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A C library for asynchronous DNS requests (grpc依赖)
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c-ares/ares_process.c

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/* Copyright 1998 by the Massachusetts Institute of Technology.
* Copyright (C) 2004-2017 by Daniel Stenberg
*
* Permission to use, copy, modify, and distribute this
* software and its documentation for any purpose and without
* fee is hereby granted, provided that the above copyright
* notice appear in all copies and that both that copyright
* notice and this permission notice appear in supporting
* documentation, and that the name of M.I.T. not be used in
* advertising or publicity pertaining to distribution of the
* software without specific, written prior permission.
* M.I.T. makes no representations about the suitability of
* this software for any purpose. It is provided "as is"
* without express or implied warranty.
*/
#include "ares_setup.h"
#ifdef HAVE_SYS_UIO_H
# include <sys/uio.h>
#endif
#ifdef HAVE_NETINET_IN_H
# include <netinet/in.h>
#endif
#ifdef HAVE_NETINET_TCP_H
# include <netinet/tcp.h>
#endif
#ifdef HAVE_NETDB_H
# include <netdb.h>
#endif
#ifdef HAVE_ARPA_INET_H
# include <arpa/inet.h>
#endif
#ifdef HAVE_ARPA_NAMESER_H
# include <arpa/nameser.h>
#else
# include "nameser.h"
#endif
#ifdef HAVE_ARPA_NAMESER_COMPAT_H
# include <arpa/nameser_compat.h>
#endif
#ifdef HAVE_STRINGS_H
# include <strings.h>
#endif
#ifdef HAVE_SYS_IOCTL_H
# include <sys/ioctl.h>
#endif
#ifdef NETWARE
# include <sys/filio.h>
#endif
#include <assert.h>
#include <fcntl.h>
#include <limits.h>
#include "ares.h"
#include "ares_dns.h"
#include "ares_nowarn.h"
#include "ares_private.h"
static int try_again(int errnum);
static void write_tcp_data(ares_channel channel, fd_set *write_fds,
ares_socket_t write_fd, struct timeval *now);
static void read_tcp_data(ares_channel channel, fd_set *read_fds,
ares_socket_t read_fd, struct timeval *now);
static void read_udp_packets(ares_channel channel, fd_set *read_fds,
ares_socket_t read_fd, struct timeval *now);
static void advance_tcp_send_queue(ares_channel channel, int whichserver,
ares_ssize_t num_bytes);
static void process_timeouts(ares_channel channel, struct timeval *now);
static void process_broken_connections(ares_channel channel,
struct timeval *now);
static void process_answer(ares_channel channel, unsigned char *abuf,
int alen, int whichserver, int tcp,
struct timeval *now);
static void handle_error(ares_channel channel, int whichserver,
struct timeval *now);
static void skip_server(ares_channel channel, struct query *query,
int whichserver);
static void next_server(ares_channel channel, struct query *query,
struct timeval *now);
static int open_tcp_socket(ares_channel channel, struct server_state *server);
static int open_udp_socket(ares_channel channel, struct server_state *server);
static int same_questions(const unsigned char *qbuf, int qlen,
const unsigned char *abuf, int alen);
static int same_address(struct sockaddr *sa, struct ares_addr *aa);
static void end_query(ares_channel channel, struct query *query, int status,
unsigned char *abuf, int alen);
/* return true if now is exactly check time or later */
int ares__timedout(struct timeval *now,
struct timeval *check)
{
long secs = (now->tv_sec - check->tv_sec);
if(secs > 0)
return 1; /* yes, timed out */
if(secs < 0)
return 0; /* nope, not timed out */
/* if the full seconds were identical, check the sub second parts */
return (now->tv_usec - check->tv_usec >= 0);
}
/* add the specific number of milliseconds to the time in the first argument */
static void timeadd(struct timeval *now, int millisecs)
{
now->tv_sec += millisecs/1000;
now->tv_usec += (millisecs%1000)*1000;
if(now->tv_usec >= 1000000) {
++(now->tv_sec);
now->tv_usec -= 1000000;
}
}
/*
* generic process function
*/
static void processfds(ares_channel channel,
fd_set *read_fds, ares_socket_t read_fd,
fd_set *write_fds, ares_socket_t write_fd)
{
struct timeval now = ares__tvnow();
write_tcp_data(channel, write_fds, write_fd, &now);
read_tcp_data(channel, read_fds, read_fd, &now);
read_udp_packets(channel, read_fds, read_fd, &now);
process_timeouts(channel, &now);
process_broken_connections(channel, &now);
}
/* Something interesting happened on the wire, or there was a timeout.
* See what's up and respond accordingly.
*/
void ares_process(ares_channel channel, fd_set *read_fds, fd_set *write_fds)
{
processfds(channel, read_fds, ARES_SOCKET_BAD, write_fds, ARES_SOCKET_BAD);
}
/* Something interesting happened on the wire, or there was a timeout.
* See what's up and respond accordingly.
*/
void ares_process_fd(ares_channel channel,
ares_socket_t read_fd, /* use ARES_SOCKET_BAD or valid
file descriptors */
ares_socket_t write_fd)
{
processfds(channel, NULL, read_fd, NULL, write_fd);
}
/* Return 1 if the specified error number describes a readiness error, or 0
* otherwise. This is mostly for HP-UX, which could return EAGAIN or
* EWOULDBLOCK. See this man page
*
* http://devrsrc1.external.hp.com/STKS/cgi-bin/man2html?
* manpage=/usr/share/man/man2.Z/send.2
*/
static int try_again(int errnum)
{
#if !defined EWOULDBLOCK && !defined EAGAIN
#error "Neither EWOULDBLOCK nor EAGAIN defined"
#endif
switch (errnum)
{
#ifdef EWOULDBLOCK
case EWOULDBLOCK:
return 1;
#endif
#if defined EAGAIN && EAGAIN != EWOULDBLOCK
case EAGAIN:
return 1;
#endif
}
return 0;
}
static ares_ssize_t socket_writev(ares_channel channel, ares_socket_t s, const struct iovec * vec, int len)
{
if (channel->sock_funcs)
return channel->sock_funcs->asendv(s, vec, len, channel->sock_func_cb_data);
return writev(s, vec, len);
}
static ares_ssize_t socket_write(ares_channel channel, ares_socket_t s, const void * data, size_t len)
{
if (channel->sock_funcs)
{
struct iovec vec;
vec.iov_base = (void*)data;
vec.iov_len = len;
return channel->sock_funcs->asendv(s, &vec, 1, channel->sock_func_cb_data);
}
return swrite(s, data, len);
}
/* If any TCP sockets select true for writing, write out queued data
* we have for them.
*/
static void write_tcp_data(ares_channel channel,
fd_set *write_fds,
ares_socket_t write_fd,
struct timeval *now)
{
struct server_state *server;
struct send_request *sendreq;
struct iovec *vec;
int i;
ares_ssize_t scount;
ares_ssize_t wcount;
size_t n;
if(!write_fds && (write_fd == ARES_SOCKET_BAD))
/* no possible action */
return;
for (i = 0; i < channel->nservers; i++)
{
/* Make sure server has data to send and is selected in write_fds or
write_fd. */
server = &channel->servers[i];
if (!server->qhead || server->tcp_socket == ARES_SOCKET_BAD ||
server->is_broken)
continue;
if(write_fds) {
if(!FD_ISSET(server->tcp_socket, write_fds))
continue;
}
else {
if(server->tcp_socket != write_fd)
continue;
}
if(write_fds)
/* If there's an error and we close this socket, then open
* another with the same fd to talk to another server, then we
* don't want to think that it was the new socket that was
* ready. This is not disastrous, but is likely to result in
* extra system calls and confusion. */
FD_CLR(server->tcp_socket, write_fds);
/* Count the number of send queue items. */
n = 0;
for (sendreq = server->qhead; sendreq; sendreq = sendreq->next)
n++;
/* Allocate iovecs so we can send all our data at once. */
vec = ares_malloc(n * sizeof(struct iovec));
if (vec)
{
/* Fill in the iovecs and send. */
n = 0;
for (sendreq = server->qhead; sendreq; sendreq = sendreq->next)
{
vec[n].iov_base = (char *) sendreq->data;
vec[n].iov_len = sendreq->len;
n++;
}
wcount = socket_writev(channel, server->tcp_socket, vec, (int)n);
ares_free(vec);
if (wcount < 0)
{
if (!try_again(SOCKERRNO))
handle_error(channel, i, now);
continue;
}
/* Advance the send queue by as many bytes as we sent. */
advance_tcp_send_queue(channel, i, wcount);
}
else
{
/* Can't allocate iovecs; just send the first request. */
sendreq = server->qhead;
scount = socket_write(channel, server->tcp_socket, sendreq->data, sendreq->len);
if (scount < 0)
{
if (!try_again(SOCKERRNO))
handle_error(channel, i, now);
continue;
}
/* Advance the send queue by as many bytes as we sent. */
advance_tcp_send_queue(channel, i, scount);
}
}
}
/* Consume the given number of bytes from the head of the TCP send queue. */
static void advance_tcp_send_queue(ares_channel channel, int whichserver,
ares_ssize_t num_bytes)
{
struct send_request *sendreq;
struct server_state *server = &channel->servers[whichserver];
while (num_bytes > 0) {
sendreq = server->qhead;
if ((size_t)num_bytes >= sendreq->len) {
num_bytes -= sendreq->len;
server->qhead = sendreq->next;
if (sendreq->data_storage)
ares_free(sendreq->data_storage);
ares_free(sendreq);
if (server->qhead == NULL) {
SOCK_STATE_CALLBACK(channel, server->tcp_socket, 1, 0);
server->qtail = NULL;
/* qhead is NULL so we cannot continue this loop */
break;
}
}
else {
sendreq->data += num_bytes;
sendreq->len -= num_bytes;
num_bytes = 0;
}
}
}
static ares_ssize_t socket_recvfrom(ares_channel channel,
ares_socket_t s,
void * data,
size_t data_len,
int flags,
struct sockaddr *from,
ares_socklen_t *from_len)
{
if (channel->sock_funcs)
return channel->sock_funcs->arecvfrom(s, data, data_len,
flags, from, from_len,
channel->sock_func_cb_data);
#ifdef HAVE_RECVFROM
return recvfrom(s, data, data_len, flags, from, from_len);
#else
return sread(s, data, data_len);
#endif
}
static ares_ssize_t socket_recv(ares_channel channel,
ares_socket_t s,
void * data,
size_t data_len)
{
if (channel->sock_funcs)
return channel->sock_funcs->arecvfrom(s, data, data_len, 0, 0, 0,
channel->sock_func_cb_data);
return sread(s, data, data_len);
}
/* If any TCP socket selects true for reading, read some data,
* allocate a buffer if we finish reading the length word, and process
* a packet if we finish reading one.
*/
static void read_tcp_data(ares_channel channel, fd_set *read_fds,
ares_socket_t read_fd, struct timeval *now)
{
struct server_state *server;
int i;
ares_ssize_t count;
if(!read_fds && (read_fd == ARES_SOCKET_BAD))
/* no possible action */
return;
for (i = 0; i < channel->nservers; i++)
{
/* Make sure the server has a socket and is selected in read_fds. */
server = &channel->servers[i];
if (server->tcp_socket == ARES_SOCKET_BAD || server->is_broken)
continue;
if(read_fds) {
if(!FD_ISSET(server->tcp_socket, read_fds))
continue;
}
else {
if(server->tcp_socket != read_fd)
continue;
}
if(read_fds)
/* If there's an error and we close this socket, then open another
* with the same fd to talk to another server, then we don't want to
* think that it was the new socket that was ready. This is not
* disastrous, but is likely to result in extra system calls and
* confusion. */
FD_CLR(server->tcp_socket, read_fds);
if (server->tcp_lenbuf_pos != 2)
{
/* We haven't yet read a length word, so read that (or
* what's left to read of it).
*/
count = socket_recv(channel, server->tcp_socket,
server->tcp_lenbuf + server->tcp_lenbuf_pos,
2 - server->tcp_lenbuf_pos);
if (count <= 0)
{
if (!(count == -1 && try_again(SOCKERRNO)))
handle_error(channel, i, now);
continue;
}
server->tcp_lenbuf_pos += (int)count;
if (server->tcp_lenbuf_pos == 2)
{
/* We finished reading the length word. Decode the
* length and allocate a buffer for the data.
*/
server->tcp_length = server->tcp_lenbuf[0] << 8
| server->tcp_lenbuf[1];
server->tcp_buffer = ares_malloc(server->tcp_length);
if (!server->tcp_buffer) {
handle_error(channel, i, now);
return; /* bail out on malloc failure. TODO: make this
function return error codes */
}
server->tcp_buffer_pos = 0;
}
}
else
{
/* Read data into the allocated buffer. */
count = socket_recv(channel, server->tcp_socket,
server->tcp_buffer + server->tcp_buffer_pos,
server->tcp_length - server->tcp_buffer_pos);
if (count <= 0)
{
if (!(count == -1 && try_again(SOCKERRNO)))
handle_error(channel, i, now);
continue;
}
server->tcp_buffer_pos += (int)count;
if (server->tcp_buffer_pos == server->tcp_length)
{
/* We finished reading this answer; process it and
* prepare to read another length word.
*/
process_answer(channel, server->tcp_buffer, server->tcp_length,
i, 1, now);
ares_free(server->tcp_buffer);
server->tcp_buffer = NULL;
server->tcp_lenbuf_pos = 0;
server->tcp_buffer_pos = 0;
}
}
}
}
/* If any UDP sockets select true for reading, process them. */
static void read_udp_packets(ares_channel channel, fd_set *read_fds,
ares_socket_t read_fd, struct timeval *now)
{
struct server_state *server;
int i;
ares_ssize_t count;
unsigned char buf[MAXENDSSZ + 1];
#ifdef HAVE_RECVFROM
ares_socklen_t fromlen;
union {
struct sockaddr sa;
struct sockaddr_in sa4;
struct sockaddr_in6 sa6;
} from;
#endif
if(!read_fds && (read_fd == ARES_SOCKET_BAD))
/* no possible action */
return;
for (i = 0; i < channel->nservers; i++)
{
/* Make sure the server has a socket and is selected in read_fds. */
server = &channel->servers[i];
if (server->udp_socket == ARES_SOCKET_BAD || server->is_broken)
continue;
if(read_fds) {
if(!FD_ISSET(server->udp_socket, read_fds))
continue;
}
else {
if(server->udp_socket != read_fd)
continue;
}
if(read_fds)
/* If there's an error and we close this socket, then open
* another with the same fd to talk to another server, then we
* don't want to think that it was the new socket that was
* ready. This is not disastrous, but is likely to result in
* extra system calls and confusion. */
FD_CLR(server->udp_socket, read_fds);
/* To reduce event loop overhead, read and process as many
* packets as we can. */
do {
if (server->udp_socket == ARES_SOCKET_BAD)
count = 0;
else {
if (server->addr.family == AF_INET)
fromlen = sizeof(from.sa4);
else
fromlen = sizeof(from.sa6);
count = socket_recvfrom(channel, server->udp_socket, (void *)buf,
sizeof(buf), 0, &from.sa, &fromlen);
}
if (count == -1 && try_again(SOCKERRNO))
continue;
else if (count <= 0)
handle_error(channel, i, now);
#ifdef HAVE_RECVFROM
else if (!same_address(&from.sa, &server->addr))
/* The address the response comes from does not match the address we
* sent the request to. Someone may be attempting to perform a cache
* poisoning attack. */
break;
#endif
else
process_answer(channel, buf, (int)count, i, 0, now);
} while (count > 0);
}
}
/* If any queries have timed out, note the timeout and move them on. */
static void process_timeouts(ares_channel channel, struct timeval *now)
{
time_t t; /* the time of the timeouts we're processing */
struct query *query;
struct list_node* list_head;
struct list_node* list_node;
/* Process all the timeouts that have fired since the last time we processed
* timeouts. If things are going well, then we'll have hundreds/thousands of
* queries that fall into future buckets, and only a handful of requests
* that fall into the "now" bucket, so this should be quite quick.
*/
for (t = channel->last_timeout_processed; t <= now->tv_sec; t++)
{
list_head = &(channel->queries_by_timeout[t % ARES_TIMEOUT_TABLE_SIZE]);
for (list_node = list_head->next; list_node != list_head; )
{
query = list_node->data;
list_node = list_node->next; /* in case the query gets deleted */
if (query->timeout.tv_sec && ares__timedout(now, &query->timeout))
{
query->error_status = ARES_ETIMEOUT;
++query->timeouts;
next_server(channel, query, now);
}
}
}
channel->last_timeout_processed = now->tv_sec;
}
/* Handle an answer from a server. */
static void process_answer(ares_channel channel, unsigned char *abuf,
int alen, int whichserver, int tcp,
struct timeval *now)
{
int tc, rcode, packetsz;
unsigned short id;
struct query *query;
struct list_node* list_head;
struct list_node* list_node;
/* If there's no room in the answer for a header, we can't do much
* with it. */
if (alen < HFIXEDSZ)
return;
/* Grab the query ID, truncate bit, and response code from the packet. */
id = DNS_HEADER_QID(abuf);
tc = DNS_HEADER_TC(abuf);
rcode = DNS_HEADER_RCODE(abuf);
/* Find the query corresponding to this packet. The queries are
* hashed/bucketed by query id, so this lookup should be quick. Note that
* both the query id and the questions must be the same; when the query id
* wraps around we can have multiple outstanding queries with the same query
* id, so we need to check both the id and question.
*/
query = NULL;
list_head = &(channel->queries_by_qid[id % ARES_QID_TABLE_SIZE]);
for (list_node = list_head->next; list_node != list_head;
list_node = list_node->next)
{
struct query *q = list_node->data;
if ((q->qid == id) && same_questions(q->qbuf, q->qlen, abuf, alen))
{
query = q;
break;
}
}
if (!query)
return;
packetsz = PACKETSZ;
/* If we use EDNS and server answers with one of these RCODES, the protocol
* extension is not understood by the responder. We must retry the query
* without EDNS enabled.
*/
if (channel->flags & ARES_FLAG_EDNS)
{
packetsz = channel->ednspsz;
if (rcode == NOTIMP || rcode == FORMERR || rcode == SERVFAIL)
{
int qlen = (query->tcplen - 2) - EDNSFIXEDSZ;
channel->flags ^= ARES_FLAG_EDNS;
query->tcplen -= EDNSFIXEDSZ;
query->qlen -= EDNSFIXEDSZ;
query->tcpbuf[0] = (unsigned char)((qlen >> 8) & 0xff);
query->tcpbuf[1] = (unsigned char)(qlen & 0xff);
DNS_HEADER_SET_ARCOUNT(query->tcpbuf + 2, 0);
query->tcpbuf = ares_realloc(query->tcpbuf, query->tcplen);
query->qbuf = query->tcpbuf + 2;
ares__send_query(channel, query, now);
return;
}
}
/* If we got a truncated UDP packet and are not ignoring truncation,
* don't accept the packet, and switch the query to TCP if we hadn't
* done so already.
*/
if ((tc || alen > packetsz) && !tcp && !(channel->flags & ARES_FLAG_IGNTC))
{
if (!query->using_tcp)
{
query->using_tcp = 1;
ares__send_query(channel, query, now);
}
return;
}
/* Limit alen to PACKETSZ if we aren't using TCP (only relevant if we
* are ignoring truncation.
*/
if (alen > packetsz && !tcp)
alen = packetsz;
/* If we aren't passing through all error packets, discard packets
* with SERVFAIL, NOTIMP, or REFUSED response codes.
*/
if (!(channel->flags & ARES_FLAG_NOCHECKRESP))
{
if (rcode == SERVFAIL || rcode == NOTIMP || rcode == REFUSED)
{
skip_server(channel, query, whichserver);
if (query->server == whichserver)
next_server(channel, query, now);
return;
}
}
end_query(channel, query, ARES_SUCCESS, abuf, alen);
}
/* Close all the connections that are no longer usable. */
static void process_broken_connections(ares_channel channel,
struct timeval *now)
{
int i;
for (i = 0; i < channel->nservers; i++)
{
struct server_state *server = &channel->servers[i];
if (server->is_broken)
{
handle_error(channel, i, now);
}
}
}
/* Swap the contents of two lists */
static void swap_lists(struct list_node* head_a,
struct list_node* head_b)
{
int is_a_empty = ares__is_list_empty(head_a);
int is_b_empty = ares__is_list_empty(head_b);
struct list_node old_a = *head_a;
struct list_node old_b = *head_b;
if (is_a_empty) {
ares__init_list_head(head_b);
} else {
*head_b = old_a;
old_a.next->prev = head_b;
old_a.prev->next = head_b;
}
if (is_b_empty) {
ares__init_list_head(head_a);
} else {
*head_a = old_b;
old_b.next->prev = head_a;
old_b.prev->next = head_a;
}
}
static void handle_error(ares_channel channel, int whichserver,
struct timeval *now)
{
struct server_state *server;
struct query *query;
struct list_node list_head;
struct list_node* list_node;
server = &channel->servers[whichserver];
/* Reset communications with this server. */
ares__close_sockets(channel, server);
/* Tell all queries talking to this server to move on and not try this
* server again. We steal the current list of queries that were in-flight to
* this server, since when we call next_server this can cause the queries to
* be re-sent to this server, which will re-insert these queries in that
* same server->queries_to_server list.
*/
ares__init_list_head(&list_head);
swap_lists(&list_head, &(server->queries_to_server));
for (list_node = list_head.next; list_node != &list_head; )
{
query = list_node->data;
list_node = list_node->next; /* in case the query gets deleted */
assert(query->server == whichserver);
skip_server(channel, query, whichserver);
next_server(channel, query, now);
}
/* Each query should have removed itself from our temporary list as
* it re-sent itself or finished up...
*/
assert(ares__is_list_empty(&list_head));
}
static void skip_server(ares_channel channel, struct query *query,
int whichserver)
{
/* The given server gave us problems with this query, so if we have the
* luxury of using other servers, then let's skip the potentially broken
* server and just use the others. If we only have one server and we need to
* retry then we should just go ahead and re-use that server, since it's our
* only hope; perhaps we just got unlucky, and retrying will work (eg, the
* server timed out our TCP connection just as we were sending another
* request).
*/
if (channel->nservers > 1)
{
query->server_info[whichserver].skip_server = 1;
}
}
static void next_server(ares_channel channel, struct query *query,
struct timeval *now)
{
/* We need to try each server channel->tries times. We have channel->nservers
* servers to try. In total, we need to do channel->nservers * channel->tries
* attempts. Use query->try to remember how many times we already attempted
* this query. Use modular arithmetic to find the next server to try. */
while (++(query->try_count) < (channel->nservers * channel->tries))
{
struct server_state *server;
/* Move on to the next server. */
query->server = (query->server + 1) % channel->nservers;
server = &channel->servers[query->server];
/* We don't want to use this server if (1) we decided this connection is
* broken, and thus about to be closed, (2) we've decided to skip this
* server because of earlier errors we encountered, or (3) we already
* sent this query over this exact connection.
*/
if (!server->is_broken &&
!query->server_info[query->server].skip_server &&
!(query->using_tcp &&
(query->server_info[query->server].tcp_connection_generation ==
server->tcp_connection_generation)))
{
ares__send_query(channel, query, now);
return;
}
/* You might think that with TCP we only need one try. However, even
* when using TCP, servers can time-out our connection just as we're
* sending a request, or close our connection because they die, or never
* send us a reply because they get wedged or tickle a bug that drops
* our request.
*/
}
/* If we are here, all attempts to perform query failed. */
end_query(channel, query, query->error_status, NULL, 0);
}
void ares__send_query(ares_channel channel, struct query *query,
struct timeval *now)
{
struct send_request *sendreq;
struct server_state *server;
int timeplus;
server = &channel->servers[query->server];
if (query->using_tcp)
{
/* Make sure the TCP socket for this server is set up and queue
* a send request.
*/
if (server->tcp_socket == ARES_SOCKET_BAD)
{
if (open_tcp_socket(channel, server) == -1)
{
skip_server(channel, query, query->server);
next_server(channel, query, now);
return;
}
}
sendreq = ares_malloc(sizeof(struct send_request));
if (!sendreq)
{
end_query(channel, query, ARES_ENOMEM, NULL, 0);
return;
}
memset(sendreq, 0, sizeof(struct send_request));
/* To make the common case fast, we avoid copies by using the query's
* tcpbuf for as long as the query is alive. In the rare case where the
* query ends while it's queued for transmission, then we give the
* sendreq its own copy of the request packet and put it in
* sendreq->data_storage.
*/
sendreq->data_storage = NULL;
sendreq->data = query->tcpbuf;
sendreq->len = query->tcplen;
sendreq->owner_query = query;
sendreq->next = NULL;
if (server->qtail)
server->qtail->next = sendreq;
else
{
SOCK_STATE_CALLBACK(channel, server->tcp_socket, 1, 1);
server->qhead = sendreq;
}
server->qtail = sendreq;
query->server_info[query->server].tcp_connection_generation =
server->tcp_connection_generation;
}
else
{
if (server->udp_socket == ARES_SOCKET_BAD)
{
if (open_udp_socket(channel, server) == -1)
{
skip_server(channel, query, query->server);
next_server(channel, query, now);
return;
}
}
if (socket_write(channel, server->udp_socket, query->qbuf, query->qlen) == -1)
{
/* FIXME: Handle EAGAIN here since it likely can happen. */
skip_server(channel, query, query->server);
next_server(channel, query, now);
return;
}
}
/* For each trip through the entire server list, double the channel's
* assigned timeout, avoiding overflow. If channel->timeout is negative,
* leave it as-is, even though that should be impossible here.
*/
timeplus = channel->timeout;
{
/* How many times do we want to double it? Presume sane values here. */
const int shift = query->try_count / channel->nservers;
/* Is there enough room to shift timeplus left that many times?
*
* To find out, confirm that all of the bits we'll shift away are zero.
* Stop considering a shift if we get to the point where we could shift
* a 1 into the sign bit (i.e. when shift is within two of the bit
* count).
*
* This has the side benefit of leaving negative numbers unchanged.
*/
if(shift <= (int)(sizeof(int) * CHAR_BIT - 1)
&& (timeplus >> (sizeof(int) * CHAR_BIT - 1 - shift)) == 0)
{
timeplus <<= shift;
}
}
query->timeout = *now;
timeadd(&query->timeout, timeplus);
/* Keep track of queries bucketed by timeout, so we can process
* timeout events quickly.
*/
ares__remove_from_list(&(query->queries_by_timeout));
ares__insert_in_list(
&(query->queries_by_timeout),
&(channel->queries_by_timeout[query->timeout.tv_sec %
ARES_TIMEOUT_TABLE_SIZE]));
/* Keep track of queries bucketed by server, so we can process server
* errors quickly.
*/
ares__remove_from_list(&(query->queries_to_server));
ares__insert_in_list(&(query->queries_to_server),
&(server->queries_to_server));
}
/*
* setsocknonblock sets the given socket to either blocking or non-blocking
* mode based on the 'nonblock' boolean argument. This function is highly
* portable.
*/
static int setsocknonblock(ares_socket_t sockfd, /* operate on this */
int nonblock /* TRUE or FALSE */)
{
#if defined(USE_BLOCKING_SOCKETS)
return 0; /* returns success */
#elif defined(HAVE_FCNTL_O_NONBLOCK)
/* most recent unix versions */
int flags;
flags = fcntl(sockfd, F_GETFL, 0);
if (FALSE != nonblock)
return fcntl(sockfd, F_SETFL, flags | O_NONBLOCK);
else
return fcntl(sockfd, F_SETFL, flags & (~O_NONBLOCK)); /* LCOV_EXCL_LINE */
#elif defined(HAVE_IOCTL_FIONBIO)
/* older unix versions */
int flags = nonblock ? 1 : 0;
return ioctl(sockfd, FIONBIO, &flags);
#elif defined(HAVE_IOCTLSOCKET_FIONBIO)
#ifdef WATT32
char flags = nonblock ? 1 : 0;
#else
/* Windows */
unsigned long flags = nonblock ? 1UL : 0UL;
#endif
return ioctlsocket(sockfd, FIONBIO, &flags);
#elif defined(HAVE_IOCTLSOCKET_CAMEL_FIONBIO)
/* Amiga */
long flags = nonblock ? 1L : 0L;
return IoctlSocket(sockfd, FIONBIO, flags);
#elif defined(HAVE_SETSOCKOPT_SO_NONBLOCK)
/* BeOS */
long b = nonblock ? 1L : 0L;
return setsockopt(sockfd, SOL_SOCKET, SO_NONBLOCK, &b, sizeof(b));
#else
# error "no non-blocking method was found/used/set"
#endif
}
static int configure_socket(ares_socket_t s, int family, ares_channel channel)
{
union {
struct sockaddr sa;
struct sockaddr_in sa4;
struct sockaddr_in6 sa6;
} local;
/* do not set options for user-managed sockets */
if (channel->sock_funcs)
return 0;
(void)setsocknonblock(s, TRUE);
#if defined(FD_CLOEXEC) && !defined(MSDOS)
/* Configure the socket fd as close-on-exec. */
if (fcntl(s, F_SETFD, FD_CLOEXEC) == -1)
return -1; /* LCOV_EXCL_LINE */
#endif
/* Set the socket's send and receive buffer sizes. */
if ((channel->socket_send_buffer_size > 0) &&
setsockopt(s, SOL_SOCKET, SO_SNDBUF,
(void *)&channel->socket_send_buffer_size,
sizeof(channel->socket_send_buffer_size)) == -1)
return -1;
if ((channel->socket_receive_buffer_size > 0) &&
setsockopt(s, SOL_SOCKET, SO_RCVBUF,
(void *)&channel->socket_receive_buffer_size,
sizeof(channel->socket_receive_buffer_size)) == -1)
return -1;
#ifdef SO_BINDTODEVICE
if (channel->local_dev_name[0]) {
if (setsockopt(s, SOL_SOCKET, SO_BINDTODEVICE,
channel->local_dev_name, sizeof(channel->local_dev_name))) {
/* Only root can do this, and usually not fatal if it doesn't work, so */
/* just continue on. */
}
}
#endif
if (family == AF_INET) {
if (channel->local_ip4) {
memset(&local.sa4, 0, sizeof(local.sa4));
local.sa4.sin_family = AF_INET;
local.sa4.sin_addr.s_addr = htonl(channel->local_ip4);
if (bind(s, &local.sa, sizeof(local.sa4)) < 0)
return -1;
}
}
else if (family == AF_INET6) {
if (memcmp(channel->local_ip6, &ares_in6addr_any,
sizeof(channel->local_ip6)) != 0) {
memset(&local.sa6, 0, sizeof(local.sa6));
local.sa6.sin6_family = AF_INET6;
memcpy(&local.sa6.sin6_addr, channel->local_ip6,
sizeof(channel->local_ip6));
if (bind(s, &local.sa, sizeof(local.sa6)) < 0)
return -1;
}
}
return 0;
}
static ares_socket_t open_socket(ares_channel channel, int af, int type, int protocol)
{
if (channel->sock_funcs != 0)
return channel->sock_funcs->asocket(af,
type,
protocol,
channel->sock_func_cb_data);
return socket(af, type, protocol);
}
static int connect_socket(ares_channel channel, ares_socket_t sockfd,
const struct sockaddr * addr,
ares_socklen_t addrlen)
{
if (channel->sock_funcs != 0)
return channel->sock_funcs->aconnect(sockfd,
addr,
addrlen,
channel->sock_func_cb_data);
return connect(sockfd, addr, addrlen);
}
static int open_tcp_socket(ares_channel channel, struct server_state *server)
{
ares_socket_t s;
int opt;
ares_socklen_t salen;
union {
struct sockaddr_in sa4;
struct sockaddr_in6 sa6;
} saddr;
struct sockaddr *sa;
switch (server->addr.family)
{
case AF_INET:
sa = (void *)&saddr.sa4;
salen = sizeof(saddr.sa4);
memset(sa, 0, salen);
saddr.sa4.sin_family = AF_INET;
if (server->addr.tcp_port) {
saddr.sa4.sin_port = aresx_sitous(server->addr.tcp_port);
} else {
saddr.sa4.sin_port = aresx_sitous(channel->tcp_port);
}
memcpy(&saddr.sa4.sin_addr, &server->addr.addrV4,
sizeof(server->addr.addrV4));
break;
case AF_INET6:
sa = (void *)&saddr.sa6;
salen = sizeof(saddr.sa6);
memset(sa, 0, salen);
saddr.sa6.sin6_family = AF_INET6;
if (server->addr.tcp_port) {
saddr.sa6.sin6_port = aresx_sitous(server->addr.tcp_port);
} else {
saddr.sa6.sin6_port = aresx_sitous(channel->tcp_port);
}
memcpy(&saddr.sa6.sin6_addr, &server->addr.addrV6,
sizeof(server->addr.addrV6));
break;
default:
return -1; /* LCOV_EXCL_LINE */
}
/* Acquire a socket. */
s = open_socket(channel, server->addr.family, SOCK_STREAM, 0);
if (s == ARES_SOCKET_BAD)
return -1;
/* Configure it. */
if (configure_socket(s, server->addr.family, channel) < 0)
{
ares__socket_close(channel, s);
return -1;
}
#ifdef TCP_NODELAY
/*
* Disable the Nagle algorithm (only relevant for TCP sockets, and thus not
* in configure_socket). In general, in DNS lookups we're pretty much
* interested in firing off a single request and then waiting for a reply,
* so batching isn't very interesting.
*/
opt = 1;
if (channel->sock_funcs == 0
&&
setsockopt(s, IPPROTO_TCP, TCP_NODELAY,
(void *)&opt, sizeof(opt)) == -1)
{
ares__socket_close(channel, s);
return -1;
}
#endif
if (channel->sock_config_cb)
{
int err = channel->sock_config_cb(s, SOCK_STREAM,
channel->sock_config_cb_data);
if (err < 0)
{
ares__socket_close(channel, s);
return err;
}
}
/* Connect to the server. */
if (connect_socket(channel, s, sa, salen) == -1)
{
int err = SOCKERRNO;
if (err != EINPROGRESS && err != EWOULDBLOCK)
{
ares__socket_close(channel, s);
return -1;
}
}
if (channel->sock_create_cb)
{
int err = channel->sock_create_cb(s, SOCK_STREAM,
channel->sock_create_cb_data);
if (err < 0)
{
ares__socket_close(channel, s);
return err;
}
}
SOCK_STATE_CALLBACK(channel, s, 1, 0);
server->tcp_buffer_pos = 0;
server->tcp_socket = s;
server->tcp_connection_generation = ++channel->tcp_connection_generation;
return 0;
}
static int open_udp_socket(ares_channel channel, struct server_state *server)
{
ares_socket_t s;
ares_socklen_t salen;
union {
struct sockaddr_in sa4;
struct sockaddr_in6 sa6;
} saddr;
struct sockaddr *sa;
switch (server->addr.family)
{
case AF_INET:
sa = (void *)&saddr.sa4;
salen = sizeof(saddr.sa4);
memset(sa, 0, salen);
saddr.sa4.sin_family = AF_INET;
if (server->addr.udp_port) {
saddr.sa4.sin_port = aresx_sitous(server->addr.udp_port);
} else {
saddr.sa4.sin_port = aresx_sitous(channel->udp_port);
}
memcpy(&saddr.sa4.sin_addr, &server->addr.addrV4,
sizeof(server->addr.addrV4));
break;
case AF_INET6:
sa = (void *)&saddr.sa6;
salen = sizeof(saddr.sa6);
memset(sa, 0, salen);
saddr.sa6.sin6_family = AF_INET6;
if (server->addr.udp_port) {
saddr.sa6.sin6_port = aresx_sitous(server->addr.udp_port);
} else {
saddr.sa6.sin6_port = aresx_sitous(channel->udp_port);
}
memcpy(&saddr.sa6.sin6_addr, &server->addr.addrV6,
sizeof(server->addr.addrV6));
break;
default:
return -1; /* LCOV_EXCL_LINE */
}
/* Acquire a socket. */
s = open_socket(channel, server->addr.family, SOCK_DGRAM, 0);
if (s == ARES_SOCKET_BAD)
return -1;
/* Set the socket non-blocking. */
if (configure_socket(s, server->addr.family, channel) < 0)
{
ares__socket_close(channel, s);
return -1;
}
if (channel->sock_config_cb)
{
int err = channel->sock_config_cb(s, SOCK_DGRAM,
channel->sock_config_cb_data);
if (err < 0)
{
ares__socket_close(channel, s);
return err;
}
}
/* Connect to the server. */
if (connect_socket(channel, s, sa, salen) == -1)
{
int err = SOCKERRNO;
if (err != EINPROGRESS && err != EWOULDBLOCK)
{
ares__socket_close(channel, s);
return -1;
}
}
if (channel->sock_create_cb)
{
int err = channel->sock_create_cb(s, SOCK_DGRAM,
channel->sock_create_cb_data);
if (err < 0)
{
ares__socket_close(channel, s);
return err;
}
}
SOCK_STATE_CALLBACK(channel, s, 1, 0);
server->udp_socket = s;
return 0;
}
static int same_questions(const unsigned char *qbuf, int qlen,
const unsigned char *abuf, int alen)
{
struct {
const unsigned char *p;
int qdcount;
char *name;
long namelen;
int type;
int dnsclass;
} q, a;
int i, j;
if (qlen < HFIXEDSZ || alen < HFIXEDSZ)
return 0;
/* Extract qdcount from the request and reply buffers and compare them. */
q.qdcount = DNS_HEADER_QDCOUNT(qbuf);
a.qdcount = DNS_HEADER_QDCOUNT(abuf);
if (q.qdcount != a.qdcount)
return 0;
/* For each question in qbuf, find it in abuf. */
q.p = qbuf + HFIXEDSZ;
for (i = 0; i < q.qdcount; i++)
{
/* Decode the question in the query. */
if (ares_expand_name(q.p, qbuf, qlen, &q.name, &q.namelen)
!= ARES_SUCCESS)
return 0;
q.p += q.namelen;
if (q.p + QFIXEDSZ > qbuf + qlen)
{
ares_free(q.name);
return 0;
}
q.type = DNS_QUESTION_TYPE(q.p);
q.dnsclass = DNS_QUESTION_CLASS(q.p);
q.p += QFIXEDSZ;
/* Search for this question in the answer. */
a.p = abuf + HFIXEDSZ;
for (j = 0; j < a.qdcount; j++)
{
/* Decode the question in the answer. */
if (ares_expand_name(a.p, abuf, alen, &a.name, &a.namelen)
!= ARES_SUCCESS)
{
ares_free(q.name);
return 0;
}
a.p += a.namelen;
if (a.p + QFIXEDSZ > abuf + alen)
{
ares_free(q.name);
ares_free(a.name);
return 0;
}
a.type = DNS_QUESTION_TYPE(a.p);
a.dnsclass = DNS_QUESTION_CLASS(a.p);
a.p += QFIXEDSZ;
/* Compare the decoded questions. */
if (strcasecmp(q.name, a.name) == 0 && q.type == a.type
&& q.dnsclass == a.dnsclass)
{
ares_free(a.name);
break;
}
ares_free(a.name);
}
ares_free(q.name);
if (j == a.qdcount)
return 0;
}
return 1;
}
static int same_address(struct sockaddr *sa, struct ares_addr *aa)
{
void *addr1;
void *addr2;
if (sa->sa_family == aa->family)
{
switch (aa->family)
{
case AF_INET:
addr1 = &aa->addrV4;
addr2 = &((struct sockaddr_in *)sa)->sin_addr;
if (memcmp(addr1, addr2, sizeof(aa->addrV4)) == 0)
return 1; /* match */
break;
case AF_INET6:
addr1 = &aa->addrV6;
addr2 = &((struct sockaddr_in6 *)sa)->sin6_addr;
if (memcmp(addr1, addr2, sizeof(aa->addrV6)) == 0)
return 1; /* match */
break;
default:
break; /* LCOV_EXCL_LINE */
}
}
return 0; /* different */
}
static void end_query (ares_channel channel, struct query *query, int status,
unsigned char *abuf, int alen)
{
int i;
/* First we check to see if this query ended while one of our send
* queues still has pointers to it.
*/
for (i = 0; i < channel->nservers; i++)
{
struct server_state *server = &channel->servers[i];
struct send_request *sendreq;
for (sendreq = server->qhead; sendreq; sendreq = sendreq->next)
if (sendreq->owner_query == query)
{
sendreq->owner_query = NULL;
assert(sendreq->data_storage == NULL);
if (status == ARES_SUCCESS)
{
/* We got a reply for this query, but this queued sendreq
* points into this soon-to-be-gone query's tcpbuf. Probably
* this means we timed out and queued the query for
* retransmission, then received a response before actually
* retransmitting. This is perfectly fine, so we want to keep
* the connection running smoothly if we can. But in the worst
* case we may have sent only some prefix of the query, with
* some suffix of the query left to send. Also, the buffer may
* be queued on multiple queues. To prevent dangling pointers
* to the query's tcpbuf and handle these cases, we just give
* such sendreqs their own copy of the query packet.
*/
sendreq->data_storage = ares_malloc(sendreq->len);
if (sendreq->data_storage != NULL)
{
memcpy(sendreq->data_storage, sendreq->data, sendreq->len);
sendreq->data = sendreq->data_storage;
}
}
if ((status != ARES_SUCCESS) || (sendreq->data_storage == NULL))
{
/* We encountered an error (probably a timeout, suggesting the
* DNS server we're talking to is probably unreachable,
* wedged, or severely overloaded) or we couldn't copy the
* request, so mark the connection as broken. When we get to
* process_broken_connections() we'll close the connection and
* try to re-send requests to another server.
*/
server->is_broken = 1;
/* Just to be paranoid, zero out this sendreq... */
sendreq->data = NULL;
sendreq->len = 0;
}
}
}
/* Invoke the callback */
query->callback(query->arg, status, query->timeouts, abuf, alen);
ares__free_query(query);
/* Simple cleanup policy: if no queries are remaining, close all network
* sockets unless STAYOPEN is set.
*/
if (!(channel->flags & ARES_FLAG_STAYOPEN) &&
ares__is_list_empty(&(channel->all_queries)))
{
for (i = 0; i < channel->nservers; i++)
ares__close_sockets(channel, &channel->servers[i]);
}
}
void ares__free_query(struct query *query)
{
/* Remove the query from all the lists in which it is linked */
ares__remove_from_list(&(query->queries_by_qid));
ares__remove_from_list(&(query->queries_by_timeout));
ares__remove_from_list(&(query->queries_to_server));
ares__remove_from_list(&(query->all_queries));
/* Zero out some important stuff, to help catch bugs */
query->callback = NULL;
query->arg = NULL;
/* Deallocate the memory associated with the query */
ares_free(query->tcpbuf);
ares_free(query->server_info);
ares_free(query);
}
void ares__socket_close(ares_channel channel, ares_socket_t s)
{
if (channel->sock_funcs)
channel->sock_funcs->aclose(s, channel->sock_func_cb_data);
else
sclose(s);
}