Added error checking for return value from 'easysock' functions

Makefile

@@ -8,6 +8,9 @@ $(EXEC_FILE): main.o easysock.o
 
 allwarn: CFLAGS+=-Wall -Wextra -pedantic
 allwarn: $(EXEC_FILE)
+
+debug: CFLAGS+=-g
+debug: $(EXEC_FILE)
 	
 clean: $(EXEC_FILE) main.o easysock.o
 	rm ./$(EXEC_FILE)

README.md

@@ -10,3 +10,4 @@ TODO
 
 ## Usage
 	./proxy <local-address> <local-port> <remote-address> <remote-port>
+### If the program doesn't work, check the errno. Run 'errno $?' to get the resulting error. Also, CHECK YOUR FIREWALL!!!

TODO.txt

@@ -1,13 +1,15 @@
 1. Finish README.md
 
 2. Add command-line argument support:
-	1. Specify IP version in arg
-	2. Specify local hostname:port in arg (enclose in paranthesis if IPv6)
-	3. Specify remote hostname:port in arg (enclose in paranthesis if IPv6)
+---SHOULD BE DONE---  1. Specify IP version in arg
+---NOT NEEDED---      2. Specify local hostname:port in arg (enclose in paranthesis if IPv6)
+---NOT NEEDED---      3. Specify remote hostname:port in arg (enclose in paranthesis if IPv6)
 	4. Try making every aspect of the program configurable via args
 
-3. Add support for configuration files, which can be specified via a command-line arg
+3. Test UDP support
 
----SHOULD BE DONE---- 4. Fix Makefile - Doesn't recompile if source files have changed, only if .o files have.
+4. Add support for configuration files, which can be specified via a command-line arg
 
-5. Check IPv6 support for remote socket
+---SHOULD BE DONE---- 5. Fix Makefile - Doesn't recompile if source files have changed, only if .o files have.
+
+---SHOULD BE DONE---  6. Check IPv6 support for remote socket

easysock.c

@@ -1,5 +1,6 @@
 #include "easysock.h"
 
+
 int create_socket(int network, char transport) {  
 	int domain;
 	int type;
@@ -25,7 +26,7 @@ int create_socket(int network, char transport) {
 }
 
 
-void create_addr(int network, char* address, int port,struct sockaddr* dest) {
+int create_addr(int network, char* address, int port,struct sockaddr* dest) {
 	if (network == 4) {
 		struct sockaddr_in listen_address;
 		
@@ -33,7 +34,7 @@ void create_addr(int network, char* address, int port,struct sockaddr* dest) {
 		listen_address.sin_port = htons(port);
 		inet_pton(AF_INET,address,&listen_address.sin_addr);
 		memcpy(dest,&listen_address,sizeof(listen_address));
-		return;	
+		return 0;	
 
 	} else if (network == 6) {
 		struct sockaddr_in6 listen_ipv6;
@@ -41,10 +42,10 @@ void create_addr(int network, char* address, int port,struct sockaddr* dest) {
 		listen_ipv6.sin6_port = htons(port);
 		inet_pton(AF_INET6,address,&listen_ipv6.sin6_addr);
 		memcpy(dest,&listen_ipv6,sizeof(listen_ipv6));
-		return;
+		return 0;
 
 	} else {
-		exit(-2);
+		return -202;
 	}
 		
 }
@@ -52,7 +53,7 @@ void create_addr(int network, char* address, int port,struct sockaddr* dest) {
 int create_local (int network, char transport, char* address, int port,struct sockaddr* addr_struct) {
 	int socket = create_socket(network,transport);
 	if (socket < 0) {
-		printf("Something went wrong creating the socket: %s\n",strerror(errno));
+		return (-1 * errno);
 	}
 	create_addr(network,address,port,addr_struct);
 	int addrlen;
@@ -61,7 +62,7 @@ int create_local (int network, char transport, char* address, int port,struct so
 	} else if (network == 6) {
 		addrlen = sizeof(struct sockaddr_in6);
 	} else {
-		exit(-7);
+		return -207;
 	}
 
 	/* The value of addrlen should be the size of the 'sockaddr'. 
@@ -70,38 +71,100 @@ int create_local (int network, char transport, char* address, int port,struct so
 
 	int i = bind (socket,addr_struct,(socklen_t)addrlen);
 	if (i < 0) {
-		printf("Something went wrong: %s\n",strerror(errno));
-		exit(-3);
+		return (-1 * errno);
 	}
 	return socket;
 }
 
-int create_remote (int network,char transport,char* address,int port) {
+int create_remote (int network,char transport,char* address,int port,struct sockaddr* remote_addr_struct) {
 
+	struct addrinfo hints;  /* Used to tell getaddrinfo what kind of address we want */
+	struct addrinfo* results; /* Used by getaddrinfo to store the addresses */
+
+
+	if (check_ip_ver(address) < 0) { /* If the address is a domain name */
+		int err_code;
+		char* port_str = malloc(10 * sizeof(char));
+
+		sprintf(port_str,"%d",port); /* getaddrinfo expects a string for its port */
+
+
+		memset(&hints,'\0',sizeof(hints));
+		hints.ai_socktype = char_to_socktype(transport);
+
+		err_code = getaddrinfo(address,port_str,&hints,&results);
+		if (err_code != 0) {
+			exit(err_code);
+		}
+		remote_addr_struct = results->ai_addr;
+		network = inet_to_int(results->ai_family);
+	} else {
+	        create_addr(network,address,port,remote_addr_struct);
+	}
 
 	int socket = create_socket(network,transport);
-	if (socket == -1) {
-                exit(-1);
+	if (socket < 0) {
+                return (-1 * errno);
         }
-	struct sockaddr remote_addr_struct;
-        create_addr(network,address,port,&remote_addr_struct);
-        int addrlen;
+
+       	int addrlen;
 	if (network == 4) {
 		addrlen = sizeof(struct sockaddr_in);
 	} else if (network == 6) {
 		addrlen = sizeof(struct sockaddr_in6);
 	} else {
-		exit(-7);
+		return (-1 * errno);
 	}
 
 	/* The value of addrlen should be the size of the 'sockaddr'. 
 	This should be set to the size of 'sockaddr_in' for IPv4, and 'sockaddr_in6' for IPv6.
 	See https://stackoverflow.com/questions/73707162/socket-bind-failed-with-invalid-argument-error-for-program-running-on-macos */
 
-        int i = connect(socket,&remote_addr_struct,(socklen_t)addrlen);
+        int i = connect(socket,remote_addr_struct,(socklen_t)addrlen);
 	if (i < 0) {
-		printf("Something went wrong: %s\n",strerror(errno));
-		exit(-3);
+		return (-1 * errno);
 	}
         return socket;
 }
+
+
+int check_ip_ver(char* address) {
+	char buffer[16]; /* 16 chars - 128 bits - is enough to hold an ipv6 address */
+	if (inet_pton(AF_INET,address,buffer) == 1) {
+		return 4;
+	} else if (inet_pton(AF_INET6,address,buffer) == 1) {
+		return 6;
+	} else {
+		return -1;
+	}
+}
+
+int int_to_inet(int network) {
+	if (network == 4) {
+		return AF_INET;
+	} else if (network == 6) {
+		return AF_INET6;
+	} else {
+		return -207;
+	}
+}
+
+int inet_to_int(int af_type) {
+	if (af_type == AF_INET) {
+		return 4;
+	} else if (af_type == AF_INET6) {
+		return 6;
+	} else {
+		return -207;
+	}
+}
+
+int char_to_socktype(char transport) {
+	if (transport == 'T') {
+		return SOCK_STREAM;
+	} else if (transport == 'U') {
+		return SOCK_DGRAM;
+	} else {
+		return -250;
+	}
+}

easysock.h

@@ -2,7 +2,9 @@
 #define EASYSOCK_H_
 
 #include <string.h>
+#include <sys/types.h>
 #include <sys/socket.h>
+#include <netdb.h>
 #include <arpa/inet.h>
 #include <stdlib.h>
 #include <stdio.h>
@@ -26,10 +28,10 @@ int create_socket(int network, char transport);
 port is self-explanatory;
 and dest is a pointer to the sockaddr struct that will be filled in. 
 
-The function exits with error code -2 if the network parameter contained neither '4'
+The function returns with -202 if the network parameter contained neither '4'
 nor '6'. */
 
-void create_addr(int network, char* address, int port,struct sockaddr* dest);
+int create_addr(int network, char* address, int port,struct sockaddr* dest);
 
 
 
@@ -37,18 +39,38 @@ void create_addr(int network, char* address, int port,struct sockaddr* dest);
 _binds_ the addresses. It is used for local sockets (server sockets). Parameters are
 same as above. 
 
-It prints the error returned by 'bind' if something went wrong, and exits with error code '-3'.*/
+It prints the error returned by 'bind' if something went wrong, and returns ( -1 * errno ).*/
 
 int create_local (int network, char transport, char* address, int port,struct sockaddr* addr_struct);
 
 
 /* This function utilizes the same functions as 'create_local' but _connects_ to the
-requested address. It is used for remoet sockets (client sockets). The paramters are same
-as above.
+requested address. It is used for remote sockets (client sockets). The paramters are same
+as above. This function needs an empty 'sockaddr *' structure passed to it, which it will fill.
 
-It prints the error returned by 'connect' if something went wrong, and exits with error code '-3'.*/
+If something goes wrong, this function returns with ( -1 * errno ). */
 
-int create_remote (int network,char transport,char* address,int port);
+int create_remote (int network,char transport,char* address,int port,struct sockaddr* remote_addr_struct);
+
+/* check_ip_ver - This function checks if the given string is an IPv4 address (returns 4), 
+IPv6 address (returns 6) or neither (returns -1). */
+
+int check_ip_ver(char* address);
+
+/* int_to_inet - Takes an int value (4 for IPv4, 6 for IPv6) and returns AF_INET or
+AF_INET6 respectively. */
+
+int int_to_inet(int network);
+
+/* char_to_socktype - Takes a character that represents a transport-layer protocol
+(currently only supports 'T' for TCP or 'U' for UDP - it returns -250 if 
+the given characters is neither of these) and return the appropriate SOCKTYPE value. */
+
+int char_to_socktype(char transport);
+
+/* inet_to_int - Takes an int value that corresponds to AF_INET or AF_INET6,
+and returns the appropriate int value. */
+int inet_to_int(int af_type);
 
 
 #endif

main.c

@@ -3,7 +3,8 @@
 #include <unistd.h>
 #include <stdlib.h>
 #include "easysock.h"
-
+#define PROG_NAME "basicproxy"
+#define PROG_VER "0.01"
 void forward_data(int from_fd, int to_fd) {
 	int n = 0;
         char* buffer = malloc(3000*sizeof(char));
@@ -12,18 +13,24 @@ void forward_data(int from_fd, int to_fd) {
 	}
 }
 
-int check_ip_ver(char* address) {
-	char buffer[16]; /* 16 chars - 128 bits - is enough to hold an ipv6 address */
-	if (inet_pton(AF_INET,address,buffer) == 1) {
-		return 4;
-	} else if (inet_pton(AF_INET6,address,buffer) == 1) {
-		return 6;
-	} else {
-		return -1;
-	}
+void print_prog_info() {
+	printf("%s [Local IP address] [local port] [remote IP address] [remote port]\n",PROG_NAME);
 }
 
+void print_version_info() {
+	printf("%s %s\n",PROG_NAME,PROG_VER);
+}
 
+void print_help_info() {
+	printf("\n%s - A simple TCP proxy written in C.\n\n",PROG_NAME);
+	printf("Syntax - ");
+	print_prog_info();
+	printf("[Local IP address] - The local address to bind to\n"
+		"[local port] - The local port to listen on\n"
+		"[remote IP address] - The remote IP to connect to\n"
+		"[remote port] - The remote port to connect to\n");
+	printf("\nExample: %s 127.0.0.1 3000 1.2.3.4 5000 - Listen on '127.0.0.1:3000', and forward all data from there to '1.2.3.4:5000'\n\n",PROG_NAME);
+}
 int main(int argc,char* argv[]) {
 
 /* argv[1] = local address
@@ -31,6 +38,22 @@ int main(int argc,char* argv[]) {
    argv[3] = remote address
    argv[4] = remote port */
 
+	if (argc == 2) {
+		if (strcmp(argv[1],"-v") == 0 || strcmp(argv[1],"--version") == 0) {
+			print_version_info();
+			exit(0);
+		} else if (strcmp(argv[1],"-h") == 0 || strcmp(argv[1],"--help") == 0) {
+			print_help_info();
+			exit(0);
+		}
+	}
+
+	if (argc != 5) {
+		print_prog_info();
+		exit(230);
+	}
+
+
 	char* local_addr = argv[1];
 	int local_port = strtol(argv[2],NULL,10);
 	char* remote_addr = argv[3];
@@ -38,47 +61,57 @@ int main(int argc,char* argv[]) {
 
 	int preferred_local_network = check_ip_ver(local_addr);
 	int preferred_remote_network = check_ip_ver(remote_addr);
-	printf("Using %d for local\nUsing %d for remote\n",preferred_local_network,preferred_remote_network);
-	
-	if ((preferred_local_network == -1) || (preferred_remote_network == -1)) {
-		exit(-7);
+	if (preferred_remote_network < 0) { /* This value will be less than 0 if the remote address is a domain name */
+		printf("Using %d for local\nUsing hostname for remote\n",preferred_local_network);
+	} else {
+		printf("Using %d for local\nUsing %d for remote\n",preferred_local_network,preferred_remote_network);
+	}
+	if (preferred_local_network == -1) {
+		exit(207);  /* If the _local_ address isn't an IP address, then we've got problems. */
 	}
 
 	char preferred_transport = 'T';
 	struct sockaddr addr_struct;
 	int server_sock = create_local(preferred_local_network,preferred_transport,local_addr,local_port,&addr_struct);
-	int addrlen = sizeof(addr_struct);
+	if (server_sock < 0) {
+		exit(-1 * server_sock);
+	}
+	int addrlen;
+	if (check_ip_ver(local_addr) == 4) {
+		addrlen = sizeof(struct sockaddr_in);
+	} else if (check_ip_ver(local_addr) == 6) {
+		addrlen = sizeof(struct sockaddr_in6);
+	} else {
+		exit(207);
+	}
 
 	listen(server_sock,50);  /* Arbitrary number, change later */
 
 	printf("Listening on %s:%d\n",local_addr,local_port);
+
+	struct sockaddr remote_addr_struct;
 	while (1) {
-	int from_client = accept(server_sock,&addr_struct,(socklen_t *)&addrlen);	
-	int to_server = create_remote(preferred_remote_network,preferred_transport,remote_addr,remote_port);
+		int from_client = accept(server_sock,&addr_struct,(socklen_t *)&addrlen);
+		int to_server = create_remote(preferred_remote_network,preferred_transport,remote_addr,remote_port,&remote_addr_struct);
+		if (to_server < 0) {
+			exit(-1 * to_server);
+		}
 
-	printf("Connection established to %s:%d\n",remote_addr,remote_port);
-	if (fork() == 0) {
-
-	/* fork returns 0 for a child, so we're in the child's execution
-	   right now */
-		close(server_sock);
+		printf("Connection established to %s:%d\n",remote_addr,remote_port);
 		if (fork() == 0) {
-			forward_data(from_client,to_server);
+			/* fork returns 0 for a child, so we're in the child's execution
+			   right now */
+			close(server_sock);
+			if (fork() == 0) {
+				forward_data(from_client,to_server);
+				exit(0);
+			}
+			if (fork() == 0) {
+				forward_data(to_server,from_client);
+				exit(0);
+			}
 			exit(0);
 		}
-		if (fork() == 0) {
-			forward_data(to_server,from_client);
-			exit(0);
-		}
-		exit(0);
-
-
-	}
-//	recv(from_client,buffer,3000,0);
-			
-
-//	printf("%s",buffer);
-	
 
 	}