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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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/* $Id$ */
/* Copyright 1998 by the Massachusetts Institute of Technology.
* Copyright (C) 2004-2008 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 "setup.h"
#if defined(WIN32) && !defined(WATT32)
#include "nameser.h"
#else
#ifdef HAVE_SYS_SOCKET_H
#include <sys/socket.h>
#endif
#ifdef HAVE_SYS_UIO_H
#include <sys/uio.h>
#endif
#ifdef HAVE_NETINET_IN_H
#include <netinet/in.h> /* <netinet/tcp.h> may need it */
#endif
#ifdef HAVE_NETINET_TCP_H
#include <netinet/tcp.h> /* for TCP_NODELAY */
#endif
#ifdef HAVE_NETDB_H
#include <netdb.h>
#endif
#ifdef HAVE_ARPA_NAMESER_H
#include <arpa/nameser.h>
#endif
#ifdef HAVE_ARPA_NAMESER_COMPAT_H
#include <arpa/nameser_compat.h>
#endif
#ifdef HAVE_SYS_TIME_H
#include <sys/time.h>
#endif
#endif /* WIN32 && !WATT32 */
#ifdef HAVE_STRINGS_H
#include <strings.h>
#endif
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif
#ifdef HAVE_SYS_IOCTL_H
#include <sys/ioctl.h>
#endif
#ifdef NETWARE
#include <sys/filio.h>
#endif
#include <assert.h>
#include <string.h>
#include <stdlib.h>
#include <fcntl.h>
#include <time.h>
#include <errno.h>
#include "ares.h"
#include "ares_dns.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,
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 configure_socket(int s, ares_channel channel);
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 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)
{
int 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 */
int ares__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;
}
return 0;
}
/* return time offset between now and (future) check, in milliseconds */
long ares__timeoffset(struct timeval *now,
struct timeval *check)
{
return (check->tv_sec - now->tv_sec)*1000 +
(check->tv_usec - now->tv_usec)/1000;
}
/* 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)
{
struct timeval now = ares__tvnow();
write_tcp_data(channel, write_fds, ARES_SOCKET_BAD, &now);
read_tcp_data(channel, read_fds, ARES_SOCKET_BAD, &now);
read_udp_packets(channel, read_fds, ARES_SOCKET_BAD, &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_fd(ares_channel channel,
ares_socket_t read_fd, /* use ARES_SOCKET_BAD or valid
file descriptors */
ares_socket_t write_fd)
{
struct timeval now = ares__tvnow();
write_tcp_data(channel, NULL, write_fd, &now);
read_tcp_data(channel, NULL, read_fd, &now);
read_udp_packets(channel, NULL, read_fd, &now);
process_timeouts(channel, &now);
}
/* 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;
}
/* 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;
ssize_t scount;
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 = 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 = (ssize_t)writev(server->tcp_socket, vec, (int)n);
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 = swrite(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,
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 (server->qhead == NULL)
{
SOCK_STATE_CALLBACK(channel, server->tcp_socket, 1, 0);
server->qtail = NULL;
}
if (sendreq->data_storage != NULL)
free(sendreq->data_storage);
free(sendreq);
}
else
{
sendreq->data += num_bytes;
sendreq->len -= num_bytes;
num_bytes = 0;
}
}
}
/* 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;
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 = sread(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 = malloc(server->tcp_length);
if (!server->tcp_buffer)
handle_error(channel, i, now);
server->tcp_buffer_pos = 0;
}
}
else
{
/* Read data into the allocated buffer. */
count = sread(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);
if (server->tcp_buffer)
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;
ssize_t count;
unsigned char buf[PACKETSZ + 1];
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 {
count = sread(server->udp_socket, buf, sizeof(buf));
if (count == -1 && try_again(SOCKERRNO))
continue;
else if (count <= 0)
handle_error(channel, i, now);
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;
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;
/* 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);
}
}
}
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);
ares__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)
{
/* Advance to the next server or try. */
query->server++;
for (; query->try < channel->tries; query->try++)
{
for (; query->server < channel->nservers; query->server++)
{
struct server_state *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;
}
}
query->server = 0;
/* 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.
*/
}
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;
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 = calloc(sizeof(struct send_request), 1);
if (!sendreq)
{
end_query(channel, query, ARES_ENOMEM, NULL, 0);
return;
}
/* 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 (swrite(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;
}
}
query->timeout = *now;
ares__timeadd(&query->timeout,
(query->try == 0) ? channel->timeout
: channel->timeout << query->try / channel->nservers);
/* 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 */)
{
#undef SETBLOCK
#define SETBLOCK 0
#ifdef HAVE_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));
#undef SETBLOCK
#define SETBLOCK 1
#endif
#if defined(HAVE_FIONBIO) && (SETBLOCK == 0)
/* older unix versions */
int flags;
flags = nonblock;
return ioctl(sockfd, FIONBIO, &flags);
#undef SETBLOCK
#define SETBLOCK 2
#endif
#if defined(HAVE_IOCTLSOCKET) && (SETBLOCK == 0)
#ifdef WATT32
char flags;
#else
/* Windows? */
unsigned long flags;
#endif
flags = nonblock;
return ioctlsocket(sockfd, FIONBIO, &flags);
#undef SETBLOCK
#define SETBLOCK 3
#endif
#if defined(HAVE_IOCTLSOCKET_CASE) && (SETBLOCK == 0)
/* presumably for Amiga */
return IoctlSocket(sockfd, FIONBIO, (long)nonblock);
#undef SETBLOCK
#define SETBLOCK 4
#endif
#if defined(HAVE_SO_NONBLOCK) && (SETBLOCK == 0)
/* BeOS */
long b = nonblock ? 1 : 0;
return setsockopt(sockfd, SOL_SOCKET, SO_NONBLOCK, &b, sizeof(b));
#undef SETBLOCK
#define SETBLOCK 5
#endif
#ifdef HAVE_DISABLED_NONBLOCKING
return 0; /* returns success */
#undef SETBLOCK
#define SETBLOCK 6
#endif
#if (SETBLOCK == 0)
#error "no non-blocking method was found/used/set"
#endif
}
static int configure_socket(int s, ares_channel channel)
{
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;
#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;
return 0;
}
static int open_tcp_socket(ares_channel channel, struct server_state *server)
{
ares_socket_t s;
int opt;
struct sockaddr_in sockin;
/* Acquire a socket. */
s = socket(AF_INET, SOCK_STREAM, 0);
if (s == ARES_SOCKET_BAD)
return -1;
/* Configure it. */
if (configure_socket(s, channel) < 0)
{
close(s);
return -1;
}
/*
* 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 in general.
*/
opt = 1;
if (setsockopt(s, IPPROTO_TCP, TCP_NODELAY,
(void *)&opt, sizeof(opt)) == -1)
{
close(s);
return -1;
}
/* Connect to the server. */
memset(&sockin, 0, sizeof(sockin));
sockin.sin_family = AF_INET;
sockin.sin_addr = server->addr;
sockin.sin_port = (unsigned short)(channel->tcp_port & 0xffff);
if (connect(s, (struct sockaddr *) &sockin, sizeof(sockin)) == -1) {
int err = SOCKERRNO;
if (err != EINPROGRESS && err != EWOULDBLOCK) {
closesocket(s);
return -1;
}
}
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;
struct sockaddr_in sockin;
/* Acquire a socket. */
s = socket(AF_INET, SOCK_DGRAM, 0);
if (s == ARES_SOCKET_BAD)
return -1;
/* Set the socket non-blocking. */
if (configure_socket(s, channel) < 0)
{
close(s);
return -1;
}
/* Connect to the server. */
memset(&sockin, 0, sizeof(sockin));
sockin.sin_family = AF_INET;
sockin.sin_addr = server->addr;
sockin.sin_port = (unsigned short)(channel->udp_port & 0xffff);
if (connect(s, (struct sockaddr *) &sockin, sizeof(sockin)) == -1)
{
closesocket(s);
return -1;
}
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)
{
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)
{
free(q.name);
return 0;
}
a.p += a.namelen;
if (a.p + QFIXEDSZ > abuf + alen)
{
free(q.name);
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)
{
free(a.name);
break;
}
free(a.name);
}
free(q.name);
if (j == a.qdcount)
return 0;
}
return 1;
}
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 = 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 */
free(query->tcpbuf);
free(query->server_info);
free(query);
}