Minimal example code for opening a TCP socket, listening for connections, and outputing incoming data to stdout. Two versions: (a) No error checking, and (b) error checking with macros.

server-macro.c

#include <stdio.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/ip.h>

#define LISTEN_PORT (1234)
#define ASSERT_FATAL(condition, function)                                                       \
	do {                                                                                        \
		if ((condition)) {                                                                      \
			perror((function));                                                                 \
			fputs("__FILE__:__LINE__: fatal: error from " function "(), exiting...\n", stderr); \
			return 1;                                                                           \
		}                                                                                       \
	} while (0)

int main()
{
	int listen_fd, connection_fd;
	struct sockaddr_in address;
	char recvbuff[65536];
	int recvlen;
	int status;
	
	address.sin_family = AF_INET;
	address.sin_port = htons(LISTEN_PORT);
	address.sin_addr.s_addr = INADDR_ANY;
	
	listen_fd = socket(AF_INET, SOCK_STREAM, 0);                                             ASSERT_FATAL(listen_fd == -1, "socket");
	status = bind(listen_fd, (const struct sockaddr*) &address, sizeof(struct sockaddr_in)); ASSERT_FATAL(status == -1, "bind");
	status = listen(listen_fd, 1);                                                           ASSERT_FATAL(status == -1, "listen");

	// @note: accept() is a blocking function by default.
	connection_fd = accept(listen_fd, NULL, NULL);                                           ASSERT_FATAL(connection_fd == -1, "accept"); 
	
	while (1)
	{
		// @note: recv() is a blocking function by default.
		// @returns: 0 on connection closure, -1 on failure.
		recvlen = recv(connection_fd, recvbuff, sizeof(recvbuff), 0);
		
		if (recvlen <= 0)
		{
			if (recvlen == -1)
				perror("recv");	
			break;
		}
		
		fwrite(recvbuff, sizeof(char), recvlen, stdout);
	}
	
	return 0;
}

server-minimal.c

#include <stdio.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/ip.h>

#define LISTEN_PORT (1234)

int main()
{
	int listen_fd, connection_fd;
	struct sockaddr_in address;
	char recvbuff[65536];
	int recvlen;
	
	address.sin_family = AF_INET;
	address.sin_port = htons(LISTEN_PORT);
	address.sin_addr.s_addr = INADDR_ANY;
	
	listen_fd = socket(AF_INET, SOCK_STREAM, 0);
	bind(listen_fd, (const struct sockaddr*) &address, sizeof(struct sockaddr_in));
	listen(listen_fd, 1);
	
	// @note: accept() is a blocking function by default.
	connection_fd = accept(listen_fd, NULL, NULL);
	
	while (1)
	{
		// @note: recv() is a blocking function by default.
		// @returns: 0 on connection closure, -1 on failure.
		recvlen = recv(connection_fd, recvbuff, sizeof(recvbuff), 0);
		
		if (recvlen <= 0)
			break;
		
		fwrite(recvbuff, sizeof(char), recvlen, stdout);
	}
	
	return 0;
}