MSS from getsockopt
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Authored by BBlack on May 15 2024, 6:58 PM.

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	F53367472: MSS from getsockopt
	May 15 2024, 6:58 PM

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	----- OUTPUT ------
	bblack@cp4049:~$ ./mss-check
	Checking text@ulsfo: MSS is 1448
	Checking upload@ulsfo: MSS is 1428

	------ UGLY QUICK HACK C SOURCE BELOW ----
	#include <stdio.h>
	#include <stdlib.h>
	#include <stddef.h>
	#include <sys/types.h>
	#include <sys/socket.h>
	#include <sys/un.h>
	#include <netinet/in_systm.h>
	#include <netinet/in.h>
	#include <netinet/ip.h>
	#include <netinet/tcp.h>
	#include <arpa/inet.h>
	#include <netdb.h>
	#include <string.h>
	#include <unistd.h>

	void check_mss(struct sockaddr_in* server) {
	const int sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
	if (connect(sock, (struct sockaddr)server, sizeof(server))) {
	perror("connect() failed");
	abort();
	}

	int maxseg = 0;
	socklen_t optlen = sizeof(maxseg);
	if (getsockopt(sock, SOL_TCP, TCP_MAXSEG, &maxseg, &optlen)) {
	perror("getsockopt() failed");
	abort();
	}

	printf("MSS is %i\n", maxseg);
	}

	int main(int argc, char* argv[]) {
	struct sockaddr_in server_text = { 0 };
	server_text.sin_family = AF_INET;
	server_text.sin_addr.s_addr = htonl(0xC6231A60);
	server_text.sin_port = htons(443);

	printf("Checking text@ulsfo: ");
	check_mss(&server_text);

	struct sockaddr_in server_upload = { 0 };
	server_upload.sin_family = AF_INET;
	server_upload.sin_addr.s_addr = htonl(0xC6231A70);
	server_upload.sin_port = htons(443);

	printf("Checking upload@ulsfo: ");
	check_mss(&server_upload);

	return 0;
	}

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