c - 使用 getaddrinfo 连接套接字超时
问题描述
我花了几个小时试图找出我的问题,只是在我写我的问题时找到了解决方案(当你需要正式化你的问题并解释它时,它总是有帮助的)。我发布它,希望它可以帮助某人。
使用 getaddrinfo,如果我尝试将套接字连接到我的服务器,执行(我认为是)正是在大量网站以及 getaddrinfo 的手册页示例代码中解释的内容,它会因“连接超时”而失败错误信息:(简化代码更简洁)
void connect_UsingGetAddrInfo_Wrong (std::string host, unsigned short int port, int& socketfd)
{
//simplified loops & error handling for concision
int x;
int domain = AF_INET; // IP_v4
int socketType = SOCK_STREAM; // Sequenced, reliable, connection-based byte streams.
addrinfo hints, *addr;
//fine-tune hints according to which socket you want to open
hints.ai_family = domain;
hints.ai_socktype = socketType;
hints.ai_protocol = 0; // no enum : possible value can be read in /etc/protocols
hints.ai_flags = AI_CANONNAME | AI_ALL | AI_ADDRCONFIG;
x = getaddrinfo(hostname, NULL, &hints, &addr);
//shall rather loop on addr linked list, but this is not the topic here.
socketfd = socket(addr->ai_family, addr->ai_socktype, addr->ai_protocol);
x = connect(socketfd, addr->ai_addr, addr->ai_addrlen);
}
但是,我能够使用 gethostbyname 方法将套接字连接到同一台服务器。
void connect_UsingGetHostByName_Deprecated (std::string host, unsigned short int port, int& socketfd)
{
//simplified loops & error handling for concision
int x;
int domain = AF_INET; // IP_v4
int socketType = SOCK_STREAM; // Sequenced, reliable, connection-based byte streams.
struct hostent DNS, *r;
char buf[1024];
x = gethostbyname_r(hostname.c_str(), & DNS, buf, sizeof(buf), & r, & err));
socketfd = socket(domain, socketType, 0);
//server.
sockaddr_in server;
memset(&server, 0x00, sizeof(server));
server.sin_family=domain;
server.sin_port=htons(port);
memcpy(& server.sin_addr.s_addr, DNS.h_addr, (size_t) DNS.h_length);
x = connect(socketfd, (struct sockaddr *) & server, sizeof(server));
}
运行代码显示两个版本都正确检索了服务器的有效 IP 地址。第一个仍然无法连接并且会超时。为什么 ?
解决方案
它一直失败的原因是:为了检索 addrinfo,我将字段“服务”设置为 NULL。它仍然会返回成功并为您提供一个地址(您可以使用 getnameinfo 将其映射到正确的 IP 地址)。该地址仍然无法用于连接您的套接字!
我在这里找到了这两种方法的混合版本: https ://codereview.stackexchange.com/questions/17863/socket-connect-realization-gethostbyname-or-getnameinfo 这个是功能性的,但我不买铸件
void connect_UsingGetAddrInfo_HYBRID (std::string host, unsigned short int port, int& socketfd)
{
//simplified loops & error handling for concision
int x;
int domain = AF_INET; // IP_v4
int socketType = SOCK_STREAM; // Sequenced, reliable, connection-based byte streams.
addrinfo hints, *addr;
//fine-tune hints according to which socket you want to open
hints.ai_family = domain;
hints.ai_socktype = socketType;
hints.ai_protocol = 0; // no enum : possible value can be read in /etc/protocols
hints.ai_flags = AI_CANONNAME | AI_ALL | AI_ADDRCONFIG;
x = getaddrinfo(host, NULL, &hints, &addr);
socketfd = socket(addr->ai_family, addr->ai_socktype, addr->ai_protocol);
//here is the hybrid part
sockaddr_in servAddr;
memset(&servAddr, 0, sizeof(servAddr));
servAddr.sin_family = addr->ai_family;
servAddr.sin_addr.s_addr = *((uint32_t*) & (((sockaddr_in*)addr->ai_addr)->sin_addr));
servAddr.sin_port = htons(port);
x=connect(socketfd, (struct sockaddr*) &servAddr, sizeof(servAddr));
}
最后,它帮助我找到了根本原因:
void connect_UsingGetAddrInfo_FIXED (std::string host, unsigned short int port, int& socketfd)
{
//simplified loops & error handling for concision
int x;
int domain = AF_INET; // IP_v4
int socketType = SOCK_STREAM; // Sequenced, reliable, connection-based byte streams.
addrinfo hints, *addr;
//fine-tune hints according to which socket you want to open
hints.ai_family = domain;
hints.ai_socktype = socketType;
hints.ai_protocol = 0; // no enum : possible value can be read in /etc/protocols
hints.ai_flags = AI_CANONNAME | AI_ALL | AI_ADDRCONFIG;
//Precise here the port !
const char* service = std::to_string(port).c_str();
x = getaddrinfo(host, service, &hints, &addr);
socketfd = socket(addr->ai_family, addr->ai_socktype, addr->ai_protocol);
x = connect(socketfd, addr->ai_addr, addr->ai_addrlen);
}
希望有一天这会对某人有所帮助!
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