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
协议rfc : https://datatracker.ietf.org/doc/html/rfc1035
我们使用getaddrinfo函数时，可以使用域名，内部自动处理了域名的请求，这个函数虽然方便，但它是阻塞的，不大适用自己写的高并发服务器。
我们可以先看create_dns_task
perl calltree.pl "create_dns_task" "" 1 1 3
create_dns_task
├── WFResolverTask::dispatch [vim src/nameservice/WFDnsResolver.cc +271]
│ ├── start [vim _include/workflow/Workflow.h +68]
│ ├── Workflow::start_series_work [vim _include/workflow/Workflow.h +169]
│ ├── Workflow::start_series_work [vim _include/workflow/Workflow.h +185]
│ ├── SubTask::subtask_done [vim src/kernel/SubTask.cc +21]
│ ├── ParallelTask::dispatch [vim src/kernel/SubTask.cc +54]
│ ├── __WFConditional::dispatch [vim src/factory/WFResourcePool.cc +44]
│ ├── start [vim src/factory/Workflow.h +68]
│ ├── Workflow::start_series_work [vim src/factory/Workflow.h +172]
│ └── Workflow::start_series_work [vim src/factory/Workflow.h +188]
├── WFDnsClient::create_dns_task [vim src/client/WFDnsClient.cc +238]
│ ├── WFResolverTask::dispatch [vim src/nameservice/WFDnsResolver.cc +271]
│ ├── WFDnsClient::create_dns_task [vim src/client/WFDnsClient.cc +238]
│ └── WFTaskFactory::create_dns_task [vim src/factory/DnsTaskImpl.cc +163]
└── WFTaskFactory::create_dns_task [vim src/factory/DnsTaskImpl.cc +163]
├── WFResolverTask::dispatch [vim src/nameservice/WFDnsResolver.cc +271]
├── WFDnsClient::create_dns_task [vim src/client/WFDnsClient.cc +238]
└── WFTaskFactory::create_dns_task [vim src/factory/DnsTaskImpl.cc +163]
大概可以看出，主要是两个来源，一个是WFDnsClient，一个是WFResolverTask
我们先看看WFDnsClient
// src/manager/WFGlobal.h
class WFGlobal
{
...
static class WFDnsClient *get_dns_client();
...
};
然后可以看到他有个dns manager单例
// src/manager/WFGlobal.cc
WFDnsClient *WFGlobal::get_dns_client()
{
return __DnsClientManager::get_instance()->get_dns_client();
}可以看出在这个地方构造的时候，生成了dnsClient
// src/manager/WFGlobal.cc
class __DnsClientManager
{
private:
__DnsClientManager()
{
const char *path = WFGlobal::get_global_settings()->resolv_conf_path;
client = NULL;
if (path && path[0])
{
int ndots = 1;
int attempts = 2;
bool rotate = false;
std::string url;
std::string search;
__parse_resolv_conf(path, url, search, &ndots, &attempts, &rotate);
if (url.size() == 0)
url = "8.8.8.8";
client = new WFDnsClient;
if (client->init(url, search, ndots, attempts, rotate) >= 0)
return;
delete client;
client = NULL;
}
}
WFDnsClient *client;
};__parse_resolv_conf 这里主要就是处理 /etc/resolv.conf 中的内容了
// src/manager/WFGlobal.cc
static int __parse_resolv_conf(const char *path,
std::string& url, std::string& search_list,
int *ndots, int *attempts, bool *rotate)
{
size_t bufsize = 0;
char *line = NULL;
FILE *fp;
int ret;
fp = fopen(path, "r");
if (!fp)
return -1;
while ((ret = getline(&line, &bufsize, fp)) > 0)
{
if (strncmp(line, "nameserver", 10) == 0)
__split_merge_str(line + 10, true, url);
else if (strncmp(line, "search", 6) == 0)
__split_merge_str(line + 6, false, search_list);
else if (strncmp(line, "options", 7) == 0)
__set_options(line + 7, ndots, attempts, rotate);
}
ret = ferror(fp) ? -1 : 0;
free(line);
fclose(fp);
return ret;
}然后 __split_merge_str 和 __set_options 细节可以看源码里面的注释，把传入的这几个参数都填上conf里读出的值
然后我们最终是把conf文件的这些参数读出来初始化WFDnsClient
那么我们再回过头看一下WFDnsClient
/src/client/WFDnsClient.h
class WFDnsClient
{
public:
WFDnsClient() : params(NULL) { }
virtual ~WFDnsClient() { }
int init(const std::string& url);
int init(const std::string& url, const std::string& search_list,
int ndots, int attempts, bool rotate);
void deinit();
WFDnsTask *create_dns_task(const std::string& name,
dns_callback_t callback);
private:
void *params;
std::atomic<size_t> id;
};
其中最主要的就是init和create_dns_task
/src/client/WFDnsClient.cc
int WFDnsClient::init(const std::string& url, const std::string& search_list,
int ndots, int attempts, bool rotate)
{
...
hosts = StringUtil::split_filter_empty(url, ',');
for (size_t i = 0; i < hosts.size(); i++)
{
host = hosts[i];
if (strncasecmp(host.c_str(), "dns://", 6) != 0 &&
strncasecmp(host.c_str(), "dnss://", 7) != 0)
{
host = "dns://" + host;
}
if (URIParser::parse(host, uri) != 0)
return -1;
uris.emplace_back(std::move(uri));
}
if (uris.empty() || ndots < 0 || attempts < 1)
{
errno = EINVAL;
return -1;
}
this->params = new DnsParams;
DnsParams::dns_params *q = ((DnsParams *)(this->params))->get_params();
q->uris = std::move(uris);
q->search_list = StringUtil::split_filter_empty(search_list, ',');
q->ndots = ndots > 15 ? 15 : ndots;
q->attempts = attempts > 5 ? 5 : attempts;
q->rotate = rotate;
return 0;
}这一步主要是做了两件事，解析我们的host，设置dns的 params
/src/client/WFDnsClient.cc
struct dns_params
{
std::vector<ParsedURI> uris;
std::vector<std::string> search_list;
int ndots;
int attempts;
bool rotate;
};第二个重要的是
/src/client/WFDnsClient.cc
WFDnsTask *WFDnsClient::create_dns_task(const std::string& name,
dns_callback_t callback)
{
DnsParams::dns_params *p = ((DnsParams *)(this->params))->get_params();
struct DnsStatus status;
size_t next_server;
WFDnsTask *task;
DnsRequest *req;
next_server = p->rotate ? this->id++ % p->uris.size() : 0;
status.origin_name = name;
status.next_domain = 0;
status.attempts_left = p->attempts;
status.try_origin_state = DNS_STATUS_TRY_ORIGIN_FIRST;
if (!name.empty() && name.back() == '.')
status.next_domain = p->uris.size();
else if (__get_ndots(name) < p->ndots)
status.try_origin_state = DNS_STATUS_TRY_ORIGIN_LAST;
__has_next_name(p, &status);
task = WFTaskFactory::create_dns_task(p->uris[next_server],
0, std::move(callback));
status.next_server = next_server;
status.last_server = (next_server + p->uris.size() - 1) % p->uris.size();
req = task->get_req();
req->set_question(status.current_name.c_str(), DNS_TYPE_A, DNS_CLASS_IN);
req->set_rd(1);
ComplexTask *ctask = static_cast<ComplexTask *>(task);
*ctask->get_mutable_ctx() = std::bind(__callback_internal,
std::placeholders::_1,
*(DnsParams *)params, status);
return task;
}
可以看到其中还有个DnsStatus, 我们看看他的内部结构
/src/client/WFDnsClient.cc
struct DnsStatus
{
std::string origin_name;
std::string current_name;
size_t next_server; // next server to try
size_t last_server; // last server to try
size_t next_domain; // next search domain to try
int attempts_left;
int try_origin_state;
};在它内部还是用的工厂创建的task
/src/factory/DnsTaskImpl.cc
WFDnsTask *WFTaskFactory::create_dns_task(const ParsedURI& uri,
int retry_max,
dns_callback_t callback)
{
ComplexDnsTask *task = new ComplexDnsTask(retry_max, std::move(callback));
const char *name;
if (uri.path && uri.path[0] && uri.path[1])
name = uri.path + 1;
else
name = ".";
DnsRequest *req = task->get_req();
req->set_question(name, DNS_TYPE_A, DNS_CLASS_IN);
task->init(uri);
task->set_keep_alive(DNS_KEEPALIVE_DEFAULT);
return task;
}我们可以看到create_dns_task实际上是new了一个ComplexDnsTask
class ComplexDnsTask : public WFComplexClientTask<DnsRequest, DnsResponse,
std::function<void (WFDnsTask *)>>
{
static struct addrinfo hints;
public:
ComplexDnsTask(int retry_max, dns_callback_t&& cb):
WFComplexClientTask(retry_max, std::move(cb))
{
// dns 是建立在 UDP 之上的应用层协议
// WFComplexClientTask中默认TT_TCP
this->set_transport_type(TT_UDP);
}
protected:
virtual CommMessageOut *message_out();
virtual CommMessageIn *message_in();
virtual bool init_success();
virtual bool finish_once();
private:
bool need_redirect();
};继承自WFComplexClientTask，构造的时候就是设置TT_UDP