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nginx 域名动态解析
概述
域名在互联网中广泛应用，而http是建立在tcp/ip协议上的，tcp/ip协议只认识ip地址，所以就需要通过某个系统（DNS）把域名转换成ip地址供底层使用。 通常linux系统下，命令行使用dig查询，c语言使用gethostbyname或getaddrinfo函数查询。实际上都是发送一个网络请求到/etc/resolv.conf下的一个服务器查询。
nginx作为一个通用的服务器也会涉及到域名解析。例如，nginx 用作反向代理可以配置upstream是一个域名。proxy_pass http://www.baidu.com/$request_uri;
那么www.baidu.com这个域名是什么时候解析的呢？又是如何解析的呢？如果没有添加$request_uri这个变量解析会有区别么？
nginx是单进程异步非阻塞服务，如果用getaddrinfo来解析势必会导致nginx阻塞。在启动阶段阻塞一小会儿不会有大的影响，如果在服务处理阶段阻塞，会导致该进程所服务的客户端延迟甚至出错。
proxy_pass 对应的域名解析分为有变量和没有变量，没有变量的是在启动阶段解析， 而有变量的是在每次请求解析的，每次请求解析在nginx是怎么做的？还是异步回调。
DNS报文
nginx会拼装DNS查询报文，所以现了解一下DNS报文格式。也可以略过直接看大框架逻辑。
报文格式
- 报文格式：
DNS format
+--+--+--+--+--+--+--+
| Header | 报文头
+--+--+--+--+--+--+--+
| Question | 查询的问题
+--+--+--+--+--+--+--+
| Answer | 应答
+--+--+--+--+--+--+--+
| Authority | 授权应答
+--+--+--+--+--+--+--+
| Additional | 附加信息
+--+--+--+--+--+--+--+
- 报文头：
Header format
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| ID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|QR| opcode |AA|TC|RD|RA| Z | RCODE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| QDCOUNT |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| ANCOUNT |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| NSCOUNT |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| ARCOUNT |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
说明： ID: 2个字节(16bit)，标识字段，客户端会解析服务器返回的DNS应答报文，获取ID值与请求报文设置的ID值做比较，如果相同，则认为是同一个DNS会话。 FLAGS: 2个字节(16bit)的标志字段。包含以下属性: QR: 0表示查询报文，1表示响应报文; opcode: 通常值为0（标准查询），其他值为1（反向查询）和2（服务器状态请求）,[3,15]保留值; AA: 表示授权回答（authoritative answer）– 这个比特位在应答的时候才有意义，指出给出应答的服务器是查询域名的授权解析服务器; TC: 表示可截断的（truncated）–用来指出报文比允许的长度还要长，导致被截断; RD: 表示期望递归(Recursion Desired) – 这个比特位被请求设置，应答的时候使用的相同的值返回。如果设置了RD，就建议域名服务器进行递归解析，递归查询的支持是可选的; RA: 表示支持递归(Recursion Available) – 这个比特位在应答中设置或取消，用来代表服务器是否支持递归查询; Z : 保留值，暂未使用; RCODE: 应答码(Response code) - 这4个比特位在应答报文中设置，代表的含义如下: 0 : 没有错误。 QDCOUNT: 无符号16bit整数表示报文请求段中的问题记录数。 ANCOUNT: 无符号16bit整数表示报文回答段中的回答记录数。 ANCOUNT: 无符号16bit整数表示报文回答段中的回答记录数。 ARCOUNT: 无符号16bit整数表示报文附加段中的附加记录数。
- 查询
Question format
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| ... |
| QNAME |
| ... |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| QTYPE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| QCLASS |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
说明： QNAME 8bit为单位表示的查询名(广泛的说就是：域名). QTYPE 无符号16bit整数表示查询的协议类型. QCLASS 无符号16bit整数表示查询的类,比如，IN代表Internet.
- 应答
Answer/Authority/Additional format
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| NAME |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| TYPE |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| CLASS |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| TTL |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| RDLENGTH |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| RDATA |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
说明： NAME 资源记录包含的域名. TYPE 表示DNS协议的类型. CLASS 表示RDATA的类. TTL 4字节无符号整数表示资源记录可以缓存的时间。0代表只能被传输，但是不能被缓存。 RDLENGTH 2个字节无符号整数表示RDATA的长度 RDATA 不定长字符串来表示记录，格式根TYPE和CLASS有关。比如，TYPE是A，CLASS 是 IN，那么RDATA就是一个4个字节的ARPA网络地址。
ngx中报文结构体
// 对应报文头的6个16bit字段。12个8bit
typedef struct {
// ID标识字段
u_char ident_hi;
u_char ident_lo;
// FLAG标识
u_char flags_hi;
u_char flags_lo;
// QDCOUNT 查询段中的问题记录数
u_char nqs_hi;
u_char nqs_lo;
// ANCOUNT 应答段中的问题记录数
u_char nan_hi;
u_char nan_lo;
// NSCOUNT 授权记录数
u_char nns_hi;
u_char nns_lo;
// ARCOUNT 附加记录数
u_char nar_hi;
u_char nar_lo;
} ngx_resolver_hdr_t;
// 对应查询报文2个16bit字段。4个8bit
typedef struct {
// QTYPE 无符号16bit整数表示查询的协议类型.
u_char type_hi;
u_char type_lo;
// 无符号16bit整数表示查询的类,比如，IN代表Internet.
u_char class_hi;
u_char class_lo;
} ngx_resolver_qs_t;
// 应答报文 4个字段
typedef struct {
// 表示DNS协议的类型.
u_char type_hi;
u_char type_lo;
// 表示RDATA的类.
u_char class_hi;
u_char class_lo;
// 4字节无符号整数表示资源记录可以缓存的时间。0代表只能被传输，但是不能被缓存。
u_char ttl[4];
// 2个字节无符号整数表示RDATA的长度
u_char len_hi;
u_char len_lo;
} ngx_resolver_an_t;
nginx域名解析源码分析
-
ngx_inet_resolve_host函数。该函数实际上是封装了getaddrinfo函数，是同步阻塞解析。
-
异步回调解析，下面以proxy模块的代码来分析异步非阻塞回调的域名解析。
启动阶段，在proxy模块的ngx_http_proxy_eval函数中，url不是ip地址，则u->resolved->sockaddr不会赋值，u->resolved->host是域名。
请求处理阶段，在解析完header头，进入content阶段，调用proxy模块的ngx_http_proxy_handler回调函数，该函数通过调用ngx_http_read_client_request_body(r, ngx_http_upstream_init)，读取body并启动upstream。读取完body后（或者读到body）调用ngx_http_upstream_init函数，该函数又调用了ngx_http_upstream_init_request函数。
在ngx_http_upstream_init_request函数中会查找上游服务器。如果是域名则会调用ngx_resolve_start函数分配域名解析结构体，调用ngx_resolve_name函数解析，该函数会创建一个事件结构添加到epoll中，解析完毕后回调ctx->handler函数，即ngx_http_upstream_resolve_handler。
static void
ngx_http_upstream_init_request(ngx_http_request_t *r)
{
......
ctx = ngx_resolve_start(clcf->resolver, &temp);
if (ctx == NULL) {
ngx_http_upstream_finalize_request(r, u,
NGX_HTTP_INTERNAL_SERVER_ERROR);
return;
}
if (ctx == NGX_NO_RESOLVER) {
ngx_log_error(NGX_LOG_ERR, r->connection->log, 0,
"no resolver defined to resolve %V", host);
ngx_http_upstream_finalize_request(r, u, NGX_HTTP_BAD_GATEWAY);
return;
}
ctx->name = *host;
ctx->handler = ngx_http_upstream_resolve_handler;
ctx->data = r;
ctx->timeout = clcf->resolver_timeout;
u->resolved->ctx = ctx;
if (ngx_resolve_name(ctx) != NGX_OK) {
u->resolved->ctx = NULL;
ngx_http_upstream_finalize_request(r, u,
NGX_HTTP_INTERNAL_SERVER_ERROR);
return;
}
......
}
ngx_resolver.h|c
主要结构：
// resolver 信息，通过resolver指令制定的解析域名的服务器
typedef struct {
ngx_connection_t *udp;
ngx_connection_t *tcp; // tcp 连接的connection
struct sockaddr *sockaddr; // resolver 地址
socklen_t socklen;
ngx_str_t server; // resolver域名
ngx_log_t log;
ngx_buf_t *read_buf; // tcp 读缓存区
ngx_buf_t *write_buf; // tcp 写缓存区
ngx_resolver_t *resolver;
} ngx_resolver_connection_t;
struct ngx_resolver_s {
/* has to be pointer because of "incomplete type" */
ngx_event_t *event;
void *dummy;
ngx_log_t *log;
/* event ident must be after 3 pointers as in ngx_connection_t */
ngx_int_t ident;
/* simple round robin DNS peers balancer */
// ngx_resolver_connection_t 结构的数组，resolver服务地址。
ngx_array_t connections;
ngx_uint_t last_connection;
ngx_rbtree_t name_rbtree;
ngx_rbtree_node_t name_sentinel;
ngx_rbtree_t srv_rbtree;
ngx_rbtree_node_t srv_sentinel;
ngx_rbtree_t addr_rbtree;
ngx_rbtree_node_t addr_sentinel;
ngx_queue_t name_resend_queue;
ngx_queue_t srv_resend_queue;
ngx_queue_t addr_resend_queue;
ngx_queue_t name_expire_queue;
ngx_queue_t srv_expire_queue;
ngx_queue_t addr_expire_queue;
#if (NGX_HAVE_INET6)
ngx_uint_t ipv6; /* unsigned ipv6:1; */
ngx_rbtree_t addr6_rbtree;
ngx_rbtree_node_t addr6_sentinel;
ngx_queue_t addr6_resend_queue;
ngx_queue_t addr6_expire_queue;
#endif
time_t resend_timeout;
time_t tcp_timeout; // tcp 连接超时时间
time_t expire;
time_t valid;
ngx_uint_t log_level;
};
struct ngx_resolver_ctx_s {
ngx_resolver_ctx_t *next;
ngx_resolver_t *resolver;
ngx_resolver_node_t *node;
/* event ident must be after 3 pointers as in ngx_connection_t */
ngx_int_t ident;
ngx_int_t state;
ngx_str_t name; // 要解析的域名
ngx_str_t service;
time_t valid;
ngx_uint_t naddrs;
ngx_resolver_addr_t *addrs; // 解析的IP
// 如果域名本来就是ip，则把ip解析到该内存。不用向dns服务器发起请求
ngx_resolver_addr_t addr;
struct sockaddr_in sin;
ngx_uint_t count;
ngx_uint_t nsrvs;
ngx_resolver_srv_name_t *srvs;
ngx_resolver_handler_pt handler; // 解析万后的回调函数
void *data;
ngx_msec_t timeout; // 域名解析超时
unsigned quick:1; // 不用向dns服务器发起查询，也可以说是快速的同步的。
unsigned async:1;
unsigned cancelable:1;
ngx_uint_t recursion;
ngx_event_t *event; // 只用做超时ngx_resolver_set_timeout函数初始化
};
typedef struct {
ngx_rbtree_node_t node;
ngx_queue_t queue;
/* PTR: resolved name, A: name to resolve */
u_char *name; // 要解析的域名
#if (NGX_HAVE_INET6)
/* PTR: IPv6 address to resolve (IPv4 address is in rbtree node key) */
struct in6_addr addr6;
#endif
u_short nlen; // 要解析的域名的长度
u_short qlen; // 发送dns解析命令的长度
u_char *query; // dns解析命令字符串
#if (NGX_HAVE_INET6)
u_char *query6;
#endif
union {
in_addr_t addr;
in_addr_t *addrs;
u_char *cname;
ngx_resolver_srv_t *srvs;
} u;
u_char code;
u_short naddrs;
u_short nsrvs;
u_short cnlen;
#if (NGX_HAVE_INET6)
union {
struct in6_addr addr6;
struct in6_addr *addrs6;
} u6;
u_short naddrs6;
#endif
time_t expire;
time_t valid;
uint32_t ttl;
unsigned tcp:1; // 是否通过tcp方式方法查询请求
#if (NGX_HAVE_INET6)
unsigned tcp6:1;
#endif
ngx_uint_t last_connection; // dns域名服务器地址下标
ngx_resolver_ctx_t *waiting;
} ngx_resolver_node_t;
主要函数：
ngx_resolver_create // 创建域名解析结构体，用于后续的域名解析
ngx_resolve_start // 初始化域名解析上下文ngx_resolver_ctx_t
ngx_resolve_name // 构建dns查询并发起查询请求
ngx_resolve_name_done // dns查询结束，清理资源
// 以下为实现的内部函数
ngx_resolver_create_name_query // 创建查询请求命令的字符串
ngx_resolver_send_query // 发送查询请求
ngx_resolver_send_udp_query // udp方式发送dns查询请求
ngx_resolver_send_tcp_query // tcp 方式发送，建立tcp连接会把连接可读可写添加到epoll
ngx_resolver_tcp_write // tcp 方式可写回调函数
ngx_resolver_tcp_read // tcp 方式可读回调函数
主要函数实现
ngx_resolver_ctx_t *
ngx_resolve_start(ngx_resolver_t *r, ngx_resolver_ctx_t *temp)
{
in_addr_t addr;
ngx_resolver_ctx_t *ctx;
// 一般使用会定义一个局部变量ngx_resolver_ctx_t tmp;
// 把tmp的指针传递进来，name赋值为要解析的域名
if (temp) {
// 校验name是否就是ip地址
addr = ngx_inet_addr(temp->name.data, temp->name.len);
if (addr != INADDR_NONE) {
// name就是ip地址
temp->resolver = r;
temp->state = NGX_OK;
temp->naddrs = 1;
temp->addrs = &temp->addr;
temp->addr.sockaddr = (struct sockaddr *) &temp->sin;
temp->addr.socklen = sizeof(struct sockaddr_in);
ngx_memzero(&temp->sin, sizeof(struct sockaddr_in));
temp->sin.sin_family = AF_INET;
temp->sin.sin_addr.s_addr = addr;
temp->quick = 1;
// 直接返回tmp指针。
return temp;
}
}
if (r->connections.nelts == 0) {
return NGX_NO_RESOLVER;
}
ctx = ngx_resolver_calloc(r, sizeof(ngx_resolver_ctx_t));
if (ctx) {
ctx->resolver = r;
}
return ctx;
}
ngx_int_t
ngx_resolve_name(ngx_resolver_ctx_t *ctx)
{
size_t slen;
ngx_int_t rc;
ngx_str_t name;
ngx_resolver_t *r;
r = ctx->resolver;
if (ctx->name.len > 0 && ctx->name.data[ctx->name.len - 1] == '.') {
ctx->name.len--;
}
ngx_log_debug1(NGX_LOG_DEBUG_CORE, r->log, 0,
"resolve: \"%V\"", &ctx->name);
if (ctx->quick) {
// 不用发起dns查询，则直接调用业务赋值的回调函数。
// 例如：upstream模块的ngx_http_upstream_resolve_handler
ctx->handler(ctx);
return NGX_OK;
}
if (ctx->service.len) {
// 目前开源的代码中没有用到
slen = ctx->service.len;
if (ngx_strlchr(ctx->service.data,
ctx->service.data + ctx->service.len, '.')
== NULL)
{
slen += sizeof("_._tcp") - 1;
}
name.len = slen + 1 + ctx->name.len;
name.data = ngx_resolver_alloc(r, name.len);
if (name.data == NULL) {
goto failed;
}
if (slen == ctx->service.len) {
ngx_sprintf(name.data, "%V.%V", &ctx->service, &ctx->name);
} else {
ngx_sprintf(name.data, "_%V._tcp.%V", &ctx->service, &ctx->name);
}
/* lock name mutex */
rc = ngx_resolve_name_locked(r, ctx, &name);
ngx_resolver_free(r, name.data);
} else {
/* lock name mutex */
// 发起dns查询
rc = ngx_resolve_name_locked(r, ctx, &ctx->name);
}
if (rc == NGX_OK) {
return NGX_OK;
}
/* unlock name mutex */
if (rc == NGX_AGAIN) {
return NGX_OK;
}
/* NGX_ERROR */
if (ctx->event) {
ngx_resolver_free(r, ctx->event);
}
failed:
ngx_resolver_free(r, ctx);
return NGX_ERROR;
}
// 发起dns查询
// name 是域名
static ngx_int_t
ngx_resolve_name_locked(ngx_resolver_t *r, ngx_resolver_ctx_t *ctx,
ngx_str_t *name)
{
uint32_t hash;
ngx_int_t rc;
ngx_str_t cname;
ngx_uint_t i, naddrs;
ngx_queue_t *resend_queue, *expire_queue;
ngx_rbtree_t *tree;
ngx_resolver_ctx_t *next, *last;
ngx_resolver_addr_t *addrs;
ngx_resolver_node_t *rn;
ngx_strlow(name->data, name->data, name->len);
hash = ngx_crc32_short(name->data, name->len);
if (ctx->service.len) {
rn = ngx_resolver_lookup_srv(r, name, hash);
tree = &r->srv_rbtree;
resend_queue = &r->srv_resend_queue;
expire_queue = &r->srv_expire_queue;
} else {
// 先从缓存中查询，缓存没有命中则返回NULL
rn = ngx_resolver_lookup_name(r, name, hash);
tree = &r->name_rbtree;
resend_queue = &r->name_resend_queue;
expire_queue = &r->name_expire_queue;
}
if (rn) {
/* ctx can be a list after NGX_RESOLVE_CNAME */
for (last = ctx; last->next; last = last->next);
if (rn->valid >= ngx_time()) {
ngx_log_debug0(NGX_LOG_DEBUG_CORE, r->log, 0, "resolve cached");
ngx_queue_remove(&rn->queue);
rn->expire = ngx_time() + r->expire;
ngx_queue_insert_head(expire_queue, &rn->queue);
naddrs = (rn->naddrs == (u_short) -1) ? 0 : rn->naddrs;
#if (NGX_HAVE_INET6)
naddrs += (rn->naddrs6 == (u_short) -1) ? 0 : rn->naddrs6;
#endif
if (naddrs) {
if (naddrs == 1 && rn->naddrs == 1) {
addrs = NULL;
} else {
addrs = ngx_resolver_export(r, rn, 1);
if (addrs == NULL) {
return NGX_ERROR;
}
}
last->next = rn->waiting;
rn->waiting = NULL;
/* unlock name mutex */
do {
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);
ctx = next;
} while (ctx);
if (addrs != NULL) {
ngx_resolver_free(r, addrs->sockaddr);
ngx_resolver_free(r, addrs);
}
return NGX_OK;
}
if (rn->nsrvs) {
last->next = rn->waiting;
rn->waiting = NULL;
/* unlock name mutex */
do {
next = ctx->next;
ngx_resolver_resolve_srv_names(ctx, rn);
ctx = next;
} while (ctx);
return NGX_OK;
}
/* NGX_RESOLVE_CNAME */
if (ctx->recursion++ < NGX_RESOLVER_MAX_RECURSION) {
cname.len = rn->cnlen;
cname.data = rn->u.cname;
return ngx_resolve_name_locked(r, ctx, &cname);
}
last->next = rn->waiting;
rn->waiting = NULL;
/* unlock name mutex */
do {
ctx->state = NGX_RESOLVE_NXDOMAIN;
ctx->valid = ngx_time() + (r->valid ? r->valid : 10);
next = ctx->next;
ctx->handler(ctx);
ctx = next;
} while (ctx);
return NGX_OK;
}
if (rn->waiting) {
if (ngx_resolver_set_timeout(r, ctx) != NGX_OK) {
return NGX_ERROR;
}
last->next = rn->waiting;
rn->waiting = ctx;
ctx->state = NGX_AGAIN;
ctx->async = 1;
do {
ctx->node = rn;
ctx = ctx->next;
} while (ctx);
return NGX_AGAIN;
}
ngx_queue_remove(&rn->queue);
/* lock alloc mutex */
if (rn->query) {
ngx_resolver_free_locked(r, rn->query);
rn->query = NULL;
#if (NGX_HAVE_INET6)
rn->query6 = NULL;
#endif
}
if (rn->cnlen) {
ngx_resolver_free_locked(r, rn->u.cname);
}
if (rn->naddrs > 1 && rn->naddrs != (u_short) -1) {
ngx_resolver_free_locked(r, rn->u.addrs);
}
#if (NGX_HAVE_INET6)
if (rn->naddrs6 > 1 && rn->naddrs6 != (u_short) -1) {
ngx_resolver_free_locked(r, rn->u6.addrs6);
}
#endif
if (rn->nsrvs) {
for (i = 0; i < (ngx_uint_t) rn->nsrvs; i++) {
if (rn->u.srvs[i].name.data) {
ngx_resolver_free_locked(r, rn->u.srvs[i].name.data);
}
}
ngx_resolver_free_locked(r, rn->u.srvs);
}
/* unlock alloc mutex */
} else {
rn = ngx_resolver_alloc(r, sizeof(ngx_resolver_node_t));
if (rn == NULL) {
return NGX_ERROR;
}
rn->name = ngx_resolver_dup(r, name->data, name->len);
if (rn->name == NULL) {
ngx_resolver_free(r, rn);
return NGX_ERROR;
}
rn->node.key = hash;
rn->nlen = (u_short) name->len;
rn->query = NULL;
#if (NGX_HAVE_INET6)
rn->query6 = NULL;
#endif
ngx_rbtree_insert(tree, &rn->node);
}
if (ctx->service.len) {
rc = ngx_resolver_create_srv_query(r, rn, name);
} else {
rc = ngx_resolver_create_name_query(r, rn, name);
}
if (rc == NGX_ERROR) {
goto failed;
}
if (rc == NGX_DECLINED) {
ngx_rbtree_delete(tree, &rn->node);
ngx_resolver_free(r, rn->query);
ngx_resolver_free(r, rn->name);
ngx_resolver_free(r, rn);
do {
ctx->state = NGX_RESOLVE_NXDOMAIN;
next = ctx->next;
ctx->handler(ctx);
ctx = next;
} while (ctx);
return NGX_OK;
}
rn->last_connection = r->last_connection++;
if (r->last_connection == r->connections.nelts) {
r->last_connection = 0;
}
rn->naddrs = (u_short) -1;
rn->tcp = 0;
#if (NGX_HAVE_INET6)
rn->naddrs6 = r->ipv6 ? (u_short) -1 : 0;
rn->tcp6 = 0;
#endif
rn->nsrvs = 0;
if (ngx_resolver_send_query(r, rn) != NGX_OK) {
goto failed;
}
// 设置超时事件
if (ngx_resolver_set_timeout(r, ctx) != NGX_OK) {
goto failed;
}
if (ngx_resolver_resend_empty(r)) {
ngx_add_timer(r->event, (ngx_msec_t) (r->resend_timeout * 1000));
}
rn->expire = ngx_time() + r->resend_timeout;
ngx_queue_insert_head(resend_queue, &rn->queue);
rn->code = 0;
rn->cnlen = 0;
rn->valid = 0;
rn->ttl = NGX_MAX_UINT32_VALUE;
rn->waiting = ctx;
ctx->state = NGX_AGAIN;
ctx->async = 1;
do {
ctx->node = rn;
ctx = ctx->next;
} while (ctx);
return NGX_AGAIN;
failed:
ngx_rbtree_delete(tree, &rn->node);
if (rn->query) {
ngx_resolver_free(r, rn->query);
}
ngx_resolver_free(r, rn->name);
ngx_resolver_free(r, rn);
return NGX_ERROR;
}
// 封装dns查询数据包
static ngx_int_t
ngx_resolver_create_name_query(ngx_resolver_t *r, ngx_resolver_node_t *rn,
ngx_str_t *name)
{
u_char *p, *s;
size_t len, nlen;
ngx_uint_t ident;
ngx_resolver_qs_t *qs;
ngx_resolver_hdr_t *query;
nlen = name->len ? (1 + name->len + 1) : 1;
len = sizeof(ngx_resolver_hdr_t) + nlen + sizeof(ngx_resolver_qs_t);
#if (NGX_HAVE_INET6)
p = ngx_resolver_alloc(r, r->ipv6 ? len * 2 : len);
#else
p = ngx_resolver_alloc(r, len);
#endif
if (p == NULL) {
return NGX_ERROR;
}
rn->qlen = (u_short) len;
rn->query = p;
#if (NGX_HAVE_INET6)
if (r->ipv6) {
rn->query6 = p + len;
}
#endif
query = (ngx_resolver_hdr_t *) p;
ident = ngx_random();
ngx_log_debug2(NGX_LOG_DEBUG_CORE, r->log, 0,
"resolve: \"%V\" A %i", name, ident & 0xffff);
query->ident_hi = (u_char) ((ident >> 8) & 0xff);
query->ident_lo = (u_char) (ident & 0xff);
/* recursion query */
query->flags_hi = 1; query->flags_lo = 0;
/* one question */
query->nqs_hi = 0; query->nqs_lo = 1;
query->nan_hi = 0; query->nan_lo = 0;
query->nns_hi = 0; query->nns_lo = 0;
query->nar_hi = 0; query->nar_lo = 0;
p += sizeof(ngx_resolver_hdr_t) + nlen;
qs = (ngx_resolver_qs_t *) p;
/* query type */
qs->type_hi = 0; qs->type_lo = NGX_RESOLVE_A;
/* IN query class */
qs->class_hi = 0; qs->class_lo = 1;
/* convert "www.example.com" to "\3www\7example\3com\0" */
len = 0;
p--;
*p-- = '\0';
if (name->len == 0) {
return NGX_DECLINED;
}
for (s = name->data + name->len - 1; s >= name->data; s--) {
if (*s != '.') {
*p = *s;
len++;
} else {
if (len == 0 || len > 255) {
return NGX_DECLINED;
}
*p = (u_char) len;
len = 0;
}
p--;
}
if (len == 0 || len > 255) {
return NGX_DECLINED;
}
*p = (u_char) len;
#if (NGX_HAVE_INET6)
if (!r->ipv6) {
return NGX_OK;
}
p = rn->query6;
ngx_memcpy(p, rn->query, rn->qlen);
query = (ngx_resolver_hdr_t *) p;
ident = ngx_random();
ngx_log_debug2(NGX_LOG_DEBUG_CORE, r->log, 0,
"resolve: \"%V\" AAAA %i", name, ident & 0xffff);
query->ident_hi = (u_char) ((ident >> 8) & 0xff);
query->ident_lo = (u_char) (ident & 0xff);
p += sizeof(ngx_resolver_hdr_t) + nlen;
qs = (ngx_resolver_qs_t *) p;
qs->type_lo = NGX_RESOLVE_AAAA;
#endif
return NGX_OK;
}
// 发送dns查询
static ngx_int_t
ngx_resolver_send_udp_query(ngx_resolver_t *r, ngx_resolver_connection_t *rec,
u_char *query, u_short qlen)
{
ssize_t n;
if (rec->udp == NULL) {
// 建立连接并把可读事件添加到epoll
if (ngx_udp_connect(rec) != NGX_OK) {
return NGX_ERROR;
}
rec->udp->data = rec;
// 可读回调
rec->udp->read->handler = ngx_resolver_udp_read;
rec->udp->read->resolver = 1;
}
// 发送dns查询数据报
n = ngx_send(rec->udp, query, qlen);
if (n == -1) {
return NGX_ERROR;
}
if ((size_t) n != (size_t) qlen) {
ngx_log_error(NGX_LOG_CRIT, &rec->log, 0, "send() incomplete");
return NGX_ERROR;
}
return NGX_OK;
}
// 设置超时事件
static ngx_int_t
ngx_resolver_set_timeout(ngx_resolver_t *r, ngx_resolver_ctx_t *ctx)
{
if (ctx->event || ctx->timeout == 0) {
return NGX_OK;
}
ctx->event = ngx_resolver_calloc(r, sizeof(ngx_event_t));
if (ctx->event == NULL) {
return NGX_ERROR;
}
ctx->event->handler = ngx_resolver_timeout_handler;
ctx->event->data = ctx;
ctx->event->log = r->log;
ctx->event->cancelable = ctx->cancelable;
ctx->ident = -1;
ngx_add_timer(ctx->event, ctx->timeout);
return NGX_OK;
}
// 超时回调
static void
ngx_resolver_timeout_handler(ngx_event_t *ev)
{
ngx_resolver_ctx_t *ctx;
ctx = ev->data;
ctx->state = NGX_RESOLVE_TIMEDOUT;
ctx->handler(ctx);
}
// 可读事件回调函数
// 解析DNS查询结果
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);
}
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;
// n为接收数据的长度，是否小于dns报头大小
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; // 应答记录数
trunc = flags & 0x0200; // QR:0 opcode:0000 AA:0 TC:1 RD:0 RA:0 Z:000 RDCODE:0000
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 */
0xf870 : 1 1111 0 0 0 0 111 0000
0x8000 : 1 0000 0 0 0 0 000 0000 QR == 1 表示相应报文
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;
}
// Response code
code = flags & 0xf;
if (code == NGX_RESOLVE_FORMERR) {
// 报文格式错误
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;
}
// 查询记录数
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
// 解析A记录，IP地址
// buf：DNS应答内容 n：内容长度
// ident：ID标识 code：应答码 qtype：协议类型 nan：应答记录数 trunc 是否截断
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;
}
// 解析A记录
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;
// 解析请求的域名
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;
}
// 请求ID标识
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;
}
