源码 502 回溯

https://github.com/nginx/nginx/blob/cb4dd56771c1af082bf3e810436712b4f48f2cf2/src/http/ngx_http_upstream.c

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;
	}

https://github.com/nginx/nginx/blob/4bf4650f2f10f7bbacfe7a33da744f18951d416d/src/core/ngx_resolver.h

#define NGX_NO_RESOLVER (void *) -1

 

if (r->connections.nelts == 0) {
	return NGX_NO_RESOLVER;
	}

https://github.com/nginx/nginx/blob/8e2949e56a13405a157e05b21aa4c4a5fa468335/src/core/ngx_resolver.c

https://github.com/nginx/nginx/blob/4bf4650f2f10f7bbacfe7a33da744f18951d416d/src/core/ngx_resolver.h

typedef struct ngx_resolver_ctx_s ngx_resolver_ctx_t;

https://github.com/nginx/nginx/blob/8e2949e56a13405a157e05b21aa4c4a5fa468335/src/core/ngx_resolver.c

ngx_resolve_start(ngx_resolver_t *r, ngx_resolver_ctx_t *temp)
{
in_addr_t addr;
ngx_resolver_ctx_t *ctx;
if (temp) {
addr = ngx_inet_addr(temp->name.data, temp->name.len);
if (addr != INADDR_NONE) {
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;
return temp;
}
}
if (r->connections.nelts == 0) {
return NGX_NO_RESOLVER;
}

https://github.com/nginx/nginx/blob/4bf4650f2f10f7bbacfe7a33da744f18951d416d/src/core/ngx_resolver.h

typedef struct ngx_resolver_ctx_s ngx_resolver_ctx_t;

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;
ngx_str_t service;

time_t valid;
ngx_uint_t naddrs;
ngx_resolver_addr_t *addrs;
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;
void *data;
ngx_msec_t timeout;

unsigned quick:1;
unsigned async:1;
unsigned cancelable:1;
ngx_uint_t recursion;
ngx_event_t *event;
};

https://github.com/nginx/nginx/blob/4bf4650f2f10f7bbacfe7a33da744f18951d416d/src/core/ngx_resolver.h

typedef struct ngx_resolver_s ngx_resolver_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_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;
time_t expire;
time_t valid;

ngx_uint_t log_level;
};

https://github.com/nginx/nginx/blob/4bf4650f2f10f7bbacfe7a33da744f18951d416d/src/core/ngx_array.h

typedef struct {
void *elts;
ngx_uint_t nelts;
size_t size;
ngx_uint_t nalloc;
ngx_pool_t *pool;
} ngx_array_t;