#! https://zhuanlan.zhihu.com/p/448013325
分析代码改动地址 : https://github.com/sogou/workflow/commit/0eed99b538d824579c3e339625a6727646dca343
项目源码 : https://github.com/sogou/workflow
更加详细的源码注释可看 : https://github.com/chanchann/workflow_annotation
关于dns cache
https://github.com/chanchann/workflow_annotation/blob/main/src_analysis/other_01_cache_lock.md
已经浅谈过，就只有两个地方出现
一个是在WFResolverTask::dispatch中取，一个是在WFResolverTask::dns_callback_internal中放
DNS_CACHE_LEVEL_0 -> NO cache
DNS_CACHE_LEVEL_1 -> TTL MIN
DNS_CACHE_LEVEL_2 -> TTL [DEFAULT]
DNS_CACHE_LEVEL_3 -> Forever其中比较常用的是LEVEL_1 和 LEVEL_2
WFDnsResolver::create_router_task
int dns_cache_level = params->retry_times == 0 ? DNS_CACHE_LEVEL_2 :
DNS_CACHE_LEVEL_1;void WFResolverTask::dispatch()
{
// part 1
// 有dns cache
if (dns_cache_level_ != DNS_CACHE_LEVEL_0)
{
DnsCache *dns_cache = WFGlobal::get_dns_cache();
// using DnsHandle = LRUHandle<HostPort, DnsCacheValue>;
const DnsCache::DnsHandle *addr_handle;
switch (dns_cache_level_)
{
case DNS_CACHE_LEVEL_1: // TTL MIN
addr_handle = dns_cache->get_confident(host_, port_);
break;
case DNS_CACHE_LEVEL_2: // TTL [DEFAULT]
addr_handle = dns_cache->get_ttl(host_, port_);
break;
case DNS_CACHE_LEVEL_3: // Forever
addr_handle = dns_cache->get(host_, port_);
break;
default:
addr_handle = NULL;
break;
}
// 如果get到了cache而且没过期
if (addr_handle)
{
// 单例
// 用来解析dns的
auto *route_manager = WFGlobal::get_route_manager();
// 拿出cache中的 addrinfo
struct addrinfo *addrinfo = addr_handle->value.addrinfo;
struct addrinfo first;
// (bool)first_addr_only_ = params->fixed_addr;
// 如果我们只需要第一个，而且addrinfo后面还有，我们还要把后面砍断
if (first_addr_only_ && addrinfo->ai_next)
{
first = *addrinfo; // 这里拷贝了一次
first.ai_next = NULL;
addrinfo = &first;
}
// 这里是核心解析了，主要就是把route_result_.request_object get到
if (route_manager->get(type_, addrinfo, info_, &endpoint_params_,
host_, this->result) < 0)
{
this->state = WFT_STATE_SYS_ERROR;
this->error = errno;
}
else
this->state = WFT_STATE_SUCCESS;
// 然后就可以release了
dns_cache->release(addr_handle);
query_dns_ = false; // 就直接不去查dns了
this->subtask_done();
return;
}
}
// part2
// 如果没有cache
// 又还有host_
// 比如www.baidu.com
if (!host_.empty())
{
char front = host_.front();
char back = host_.back();
struct in6_addr addr;
int ret;
// 假如是ip
// ipv6 : 2001:0db8:02de:0000:0000:0000:0000:0e13
if (host_.find(':') != std::string::npos)
ret = inet_pton(AF_INET6, host_.c_str(), &addr);
// ipv4 : 192.11.11.11
// 其中没有 ':' , 而且首位都是数字
else if (isdigit(back) && isdigit(front))
ret = inet_pton(AF_INET, host_.c_str(), &addr);
else if (front == '/') // 这个是local path的时候 // todo
ret = 1;
else
ret = 0;
if (ret == 1)
{
DnsInput dns_in;
DnsOutput dns_out;
dns_in.reset(host_, port_);
DnsRoutine::run(&dns_in, &dns_out); // 这里通过getaddrino 得到了addrinfo(在dns_out中)
// 获得了才加上AI_PASSIVE
// 为什么在之后再add_passive？
__add_passive_flags((struct addrinfo *)dns_out.get_addrinfo());
dns_callback_internal(&dns_out, (unsigned int)-1, (unsigned int)-1);
query_dns_ = false;
this->subtask_done();
return;
}
}
// part3
// 如果没有cache
// 还没有host_
// for server?
// "/etc/hosts"
// 操作和上面基本相同
const char *hosts = WFGlobal::get_global_settings()->hosts_path;
if (hosts)
{
struct addrinfo *ai;
int ret = __readaddrinfo(hosts, host_.c_str(), port_, &__ai_hints, &ai);
if (ret == 0)
{
DnsOutput out;
// 注意这里是create
DnsRoutine::create(&out, ret, ai);
__add_passive_flags((struct addrinfo *)out.get_addrinfo());
dns_callback_internal(&out, dns_ttl_default_, dns_ttl_min_);
query_dns_ = false;
this->subtask_done();
return;
}
}
// 如果都没有"/etc/hosts"，那么我们就得
WFDnsClient *client = WFGlobal::get_dns_client();
if (client)
{
static int family = __default_family();
WFDnsResolver *resolver = WFGlobal::get_dns_resolver();
if (family == AF_INET || family == AF_INET6)
{
auto&& cb = std::bind(&WFResolverTask::dns_single_callback,
this,
std::placeholders::_1);
WFDnsTask *dns_task = client->create_dns_task(host_, std::move(cb));
if (family == AF_INET6)
dns_task->get_req()->set_question_type(DNS_TYPE_AAAA);
WFConditional *cond = resolver->respool.get(dns_task);
series_of(this)->push_front(cond);
}
else
{
/*
struct DnsContext
{
int state;
int error;
int eai_error;
unsigned short port;
struct addrinfo *ai;
};
*/
struct DnsContext *dctx = new struct DnsContext[2];
WFDnsTask *task_v4;
WFDnsTask *task_v6;
ParallelWork *pwork;
dctx[0].ai = NULL;
dctx[1].ai = NULL;
dctx[0].port = port_;
dctx[1].port = port_;
task_v4 = client->create_dns_task(host_, dns_partial_callback);
task_v4->user_data = dctx;
task_v6 = client->create_dns_task(host_, dns_partial_callback);
task_v6->get_req()->set_question_type(DNS_TYPE_AAAA);
task_v6->user_data = dctx + 1;
auto&& cb = std::bind(&WFResolverTask::dns_parallel_callback,
this,
std::placeholders::_1);
pwork = Workflow::create_parallel_work(std::move(cb));
pwork->set_context(dctx);
WFConditional *cond_v4 = resolver->respool.get(task_v4);
WFConditional *cond_v6 = resolver->respool.get(task_v6);
pwork->add_series(Workflow::create_series_work(cond_v4, nullptr));
pwork->add_series(Workflow::create_series_work(cond_v6, nullptr));
series_of(this)->push_front(pwork);
}
}
else
{
auto&& cb = std::bind(&WFResolverTask::thread_dns_callback,
this,
std::placeholders::_1);
ThreadDnsTask *dns_task = __create_thread_dns_task(host_, port_,
std::move(cb));
series_of(this)->push_front(dns_task);
}
query_dns_ = true;
this->subtask_done();
}const DnsHandle *get_confident(const HostPort& host_port)
{
return get_inner(host_port, GET_TYPE_CONFIDENT);
}const DnsHandle *get_ttl(const HostPort& host_port)
{
return get_inner(host_port, GET_TYPE_TTL);
}其实这两个接口都是调用get_inner
不过传的type不一样罢了
这里在DnsCache解析时，详细探究，这里我们只用知道他得到了DnsHandle(using DnsHandle = LRUHandle<HostPort, DnsCacheValue>;) 即可
这里我们看RouteManager解析部分
https://github.com/chanchann/workflow_annotation/blob/main/src_analysis/20_RouteManager.md
其中一个重要的点是DnsRoutine，详细见DnsRoutine的文章
static void __add_passive_flags(struct addrinfo *ai)
{
while (ai)
{
ai->ai_flags |= AI_PASSIVE;
ai = ai->ai_next;
}
}通常服务器端在调用getaddrinfo之前，ai_flags设置AI_PASSIVE，用于bind；主机名nodename通常会设置为NULL，返回通配地址[::]。
就是把获取到的addrinfo 放到dns_cache 中，然后利用我们得到的addrinfo, 把WFResolverTask的父类的result获取到
class WFRouterTask : public WFGenericTask
{
...
RouteManager::RouteResult result;
};void WFResolverTwask::dns_callback_internal(DnsOutput *dns_out,
unsigned int ttl_default,
unsigned int ttl_min)
{
...
struct addrinfo *addrinfo = dns_out->move_addrinfo();
...
addr_handle = dns_cache->put(host_, port_, addrinfo,
(unsigned int)ttl_default,
(unsigned int)ttl_min);
route_manager->get(type_, addrinfo, info_, &endpoint_params_,
host_, this->result);
dns_cache->release(addr_handle);
}这里基本和part2操作相同，有个最大的区别就在于__readaddrinfo
static int __readaddrinfo(const char *path,
const char *name, unsigned short port,
const struct addrinfo *hints,
struct addrinfo **res)
{
char port_str[PORT_STR_MAX + 1];
size_t bufsize = 0;
char *line = NULL;
int count = 0;
struct addrinfo h;
int errno_bak;
FILE *fp;
int ret;
fp = fopen(path, "r");
if (!fp)
return EAI_SYSTEM;
h = *hints;
h.ai_flags |= AI_NUMERICSERV | AI_NUMERICHOST,
snprintf(port_str, PORT_STR_MAX + 1, "%u", port);
errno_bak = errno;
while ((ret = getline(&line, &bufsize, fp)) > 0)
{
if (__readaddrinfo_line(line, name, port_str, &h, res) == 0)
{
count++;
res = &(*res)->ai_next;
}
}
ret = ferror(fp) ? EAI_SYSTEM : EAI_NONAME;
free(line);
fclose(fp);
if (count != 0)
{
errno = errno_bak;
return 0;
}
return ret;
}// hosts line format: IP canonical_name [aliases...] [# Comment]
static int __readaddrinfo_line(char *p, const char *name, const char *port,
const struct addrinfo *hints,
struct addrinfo **res)
{
const char *ip = NULL;
char *start;
start = p;
while (*start != '\0' && *start != '#')
start++;
*start = '\0';
while (1)
{
while (isspace(*p))
p++;
start = p;
while (*p != '\0' && !isspace(*p))
p++;
if (start == p)
break;
if (*p != '\0')
*p++ = '\0';
if (ip == NULL)
{
ip = start;
continue;
}
if (strcasecmp(name, start) == 0)
{
if (getaddrinfo(ip, port, hints, res) == 0)
return 0;
}
}
return 1;
}