eventdns.c

关于tor匿名通信的源代码

		4;	/* space for the resource type */
}

/* build a dns request packet into buf. buf should be at least as long */
/* as evdns_request_len told you it should be. */
/* */
/* Returns the amount of space used. Negative on error. */
static int
evdns_request_data_build(const char *const name, const size_t name_len,
						 const u16 trans_id, const u16 type, const u16 class,
						 u8 *const buf, size_t buf_len) {
	off_t j = 0;	/* current offset into buf */
	u16 _t;	 /* used by the macros */

	APPEND16(trans_id);
	APPEND16(0x0100);  /* standard query, recusion needed */
	APPEND16(1);  /* one question */
	APPEND16(0);  /* no answers */
	APPEND16(0);  /* no authority */
	APPEND16(0);  /* no additional */

	j = dnsname_to_labels(buf, buf_len, j, name, name_len, NULL);
	if (j < 0) {
		return (int)j;
	}

	APPEND16(type);
	APPEND16(class);

	return (int)j;
 overflow:
	return (-1);
}

/* exported function */
struct evdns_server_port *
evdns_add_server_port(int socket, int is_tcp, evdns_request_callback_fn_type cb, void *user_data)
{
	struct evdns_server_port *port;
	if (!(port = malloc(sizeof(struct evdns_server_port))))
		return NULL;
	memset(port, 0, sizeof(struct evdns_server_port));

	assert(!is_tcp); /* TCP sockets not yet implemented */
	port->socket = socket;
	port->refcnt = 1;
	port->choked = 0;
	port->closing = 0;
	port->user_callback = cb;
	port->user_data = user_data;
	port->pending_replies = NULL;

	event_set(&port->event, port->socket, EV_READ | EV_PERSIST,
			  server_port_ready_callback, port);
	if (event_add(&port->event, NULL)<0) {
		free(port);
		return NULL;
	}
	return port;
}

/* exported function */
void
evdns_close_server_port(struct evdns_server_port *port)
{
	if (--port->refcnt == 0)
		server_port_free(port);
	port->closing = 1;
}

/* exported function */
int
evdns_server_request_add_reply(struct evdns_server_request *_req, int section, const char *name, int type, int class, int ttl, int datalen, int is_name, const char *data)
{
	struct server_request *req = TO_SERVER_REQUEST(_req);
	struct server_reply_item **itemp, *item;
	int *countp;

	if (req->response) /* have we already answered? */
		return (-1);

	switch (section) {
	case EVDNS_ANSWER_SECTION:
		itemp = &req->answer;
		countp = &req->n_answer;
		break;
	case EVDNS_AUTHORITY_SECTION:
		itemp = &req->authority;
		countp = &req->n_authority;
		break;
	case EVDNS_ADDITIONAL_SECTION:
		itemp = &req->additional;
		countp = &req->n_additional;
		break;
	default:
		return (-1);
	}
	while (*itemp) {
		itemp = &((*itemp)->next);
	}
	item = malloc(sizeof(struct server_reply_item));
	if (!item)
		return -1;
	CLEAR(item);
	item->next = NULL;
	if (!(item->name = strdup(name))) {
		CLEAR(item);
		free(item);
		return -1;
	}
	item->type = type;
	item->class = class;
	item->ttl = ttl;
	item->is_name = is_name != 0;
	item->datalen = 0;
	item->data = NULL;
	if (data) {
		if (item->is_name) {
			if (!(item->data = strdup(data))) {
				free(item->name);
				CLEAR(item);
				free(item);
				return -1;
			}
			item->datalen = (u16)-1;
		} else {
			if (!(item->data = malloc(datalen))) {
				free(item->name);
				CLEAR(item);
				free(item);
				return -1;
			}
			item->datalen = datalen;
			memcpy(item->data, data, datalen);
		}
	}

	*itemp = item;
	++(*countp);
	return 0;
}

/* exported function */
int
evdns_server_request_add_a_reply(struct evdns_server_request *req, const char *name, int n, void *addrs, int ttl)
{
	return evdns_server_request_add_reply(
		  req, EVDNS_ANSWER_SECTION, name, TYPE_A, CLASS_INET,
		  ttl, n*4, 0, addrs);
}

/* exported function */
int
evdns_server_request_add_aaaa_reply(struct evdns_server_request *req, const char *name, int n, void *addrs, int ttl)
{
	return evdns_server_request_add_reply(
		  req, EVDNS_ANSWER_SECTION, name, TYPE_AAAA, CLASS_INET,
		  ttl, n*16, 0, addrs);
}

/* exported function */
int
evdns_server_request_add_ptr_reply(struct evdns_server_request *req, struct in_addr *in, const char *inaddr_name, const char *hostname, int ttl)
{
	u32 a;
	char buf[32];
	assert(in || inaddr_name);
	assert(!(in && inaddr_name));
	if (in) {
		a = ntohl(in->s_addr);
		snprintf(buf, sizeof(buf), "%d.%d.%d.%d.in-addr.arpa",
				(int)(u8)((a	)&0xff),
				(int)(u8)((a>>8 )&0xff),
				(int)(u8)((a>>16)&0xff),
				(int)(u8)((a>>24)&0xff));
		inaddr_name = buf;
	}
	return evdns_server_request_add_reply(
		  req, EVDNS_ANSWER_SECTION, inaddr_name, TYPE_PTR, CLASS_INET,
		  ttl, -1, 1, hostname);
}

/* exported function */
int
evdns_server_request_add_cname_reply(struct evdns_server_request *req, const char *name, const char *cname, int ttl)
{
	return evdns_server_request_add_reply(
		  req, EVDNS_ANSWER_SECTION, name, TYPE_A, CLASS_INET,
		  ttl, -1, 1, cname);
}


static int
evdns_server_request_format_response(struct server_request *req, int err)
{
	unsigned char buf[1500];
	size_t buf_len = sizeof(buf);
	off_t j = 0, r;
	u16 _t;
	u32 _t32;
	int i;
	u16 flags;
	struct dnslabel_table table;

	if (err < 0 || err > 15) return -1;

	/* Set response bit and error code; copy OPCODE and RD fields from
	 * question; copy RA and AA if set by caller. */
	flags = req->base.flags;
	flags |= (0x8000 | err);

	dnslabel_table_init(&table);
	APPEND16(req->trans_id);
	APPEND16(flags);
	APPEND16(req->base.nquestions);
	APPEND16(req->n_answer);
	APPEND16(req->n_authority);
	APPEND16(req->n_additional);

	/* Add questions. */
	for (i=0; i < req->base.nquestions; ++i) {
		const char *s = req->base.questions[i]->name;
		j = dnsname_to_labels(buf, buf_len, j, s, strlen(s), &table);
		if (j < 0) {
			dnslabel_clear(&table);
			return (int) j;
		}
		APPEND16(req->base.questions[i]->type);
		APPEND16(req->base.questions[i]->class);
	}

	/* Add answer, authority, and additional sections. */
	for (i=0; i<3; ++i) {
		struct server_reply_item *item;
		if (i==0)
			item = req->answer;
		else if (i==1)
			item = req->authority;
		else
			item = req->additional;
		while (item) {
			r = dnsname_to_labels(buf, buf_len, j, item->name, strlen(item->name), &table);
			if (r < 0)
				goto overflow;
			j = r;

			APPEND16(item->type);
			APPEND16(item->class);
			APPEND32(item->ttl);
			if (item->is_name) {
				off_t len_idx = j, name_start;
				j += 2;
				name_start = j;
				r = dnsname_to_labels(buf, buf_len, j, item->data, strlen(item->data), &table);
				if (r < 0)
					goto overflow;
				j = r;
				_t = htons( (j-name_start) );
				memcpy(buf+len_idx, &_t, 2);
			} else {
				APPEND16(item->datalen);
				if (j+item->datalen > (off_t)buf_len)
					goto overflow;
				memcpy(buf+j, item->data, item->datalen);
				j += item->datalen;
			}
			item = item->next;
		}
	}

	if (j > 512) {
overflow:
		j = 512;
		buf[3] |= 0x02; /* set the truncated bit. */
	}

	req->response_len = (size_t)j;

	if (!(req->response = malloc(req->response_len))) {
		server_request_free_answers(req);
		dnslabel_clear(&table);
		return (-1);
	}
	memcpy(req->response, buf, req->response_len);
	server_request_free_answers(req);
	dnslabel_clear(&table);
	return (0);
}

/* exported function */
int
evdns_server_request_respond(struct evdns_server_request *_req, int err)
{
	struct server_request *req = TO_SERVER_REQUEST(_req);
	struct evdns_server_port *port = req->port;
	ssize_t r;
	if (!req->response) {
		if ((r = evdns_server_request_format_response(req, err))<0)
			return (int)r;
	}

	r = sendto(port->socket, req->response, req->response_len, 0,
			   (struct sockaddr*) &req->addr, req->addrlen);
	if (r<0) {
		int err = last_error(port->socket);
		if (! error_is_eagain(err))
			return -1;

		if (port->pending_replies) {
			req->prev_pending = port->pending_replies->prev_pending;
			req->next_pending = port->pending_replies;
			req->prev_pending->next_pending =
				req->next_pending->prev_pending = req;
		} else {
			req->prev_pending = req->next_pending = req;
			port->pending_replies = req;
			port->choked = 1;

			(void) event_del(&port->event);
			CLEAR(&port->event);
			event_set(&port->event, port->socket, (port->closing?0:EV_READ) | EV_WRITE | EV_PERSIST, server_port_ready_callback, port);

			if (event_add(&port->event, NULL) < 0) {
				log(EVDNS_LOG_WARN, "Error from libevent when adding event for DNS server");
			}

		}

		return 1;
	}
	if (server_request_free(req))
		return 0;

	if (port->pending_replies)
		server_port_flush(port);

	return 0;
}

/* Free all storage held by RRs in req. */
static void
server_request_free_answers(struct server_request *req)
{
	struct server_reply_item *victim, *next, **list;
	int i;
	for (i = 0; i < 3; ++i) {
		if (i==0)
			list = &req->answer;
		else if (i==1)
			list = &req->authority;
		else
			list = &req->additional;

		victim = *list;
		while (victim) {
			next = victim->next;
			free(victim->name);
			if (victim->data)
				free(victim->data);
			free(victim);
			victim = next;
		}
		*list = NULL;
	}
}

/* Free all storage held by req, and remove links to it. */
/* return true iff we just wound up freeing the server_port. */
static int
server_request_free(struct server_request *req)
{
	int i, rc=1;
	if (req->base.questions) {
		for (i = 0; i < req->base.nquestions; ++i)
			free(req->base.questions[i]);
		free(req->base.questions);
	}

	if (req->port) {
		if (req->port->pending_replies == req) {
			if (req->next_pending)
				req->port->pending_replies = req->next_pending;
			else
				req->port->pending_replies = NULL;
		}
		rc = --req->port->refcnt;
	}

	if (req->response) {
		free(req->response);
	}

	server_request_free_answers(req);

	if (req->next_pending && req->next_pending != req) {
		req->next_pending->prev_pending = req->prev_pending;
		req->prev_pending->next_pending = req->next_pending;
	}

	if (rc == 0) {
		server_port_free(req->port);
		CLEAR(req);
		free(req);
		return (1);
	}
	CLEAR(req);
	free(req);
	return (0);
}

/* Free all storage held by an evdns_server_port.  Only called when  */
static void
server_port_free(struct evdns_server_port *port)
{
	assert(port);
	assert(!port->refcnt);
	assert(!port->pending_replies);
	if (port->socket > 0) {
		CLOSE_SOCKET(port->socket);
		port->socket = -1;
	}
	(void) event_del(&port->event);
	CLEAR(&port->event);
	/* XXXX021 actually free the port? -NM */
	/* XXXX yes, and fix up evdns_close_server_port to dtrt. -NM */
}

/* exported function */
int
evdns_server_request_drop(struct evdns_server_request *_req)
{
	struct server_request *req = TO_SERVER_REQUEST(_req);
	server_request_free(req);
	return 0;
}

/* exported function */
int
evdns_server_request_get_requesting_addr(struct evdns_server_request *_req, struct sockaddr *sa, int addr_len)
{
	struct server_request *req = TO_SERVER_REQUEST(_req);
	if (addr_len < (int)req->addrlen)
		return -1;
	memcpy(sa, &(req->addr), req->addrlen);
	return req->addrlen;
}

#undef APPEND16
#undef APPEND32

/* this is a libevent callback function which is called when a request */
/* has timed out. */
static void
evdns_request_timeout_callback(int fd, short events, void *arg) {
	struct request *const req = (struct request *) arg;
	(void) fd;
	(void) events;

	log(EVDNS_LOG_DEBUG, "Request %lx timed out", (unsigned long) arg);

	req->ns->timedout++;
	if (req->ns->timedout > global_max_nameserver_timeout) {
		req->ns->timedout = 0;
		nameserver_failed(req->ns, "request timed out.");
	}

	(void) evtimer_del(&req->timeout_event);
	CLEAR(&req->timeout_event);
	if (req->tx_count >= global_max_retransmits) {
		/* this request has failed */
		reply_callback(req, 0, DNS_ERR_TIMEOUT, NULL);
		request_finished(req, &req_head);