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tftp.c
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tftp.c
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/*
* Copyright (C) 2013 Sol Boucher
* This is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with it. If not, see <http://www.gnu.org/licenses/>.
*/
// Simple TFTP client implementation.
// Author: Sol Boucher <slb1566@rit.edu>
#include "tftp_protoc.h"
#include <fcntl.h>
#include <libgen.h>
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
// Sex appeal:
static const char *const SHL_PS1 = "tftp> ";
// Interactive commands (must be wholly unambiguous):
static const char *const CMD_CON = "connect";
static const char *const CMD_PUT = "put";
static const char *const CMD_GET = "get";
static const char *const CMD_GFO = "quit";
static const char *const CMD_HLP = "?";
static void readin(char **, size_t *);
static bool homog(const char *, char);
static void usage(const char *, const char *, const char *);
static void noconn(const char *);
static void sendreq(int, const char*, int, struct sockaddr *);
// Runs the interactive loop and all file transfers.
// Returns: exit status
int main(void)
{
// Used to control DNS resolution requests:
struct addrinfo hints;
memset(&hints, 0, sizeof hints);
hints.ai_family = AF_INET;
hints.ai_socktype = SOCK_DGRAM;
// Bind to an ephemeral network port:
struct addrinfo *server = NULL;
int sfd = openudp(0);
if(sfd < 0)
handle_error("bind()");
// Allocate (small) space to store user input:
char *buf = malloc(1);
size_t cap = 1;
char *cmd; // First word of buf
size_t len; // Length of cmd
// Main input loop, which normally only breaks upon a GFO:
do
{
// Keep prompting until the user brings us back something good:
do
{
printf("%s", SHL_PS1);
readin(&buf, &cap);
}
while(homog(buf, ' '));
// Cleave off the command (first word):
cmd = strtok(buf, " ");
len = strlen(cmd);
if(strncmp(cmd, CMD_CON, len) == 0)
{
// Read the arguments:
const char *hostname = strtok(NULL, " ");
const char *tmp = strtok(NULL, " ");
in_port_t port = PORT_UNPRIVILEGED;
if(tmp)
port = atoi(tmp);
// Ensure a hostname or IP has been provided:
if(!hostname)
{
usage(CMD_CON, "hostname", "port");
continue;
}
// Avoid leaking any existing address:
if(server)
{
freeaddrinfo(server);
server = NULL;
}
// Try to resolve the requested hostname:
if(getaddrinfo(hostname, NULL, &hints, &server))
{
fprintf(stderr, "Unable to resolve hostname\n");
freeaddrinfo(server);
server = NULL;
continue;
}
((struct sockaddr_in *)server->ai_addr)->sin_port = htons(port);
}
else if(strncmp(cmd, CMD_GET, len) == 0 || strncmp(cmd, CMD_PUT, len) == 0)
{
bool putting = strncmp(cmd, CMD_PUT, 1) == 0;
// Ensure we're already connected to a server:
if(!server)
{
noconn(cmd);
continue;
}
// Make sure we were given a path argument:
char *pathname = strtok(NULL, "");
if(!pathname)
{
usage(putting ? CMD_PUT : CMD_GET, "pathname", NULL);
continue;
}
// Since basename() might modify pathname, copy it:
char filename[strlen(pathname)+1];
memcpy(filename, pathname, sizeof filename);
int fd;
if(putting)
{
// Try opening the file for reading:
if((fd = open(pathname, O_RDONLY)) < 0)
{
fprintf(stderr, "local: Unable to read specified file\n");
continue;
}
// Send a request and record the port used to acknowledge:
struct sockaddr_in dest_addr;
sendreq(sfd, basename(filename), OPC_WRQ, server->ai_addr);
uint8_t *rmtack = recvpkta(sfd, &dest_addr);
if(iserr(rmtack))
{
fprintf(stderr, "remote: %s\n", strerr(rmtack));
free(rmtack);
continue;
}
free(rmtack);
// Transmit the file:
sendfile(sfd, fd, &dest_addr);
}
else // getting
{
// Try opening a file of that name for writing:
if((fd = open(basename(filename), O_WRONLY|O_CREAT|O_EXCL, 0666)) < 0)
{
fprintf(stderr, "local: Unable to create the new file\n");
continue;
}
// Send a request and await the incoming file:
sendreq(sfd, pathname, OPC_RRQ, server->ai_addr);
const char *res = recvfile(sfd, fd);
if(res)
{
fprintf(stderr, "remote: %s\n", res);
close(fd);
fd = -1;
unlink(basename(filename));
}
}
if(fd >= 0)
close(fd);
}
else if(strncmp(cmd, CMD_HLP, len) == 0)
{
printf("Commands may be abbreviated. Commands are:\n\n");
printf("%s\t\tconnect to remote tftp\n", CMD_CON);
printf("%s\t\tsend file\n", CMD_PUT);
printf("%s\t\treceive file\n", CMD_GET);
printf("%s\t\texit tftp\n", CMD_GFO);
printf("%s\t\tprint help information\n", CMD_HLP);
}
else if(strncmp(cmd, CMD_GFO, len) != 0)
{
fprintf(stderr, "%s: unknown directive\n", cmd);
fprintf(stderr, "Try ? for help.\n");
}
}
while(strncmp(cmd, CMD_GFO, len) != 0);
free(buf);
if(server)
freeaddrinfo(server);
return 0;
}
// Reads one line of input from standard input into the provided buffer. Each time the buffer would overflow, it is reallocated at double its previous size.
// Accepts: the target buffer, its length in bytes
void readin(char **bufptr, size_t *bufcap)
{
char *buf = *bufptr;
bool fits;
int index = 0;
while(1)
{
fits = 0;
for(; index < *bufcap; ++index)
{
buf[index] = getc(stdin);
if(buf[index] == '\n')
buf[index] = '\0';
if(!buf[index])
{
fits = 1;
break;
}
}
if(fits) break;
buf = malloc(*bufcap*2);
memcpy(buf, *bufptr, *bufcap);
free(*bufptr);
*bufptr = buf;
*bufcap = *bufcap*2;
}
}
// Tests whether a string is entirely composed of a particular character.
// Accepts: the string and the character
bool homog(const char *str, char chr)
{
size_t len = strlen(str);
int ind;
for(ind = 0; ind < len; ++ind)
if(str[ind] != chr)
return 0;
return 1;
}
// Prints to standard error the usage string describing a command expecting one required argument and up to one optional argument.
// Accepts: the command, its required argument, and its optional argument or NULL
void usage(const char *cmd, const char *reqd, const char *optl)
{
char trailer[optl ? strlen(optl)+4 : 1];
trailer[0] = '\0';
if(optl)
sprintf(trailer, " [%s]", optl);
fprintf(stderr, "USAGE: %s <%s>%s\n", cmd, reqd, trailer);
fprintf(stderr, "Required argument %s not provided.\n", reqd);
}
// Complains to standard error that a connection should have been established before typing something.
// Accepts: that which was typed
void noconn(const char *typed)
{
fprintf(stderr, "%s: expects existing connection\n", typed);
fprintf(stderr, "Did you call %s?\n", CMD_CON);
}
// Sends a request datagram over the network specifying transfer type octal.
// Accepts: local socket file descriptor, requested filename, OPC_RRQ or OPC_WRQ, and remote socket address
void sendreq(int sfd, const char* pathname, int opcode, struct sockaddr *dest)
{
uint8_t req[2+strlen(pathname)+1+strlen(MODE_OCTET)+1];
*(uint16_t *)req = opcode;
strcpy(req+2, pathname);
strcpy(req+2+strlen(pathname)+1, MODE_OCTET);
sendto(sfd, req, sizeof req, 0, dest, sizeof(struct sockaddr_in));
}