Hi Oliver,

On Sun, Mar 17, 2024 at 09:55:50AM -0400, Oliver Crumrine wrote:

It was not made clear in several socket options that they were not
supported by SOCK_STREAM; this patch fixes that.

Socket options not supported by SOCK_STREAM are handled in the
ip_cmsg_recv_offset function in net/ipv4/ip_sockglue.c. The function is
called for udp sockets, and indirectly by ping and raw sockets, but not
for STREAM sockets, as they don't support these options.

Signed-off-by: Oliver Crumrine <redacted>

Patch applied; thanks.
<https://www.alejandro-colomar.es/src/alx/linux/man-pages/man-pages.git/commit/?h=contrib&id=5675cf3b048ec65b241d51c1130b55420a5d2456>

Have a lovely day!
Alex

#include <stdio.h>
#include <err.h>
#include <string.h>
#include <stdlib.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <unistd.h>

#define PORT 8888 //The port on which to send data
#define ADDR "127.0.0.1" //The internet address to send packets to

int main(void){
	int s;
	struct sockaddr_in server_addr;

	char buf[] = "testing 1 2 3\n";

	s = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
	if(s == -1){
		err(1, "error creating socket");
	}

	uint8_t options = 1; //noop in the language of ip options

	if(setsockopt(s, IPPROTO_IP, IP_OPTIONS, &options, 1) == -1){
		err(1, "error setting socket options");
	}

	memset(&server_addr, 0, sizeof(server_addr));
	
	server_addr.sin_family = AF_INET;
	server_addr.sin_port = htons(PORT);
	if(inet_pton(AF_INET, ADDR, &server_addr.sin_addr) != 1){ // I realize I'm checking the return value differently here. If you read the man page for inet_pton, it'll make sense.
		err(1, "error converting network address");
	}

	if(sendto(s, buf, strlen(buf), 0, (struct sockaddr*)&server_addr, sizeof(server_addr)) == -1){
		err(1, "error sending data");
	}
	
	close(s);
}

#include<stdio.h>
#include<err.h>
#include<string.h>
#include<stdlib.h>
#include<arpa/inet.h>
#include<sys/socket.h>
#include<unistd.h>

#define PORT 8888	//The port on which to listen for incoming data


//Hi Alex,
//These are the two lines that allow you to switch between the three socket options outlined in my patch
//The socket options tell the kernel to add a control message (cmsg), allowing the program
//to recieve the data it is requesting. The three options are: IP_RECVTOS for the type of service byte,
//IP_RECVORIGDSTADDR for the orignial dst address, and IP_PKTINFO for some random packet info, and IP_RETOPTS
//for some random ip packet options
#define SOCKOPT IP_RECVORIGDSTADDR
//This field is synonymous with the above one. Valid options are: IP_TOS, IP_ORIGDSTADDR, IP_PKTINFO, and IP_OPTIONS
#define RECIVEOPTION IP_ORIGDSTADDR

int main(void){
	struct sockaddr_in local_addr;
	int s;
	
	s = socket(AF_INET, SOCK_DGRAM, 0);
	if (s == -1){
		err(1, "error creating socket");
	}
	
	memset(&local_addr, 0, sizeof(local_addr));
	
	local_addr.sin_family = AF_INET;
	local_addr.sin_port = htons(PORT);
	local_addr.sin_addr.s_addr = htonl(INADDR_ANY);

	int yes = 1;
	if(setsockopt(s, IPPROTO_IP, SOCKOPT, &yes, sizeof(yes)) == -1){
		err(1, "error setting socket option");
	}


	if(bind(s, (struct sockaddr*)&local_addr, sizeof(local_addr) ) == -1){
		err(1, "error binding to port. try changing it or running as root");
	}

	while(1){
		struct msghdr mhdr;
		struct iovec iov[1];
		struct cmsghdr *cmhdr;
		char control[1000];
		char databuf[BUFSIZ];
		unsigned char tos = 0;

		mhdr.msg_name = &local_addr;
		mhdr.msg_namelen = sizeof(local_addr);
		mhdr.msg_iov = iov;
		mhdr.msg_iovlen = 1;
		mhdr.msg_control = &control;
		mhdr.msg_controllen = sizeof(control);
		iov[0].iov_base = databuf;
		iov[0].iov_len = sizeof(databuf);
		memset(databuf, 0, sizeof(databuf));	
		
		//this is blocking
		int msglen = recvmsg(s, &mhdr, 0);
		if (msglen == -1){
			err(1, "recvmsg");
		}
		cmhdr = CMSG_FIRSTHDR(&mhdr);
		while (cmhdr) {
			printf("cmsg recieved\n");
			if (cmhdr->cmsg_level == IPPROTO_IP && cmhdr->cmsg_type == RECIVEOPTION) {
				//read the byte recieved
				tos = ((unsigned char *)CMSG_DATA(cmhdr))[0];
			}
			cmhdr = CMSG_NXTHDR(&mhdr, cmhdr);
		}
		//print out the first byte of data recieved in hex. You can verify this in wireshark if you like.
		printf("data read: %sbyte = %02X\n", databuf, tos);
	}

	close(s);
	return 0;
}

#include <stdio.h>
#include <err.h>
#include <string.h>
#include <stdlib.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <unistd.h>

#define PORT 8888 //The port on which to send data
#define ADDR "127.0.0.1" //The internet address to send packets to

int main(void){
	int s;
	struct sockaddr_in server_addr;

	char buf[] = "testing 1 2 3\n";

	s = socket(AF_INET, SOCK_STREAM, 0);
	if(s == -1){
		err(1, "error creating socket");
	}

	uint8_t options = 1; //noop in the language of ip options

	if(setsockopt(s, IPPROTO_IP, IP_OPTIONS, &options, 1) == -1){
		err(1, "error setting socket options");
	}

	memset(&server_addr, 0, sizeof(server_addr));
	
	server_addr.sin_family = AF_INET;
	server_addr.sin_port = htons(PORT);
	if(inet_pton(AF_INET, ADDR, &server_addr.sin_addr) != 1){ // I realize I'm checking the return value differently here. If you read the man page for inet_pton, it'll make sense.
		err(1, "error converting network address");
	}

	if(connect(s, (struct sockaddr*)&server_addr, sizeof(server_addr)) == -1){
		err(1, "error connecting");
	}
	if(send(s, buf, strlen(buf), 0) == -1){
		err(1, "error sending data");
	}
	
	close(s);
}

#include<stdio.h>
#include<err.h>
#include<string.h>
#include<stdlib.h>
#include<arpa/inet.h>
#include<sys/socket.h>
#include<unistd.h>

#define PORT 8888	//The port on which to listen for incoming data


//Hi Alex,
//These are the two lines that allow you to switch between the three socket options outlined in my patch
//The socket options tell the kernel to add a control message (cmsg), allowing the program
//to recieve the data it is requesting. The three options are: IP_RECVTOS for the type of service byte,
//IP_RECVORIGDSTADDR for the orignial dst address, and IP_PKTINFO for some random packet info, and IP_RETOPTS
//for some random ip packet options
#define SOCKOPT IP_RECVORIGDSTADDR
//This field is synonymous with the above one. Valid options are: IP_TOS, IP_ORIGDSTADDR, IP_PKTINFO, and IP_OPTIONS
#define RECIVEOPTION IP_ORIGDSTADDR

int main(void){
	struct sockaddr_in local_addr;
	int s;
	
	s = socket(AF_INET, SOCK_STREAM, 0);
	if (s == -1){
		err(1, "error creating socket");
	}
	
	memset(&local_addr, 0, sizeof(local_addr));
	
	local_addr.sin_family = AF_INET;
	local_addr.sin_port = htons(PORT);
	local_addr.sin_addr.s_addr = htonl(INADDR_ANY);

	int yes = 1;
	if(setsockopt(s, IPPROTO_IP, SOCKOPT, &yes, sizeof(yes)) == -1){
		err(1, "error setting socket option");
	}


	if(bind(s, (struct sockaddr*)&local_addr, sizeof(local_addr) ) == -1){
		err(1, "error binding to port. try changing it or running as root");
	}
	
	if(listen(s, 10) == -1){ //10 is the backlog of un-accepted connections. its just an arbitrary number
		err(1, "error listening on port");
	}

	while(1){
		int connfd = accept(s, (struct sockaddr*)NULL, NULL);
		if(connfd == -1){
			err(1, "error accepting connection");
		}
		if(setsockopt(s, IPPROTO_IP, SOCKOPT, &yes, sizeof(yes)) == -1){ //stream sockets should have this set on the connected socket as well. I left it above for uniformity between the two programs.
			err(1, "error setting socket option");
		}
	
		struct msghdr mhdr;
		struct iovec iov[1];
		struct cmsghdr *cmhdr;
		char control[1000];
		char databuf[BUFSIZ];
		unsigned char tos = 0;

		mhdr.msg_name = &local_addr;
		mhdr.msg_namelen = sizeof(local_addr);
		mhdr.msg_iov = iov;
		mhdr.msg_iovlen = 1;
		mhdr.msg_control = &control;
		mhdr.msg_controllen = sizeof(control);
		iov[0].iov_base = databuf;
		iov[0].iov_len = sizeof(databuf);
		memset(databuf, 0, sizeof(databuf));	
		
		//this is blocking
		int msglen = recvmsg(connfd, &mhdr, 0);
		if (msglen == -1){
			err(1, "recvmsg");
		}
		cmhdr = CMSG_FIRSTHDR(&mhdr);
		while (cmhdr) {
			printf("cmsg recieved\n");
			if (cmhdr->cmsg_level == IPPROTO_IP && cmhdr->cmsg_type == RECIVEOPTION) {
				//read the byte recieved
				tos = ((unsigned char *)CMSG_DATA(cmhdr))[0];
			}
			cmhdr = CMSG_NXTHDR(&mhdr, cmhdr);
		}
		//print out the first byte of data recieved in hex. You can verify this in wireshark if you like.
		printf("data read: %sbyte = %02X\n", databuf, tos);
		close(connfd);
	}

	close(s);
	return 0;
}

-- 
<https://www.alejandro-colomar.es/>
Looking for a remote C programming job at the moment.