server.c

#include "sFunctions.h"

int main(int argc, char *argv[]) {
	char buf[MAX_LINE];// Buffer we will use to send(), recv(), and read()
	char fileList[MAX_LIST_LEN * sizeof(char) + 1], logFileName[37];
	const char * SERVER_PORT = argv[1];
	const char * SERVER_PASSWORD = argv[2];
	int s, new_s, size, timeoutVal = 0;
	struct sockaddr_in clientAddr;// Holds our client address
	socklen_t clientAddrSize = sizeof(struct sockaddr_in);
	fd_set readfds;// Create a structure to hold file descriptors
	FD_ZERO(&readfds);// Reset the file set

	if (!argv[1] || !argv[2]) {// Check that port and password are given by user
		fprintf(stderr, "S: Incorrect arguments,\nUSAGE: PORT# PASSWORD -[OPTIONS]\n");
		exit(1);
	}

	// Get all the options asked for, if any -- Options can be selected in any order
	int debugPrint = 0, noPass = 0, noTimer = 0, stayUp = 0, recoverFail = 0, printFile = 0, logOutput = 0;
	if (argc != 3) {
		for (int i = 3; i < argc; i++) {
			if (strcmp(argv[i], "-D") == 0) {debugPrint = 1;}// Debug mode for more verbose printing during process
			else if (strcmp(argv[i], "-NP") == 0) {noPass = 1;}// No password mode to allow any password to be accepted
			else if (strcmp(argv[i], "-NT") == 0) {noTimer = 1;}// No timeout mode to allow infinite time for client to choose file on receipt of list
			else if (strcmp(argv[i], "-SU") == 0) {stayUp = 1;}// Stay up mode to keep the server up and ready to receive the next client after each transfer process until such time the user exits
			else if (strcmp(argv[i], "-RM") == 0) {recoverFail = 1;}// Recovers server to continue (resets) after fatal error (IE: Client requesting bad file)
			else if (strcmp(argv[i], "-PF") == 0) {printFile = 1;}// Prints file as we read() it into stdout
			else if (strcmp(argv[i], "-LO") == 0) {logOutput = 1;}// Logs interactions between server/client
			else if (strcmp(argv[i], "-H") == 0) {printf("S: Usage is as follows -- PORT# PASSWORD -[OPTIONS]\n"); return 0;}
			else {fprintf(stderr, "S: Invalid option '%s'\nS: The valid options are listed in the README.md, continuing with process\n", argv[i]);}
		}
	}

	// Create a log file
	if (logOutput == 1) {printf("S: Logfile '%s' %s\n", logFileName, makeLogFile(logFileName) > 0 ? "opened. Writing activity to the file.\n" : "couldn't be opened, continuing.\n");}

	// Bind socket to local interface and passive open
	if ((s = bind_and_listen(SERVER_PORT)) < 0) {exit(1);}
	if (varPrint(logOutput, logFileName, 0, "S: Starting server on port '%s'.\n", SERVER_PORT) == -1) {fprintf(stderr, "S: Error with log file. Please check output.\n");}

	// Go into the main loop that waits for a potential client, this loop will allow us to receive multiple clients consecutively
	while (1) {
		// Try to accept a potential client on new_s
		if ((new_s = accept(s, (struct sockaddr *)&clientAddr, &clientAddrSize)) < 0) {
			fprintf(stderr, "S: Error accepting new client on new_s\n");
			close(s);
			exit(1);
		}

		// Print appropriate message for finding a potential client
		getpeername(new_s, (struct sockaddr *)&clientAddr, &clientAddrSize);// Get the adress of the client trying to connect to server
		if (debugPrint == 1) {
			time_t timeNow = time(NULL);
			varPrint(logOutput, logFileName, 0, "S: We found a potential client with address of '%s' - %s", inet_ntoa(clientAddr.sin_addr), ctime(&timeNow));
		}
		else {varPrint(logOutput, logFileName, 0, "S: We found a potential client with address of '%s'\n", inet_ntoa(clientAddr.sin_addr));}

		// Grab the password from the client
		if (isReceiving(new_s, readfds, 0, 500000) == 1) {
			memset(buf, 0, MAX_LINE);
			recv(new_s, buf, MAX_LINE, 0);
		}
		else {
			varPrint(logOutput, logFileName, 1, "S: Error receiving the client's password. Possible issue on either end.");
			if (recoverFail == 1) {goto endClientInteraction;}
			close(new_s);
			close(s);
			return 1;
		}

		// Verify the password we got from client
		if (strcmp(buf, SERVER_PASSWORD) != 0 && noPass == 0) {// Verify the password given by client matches what's in argv[2]
			varPrint(logOutput, logFileName, 0, "S: Bad password given, '%s', looking for '%s'. Terminating connection with client.\n", buf, SERVER_PASSWORD);
			send(new_s, "BAD", 3, 0);
			if (recoverFail == 1) {goto endClientInteraction;}
			close(new_s);
			close(s);
			return 0;
		}

		// Alert server of good password as well as send the response with timeout settings to client 
		varPrint(logOutput, logFileName, 0, "S: Valid password from client, sending a good response and waiting for them to accept the list\n");
		noTimer == 0 ? send(new_s, "VALID-TS", 8, 0) : send(new_s, "VALID-NT", 8, 0);
		
		// Receive the client response on whether they want to receive the list (it could be massive depending on directory)
		memset(buf, 0, MAX_LINE);
		recv(new_s, buf, 1, 0);

		// Alert the Server to the response from client
		if (strcmp(buf, "y") == 0 || strcmp(buf, "Y") == 0) {varPrint(logOutput, logFileName, 0, "S: The client accepted the list, sending the file name list\n");} 
		else {
			if (strcmp(buf, "n") == 0 || strcmp(buf, "N") == 0) {varPrint(logOutput, logFileName, 0, "S: The client denied the list. Terminating connection with client.\n");}
			else {varPrint(logOutput, logFileName, 1, "S: The client responded with invalid input, likely premature disconnection. Terminating connection with client.\n");}
			if (recoverFail == 1) {goto endClientInteraction;}
			close(new_s);
			close(s);
			return 0;
		}

		// We can make the assumption that the client responded "y" from here, so we create the list
		if (createList() != 0) {// createList() returns 1 for errors
			varPrint(logOutput, logFileName, 1, "S: Couldn't create/open the list. Terminating connection with client.\n");
			if (recoverFail == 1) {goto endClientInteraction;}
			close(new_s);
			close(s);
			exit(1);
		}

		// Attempt to open newly create file with list
		int listFile = open("DirectoryList", O_RDWR);
		if (listFile < 0) {// Verify we can open the file that contains our list of files in directory
			varPrint(logOutput, logFileName, 1, "S: Error opening list file after creating it. Terminating connection with client.\n");
			send(new_s, "Unable to open file.", 20, 0);// Alert client to error
			if (recoverFail == 1) {goto endClientInteraction;}
			close(new_s);
			close(s);
			exit(1);
		}

		// Send list of file names to the client so they can choose from that list
		memset(buf, 0, MAX_LINE);
		varPrint(logOutput, logFileName, 0, "%s", debugPrint == 1 ? " -- Start list --\n\n" : "");
		while ((size = read(listFile, buf, MAX_SIZE)) != 0) {
			buf[MAX_LINE - 1] = '\0';
			send(new_s, buf, size, 0);// Send buffer to client as it is modified by read()
			varPrint(logOutput, logFileName, 0, "%s", debugPrint == 1 ? buf : "");
		}
		varPrint(logOutput, logFileName, 0, "%s", debugPrint == 1 ? "\n -- End list --\n" : "");
		close(listFile);
		remove("DirectoryList");

		// Wait up to 60 seconds or forever if -NT is set for client to send us their filename choice
		varPrint(logOutput, logFileName, 0, "%s", noTimer == 0 ? "S: Waiting 1 minute for a request response from client.\n" : "S: Waiting for a request response from client.\n");
		while (1) {
			// Wait for input to recv() on new_s for the next 10 seconds
			if (isReceiving(new_s, readfds, 10, 0) == 1) {
				memset(fileList, 0, MAX_LIST_LEN);		
				recv(new_s, fileList, MAX_LIST_LEN, 0);
				if (debugPrint == 0) {varPrint(logOutput, logFileName, 0, "S: We received a request list from the client\n\n");}
				else {varPrint(logOutput, logFileName, 0, "S: We received a request list of '%s' from client\n\n", fileList);}
				break;
			}

			// Otherwise, we increment the timeout value and alert the server appropriately (and log it depending out noTimer setting)
			timeoutVal++;
			if (noTimer == 0) {varPrint(logOutput, logFileName, 0, "S: Client hasn't sent a file list yet, %i seconds remaining until client is dropped.\n", ((6-timeoutVal)*10));}
			else {varPrint(logOutput, logFileName, 0, "S: Client hasn't sent a file list yet. %i seconds have passed.\n", (timeoutVal*10));}

			// If the user didn't set NT and it's been 60 seconds, conditionally leave the loop
			if (noTimer == 0 && timeoutVal == 6) {
				varPrint(logOutput, logFileName, 1, "S: We didn't receive a filename in the alloted time. Terminating connection with client.\n");		
				if (recoverFail == 1) {goto endClientInteraction;}
				close(new_s);
				close(s);
				return 0;
			}
		}

		// Check to make sure we didn't receive an empty request list
		if (atoi(fileList) == 0) {
			varPrint(logOutput, logFileName, 0, "S: Client didn't select any files in their list. Terminating connection with client.\n");
			if (recoverFail == 1) {goto endClientInteraction;}
			close(new_s);
			close(s);
			return 0;
		}
		
		// Setup structures to use list we received from client
		char curFile[MAX_LINE];
		char *ptr = strtok(fileList, ";;");
		ptr = strtok(NULL, ";;");
		
		// Go through the transfer process with each file in the list we just received (Check the name against files in PWD -> Open file -> Send file -> SHA1 Check)
		while (ptr != NULL) {
			// Set the curFile equal to the file in the list we're current at as defined by ptr
			strcpy(curFile, ptr);
			curFile[strlen(ptr)] = '\0';
			varPrint(logOutput, logFileName, 0, "S: Processing the request for file '%s'\n", curFile);

			// If we fail to open the requested file, send a bad response "n" to client
			int requestedFile = open(curFile, O_RDWR);
			if (requestedFile < 0) {
				varPrint(logOutput, logFileName, 1, "S: Error opening requested file. Terminating connection with client.\n");
				send(new_s, "n", 1, 0);// Alert client to error
				if (recoverFail == 1) {goto endClientInteraction;}
				close(new_s);
				close(s);
				exit(1);
			}

			// Check this specific file against all files in folder to make sure the requested file matches one of them
			struct dirent* DirEntry;
			DIR* directory;
			directory = opendir(".");
			int gotFile = 0;
			while ((DirEntry = readdir(directory))) {if (strcmp(DirEntry->d_name, curFile) == 0) {gotFile = 1; break;}}
			closedir(directory);

			// If we didn't find the file requested withing our current directory, alert client and terminate connection
			if (gotFile != 1) {
				varPrint(logOutput, logFileName, 1, "S: Error finding requested file '%s'. Terminating connection with client.\n", curFile);
				send(new_s, "n", 1, 0);// Alert client to error
				if (recoverFail == 1) {goto endClientInteraction;}
				close(new_s);
				close(s);
				exit(1);
			}

			// We see the requested file is in our PWD and can open it, return a good response "y" to client
			send(new_s, "y", 1, 0);

			// Build structure for the SHA1 and initalize it to use it during transfer
			SHA_CTX ctx;
			SHA1_Init(&ctx);

			// Send the file data to the client as we read() it into buf
			varPrint(logOutput, logFileName, 0, "%s", printFile == 1 ? " -- Start file --\n\n" : "");
			int bytes = 0;
			while ((size = read(requestedFile, buf, MAX_SIZE)) != 0) {
				buf[MAX_LINE - 1] = '\0';
				send(new_s, buf, size, 0);
				SHA1_Update(&ctx, buf, size);// Update the SHA1 as buf keeps getting read() into
				bytes += size;// Increment bytes by size of packet sent each time
				varPrint(logOutput, logFileName, 0, "%s", printFile == 1 ? buf : "");
			}
			varPrint(logOutput, logFileName, 0, "%s", printFile == 1 ? "\n\n -- End file --\n" : "");
			varPrint(logOutput, logFileName, 0, "S: Finished sending file to client. %i total bytes sent.\n%s", bytes, printFile == 1 ? "\n\n" : "");
			close(requestedFile);

			// Build structure for the file hash and use SHA1_Final()
			unsigned char fileHash[SHA_DIGEST_LENGTH];// Reminder: SHA_DIGEST_LENGTH = 20 bytes
			SHA1_Final(fileHash, &ctx);

			// Use sprintf() to put the file hash into a workable string
			char serverSHA1[SHA_DIGEST_LENGTH*2];
			for (int pos = 0; pos < SHA_DIGEST_LENGTH; sprintf((char*)&(serverSHA1[pos*2]), "%02x", fileHash[pos]), pos++);

			// Now we receive the SHA1 the client got to check against it as a check
			varPrint(logOutput, logFileName, 0, "S: Waiting for the client's SHA1 to check against our local SHA1\n");
			while (1) {
				if (isReceiving(new_s, readfds, 0, 500000) == 1) {// If we're receiving data from client on new_s
					memset(buf, 0, MAX_LINE);
					recv(new_s, buf, MAX_LINE, 0);

					// Check if our file SHA1 is the same as client's
					if (strcmp(buf, serverSHA1) == 0) {
						send(new_s, "y", 1, 0);
						varPrint(logOutput, logFileName, 0, "S: The client's SHA1 matched. Sending good response message and moving on...\n\n");
						break;
					} else {
						varPrint(logOutput, logFileName, 1, "S: The client's SHA1 '%s' didn't match our SHA1 '%s'. Sending error message and terminating connection with client.\n\n", buf, serverSHA1);
						send(new_s, "n", 1, 0);
						if (recoverFail == 1) {goto endClientInteraction;}
						close(new_s);
						close(s);
						exit(1);
					}
				}
			}
			ptr = strtok(NULL, ";;");// Increment the ptr to go to the next token (filename) in fileList
		}
	
		// We reached the end of an interaction with a particular client
		endClientInteraction: ;

		// We need to ask if SU is off, in which case we need to get User to decide how to proceed 
		if (stayUp == 0) {
			varPrint(logOutput, logFileName, 0, "S: We finished with our current client, would you like to stay up for the next client? (yes = y, no = n)\n");
			while (1) {
				memset(buf, 0, MAX_LINE);
				fgets(buf, MAX_LINE, stdin);
				buf[1] = '\0';// Correction for new line on fgets
				if (strcmp(buf, "y") == 0 || strcmp(buf, "Y") == 0) {
					varPrint(logOutput, logFileName, 0, "S: User chose to continue with '%s'...\n", buf);
					break;
				} else if (strcmp(buf, "n") == 0 || strcmp(buf, "N") == 0) {
					varPrint(logOutput, logFileName, 0, "S: User terminated with '%s'. Ending processes.\n", buf);
					close(new_s);
					close(s);
					return 0;
				} else {
					varPrint(logOutput, logFileName, 1, "S: Invalid input, please type 'y' for yes, or 'n' for no\n");
				}
			}
		}

		// Server would've returned/exited by this point based on if-statement conditions, so we alert them that we're restarting (going back to start of while-loop)
		varPrint(logOutput, logFileName, 0, "\nS: Restarting the server and listening for a connection on port '%s' for a new client.\n", SERVER_PORT);
	}
	close(new_s);
	close(s);
	return 0;
}