core/ngx_resolver.c源文件分析(2)
本章我们主要介绍一下ngx_resolver.c源文件，其主要是实现对nginx中涉及到的域名的解析。
1. 函数ngx_resolver_resend_handler()
static void
ngx_resolver_resend_handler(ngx_event_t *ev)
{
time_t timer, atimer, stimer, ntimer;
#if (NGX_HAVE_INET6)
time_t a6timer;
#endif
ngx_resolver_t *r;
r = ev->data;
ngx_log_debug0(NGX_LOG_DEBUG_CORE, r->log, 0,
"resolver resend handler");
/* lock name mutex */
ntimer = ngx_resolver_resend(r, &r->name_rbtree, &r->name_resend_queue);
stimer = ngx_resolver_resend(r, &r->srv_rbtree, &r->srv_resend_queue);
/* unlock name mutex */
/* lock addr mutex */
atimer = ngx_resolver_resend(r, &r->addr_rbtree, &r->addr_resend_queue);
/* unlock addr mutex */
#if (NGX_HAVE_INET6)
/* lock addr6 mutex */
a6timer = ngx_resolver_resend(r, &r->addr6_rbtree, &r->addr6_resend_queue);
/* unlock addr6 mutex */
#endif
timer = ntimer;
if (timer == 0) {
timer = atimer;
} else if (atimer) {
timer = ngx_min(timer, atimer);
}
if (timer == 0) {
timer = stimer;
} else if (stimer) {
timer = ngx_min(timer, stimer);
}
#if (NGX_HAVE_INET6)
if (timer == 0) {
timer = a6timer;
} else if (a6timer) {
timer = ngx_min(timer, a6timer);
}
#endif
if (timer) {
ngx_add_timer(r->event, (ngx_msec_t) (timer * 1000));
}
}此函数的作用是使用ngx_resolver_t.event来建立定时器事件，从而发发送resend队列中的任务。
2. 函数ngx_resolver_resend()
static time_t
ngx_resolver_resend(ngx_resolver_t *r, ngx_rbtree_t *tree, ngx_queue_t *queue)
{
time_t now;
ngx_queue_t *q;
ngx_resolver_node_t *rn;
now = ngx_time();
for ( ;; ) {
if (ngx_queue_empty(queue)) {
return 0;
}
q = ngx_queue_last(queue);
rn = ngx_queue_data(q, ngx_resolver_node_t, queue);
if (now < rn->expire) {
return rn->expire - now;
}
ngx_log_debug3(NGX_LOG_DEBUG_CORE, r->log, 0,
"resolver resend \"%*s\" %p",
(size_t) rn->nlen, rn->name, rn->waiting);
ngx_queue_remove(q);
if (rn->waiting) {
if (++rn->last_connection == r->connections.nelts) {
rn->last_connection = 0;
}
(void) ngx_resolver_send_query(r, rn);
rn->expire = now + r->resend_timeout;
ngx_queue_insert_head(queue, q);
continue;
}
ngx_rbtree_delete(tree, &rn->node);
ngx_resolver_free_node(r, rn);
}
}此函数用于处理resend队列中的到期任务，并返回最近一个没有到期的任务的剩余时间。
3. 函数ngx_resolver_resend_empty()
static ngx_uint_t
ngx_resolver_resend_empty(ngx_resolver_t *r)
{
return ngx_queue_empty(&r->name_resend_queue)
#if (NGX_HAVE_INET6)
&& ngx_queue_empty(&r->addr6_resend_queue)
#endif
&& ngx_queue_empty(&r->addr_resend_queue);
}用于判断resend_queue中是否仍有待发送任务。
4. 函数ngx_resolver_udp_read()
static void
ngx_resolver_udp_read(ngx_event_t *rev)
{
ssize_t n;
ngx_connection_t *c;
ngx_resolver_connection_t *rec;
u_char buf[NGX_RESOLVER_UDP_SIZE];
c = rev->data;
rec = c->data;
do {
n = ngx_udp_recv(c, buf, NGX_RESOLVER_UDP_SIZE);
if (n < 0) {
return;
}
ngx_resolver_process_response(rec->resolver, buf, n, 0);
} while (rev->ready);
}从rev->data所表示的ngx_connection_t中读取UDP数据，然后调用相应的方法处理数据。
5. 函数ngx_resolver_tcp_write()
static void
ngx_resolver_tcp_write(ngx_event_t *wev)
{
off_t sent;
ssize_t n;
ngx_buf_t *b;
ngx_resolver_t *r;
ngx_connection_t *c;
ngx_resolver_connection_t *rec;
c = wev->data;
rec = c->data;
b = rec->write_buf;
r = rec->resolver;
if (wev->timedout) {
goto failed;
}
sent = c->sent;
while (wev->ready && b->pos < b->last) {
n = ngx_send(c, b->pos, b->last - b->pos);
if (n == NGX_AGAIN) {
break;
}
if (n == NGX_ERROR) {
goto failed;
}
b->pos += n;
}
if (b->pos != b->start) {
b->last = ngx_movemem(b->start, b->pos, b->last - b->pos);
b->pos = b->start;
}
if (c->sent != sent) {
ngx_add_timer(wev, (ngx_msec_t) (r->tcp_timeout * 1000));
}
if (ngx_handle_write_event(wev, 0) != NGX_OK) {
goto failed;
}
return;
failed:
ngx_close_connection(c);
rec->tcp = NULL;
}此函数用于发送对应write_buf中的数据。下面简要介绍一下实现流程：
static void
ngx_resolver_tcp_write(ngx_event_t *wev)
{
//1) 如果wev已经处于timeout状态，则关闭对应的连接
//2) 循环发送TCP数据，直到不能发送更多的数据或发送失败为止
//3) 调用ngx_handle_write_event()重置相应发送状态，以准备下一次的发送
}6. 函数ngx_resolver_tcp_read()
static void
ngx_resolver_tcp_read(ngx_event_t *rev)
{
u_char *p;
size_t size;
ssize_t n;
u_short qlen;
ngx_buf_t *b;
ngx_resolver_t *r;
ngx_connection_t *c;
ngx_resolver_connection_t *rec;
c = rev->data;
rec = c->data;
b = rec->read_buf;
r = rec->resolver;
while (rev->ready) {
n = ngx_recv(c, b->last, b->end - b->last);
if (n == NGX_AGAIN) {
break;
}
if (n == NGX_ERROR || n == 0) {
goto failed;
}
b->last += n;
for ( ;; ) {
p = b->pos;
size = b->last - p;
if (size < 2) {
break;
}
qlen = (u_short) *p++ << 8;
qlen += *p++;
if (size < (size_t) (2 + qlen)) {
break;
}
ngx_resolver_process_response(r, p, qlen, 1);
b->pos += 2 + qlen;
}
if (b->pos != b->start) {
b->last = ngx_movemem(b->start, b->pos, b->last - b->pos);
b->pos = b->start;
}
}
if (ngx_handle_read_event(rev, 0) != NGX_OK) {
goto failed;
}
return;
failed:
ngx_close_connection(c);
rec->tcp = NULL;
}此函数读取TCP数据到buf中，并在读取到足够数据时调用ngx_resolver_process_response()来对DNS返回的数据进行处理。
7. 函数ngx_resolver_process_response()
static void
ngx_resolver_process_response(ngx_resolver_t *r, u_char *buf, size_t n,
ngx_uint_t tcp)
{
char *err;
ngx_uint_t i, times, ident, qident, flags, code, nqs, nan, trunc,
qtype, qclass;
#if (NGX_HAVE_INET6)
ngx_uint_t qident6;
#endif
ngx_queue_t *q;
ngx_resolver_qs_t *qs;
ngx_resolver_hdr_t *response;
ngx_resolver_node_t *rn;
if (n < sizeof(ngx_resolver_hdr_t)) {
goto short_response;
}
response = (ngx_resolver_hdr_t *) buf;
ident = (response->ident_hi << 8) + response->ident_lo;
flags = (response->flags_hi << 8) + response->flags_lo;
nqs = (response->nqs_hi << 8) + response->nqs_lo;
nan = (response->nan_hi << 8) + response->nan_lo;
trunc = flags & 0x0200;
ngx_log_debug6(NGX_LOG_DEBUG_CORE, r->log, 0,
"resolver DNS response %ui fl:%04Xi %ui/%ui/%ud/%ud",
ident, flags, nqs, nan,
(response->nns_hi << 8) + response->nns_lo,
(response->nar_hi << 8) + response->nar_lo);
/* response to a standard query */
if ((flags & 0xf870) != 0x8000 || (trunc && tcp)) {
ngx_log_error(r->log_level, r->log, 0,
"invalid %s DNS response %ui fl:%04Xi",
tcp ? "TCP" : "UDP", ident, flags);
return;
}
code = flags & 0xf;
if (code == NGX_RESOLVE_FORMERR) {
times = 0;
for (q = ngx_queue_head(&r->name_resend_queue);
q != ngx_queue_sentinel(&r->name_resend_queue) && times++ < 100;
q = ngx_queue_next(q))
{
rn = ngx_queue_data(q, ngx_resolver_node_t, queue);
qident = (rn->query[0] << 8) + rn->query[1];
if (qident == ident) {
goto dns_error_name;
}
#if (NGX_HAVE_INET6)
if (rn->query6) {
qident6 = (rn->query6[0] << 8) + rn->query6[1];
if (qident6 == ident) {
goto dns_error_name;
}
}
#endif
}
goto dns_error;
}
if (code > NGX_RESOLVE_REFUSED) {
goto dns_error;
}
if (nqs != 1) {
err = "invalid number of questions in DNS response";
goto done;
}
i = sizeof(ngx_resolver_hdr_t);
while (i < (ngx_uint_t) n) {
if (buf[i] == '\0') {
goto found;
}
i += 1 + buf[i];
}
goto short_response;
found:
if (i++ == sizeof(ngx_resolver_hdr_t)) {
err = "zero-length domain name in DNS response";
goto done;
}
if (i + sizeof(ngx_resolver_qs_t) + nan * (2 + sizeof(ngx_resolver_an_t))
> (ngx_uint_t) n)
{
goto short_response;
}
qs = (ngx_resolver_qs_t *) &buf[i];
qtype = (qs->type_hi << 8) + qs->type_lo;
qclass = (qs->class_hi << 8) + qs->class_lo;
ngx_log_debug2(NGX_LOG_DEBUG_CORE, r->log, 0,
"resolver DNS response qt:%ui cl:%ui", qtype, qclass);
if (qclass != 1) {
ngx_log_error(r->log_level, r->log, 0,
"unknown query class %ui in DNS response", qclass);
return;
}
switch (qtype) {
case NGX_RESOLVE_A:
#if (NGX_HAVE_INET6)
case NGX_RESOLVE_AAAA:
#endif
ngx_resolver_process_a(r, buf, n, ident, code, qtype, nan, trunc,
i + sizeof(ngx_resolver_qs_t));
break;
case NGX_RESOLVE_SRV:
ngx_resolver_process_srv(r, buf, n, ident, code, nan, trunc,
i + sizeof(ngx_resolver_qs_t));
break;
case NGX_RESOLVE_PTR:
ngx_resolver_process_ptr(r, buf, n, ident, code, nan);
break;
default:
ngx_log_error(r->log_level, r->log, 0,
"unknown query type %ui in DNS response", qtype);
return;
}
return;
short_response:
err = "short DNS response";
done:
ngx_log_error(r->log_level, r->log, 0, err);
return;
dns_error_name:
ngx_log_error(r->log_level, r->log, 0,
"DNS error (%ui: %s), query id:%ui, name:\"%*s\"",
code, ngx_resolver_strerror(code), ident,
(size_t) rn->nlen, rn->name);
return;
dns_error:
ngx_log_error(r->log_level, r->log, 0,
"DNS error (%ui: %s), query id:%ui",
code, ngx_resolver_strerror(code), ident);
return;
}本函数用于解析DNS返回的应答信息。下面我们简单分析一下实现流程：
static void
ngx_resolver_process_response(ngx_resolver_t *r, u_char *buf, size_t n,
ngx_uint_t tcp)
{
//1) 解析头部信息ngx_resolver_hdr_t
//2) 如果code == NGX_RESOLVE_FORMERR, 表明有DNS格式错误
//3) 解析ngx_resolver_qs_t头部
//4) 如下是跳过query区域的name字段
while (i < (ngx_uint_t) n) {
if (buf[i] == '\0') {
goto found;
}
i += 1 + buf[i];
}
//4) 根据qtype分别调用不同的函数来处理相应的应答
}8. 函数ngx_resolver_process_a()
static void
ngx_resolver_process_a(ngx_resolver_t *r, u_char *buf, size_t n,
ngx_uint_t ident, ngx_uint_t code, ngx_uint_t qtype,
ngx_uint_t nan, ngx_uint_t trunc, ngx_uint_t ans)
{
char *err;
u_char *cname;
size_t len;
int32_t ttl;
uint32_t hash;
in_addr_t *addr;
ngx_str_t name;
ngx_uint_t type, class, qident, naddrs, a, i, j, start;
#if (NGX_HAVE_INET6)
struct in6_addr *addr6;
#endif
ngx_resolver_an_t *an;
ngx_resolver_ctx_t *ctx, *next;
ngx_resolver_node_t *rn;
ngx_resolver_addr_t *addrs;
ngx_resolver_connection_t *rec;
if (ngx_resolver_copy(r, &name, buf,
buf + sizeof(ngx_resolver_hdr_t), buf + n)
!= NGX_OK)
{
return;
}
ngx_log_debug1(NGX_LOG_DEBUG_CORE, r->log, 0, "resolver qs:%V", &name);
hash = ngx_crc32_short(name.data, name.len);
/* lock name mutex */
rn = ngx_resolver_lookup_name(r, &name, hash);
if (rn == NULL) {
ngx_log_error(r->log_level, r->log, 0,
"unexpected response for %V", &name);
ngx_resolver_free(r, name.data);
goto failed;
}
switch (qtype) {
#if (NGX_HAVE_INET6)
case NGX_RESOLVE_AAAA:
if (rn->query6 == NULL || rn->naddrs6 != (u_short) -1) {
ngx_log_error(r->log_level, r->log, 0,
"unexpected response for %V", &name);
ngx_resolver_free(r, name.data);
goto failed;
}
if (trunc && rn->tcp6) {
ngx_resolver_free(r, name.data);
goto failed;
}
qident = (rn->query6[0] << 8) + rn->query6[1];
break;
#endif
default: /* NGX_RESOLVE_A */
if (rn->query == NULL || rn->naddrs != (u_short) -1) {
ngx_log_error(r->log_level, r->log, 0,
"unexpected response for %V", &name);
ngx_resolver_free(r, name.data);
goto failed;
}
if (trunc && rn->tcp) {
ngx_resolver_free(r, name.data);
goto failed;
}
qident = (rn->query[0] << 8) + rn->query[1];
}
if (ident != qident) {
ngx_log_error(r->log_level, r->log, 0,
"wrong ident %ui response for %V, expect %ui",
ident, &name, qident);
ngx_resolver_free(r, name.data);
goto failed;
}
ngx_resolver_free(r, name.data);
if (trunc) {
ngx_queue_remove(&rn->queue);
if (rn->waiting == NULL) {
ngx_rbtree_delete(&r->name_rbtree, &rn->node);
ngx_resolver_free_node(r, rn);
goto next;
}
rec = r->connections.elts;
rec = &rec[rn->last_connection];
switch (qtype) {
#if (NGX_HAVE_INET6)
case NGX_RESOLVE_AAAA:
rn->tcp6 = 1;
(void) ngx_resolver_send_tcp_query(r, rec, rn->query6, rn->qlen);
break;
#endif
default: /* NGX_RESOLVE_A */
rn->tcp = 1;
(void) ngx_resolver_send_tcp_query(r, rec, rn->query, rn->qlen);
}
rn->expire = ngx_time() + r->resend_timeout;
ngx_queue_insert_head(&r->name_resend_queue, &rn->queue);
goto next;
}
if (code == 0 && rn->code) {
code = rn->code;
}
if (code == 0 && nan == 0) {
#if (NGX_HAVE_INET6)
switch (qtype) {
case NGX_RESOLVE_AAAA:
rn->naddrs6 = 0;
if (rn->naddrs == (u_short) -1) {
goto next;
}
if (rn->naddrs) {
goto export;
}
break;
default: /* NGX_RESOLVE_A */
rn->naddrs = 0;
if (rn->naddrs6 == (u_short) -1) {
goto next;
}
if (rn->naddrs6) {
goto export;
}
}
#endif
code = NGX_RESOLVE_NXDOMAIN;
}
if (code) {
#if (NGX_HAVE_INET6)
switch (qtype) {
case NGX_RESOLVE_AAAA:
rn->naddrs6 = 0;
if (rn->naddrs == (u_short) -1) {
rn->code = (u_char) code;
goto next;
}
break;
default: /* NGX_RESOLVE_A */
rn->naddrs = 0;
if (rn->naddrs6 == (u_short) -1) {
rn->code = (u_char) code;
goto next;
}
}
#endif
next = rn->waiting;
rn->waiting = NULL;
ngx_queue_remove(&rn->queue);
ngx_rbtree_delete(&r->name_rbtree, &rn->node);
/* unlock name mutex */
while (next) {
ctx = next;
ctx->state = code;
ctx->valid = ngx_time() + (r->valid ? r->valid : 10);
next = ctx->next;
ctx->handler(ctx);
}
ngx_resolver_free_node(r, rn);
return;
}
i = ans;
naddrs = 0;
cname = NULL;
for (a = 0; a < nan; a++) {
start = i;
while (i < n) {
if (buf[i] & 0xc0) {
i += 2;
goto found;
}
if (buf[i] == 0) {
i++;
goto test_length;
}
i += 1 + buf[i];
}
goto short_response;
test_length:
if (i - start < 2) {
err = "invalid name in DNS response";
goto invalid;
}
found:
if (i + sizeof(ngx_resolver_an_t) >= n) {
goto short_response;
}
an = (ngx_resolver_an_t *) &buf[i];
type = (an->type_hi << 8) + an->type_lo;
class = (an->class_hi << 8) + an->class_lo;
len = (an->len_hi << 8) + an->len_lo;
ttl = (an->ttl[0] << 24) + (an->ttl[1] << 16)
+ (an->ttl[2] << 8) + (an->ttl[3]);
if (class != 1) {
ngx_log_error(r->log_level, r->log, 0,
"unexpected RR class %ui", class);
goto failed;
}
if (ttl < 0) {
ttl = 0;
}
rn->ttl = ngx_min(rn->ttl, (uint32_t) ttl);
i += sizeof(ngx_resolver_an_t);
switch (type) {
case NGX_RESOLVE_A:
if (qtype != NGX_RESOLVE_A) {
err = "unexpected A record in DNS response";
goto invalid;
}
if (len != 4) {
err = "invalid A record in DNS response";
goto invalid;
}
if (i + 4 > n) {
goto short_response;
}
naddrs++;
break;
#if (NGX_HAVE_INET6)
case NGX_RESOLVE_AAAA:
if (qtype != NGX_RESOLVE_AAAA) {
err = "unexpected AAAA record in DNS response";
goto invalid;
}
if (len != 16) {
err = "invalid AAAA record in DNS response";
goto invalid;
}
if (i + 16 > n) {
goto short_response;
}
naddrs++;
break;
#endif
case NGX_RESOLVE_CNAME:
cname = &buf[i];
break;
case NGX_RESOLVE_DNAME:
break;
default:
ngx_log_error(r->log_level, r->log, 0,
"unexpected RR type %ui", type);
}
i += len;
}
ngx_log_debug3(NGX_LOG_DEBUG_CORE, r->log, 0,
"resolver naddrs:%ui cname:%p ttl:%uD",
naddrs, cname, rn->ttl);
if (naddrs) {
switch (qtype) {
#if (NGX_HAVE_INET6)
case NGX_RESOLVE_AAAA:
if (naddrs == 1) {
addr6 = &rn->u6.addr6;
rn->naddrs6 = 1;
} else {
addr6 = ngx_resolver_alloc(r, naddrs * sizeof(struct in6_addr));
if (addr6 == NULL) {
goto failed;
}
rn->u6.addrs6 = addr6;
rn->naddrs6 = (u_short) naddrs;
}
#if (NGX_SUPPRESS_WARN)
addr = NULL;
#endif
break;
#endif
default: /* NGX_RESOLVE_A */
if (naddrs == 1) {
addr = &rn->u.addr;
rn->naddrs = 1;
} else {
addr = ngx_resolver_alloc(r, naddrs * sizeof(in_addr_t));
if (addr == NULL) {
goto failed;
}
rn->u.addrs = addr;
rn->naddrs = (u_short) naddrs;
}
#if (NGX_HAVE_INET6 && NGX_SUPPRESS_WARN)
addr6 = NULL;
#endif
}
j = 0;
i = ans;
for (a = 0; a < nan; a++) {
for ( ;; ) {
if (buf[i] & 0xc0) {
i += 2;
break;
}
if (buf[i] == 0) {
i++;
break;
}
i += 1 + buf[i];
}
an = (ngx_resolver_an_t *) &buf[i];
type = (an->type_hi << 8) + an->type_lo;
len = (an->len_hi << 8) + an->len_lo;
i += sizeof(ngx_resolver_an_t);
if (type == NGX_RESOLVE_A) {
addr[j] = htonl((buf[i] << 24) + (buf[i + 1] << 16)
+ (buf[i + 2] << 8) + (buf[i + 3]));
if (++j == naddrs) {
#if (NGX_HAVE_INET6)
if (rn->naddrs6 == (u_short) -1) {
goto next;
}
#endif
break;
}
}
#if (NGX_HAVE_INET6)
else if (type == NGX_RESOLVE_AAAA) {
ngx_memcpy(addr6[j].s6_addr, &buf[i], 16);
if (++j == naddrs) {
if (rn->naddrs == (u_short) -1) {
goto next;
}
break;
}
}
#endif
i += len;
}
}
switch (qtype) {
#if (NGX_HAVE_INET6)
case NGX_RESOLVE_AAAA:
if (rn->naddrs6 == (u_short) -1) {
rn->naddrs6 = 0;
}
break;
#endif
default: /* NGX_RESOLVE_A */
if (rn->naddrs == (u_short) -1) {
rn->naddrs = 0;
}
}
if (rn->naddrs != (u_short) -1
#if (NGX_HAVE_INET6)
&& rn->naddrs6 != (u_short) -1
#endif
&& rn->naddrs
#if (NGX_HAVE_INET6)
+ rn->naddrs6
#endif
> 0)
{
#if (NGX_HAVE_INET6)
export:
#endif
naddrs = rn->naddrs;
#if (NGX_HAVE_INET6)
naddrs += rn->naddrs6;
#endif
if (naddrs == 1 && rn->naddrs == 1) {
addrs = NULL;
} else {
addrs = ngx_resolver_export(r, rn, 0);
if (addrs == NULL) {
goto failed;
}
}
ngx_queue_remove(&rn->queue);
rn->valid = ngx_time() + (r->valid ? r->valid : (time_t) rn->ttl);
rn->expire = ngx_time() + r->expire;
ngx_queue_insert_head(&r->name_expire_queue, &rn->queue);
next = rn->waiting;
rn->waiting = NULL;
/* unlock name mutex */
while (next) {
ctx = next;
ctx->state = NGX_OK;
ctx->valid = rn->valid;
ctx->naddrs = naddrs;
if (addrs == NULL) {
ctx->addrs = &ctx->addr;
ctx->addr.sockaddr = (struct sockaddr *) &ctx->sin;
ctx->addr.socklen = sizeof(struct sockaddr_in);
ngx_memzero(&ctx->sin, sizeof(struct sockaddr_in));
ctx->sin.sin_family = AF_INET;
ctx->sin.sin_addr.s_addr = rn->u.addr;
} else {
ctx->addrs = addrs;
}
next = ctx->next;
ctx->handler(ctx);
}
if (addrs != NULL) {
ngx_resolver_free(r, addrs->sockaddr);
ngx_resolver_free(r, addrs);
}
ngx_resolver_free(r, rn->query);
rn->query = NULL;
#if (NGX_HAVE_INET6)
rn->query6 = NULL;
#endif
return;
}
if (cname) {
/* CNAME only */
if (rn->naddrs == (u_short) -1
#if (NGX_HAVE_INET6)
|| rn->naddrs6 == (u_short) -1
#endif
)
{
goto next;
}
if (ngx_resolver_copy(r, &name, buf, cname, buf + n) != NGX_OK) {
goto failed;
}
ngx_log_debug1(NGX_LOG_DEBUG_CORE, r->log, 0,
"resolver cname:\"%V\"", &name);
ngx_queue_remove(&rn->queue);
rn->cnlen = (u_short) name.len;
rn->u.cname = name.data;
rn->valid = ngx_time() + (r->valid ? r->valid : (time_t) rn->ttl);
rn->expire = ngx_time() + r->expire;
ngx_queue_insert_head(&r->name_expire_queue, &rn->queue);
ngx_resolver_free(r, rn->query);
rn->query = NULL;
#if (NGX_HAVE_INET6)
rn->query6 = NULL;
#endif
ctx = rn->waiting;
rn->waiting = NULL;
if (ctx) {
if (ctx->recursion++ >= NGX_RESOLVER_MAX_RECURSION) {
/* unlock name mutex */
do {
ctx->state = NGX_RESOLVE_NXDOMAIN;
next = ctx->next;
ctx->handler(ctx);
ctx = next;
} while (ctx);
return;
}
for (next = ctx; next; next = next->next) {
next->node = NULL;
}
(void) ngx_resolve_name_locked(r, ctx, &name);
}
/* unlock name mutex */
return;
}
ngx_log_error(r->log_level, r->log, 0,
"no A or CNAME types in DNS response");
return;
short_response:
err = "short DNS response";
invalid:
/* unlock name mutex */
ngx_log_error(r->log_level, r->log, 0, err);
return;
failed:
next:
/* unlock name mutex */
return;
}此函数用于处理由域名获得IPv4（或IPv6)地址的解析。下面简单介绍一下函数的处理流程：
static void
ngx_resolver_process_a(ngx_resolver_t *r, u_char *buf, size_t n,
ngx_uint_t ident, ngx_uint_t code, ngx_uint_t qtype,
ngx_uint_t nan, ngx_uint_t trunc, ngx_uint_t ans)
{
//1) 调用ngx_resolver_copy()分离出查询的域名name
//2) 调用ngx_resolver_lookup_name()查找对应的ngx_resolver_node_t节点
//3) 根据qtype获得当前的查询标识符(qident), 并判断我们本地保存的查询标识符与DNS返回的标识符是否一样，不一样的话表示响应有问题
//4) 处理trunc情况，表示有截断，此时可能需要重新发起查询请求
//5) 如果code==0 且 nan==0(即应答资源记录数为0），则一般情况表示出现了异常，此种情况会将ctx->state设置为相应的异常状态，
// 直接调用ctx->handler()来处理
//6) 如果有相应的资源记录数，即nan不为0，那么
if nan > 0{
for(i = 0; i<nan; i++)
{
//6.1) 解析应答头部ngx_resolver_an_t
//6.2) 获得返回的IP地址数
}
// 6.3 然后, 解析返回的IP地址
}
//调用ngx_resolver_export()导出相应的IP地址到ctx->addrs
//7) 处理cname不为NULL的情况， 此时表示还返回了所查询域名的规范名称，这种情况下会再调用
// ngx_resolve_name_locked()进行递归查询
}9. 函数ngx_resolver_process_srv()
static void
ngx_resolver_process_srv(ngx_resolver_t *r, u_char *buf, size_t n,
ngx_uint_t ident, ngx_uint_t code, ngx_uint_t nan,
ngx_uint_t trunc, ngx_uint_t ans)
{
char *err;
u_char *cname;
size_t len;
int32_t ttl;
uint32_t hash;
ngx_str_t name;
ngx_uint_t type, qident, class, start, nsrvs, a, i, j;
ngx_resolver_an_t *an;
ngx_resolver_ctx_t *ctx, *next;
ngx_resolver_srv_t *srvs;
ngx_resolver_node_t *rn;
ngx_resolver_connection_t *rec;
if (ngx_resolver_copy(r, &name, buf,
buf + sizeof(ngx_resolver_hdr_t), buf + n)
!= NGX_OK)
{
return;
}
ngx_log_debug1(NGX_LOG_DEBUG_CORE, r->log, 0, "resolver qs:%V", &name);
hash = ngx_crc32_short(name.data, name.len);
rn = ngx_resolver_lookup_srv(r, &name, hash);
if (rn == NULL || rn->query == NULL) {
ngx_log_error(r->log_level, r->log, 0,
"unexpected response for %V", &name);
ngx_resolver_free(r, name.data);
goto failed;
}
if (trunc && rn->tcp) {
ngx_resolver_free(r, name.data);
goto failed;
}
qident = (rn->query[0] << 8) + rn->query[1];
if (ident != qident) {
ngx_log_error(r->log_level, r->log, 0,
"wrong ident %ui response for %V, expect %ui",
ident, &name, qident);
ngx_resolver_free(r, name.data);
goto failed;
}
ngx_resolver_free(r, name.data);
if (trunc) {
ngx_queue_remove(&rn->queue);
if (rn->waiting == NULL) {
ngx_rbtree_delete(&r->srv_rbtree, &rn->node);
ngx_resolver_free_node(r, rn);
return;
}
rec = r->connections.elts;
rec = &rec[rn->last_connection];
rn->tcp = 1;
(void) ngx_resolver_send_tcp_query(r, rec, rn->query, rn->qlen);
rn->expire = ngx_time() + r->resend_timeout;
ngx_queue_insert_head(&r->srv_resend_queue, &rn->queue);
return;
}
if (code == 0 && rn->code) {
code = rn->code;
}
if (code == 0 && nan == 0) {
code = NGX_RESOLVE_NXDOMAIN;
}
if (code) {
next = rn->waiting;
rn->waiting = NULL;
ngx_queue_remove(&rn->queue);
ngx_rbtree_delete(&r->srv_rbtree, &rn->node);
while (next) {
ctx = next;
ctx->state = code;
ctx->valid = ngx_time() + (r->valid ? r->valid : 10);
next = ctx->next;
ctx->handler(ctx);
}
ngx_resolver_free_node(r, rn);
return;
}
i = ans;
nsrvs = 0;
cname = NULL;
for (a = 0; a < nan; a++) {
start = i;
while (i < n) {
if (buf[i] & 0xc0) {
i += 2;
goto found;
}
if (buf[i] == 0) {
i++;
goto test_length;
}
i += 1 + buf[i];
}
goto short_response;
test_length:
if (i - start < 2) {
err = "invalid name DNS response";
goto invalid;
}
found:
if (i + sizeof(ngx_resolver_an_t) >= n) {
goto short_response;
}
an = (ngx_resolver_an_t *) &buf[i];
type = (an->type_hi << 8) + an->type_lo;
class = (an->class_hi << 8) + an->class_lo;
len = (an->len_hi << 8) + an->len_lo;
ttl = (an->ttl[0] << 24) + (an->ttl[1] << 16)
+ (an->ttl[2] << 8) + (an->ttl[3]);
if (class != 1) {
ngx_log_error(r->log_level, r->log, 0,
"unexpected RR class %ui", class);
goto failed;
}
if (ttl < 0) {
ttl = 0;
}
rn->ttl = ngx_min(rn->ttl, (uint32_t) ttl);
i += sizeof(ngx_resolver_an_t);
switch (type) {
case NGX_RESOLVE_SRV:
if (i + 6 > n) {
goto short_response;
}
if (ngx_resolver_copy(r, NULL, buf, &buf[i + 6], buf + n)
!= NGX_OK)
{
goto failed;
}
nsrvs++;
break;
case NGX_RESOLVE_CNAME:
cname = &buf[i];
break;
case NGX_RESOLVE_DNAME:
break;
default:
ngx_log_error(r->log_level, r->log, 0,
"unexpected RR type %ui", type);
}
i += len;
}
ngx_log_debug3(NGX_LOG_DEBUG_CORE, r->log, 0,
"resolver nsrvs:%ui cname:%p ttl:%uD",
nsrvs, cname, rn->ttl);
if (nsrvs) {
srvs = ngx_resolver_calloc(r, nsrvs * sizeof(ngx_resolver_srv_t));
if (srvs == NULL) {
goto failed;
}
rn->u.srvs = srvs;
rn->nsrvs = (u_short) nsrvs;
j = 0;
i = ans;
for (a = 0; a < nan; a++) {
for ( ;; ) {
if (buf[i] & 0xc0) {
i += 2;
break;
}
if (buf[i] == 0) {
i++;
break;
}
i += 1 + buf[i];
}
an = (ngx_resolver_an_t *) &buf[i];
type = (an->type_hi << 8) + an->type_lo;
len = (an->len_hi << 8) + an->len_lo;
i += sizeof(ngx_resolver_an_t);
if (type == NGX_RESOLVE_SRV) {
srvs[j].priority = (buf[i] << 8) + buf[i + 1];
srvs[j].weight = (buf[i + 2] << 8) + buf[i + 3];
if (srvs[j].weight == 0) {
srvs[j].weight = 1;
}
srvs[j].port = (buf[i + 4] << 8) + buf[i + 5];
if (ngx_resolver_copy(r, &srvs[j].name, buf, &buf[i + 6],
buf + n)
!= NGX_OK)
{
goto failed;
}
j++;
}
i += len;
}
ngx_sort(srvs, nsrvs, sizeof(ngx_resolver_srv_t),
ngx_resolver_cmp_srvs);
ngx_resolver_free(r, rn->query);
rn->query = NULL;
ngx_queue_remove(&rn->queue);
rn->valid = ngx_time() + (r->valid ? r->valid : (time_t) rn->ttl);
rn->expire = ngx_time() + r->expire;
ngx_queue_insert_head(&r->srv_expire_queue, &rn->queue);
next = rn->waiting;
rn->waiting = NULL;
while (next) {
ctx = next;
next = ctx->next;
ngx_resolver_resolve_srv_names(ctx, rn);
}
return;
}
rn->nsrvs = 0;
if (cname) {
/* CNAME only */
if (ngx_resolver_copy(r, &name, buf, cname, buf + n) != NGX_OK) {
goto failed;
}
ngx_log_debug1(NGX_LOG_DEBUG_CORE, r->log, 0,
"resolver cname:\"%V\"", &name);
ngx_queue_remove(&rn->queue);
rn->cnlen = (u_short) name.len;
rn->u.cname = name.data;
rn->valid = ngx_time() + (r->valid ? r->valid : (time_t) rn->ttl);
rn->expire = ngx_time() + r->expire;
ngx_queue_insert_head(&r->srv_expire_queue, &rn->queue);
ngx_resolver_free(r, rn->query);
rn->query = NULL;
#if (NGX_HAVE_INET6)
rn->query6 = NULL;
#endif
ctx = rn->waiting;
rn->waiting = NULL;
if (ctx) {
if (ctx->recursion++ >= NGX_RESOLVER_MAX_RECURSION) {
/* unlock name mutex */
do {
ctx->state = NGX_RESOLVE_NXDOMAIN;
next = ctx->next;
ctx->handler(ctx);
ctx = next;
} while (ctx);
return;
}
for (next = ctx; next; next = next->next) {
next->node = NULL;
}
(void) ngx_resolve_name_locked(r, ctx, &name);
}
/* unlock name mutex */
return;
}
ngx_log_error(r->log_level, r->log, 0, "no SRV type in DNS response");
return;
short_response:
err = "short DNS response";
invalid:
/* unlock name mutex */
ngx_log_error(r->log_level, r->log, 0, err);
return;
failed:
/* unlock name mutex */
return;
}此函数用于处理由服务名获得IPv4(或IPv6)地址的解析。下面简要介绍一下函数的处理流程：
static void
ngx_resolver_process_srv(ngx_resolver_t *r, u_char *buf, size_t n,
ngx_uint_t ident, ngx_uint_t code, ngx_uint_t nan,
ngx_uint_t trunc, ngx_uint_t ans)
{
//1) 调用ngx_resolver_copy()分离出查询的域名name
//2) 调用ngx_resolver_lookup_srv()查找对应的ngx_resolver_node_t节点
//3) 根据qtype获得当前的查询标识符(qident), 并判断我们本地保存的查询标识符与DNS返回的标识符是否一样，不一样的话表示响应有问题
//4) 处理trunc情况，表示有截断，此时可能需要重新发起查询请求
//5) 如果code==0 且 nan==0(即应答资源记录数为0），则一般情况表示出现了异常，此种情况会将ctx->state设置为相应的异常状态，
// 直接调用ctx->handler()来处理
//6) 解析应答报文，获取srvs的个数
//7) 假如srvs个数大于0，
// 7.1) 循环解析应答报文，获得所查询服务的domain name、优先级、权重、端口等等
// 7.2) 对返回的srvs进行排序，并将该ngx_resolver_node_t节点插入到resolver的srv_expire_queue队列中
// 7.3) 接着再根据服务的domain name等查询具体的IP地址等信息（通过调用ngx_resolver_resolve_srv_names())
//8) 如果cname不为NULL，将rn->nsrvs设置为0，表示返回的是规范化名称CNAME，此时可能需要再采用该canonical name
//来进行继续的解析(注意： 在解析时可能产生递归，这里判别当出现NGX_RESOLVER_MAX_RECURSION次递归时，直接结束查询)
}10. 函数ngx_resolver_resolve_srv_names()
static void
ngx_resolver_resolve_srv_names(ngx_resolver_ctx_t *ctx, ngx_resolver_node_t *rn)
{
ngx_uint_t i;
ngx_resolver_t *r;
ngx_resolver_ctx_t *cctx;
ngx_resolver_srv_name_t *srvs;
r = ctx->resolver;
ctx->node = NULL;
ctx->state = NGX_OK;
ctx->valid = rn->valid;
ctx->count = rn->nsrvs;
srvs = ngx_resolver_calloc(r, rn->nsrvs * sizeof(ngx_resolver_srv_name_t));
if (srvs == NULL) {
goto failed;
}
ctx->srvs = srvs;
ctx->nsrvs = rn->nsrvs;
for (i = 0; i < rn->nsrvs; i++) {
srvs[i].name.data = ngx_resolver_alloc(r, rn->u.srvs[i].name.len);
if (srvs[i].name.data == NULL) {
goto failed;
}
srvs[i].name.len = rn->u.srvs[i].name.len;
ngx_memcpy(srvs[i].name.data, rn->u.srvs[i].name.data,
srvs[i].name.len);
cctx = ngx_resolve_start(r, NULL);
if (cctx == NULL) {
goto failed;
}
cctx->name = srvs[i].name;
cctx->handler = ngx_resolver_srv_names_handler;
cctx->data = ctx;
cctx->srvs = &srvs[i];
cctx->timeout = 0;
srvs[i].priority = rn->u.srvs[i].priority;
srvs[i].weight = rn->u.srvs[i].weight;
srvs[i].port = rn->u.srvs[i].port;
srvs[i].ctx = cctx;
if (ngx_resolve_name(cctx) == NGX_ERROR) {
srvs[i].ctx = NULL;
goto failed;
}
}
return;
failed:
ctx->state = NGX_ERROR;
ctx->valid = ngx_time() + (r->valid ? r->valid : 10);
ctx->handler(ctx);
}此函数用于解析rn->u.srvs，即将规范化服务名称解析为IP地址。下面简要讲解一下本函数的实现流程：
static void
ngx_resolver_resolve_srv_names(ngx_resolver_ctx_t *ctx, ngx_resolver_node_t *rn)
{
//循环rn->nsrvs，重新创建ngx_resolver_ctx_t来进行'规范化服务名称解析为IP地址'
for (i = 0; i < rn->nsrvs; i++) {
//创建新的ctx对象
cctx = ngx_resolve_start(r, NULL);
//使用新的ctx完成解析
ngx_resolve_name()
}
}11. 函数ngx_resolver_srv_names_handler()
static void
ngx_resolver_srv_names_handler(ngx_resolver_ctx_t *cctx)
{
ngx_uint_t i;
u_char (*sockaddr)[NGX_SOCKADDRLEN];
ngx_addr_t *addrs;
ngx_resolver_t *r;
struct sockaddr_in *sin;
ngx_resolver_ctx_t *ctx;
ngx_resolver_srv_name_t *srv;
#if (NGX_HAVE_INET6)
struct sockaddr_in6 *sin6;
#endif
r = cctx->resolver;
ctx = cctx->data;
srv = cctx->srvs;
ctx->count--;
srv->ctx = NULL;
if (cctx->naddrs) {
ctx->valid = ngx_min(ctx->valid, cctx->valid);
addrs = ngx_resolver_calloc(r, cctx->naddrs * sizeof(ngx_addr_t));
if (addrs == NULL) {
ngx_resolve_name_done(cctx);
ctx->state = NGX_ERROR;
ctx->valid = ngx_time() + (r->valid ? r->valid : 10);
ctx->handler(ctx);
return;
}
sockaddr = ngx_resolver_alloc(r, cctx->naddrs * NGX_SOCKADDRLEN);
if (sockaddr == NULL) {
ngx_resolver_free(r, addrs);
ngx_resolve_name_done(cctx);
ctx->state = NGX_ERROR;
ctx->valid = ngx_time() + (r->valid ? r->valid : 10);
ctx->handler(ctx);
return;
}
for (i = 0; i < cctx->naddrs; i++) {
addrs[i].sockaddr = (struct sockaddr *) sockaddr[i];
addrs[i].socklen = cctx->addrs[i].socklen;
ngx_memcpy(sockaddr[i], cctx->addrs[i].sockaddr,
addrs[i].socklen);
switch (addrs[i].sockaddr->sa_family) {
#if (NGX_HAVE_INET6)
case AF_INET6:
sin6 = (struct sockaddr_in6 *) addrs[i].sockaddr;
sin6->sin6_port = htons(srv->port);
break;
#endif
default: /* AF_INET */
sin = (struct sockaddr_in *) addrs[i].sockaddr;
sin->sin_port = htons(srv->port);
}
}
srv->addrs = addrs;
srv->naddrs = cctx->naddrs;
}
ngx_resolve_name_done(cctx);
if (ctx->count == 0) {
ngx_resolver_report_srv(r, ctx);
}
}本函数是将规范化服务名称解析为IP地址完成后的回调函数。涉及到两个context: 首先context_1将尝试将服务名解析为IP地址，但是只返回了规范化服务名称； 接着会创建一个新的context_2来将该规范化服务名成解析为IP地址。这里可以认为context_1是context_2的父上下文。
基本实现步骤如下：
static void
ngx_resolver_srv_names_handler(ngx_resolver_ctx_t *cctx)
{
//1) 如果成功解析到了IP地址
if (cctx->naddrs) {
//将解析到的IP地址保存到cctx->srvs->addrs里面(一个规范化名称，可能会对应多个IP地址)
}
//2) 执行ngx_resolve_name_done(cctx)，表明当前context已经处理完，进行相应的收尾工作
//3) 如果cctx->data所表示的context的count为0，表示已经完成了所有规范名称的IP地址转换，此时ngx_resolver_report_srv()
}12. 函数ngx_resolver_process_ptr()
static void
ngx_resolver_process_ptr(ngx_resolver_t *r, u_char *buf, size_t n,
ngx_uint_t ident, ngx_uint_t code, ngx_uint_t nan)
{
char *err;
size_t len;
in_addr_t addr;
int32_t ttl;
ngx_int_t octet;
ngx_str_t name;
ngx_uint_t mask, type, class, qident, a, i, start;
ngx_queue_t *expire_queue;
ngx_rbtree_t *tree;
ngx_resolver_an_t *an;
ngx_resolver_ctx_t *ctx, *next;
ngx_resolver_node_t *rn;
#if (NGX_HAVE_INET6)
uint32_t hash;
ngx_int_t digit;
struct in6_addr addr6;
#endif
if (ngx_resolver_copy(r, &name, buf,
buf + sizeof(ngx_resolver_hdr_t), buf + n)
!= NGX_OK)
{
return;
}
ngx_log_debug1(NGX_LOG_DEBUG_CORE, r->log, 0, "resolver qs:%V", &name);
/* AF_INET */
addr = 0;
i = sizeof(ngx_resolver_hdr_t);
for (mask = 0; mask < 32; mask += 8) {
len = buf[i++];
octet = ngx_atoi(&buf[i], len);
if (octet == NGX_ERROR || octet > 255) {
goto invalid_in_addr_arpa;
}
addr += octet << mask;
i += len;
}
if (ngx_strcasecmp(&buf[i], (u_char *) "\7in-addr\4arpa") == 0) {
i += sizeof("\7in-addr\4arpa");
/* lock addr mutex */
rn = ngx_resolver_lookup_addr(r, addr);
tree = &r->addr_rbtree;
expire_queue = &r->addr_expire_queue;
goto valid;
}
invalid_in_addr_arpa:
#if (NGX_HAVE_INET6)
i = sizeof(ngx_resolver_hdr_t);
for (octet = 15; octet >= 0; octet--) {
if (buf[i++] != '\1') {
goto invalid_ip6_arpa;
}
digit = ngx_hextoi(&buf[i++], 1);
if (digit == NGX_ERROR) {
goto invalid_ip6_arpa;
}
addr6.s6_addr[octet] = (u_char) digit;
if (buf[i++] != '\1') {
goto invalid_ip6_arpa;
}
digit = ngx_hextoi(&buf[i++], 1);
if (digit == NGX_ERROR) {
goto invalid_ip6_arpa;
}
addr6.s6_addr[octet] += (u_char) (digit * 16);
}
if (ngx_strcasecmp(&buf[i], (u_char *) "\3ip6\4arpa") == 0) {
i += sizeof("\3ip6\4arpa");
/* lock addr mutex */
hash = ngx_crc32_short(addr6.s6_addr, 16);
rn = ngx_resolver_lookup_addr6(r, &addr6, hash);
tree = &r->addr6_rbtree;
expire_queue = &r->addr6_expire_queue;
goto valid;
}
invalid_ip6_arpa:
#endif
ngx_log_error(r->log_level, r->log, 0,
"invalid in-addr.arpa or ip6.arpa name in DNS response");
ngx_resolver_free(r, name.data);
return;
valid:
if (rn == NULL || rn->query == NULL) {
ngx_log_error(r->log_level, r->log, 0,
"unexpected response for %V", &name);
ngx_resolver_free(r, name.data);
goto failed;
}
qident = (rn->query[0] << 8) + rn->query[1];
if (ident != qident) {
ngx_log_error(r->log_level, r->log, 0,
"wrong ident %ui response for %V, expect %ui",
ident, &name, qident);
ngx_resolver_free(r, name.data);
goto failed;
}
ngx_resolver_free(r, name.data);
if (code == 0 && nan == 0) {
code = NGX_RESOLVE_NXDOMAIN;
}
if (code) {
next = rn->waiting;
rn->waiting = NULL;
ngx_queue_remove(&rn->queue);
ngx_rbtree_delete(tree, &rn->node);
/* unlock addr mutex */
while (next) {
ctx = next;
ctx->state = code;
ctx->valid = ngx_time() + (r->valid ? r->valid : 10);
next = ctx->next;
ctx->handler(ctx);
}
ngx_resolver_free_node(r, rn);
return;
}
i += sizeof(ngx_resolver_qs_t);
for (a = 0; a < nan; a++) {
start = i;
while (i < n) {
if (buf[i] & 0xc0) {
i += 2;
goto found;
}
if (buf[i] == 0) {
i++;
goto test_length;
}
i += 1 + buf[i];
}
goto short_response;
test_length:
if (i - start < 2) {
err = "invalid name in DNS response";
goto invalid;
}
found:
if (i + sizeof(ngx_resolver_an_t) >= n) {
goto short_response;
}
an = (ngx_resolver_an_t *) &buf[i];
type = (an->type_hi << 8) + an->type_lo;
class = (an->class_hi << 8) + an->class_lo;
len = (an->len_hi << 8) + an->len_lo;
ttl = (an->ttl[0] << 24) + (an->ttl[1] << 16)
+ (an->ttl[2] << 8) + (an->ttl[3]);
if (class != 1) {
ngx_log_error(r->log_level, r->log, 0,
"unexpected RR class %ui", class);
goto failed;
}
if (ttl < 0) {
ttl = 0;
}
ngx_log_debug3(NGX_LOG_DEBUG_CORE, r->log, 0,
"resolver qt:%ui cl:%ui len:%uz",
type, class, len);
i += sizeof(ngx_resolver_an_t);
switch (type) {
case NGX_RESOLVE_PTR:
goto ptr;
case NGX_RESOLVE_CNAME:
break;
default:
ngx_log_error(r->log_level, r->log, 0,
"unexpected RR type %ui", type);
}
i += len;
}
/* unlock addr mutex */
ngx_log_error(r->log_level, r->log, 0,
"no PTR type in DNS response");
return;
ptr:
if (ngx_resolver_copy(r, &name, buf, buf + i, buf + n) != NGX_OK) {
goto failed;
}
ngx_log_debug1(NGX_LOG_DEBUG_CORE, r->log, 0, "resolver an:%V", &name);
if (name.len != (size_t) rn->nlen
|| ngx_strncmp(name.data, rn->name, name.len) != 0)
{
if (rn->nlen) {
ngx_resolver_free(r, rn->name);
}
rn->nlen = (u_short) name.len;
rn->name = name.data;
name.data = ngx_resolver_dup(r, rn->name, name.len);
if (name.data == NULL) {
goto failed;
}
}
ngx_queue_remove(&rn->queue);
rn->valid = ngx_time() + (r->valid ? r->valid : ttl);
rn->expire = ngx_time() + r->expire;
ngx_queue_insert_head(expire_queue, &rn->queue);
next = rn->waiting;
rn->waiting = NULL;
/* unlock addr mutex */
while (next) {
ctx = next;
ctx->state = NGX_OK;
ctx->valid = rn->valid;
ctx->name = name;
next = ctx->next;
ctx->handler(ctx);
}
ngx_resolver_free(r, name.data);
return;
short_response:
err = "short DNS response";
invalid:
/* unlock addr mutex */
ngx_log_error(r->log_level, r->log, 0, err);
return;
failed:
/* unlock addr mutex */
return;
}此函数用于处理将IP地址转换为域名的响应。下面简要介绍一下函数的实现流程：
static void
ngx_resolver_process_ptr(ngx_resolver_t *r, u_char *buf, size_t n,
ngx_uint_t ident, ngx_uint_t code, ngx_uint_t nan)
{
//1) 调用ngx_resolver_copy()分离出查询的域名name,
//2) 从response的buf中解析出IP地址
//3) 通过ngx_resolver_lookup_addr查询出本地保存的标识符qident与查询返回的标识符是否一致，如果不一样的话表示响应有问题
//4) 如果code不为0， 则一般情况表示出现了异常， 打印相应的错误退出
//5) 若nan>0，表示有相应的应答资源记录数，那么解析出对应的name，接着回调rn->waiting上下文列表中的handler()
ngx_resolver_copy(r, &name, buf, buf + i, buf + n)；
}
[参看]
