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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.
*
* 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
#include <sys/socket.h>
#ifdef HAVE_SYS_UIO_H
#include <sys/uio.h>
#endif
#include <netinet/in.h>
#include <netdb.h>
#include <arpa/nameser.h>
#ifdef HAVE_ARPA_NAMESER_COMPAT_H
#include <arpa/nameser_compat.h>
#endif
#endif /* WIN32 && !WATT32 */
#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 <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,
time_t now);
static void read_tcp_data(ares_channel channel, fd_set *read_fds, time_t now);
static void read_udp_packets(ares_channel channel, fd_set *read_fds,
time_t now);
static void process_timeouts(ares_channel channel, time_t now);
static void process_answer(ares_channel channel, unsigned char *abuf,
int alen, int whichserver, int tcp, int now);
static void handle_error(ares_channel channel, int whichserver, time_t now);
static struct query *next_server(ares_channel channel, struct query *query, time_t 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 struct query *end_query(ares_channel channel, struct query *query, int status,
unsigned char *abuf, int alen);
/* 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)
{
time_t now;
time(&now);
write_tcp_data(channel, write_fds, now);
read_tcp_data(channel, read_fds, now);
read_udp_packets(channel, read_fds, 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, time_t now)
{
struct server_state *server;
struct send_request *sendreq;
struct iovec *vec;
int i;
ssize_t scount;
ssize_t wcount;
size_t n;
for (i = 0; i < channel->nservers; i++)
{
/* Make sure server has data to send and is selected in write_fds. */
server = &channel->servers[i];
if (!server->qhead || server->tcp_socket == ARES_SOCKET_BAD
|| !FD_ISSET(server->tcp_socket, write_fds))
continue;
/* 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. */
while (wcount)
{
sendreq = server->qhead;
if ((size_t)wcount >= sendreq->len)
{
wcount -= sendreq->len;
server->qhead = sendreq->next;
if (server->qhead == NULL)
{
SOCK_STATE_CALLBACK(channel, server->tcp_socket, 1, 0);
server->qtail = NULL;
}
free(sendreq);
}
else
{
sendreq->data += wcount;
sendreq->len -= wcount;
break;
}
}
}
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. */
if ((size_t)scount == sendreq->len)
{
server->qhead = sendreq->next;
if (server->qhead == NULL)
{
SOCK_STATE_CALLBACK(channel, server->tcp_socket, 1, 0);
server->qtail = NULL;
}
free(sendreq);
}
else
{
sendreq->data += scount;
sendreq->len -= scount;
}
}
}
}
/* 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, time_t now)
{
struct server_state *server;
int i;
ssize_t count;
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 ||
!FD_ISSET(server->tcp_socket, read_fds))
continue;
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,
time_t now)
{
struct server_state *server;
int i;
ssize_t count;
unsigned char buf[PACKETSZ + 1];
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 ||
!FD_ISSET(server->udp_socket, read_fds))
continue;
count = sread(server->udp_socket, buf, sizeof(buf));
if (count == -1 && try_again(SOCKERRNO))
continue;
else if (count <= 0)
handle_error(channel, i, now);
process_answer(channel, buf, (int)count, i, 0, now);
}
}
/* If any queries have timed out, note the timeout and move them on. */
static void process_timeouts(ares_channel channel, time_t now)
{
struct query *query, *next;
for (query = channel->queries; query; query = next)
{
next = query->next;
if (query->timeout != 0 && now >= query->timeout)
{
query->error_status = ARES_ETIMEOUT;
next = next_server(channel, query, now);
}
}
}
/* Handle an answer from a server. */
static void process_answer(ares_channel channel, unsigned char *abuf,
int alen, int whichserver, int tcp, int now)
{
int id, tc, rcode;
struct query *query;
/* 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. */
for (query = channel->queries; query; query = query->next)
{
if (query->qid == id)
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)
{
query->skip_server[whichserver] = 1;
if (query->server == whichserver)
next_server(channel, query, now);
return;
}
if (!same_questions(query->qbuf, query->qlen, abuf, alen))
{
if (query->server == whichserver)
next_server(channel, query, now);
return;
}
}
end_query(channel, query, ARES_SUCCESS, abuf, alen);
}
static void handle_error(ares_channel channel, int whichserver, time_t now)
{
struct query *query, *next;
/* Reset communications with this server. */
ares__close_sockets(channel, &channel->servers[whichserver]);
/* Tell all queries talking to this server to move on and not try
* this server again.
*/
for (query = channel->queries; query; query = next)
{
next = query->next;
if (query->server == whichserver)
{
query->skip_server[whichserver] = 1;
next = next_server(channel, query, now);
}
}
}
static struct query *next_server(ares_channel channel, struct query *query, time_t now)
{
/* Advance to the next server or try. */
query->server++;
for (; query->try < channel->tries; query->try++)
{
for (; query->server < channel->nservers; query->server++)
{
if (!query->skip_server[query->server])
{
ares__send_query(channel, query, now);
return (query->next);
}
}
query->server = 0;
/* Only one try if we're using TCP. */
if (query->using_tcp)
break;
}
return end_query(channel, query, query->error_status, NULL, 0);
}
void ares__send_query(ares_channel channel, struct query *query, time_t 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)
{
query->skip_server[query->server] = 1;
next_server(channel, query, now);
return;
}
}
sendreq = calloc(sizeof(struct send_request), 1);
if (!sendreq)
{
end_query(channel, query, ARES_ENOMEM, NULL, 0);
return;
}
sendreq->data = query->tcpbuf;
sendreq->len = query->tcplen;
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->timeout = 0;
}
else
{
if (server->udp_socket == ARES_SOCKET_BAD)
{
if (open_udp_socket(channel, server) == -1)
{
query->skip_server[query->server] = 1;
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. */
query->skip_server[query->server] = 1;
next_server(channel, query, now);
return;
}
query->timeout = now
+ ((query->try == 0) ? channel->timeout
: channel->timeout << query->try / channel->nservers);
}
}
/*
* nonblock() set the given socket to either blocking or non-blocking mode
* based on the 'nonblock' boolean argument. This function is highly portable.
*/
static int nonblock(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 open_tcp_socket(ares_channel channel, struct server_state *server)
{
ares_socket_t s;
struct sockaddr_in sockin;
/* Acquire a socket. */
s = socket(AF_INET, SOCK_STREAM, 0);
if (s == ARES_SOCKET_BAD)
return -1;
/* Set the socket non-blocking. */
nonblock(s, TRUE);
/* 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;
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. */
nonblock(s, TRUE);
/* 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 struct query *end_query (ares_channel channel, struct query *query, int status,
unsigned char *abuf, int alen)
{
struct query **q, *next;
int i;
query->callback(query->arg, status, abuf, alen);
for (q = &channel->queries; *q; q = &(*q)->next)
{
if (*q == query)
break;
}
*q = query->next;
if (*q)
next = (*q)->next;
else
next = NULL;
free(query->tcpbuf);
free(query->skip_server);
free(query);
/* Simple cleanup policy: if no queries are remaining, close all
* network sockets unless STAYOPEN is set.
*/
if (!channel->queries && !(channel->flags & ARES_FLAG_STAYOPEN))
{
for (i = 0; i < channel->nservers; i++)
ares__close_sockets(channel, &channel->servers[i]);
}
return (next);
}