关于getsockname函数的使用

winston

     getsockname可以获得一个与socket相关的地址。
      服务器端可以通过它得到相关客户端地址。
       而客户端也可以得到当前已连接成功的socket的ip和端口。
第二种情况在客户端不进行bind而直接连接服务器时，而且客户端需要知道当前使用哪个ip进行通信时比较有用（如多网卡的情况）。
笔者分别通过TCP和UDP协议进行测试，测试结果表明：
对于TCP连接的情况，如果不进行bind指定IP和端口，那么调用connect连接成功后，使用getsockname可以正确获得当前正在通信的socket的IP和端口地址。
而对于UDP的情况，无论是在调用sendto之后还是收到服务器返回的信息之后调用，都无法得到正确的ip地址：使用getsockname得到ip为0，端口正确。

测试用例如下：
1. TCP

2. //client
3. int _tmain(int argc,
4. _TCHAR* argv[])
5. {
6. WSADATA wsadata;
7. int ret = WSAStartup ( 0x0202 ,
8. & wsadata );
9. if ( ret != 0 || 0x0202 != wsadata.wVersion
10. )
11. {
12.   cout<<"WSAStartup Error!";
13.   return 0;
14. }
15. SOCKET
16. mySock = INVALID_SOCKET;
17. mySock = socket(AF_INET,SOCK_STREAM,0);
18. if
19. (mySock == INVALID_SOCKET)
20. {
21.   cout<<"Create Socket
22. Error!";
23.   return 0;
24. }
25. sockaddr_in
26. addrDest;
27. memset(&addrDest,0,sizeof(addrDest));
28. addrDest.sin_family
29. = AF_INET;
30. addrDest.sin_addr.s_addr =
31. inet_addr("10.10.44.76");
32. addrDest.sin_port = htons(9000);
33. ret = connect(mySock,(sockaddr*)&addrDest,sizeof(addrDest));
34. if (ret
35. == -1)
36. {
37.   cout<<GetLastError()<<endl;
38.   return
39. 0;
40. }
42. cout<<"Connect to Server Success!"<<endl;
44. sockaddr_in addrMy;
45. memset(&addrMy,0,sizeof(addrMy));
46. int
47. len = sizeof(addrMy);
48. ret = getsockname(mySock,(sockaddr*)&addrMy,&len);
49. if (ret !=
50. 0)
51. {
52.   cout<<"Getsockname Error!"<<endl;
53.   return
54. 0;
55. }
56. cout<<"Current Socket
57. IP:"<<inet_ntoa(addrMy.sin_addr)<<":"<<ntohs(addrMy.sin_port)<<endl;
58. getchar();
59. closesocket(mySock);
60. WSACleanup();
61. return 0;
62. }
63. //server
64. int
65. _tmain(int argc, _TCHAR* argv[])
66. {
67. WSADATA wsadata;
68. int ret =
69. WSAStartup ( 0x0202 , & wsadata );
70. if ( ret != 0 || 0x0202 !=
71. wsadata.wVersion )
72. {
73.   cout<<"WSAStartup Error!";
74.   return
75. 0;
76. }
77. SOCKET listenSock = INVALID_SOCKET;
78. listenSock =
79. socket(AF_INET,SOCK_STREAM,0);
80. if (listenSock ==
81. INVALID_SOCKET)
82. {
83.   cout<<"Create Socket Error!";
84.   return
85. 0;
86. }
87. sockaddr_in
88. addrBind;
89. memset(&addrBind,0,sizeof(addrBind));
90. addrBind.sin_family
91. = AF_INET;
92. addrBind.sin_addr.s_addr = INADDR_ANY;
93. addrBind.sin_port =
94. htons(9000);
95. ret = bind(listenSock,(sockaddr*)&addrBind,sizeof(addrBind));
96. if
97. (ret == SOCKET_ERROR)
98. {
99.   cout<<"Bind
100. Error"<<endl;
101.   return 0;
102. }
104. ret =
105. listen(listenSock,5);
106. if (ret != 0)
107. {
108.   cout<<"Listen
109. Error"<<endl;
110.   return 0;
111. }
113. SOCKET
114. conSock;
115. sockaddr_in addrCon;
116. int len = sizeof(addrCon);
117. while
118. (true)
119. {
120.   conSock =
121. accept(listenSock,(sockaddr*)&addrCon,&len);
122.   if (conSock ==
123. INVALID_SOCKET)
124.   {
125.    cout<<"Accept
126. Error"<<endl;
127.    return
128. 0;
129.   }
130.   cout<<inet_ntoa(addrCon.sin_addr)<<" Connect to
131. Server!"<<endl;
132.   
133. }
134. closesocket(conSock);
135. closesocket(listenSock);
136. WSACleanup();
137. return 0;
138. }

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2. UDP

2. //client
3. int
4. _tmain(int argc, _TCHAR* argv[])
5. {
6. WSADATA wsadata;
7. int ret =
8. WSAStartup ( 0x0202 , & wsadata );
9. if ( ret != 0 || 0x0202 !=
10. wsadata.wVersion )
11. {
12.   cout<<"WSAStartup Error!";
13.   return
14. 0;
15. }
16. SOCKET mySock = INVALID_SOCKET;
17. mySock =
18. socket(AF_INET,SOCK_DGRAM,0);
19. if (mySock ==
20. INVALID_SOCKET)
21. {
22.   cout<<"Create Socket Error!";
23.   return
24. 0;
25. }
26. sockaddr_in
27. addrDest;
28. memset(&addrDest,0,sizeof(addrDest));
29. addrDest.sin_family
30. = AF_INET;
31. addrDest.sin_addr.s_addr =
32. inet_addr("10.10.44.76");
33. addrDest.sin_port = htons(9000);
36. //set non-blocking
37. int nMode = 1;
39. ioctlsocket(mySock,FIONBIO,(u_long FAR*) &nMode);
40. char
41. sendchar[20];
42. strcpy_s(sendchar,"login");
43. sendto(mySock,sendchar,strlen(sendchar)+1,0,(sockaddr*)&addrDest,sizeof(sockaddr));
44. //get send socket ip
45. sockaddr_in
46. addrMy;
47. memset(&addrMy,0,sizeof(addrMy));
48. int leng =
49. sizeof(addrMy);
50. ret =
51. getsockname(mySock,(sockaddr*)&addrMy,&leng);
52. if (ret !=
53. 0)
54. {
55.   cout<<"Getsockname Error!"<<endl;
56.   return
57. 0;
58. }
59. cout<<"Current Socket
60. IP:"<<inet_ntoa(addrMy.sin_addr)<<":"<<ntohs(addrMy.sin_port)<<endl;
61. char recvchar[20];
62. sockaddr_in
63. addrRev;
64. memset(&addrRev,0,sizeof(addrRev));
65. memset(recvchar,0,20);
66. int
67. len = sizeof(sockaddr);
68. while (true)
69. {
70.   if
71. (recvfrom(mySock,recvchar,20,0,(sockaddr*)&addrRev,&len) ==
72. SOCKET_ERROR)
73.   {
74.    if (GetLastError() == WSAEWOULDBLOCK ||
75. GetLastError() ==
76. 10054)
77.    {
78.     continue;
79.    }
80.    else
81.    {
82.     cout<<"Receive
83. Error!"<<GetLastError()<<endl;
84.     return
85. 0;
86.    }
87.   }
88.   cout<<"login
89. success!"<<endl;
90.   //get send socket ip
91.   sockaddr_in
92. addrMy;
93.   memset(&addrMy,0,sizeof(addrMy));
94.   int leng =
95. sizeof(addrMy);
96.   ret =
97. getsockname(mySock,(sockaddr*)&addrMy,&leng);
98.   if (ret !=
99. 0)
100.   {
101.    cout<<"Getsockname Error!"<<endl;
102.    return
103. 0;
104.   }
105.   cout<<"Current Socket
106. IP:"<<inet_ntoa(addrMy.sin_addr)<<":"<<ntohs(addrMy.sin_port)<<endl;
107. }
108. return 0;
109. }
110. //server
111. int _tmain(int argc, _TCHAR*
112. argv[])
113. {
114. WSADATA wsadata;
115. int ret = WSAStartup ( 0x0202 , &
116. wsadata );
117. if ( ret != 0 || 0x0202 != wsadata.wVersion
118. )
119. {
120.   cout<<"WSAStartup Error!";
121.   return 0;
122. }
123. SOCKET
124. mySock = INVALID_SOCKET;
125. mySock = socket(AF_INET,SOCK_DGRAM,0);
126. if
127. (mySock == INVALID_SOCKET)
128. {
129.   cout<<"Create Socket
130. Error!";
131.   return 0;
132. }
133. sockaddr_in
134. addrBind;
135. memset(&addrBind,0,sizeof(addrBind));
136. addrBind.sin_family
137. = AF_INET;
138. addrBind.sin_addr.s_addr = INADDR_ANY;
139. addrBind.sin_port =
140. htons(9000);
141. ret =
142. bind(mySock,(sockaddr*)&addrBind,sizeof(addrBind));
143. if (ret ==
144. SOCKET_ERROR)
145. {
146.   cout<<"Bind Error"<<endl;
147.   return
148. 0;
149. }
150. //set non-blocking
151. int nMode = 1;
153. ioctlsocket(mySock,FIONBIO,(u_long FAR*) &nMode);
154. char recvchar[20];
155. sockaddr_in
156. addrRev;
157. memset(&addrRev,0,sizeof(addrRev));
158. memset(recvchar,0,20);
159. int
160. len = sizeof(sockaddr);
161. while (true)
162. {
163.   if
164. (recvfrom(mySock,recvchar,20,0,(sockaddr*)&addrRev,&len) ==
165. SOCKET_ERROR)
166.   {
167.    if (GetLastError() == WSAEWOULDBLOCK ||
168. GetLastError() ==
169. 10054)
170.    {
171.     continue;
172.    }
173.    else
174.    {
175.     cout<<"Receive
176. Error!"<<GetLastError()<<endl;
177.     return
178. 0;
179.    }
180.   }
181.   cout<<recvchar<<" from
182. "<<inet_ntoa(addrRev.sin_addr)<<":"<<ntohs(addrRev.sin_port)<<endl;
183.   sendto(mySock,recvchar,strlen(recvchar)+1,0,(sockaddr*)&addrRev,sizeof(sockaddr));
184. }
185. return 0;
186. }

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