ftpd.c

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

			*(arg+n-4) = 0;
			d = dirstat(arg);
			if(d != nil){
				if(d->qid.type & QTDIR){
					retrievedir(arg);
					free(d);
					return;
				}
				free(d);
			}
		}
		logit("get %s failed", arg);
		reply("550 Error opening %s: %r", arg);
		return;
	}
	if(offset != 0)
		if(seek(fd, offset, 0) < 0){
			reply("550 %s: seek to %lld failed", arg, offset);
			close(fd);
			return;
		}
	d = dirfstat(fd);
	if(d != nil){
		if(d->qid.type & QTDIR){
			reply("550 %s: not a plain file.", arg);
			close(fd);
			free(d);
			return;
		}
		free(d);
	}

	n = read(fd, buf, sizeof(buf));
	if(n < 0){
		logit("get %s failed", arg, mailaddr, nci->rsys);
		reply("550 Error reading %s: %r", arg);
		close(fd);
		return;
	}

	if(type != Timage)
		for(p = buf, ep = &buf[n]; p < ep; p++)
			if(*p & 0x80){
				close(fd);
				reply("550 This file requires type binary/image");
				return;
			}

	reply("150 Opening data connection for %s (%s)", arg, data);
	dfd = dialdata();
	if(dfd < 0){
		reply("425 Error opening data connection:%r");
		close(fd);
		return;
	}

	bytes = 0;
	do {
		switch(type){
		case Timage:
			i = write(dfd, buf, n);
			break;
		default:
			i = crlfwrite(dfd, buf, n);
			break;
		}
		if(i != n){
			close(fd);
			close(dfd);
			logit("get %s %r to data connection after %d", arg, bytes);
			reply("550 Error writing to data connection: %r");
			return;
		}
		bytes += n;
	} while((n = read(fd, buf, sizeof(buf))) > 0);

	if(n < 0)
		logit("get %s %r after %d", arg, bytes);

	close(fd);
	close(dfd);
	reply("226 Transfer complete");
	logit("get %s OK %d", arg, bytes);
}
int
retrievecmd(char *arg)
{
	if(arg == 0)
		return reply("501 Retrieve command requires an argument");
	arg = abspath(arg);
	if(arg == 0)
		return reply("550 Permission denied");

	return asproc(retrieve, arg, 0);
}

/*
 *  get a file from the user
 */
int
lfwrite(int fd, char *p, int n)
{
	char *ep, *np;
	char buf[Nbuf];

	for(np = buf, ep = p + n; p < ep; p++){
		if(*p != '\r')
			*np++ = *p;
	}
	if(write(fd, buf, np - buf) == np - buf)
		return n;
	else
		return -1;
}
void
store(char *arg, int fd)
{
	int dfd, n, i;
	char buf[Nbuf];

	reply("150 Opening data connection for %s (%s)", arg, data);
	dfd = dialdata();
	if(dfd < 0){
		reply("425 Error opening data connection:%r");
		close(fd);
		return;
	}

	while((n = read(dfd, buf, sizeof(buf))) > 0){
		switch(type){
		case Timage:
			i = write(fd, buf, n);
			break;
		default:
			i = lfwrite(fd, buf, n);
			break;
		}
		if(i != n){
			close(fd);
			close(dfd);
			reply("550 Error writing file");
			return;
		}
	}
	close(fd);
	close(dfd);
	logit("put %s OK", arg);
	reply("226 Transfer complete");
}
int
storecmd(char *arg)
{
	int fd, rv;

	if(arg == 0)
		return reply("501 Store command requires an argument");
	arg = abspath(arg);
	if(arg == 0)
		return reply("550 Permission denied");
	if(isnone && strncmp(arg, "/incoming/", sizeof("/incoming/")-1))
		return reply("550 Permission denied");
	if(offset){
		fd = open(arg, OWRITE);
		if(fd == -1)
			return reply("550 Error opening %s: %r", arg);
		if(seek(fd, offset, 0) == -1)
			return reply("550 Error seeking %s to %d: %r",
				arg, offset);
	} else {
		fd = create(arg, OWRITE, createperm);
		if(fd == -1)
			return reply("550 Error creating %s: %r", arg);
	}

	rv = asproc(store, arg, fd);
	close(fd);
	return rv;
}
int
appendcmd(char *arg)
{
	int fd, rv;

	if(arg == 0)
		return reply("501 Append command requires an argument");
	if(isnone)
		return reply("550 Permission denied");
	arg = abspath(arg);
	if(arg == 0)
		return reply("550 Error creating %s: Permission denied", arg);
	fd = open(arg, OWRITE);
	if(fd == -1){
		fd = create(arg, OWRITE, createperm);
		if(fd == -1)
			return reply("550 Error creating %s: %r", arg);
	}
	seek(fd, 0, 2);

	rv = asproc(store, arg, fd);
	close(fd);
	return rv;
}
int
storeucmd(char *arg)
{
	int fd, rv;
	char name[Maxpath];

	USED(arg);
	if(isnone)
		return reply("550 Permission denied");
	strncpy(name, "ftpXXXXXXXXXXX", sizeof name);
	mktemp(name);
	fd = create(name, OWRITE, createperm);
	if(fd == -1)
		return reply("550 Error creating %s: %r", name);

	rv = asproc(store, name, fd);
	close(fd);
	return rv;
}

int
mkdircmd(char *name)
{
	int fd;

	if(name == 0)
		return reply("501 Mkdir command requires an argument");
	if(isnone)
		return reply("550 Permission denied");
	name = abspath(name);
	if(name == 0)
		return reply("550 Permission denied");
	fd = create(name, OREAD, DMDIR|0775);
	if(fd < 0)
		return reply("550 Can't create %s: %r", name);
	close(fd);
	return reply("226 %s created", name);
}

int
delcmd(char *name)
{
	if(name == 0)
		return reply("501 Rmdir/delete command requires an argument");
	if(isnone)
		return reply("550 Permission denied");
	name = abspath(name);
	if(name == 0)
		return reply("550 Permission denied");
	if(remove(name) < 0)
		return reply("550 Can't remove %s: %r", name);
	else
		return reply("226 %s removed", name);
}

/*
 *  kill off the last transfer (if the process still exists)
 */
int
abortcmd(char *arg)
{
	USED(arg);

	logit("abort pid %d", pid);
	if(pid){
		if(postnote(PNPROC, pid, "kill") == 0)
			reply("426 Command aborted");
		else
			logit("postnote pid %d %r", pid);
	}
	return reply("226 Abort processed");
}

int
systemcmd(char *arg)
{
	USED(arg);
	return reply("215 UNIX Type: L8 Version: Plan 9");
}

int
helpcmd(char *arg)
{
	int i;
	char buf[80];
	char *p, *e;

	USED(arg);
	reply("214- the following commands are implemented:");
	p = buf;
	e = buf+sizeof buf;
	for(i = 0; cmdtab[i].name; i++){
		if((i%8) == 0){
			reply("214-%s", buf);
			p = buf;
		}
		p = seprint(p, e, " %-5.5s", cmdtab[i].name);
	}
	if(p != buf)
		reply("214-%s", buf);
	reply("214 ");
	return 0;
}

/*
 *  renaming a file takes two commands
 */
static String *filepath;

int
rnfrcmd(char *from)
{
	if(isnone)
		return reply("550 Permission denied");
	if(from == 0)
		return reply("501 Rename command requires an argument");
	from = abspath(from);
	if(from == 0)
		return reply("550 Permission denied");
	if(filepath == nil)
		filepath = s_copy(from);
	else{
		s_reset(filepath);
		s_append(filepath, from);
	}
	return reply("350 Rename %s to ...", s_to_c(filepath));
}
int
rntocmd(char *to)
{
	int r;
	Dir nd;
	char *fp, *tp;

	if(isnone)
		return reply("550 Permission denied");
	if(to == 0)
		return reply("501 Rename command requires an argument");
	to = abspath(to);
	if(to == 0)
		return reply("550 Permission denied");
	if(filepath == nil || *(s_to_c(filepath)) == 0)
		return reply("503 Rnto must be preceeded by an rnfr");

	tp = strrchr(to, '/');
	fp = strrchr(s_to_c(filepath), '/');
	if((tp && fp == 0) || (fp && tp == 0)
	|| (fp && tp && (fp-s_to_c(filepath) != tp-to || memcmp(s_to_c(filepath), to, tp-to))))
		return reply("550 Rename can't change directory");
	if(tp)
		to = tp+1;

	nulldir(&nd);
	nd.name = to;
	if(dirwstat(s_to_c(filepath), &nd) < 0)
		r = reply("550 Can't rename %s to %s: %r\n", s_to_c(filepath), to);
	else
		r = reply("250 %s now %s", s_to_c(filepath), to);
	s_reset(filepath);

	return r;
}

/*
 *  to dial out we need the network file system in our
 *  name space.
 */
int
dialdata(void)
{
	int fd, cfd;
	char ldir[40];
	char err[Maxerr];

	if(mountnet() < 0)
		return -1;

	if(!passive.inuse){
		fd = dial(data, "20", 0, 0);
		errstr(err, sizeof err);
	} else {
		alarm(5*60*1000);
		cfd = listen(passive.adir, ldir);
		alarm(0);
		errstr(err, sizeof err);
		if(cfd < 0)
			return -1;
		fd = accept(cfd, ldir);
		errstr(err, sizeof err);
		close(cfd);
	}
	if(fd < 0)
		logit("can't dial %s: %s", data, err);

	unmountnet();
	werrstr(err, sizeof err);
	return fd;
}

int
postnote(int group, int pid, char *note)
{
	char file[128];
	int f, r;

	/*
	 * Use #p because /proc may not be in the namespace.
	 */
	switch(group) {
	case PNPROC:
		sprint(file, "#p/%d/note", pid);
		break;
	case PNGROUP:
		sprint(file, "#p/%d/notepg", pid);
		break;
	default:
		return -1;
	}

	f = open(file, OWRITE);
	if(f < 0)
		return -1;

	r = strlen(note);
	if(write(f, note, r) != r) {
		close(f);
		return -1;
	}
	close(f);
	return 0;
}

/*
 *  to circumscribe the accessible files we have to eliminate ..'s
 *  and resolve all names from the root.  We also remove any /bin/rc
 *  special characters to avoid later problems with executed commands.
 */
char *special = "`;| ";

char*
abspath(char *origpath)
{
	char *p, *sp, *path;
	static String *rpath;

	if(rpath == nil)
		rpath = s_new();
	else
		s_reset(rpath);

	if(origpath == nil)
		s_append(rpath, curdir);
	else{
		if(*origpath != '/'){
			s_append(rpath, curdir);
			s_append(rpath, "/");
		}
		s_append(rpath, origpath);
	}
	path = s_to_c(rpath);

	for(sp = special; *sp; sp++){
		p = strchr(path, *sp);
		if(p)
			*p = 0;
	}

	cleanname(s_to_c(rpath));
	rpath->ptr = rpath->base+strlen(rpath->base);

	if(!accessok(s_to_c(rpath)))
		return nil;

	return s_to_c(rpath);
}

typedef struct Path Path;
struct Path {
	Path	*next;
	String	*path;
	int	inuse;
	int	ok;
};

enum
{
	Maxlevel = 16,
	Maxperlevel= 8,
};

Path *pathlevel[Maxlevel];

Path*
unlinkpath(char *path, int level)
{
	String *s;
	Path **l, *p;
	int n;

	n = 0;
	for(l = &pathlevel[level]; *l; l = &(*l)->next){
		p = *l;
		/* hit */
		if(strcmp(s_to_c(p->path), path) == 0){
			*l = p->next;
			p->next = nil;
			return p;
		}
		/* reuse */
		if(++n >= Maxperlevel){
			*l = p->next;
			s = p->path;
			s_reset(p->path);
			memset(p, 0, sizeof *p);
			p->path = s_append(s, path);
			return p;
		}
	}

	/* allocate */
	p = mallocz(sizeof *p, 1);
	p->path = s_copy(path);
	return p;
}

void
linkpath(Path *p, int level)
{
	p->next = pathlevel[level];
	pathlevel[level] = p;
	p->inuse = 1;
}

void
addpath(Path *p, int level, int ok)
{
	p->ok = ok;
	p->next = pathlevel[level];
	pathlevel[level] = p;
}

int
_accessok(String *s, int level)
{
	Path *p;
	char *cp;
	int lvl, offset;
	static char httplogin[] = "/.httplogin";

	if(level < 0)
		return 1;
	lvl = level;
	if(lvl >= Maxlevel)
		lvl = Maxlevel - 1;

	p = unlinkpath(s_to_c(s), lvl);
	if(p->inuse){
		/* move to front */
		linkpath(p, lvl);
		return p->ok;
	}
	cp = strrchr(s_to_c(s), '/');
	if(cp == nil)
		offset = 0;
	else
		offset = cp - s_to_c(s);
	s_append(s, httplogin);
	if(access(s_to_c(s), AEXIST) == 0){
		addpath(p, lvl, 0);
		return 0;
	}

	/*
	 * There's no way to shorten a String without
	 * knowing the implementation.
	 */
	s->ptr = s->base+offset;
	s_terminate(s);
	addpath(p, lvl, _accessok(s, level-1));

	return p->ok;
}

/*
 * check for a subdirectory containing .httplogin
 * at each level of the path.
 */
int
accessok(char *path)
{
	int level, r;
	char *p;
	String *npath;

	npath = s_copy(path);
	p = s_to_c(npath)+1;
	for(level = 1; level < Maxlevel; level++){
		p = strchr(p, '/');
		if(p == nil)
			break;
		p++;
	}

	r = _accessok(npath, level-1);
	s_free(npath);

	return r;
}