF_INET, 
		    SOCK_RAW, 
		    IPPROTO_TCP);

    if (client_socket < 0) {
        perror("Socket creation failed");
        exit(EXIT_FAILURE);
    }

    server_addr.sin_family = AF_INET;
    server_addr.sin_port = htons(PORT);
    validate_convert_addr(argv[1],
    &server_addr);

    len = strlen(message);

    craft_tcp_packet(buffer, 
    message, len);

    strcpy(buffer + 3, message);   

    i = 0;
    while (i < NUM_MESSAGES) { 
   
    ret = sendto(client_socket, 
    buffer + 3, 
    sizeof(struct iphdr) + 
    sizeof(struct tcphdr) + len,
    0, (struct sockaddr *)&server_addr, 
    sizeof(server_addr));

    if (ret < 0) {
        perror("Send failed");
        (void)close(client_socket);
        exit(EXIT_FAILURE);
    }

    printf("Sentpacket: %s\n", 
    message);
    ++i;
    }

    (void)close(client_socket);

    return 0;
}

Program2 : Step 6: Compile and Execute Client.c

$ gcc -o client client.c

$ sudo ./client 127.0.0.1

IP Address: 127.0.0.1
Sentpacket: Hello from client!
Sentpacket: Hello from client!
Sentpacket: Hello from client!
Sentpacket: Hello from client!
Sentpacket: Hello from client!
Sentpacket: Hello from client!
Sentpacket: Hello from client!
Sentpacket: Hello from client!
Sentpacket: Hello from client!
Sentpacket: Hello from client!

Enhanced Socket Flexibility with AF_INET and PF_INET Domains

Default Domain:

By default, the socket is configured to work in the AF_INET domain, handling all types of network data.

Additional Domain Support:

We expand the socket’s capabilities to also function in the PF_INET domain, allowing it to operate similarly to AF_INET.

Socket Creation:

We set up a network connection point known as a socket using socket(PF_INET, SOCK_RAW, IPPROTO_TCP).

Working Scenario:

Despite the change in domain to PF_INET, the socket continues to operate the same way, handling general network data.

Summary

Socket API	Learning
socket	Create a new socket
recvfrom	It provides information about the source (sender) of the data, including the sender’s IP address and port number.
sendto	Send the encoded message to the specified server address and port using a socket.

See Also

• Previous topic

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• Next topic

  • IPV4 RAW AF INET TCP server client program with Select system call

• Other sockets

  • ipv4_raw_af_inet_udp

  • ipv6_af_inet6_tcp

  • ipv6_af_inet6_udp

  • //TODO ipv6_raw_af_inet6_icmp

  • //TODO ipv6_raw_af_inet6_tcp

  • //TODO ipv6_raw_af_inet6_udp

  • // TODO ipv6_raw_af_inet6_raw

  • raw_af_packet_raw_htons_ETH_P_ALL

  • raw_af_packet_tcp_htons_ETH_P_ALL

  • raw_af_packet_udp_htons_ETH_P_ALL

• Other IPCs

  • Message_queues

  • NamedPipes

  • Netlink

  • Shared_Memory

  • Shared_Memory_2_FDS

  • SocketPair

  • Timerfd