NETWORK

• TCP #

• UDP #

• InetAddress #

  • 流程解析 #

    根据域名实例化一个InetAddress对象的流程解析。
    比如：InetAddress byName = InetAddress.getByName("wtfu.site");。如果是域名的话，会涉及到系统调用getaddrinfo.里面包括DNS解析。
    
    1. getAllByName(String host, InetAddress reqAddr)
    2. 不属于ip地址的话，会继续进入到getAllByName0()
    3. addresses = getAddressesFromNameService(host, reqAddr);
    4. addresses = nameService.lookupAllHostAddr(host);
    5. impl.lookupAllHostAddr(host); // impl为Inet6AddressImpl类型，且lookupAllHostAddr为native方法。
    6. 定位到c源码后如下：可以看到关键的getaddrinfo系统调用。

    //src/java.base/unix/native/libnet/Inet6AddressImpl.c
    JNIEXPORT jobjectArray JNICALL
    Java_java_net_Inet6AddressImpl_lookupAllHostAddr(JNIEnv *env, jobject this,
                                                    jstring host, jint characteristics) {
        error = getaddrinfo(hostname, NULL, &hints, &res);
    }
    

  • 测试系统调用流程 #

    1. 编写样例代码

       #include <sys/types.h>
       #include <sys/socket.h>
       #include <netdb.h>
       #include <stdio.h>
       #include <sys/socket.h>
       #include <netinet/in.h>
       #include <arpa/inet.h>
       #include <string.h>
       
       int main(int argc, char * argv[])
       {
           struct addrinfo hints, *res;
           memset (&hints, 0, sizeof (hints));
           hints.ai_family = AF_INET;
           hints.ai_flags = AI_CANONNAME;
       
           if (0 > getaddrinfo("wtfu.site", NULL, &hints, &res)){
               perror("get error:");
               return -1;
           }
           struct sockaddr_in * get_addr = res->ai_addr;
           printf("ip for wtfu: %s\n", inet_ntoa(get_addr->sin_addr));
           return 0;
       }
       

    2. 追踪系统调用

       使用gcc -o test test.c编译源码，然后使用strace ./test 追踪调用。按顺序摘选输出：
       可以看到从/etc/resolv.conf中读取到nameserver,然后使用53端口进行连接查询。

       execve("./test", ["./test"], 0x7ffe34b4bc10 /* 23 vars */) = 0
       open("/etc/nsswitch.conf", O_RDONLY|O_CLOEXEC) = 3
       fstat(3, {st_mode=S_IFREG|0644, st_size=1746, ...}) = 0
       mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f553499f000
       read(3, "#\n# /etc/nsswitch.conf\n#\n# An ex"..., 4096) = 1746
       read(3, "", 4096)                       = 0
       close(3)                                = 0
       munmap(0x7f553499f000, 4096)            = 0
       stat("/etc/resolv.conf", {st_mode=S_IFREG|0644, st_size=89, ...}) = 0
       open("/etc/host.conf", O_RDONLY|O_CLOEXEC) = 3
       fstat(3, {st_mode=S_IFREG|0644, st_size=9, ...}) = 0
       mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f553499f000
       read(3, "multi on\n", 4096)             = 9
       read(3, "", 4096)                       = 0
       close(3)                                = 0
       munmap(0x7f553499f000, 4096)            = 0
       open("/etc/resolv.conf", O_RDONLY|O_CLOEXEC) = 3
       fstat(3, {st_mode=S_IFREG|0644, st_size=89, ...}) = 0
       mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f553499f000
       read(3, "; generated by /usr/sbin/dhclien"..., 4096) = 89
       read(3, "", 4096)                       = 0
       close(3)                                = 0
       mprotect(0x7f55343aa000, 4096, PROT_READ) = 0
       munmap(0x7f5534998000, 30945)           = 0
       open("/etc/hosts", O_RDONLY|O_CLOEXEC)  = 3
       fstat(3, {st_mode=S_IFREG|0644, st_size=201, ...}) = 0
       mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f553499f000
       read(3, "127.0.0.1 12302 12302\n127.0.0.1 "..., 4096) = 201
       read(3, "", 4096)                       = 0
       close(3)                                = 0
       ...
       socket(AF_INET, SOCK_DGRAM|SOCK_CLOEXEC|SOCK_NONBLOCK, IPPROTO_IP) = 3
       setsockopt(3, SOL_IP, IP_RECVERR, [1], 4) = 0
       connect(3, {sa_family=AF_INET, sin_port=htons(53), sin_addr=inet_addr("183.60.82.98")}, 16) = 0
       poll([{fd=3, events=POLLOUT}], 1, 0)    = 1 ([{fd=3, revents=POLLOUT}])
       sendto(3, "\342\377\1\0\0\1\0\0\0\0\0\0\4wtfu\4site\0\0\1\0\1", 27, MSG_NOSIGNAL, NULL, 0) = 27
       poll([{fd=3, events=POLLIN}], 1, 5000)  = 1 ([{fd=3, revents=POLLIN}])
       ioctl(3, FIONREAD, [43])                = 0
       recvfrom(3, "\342\377\201\200\0\1\0\1\0\0\0\0\4wtfu\4site\0\0\1\0\1\300\f\0\1\0"..., 1024, 0, {sa_family=AF_INET, sin_port=htons(53), sin_addr=inet_addr("183.60.82.98")}, [28->16]) = 43
       close(3)                                = 0
       fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 1), ...}) = 0
       mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f553499f000
       write(1, "ip for wtfu: 139.155.77.112\n", 28ip for wtfu: 139.155.77.112
       ) = 28
       exit_group(0)                           = ?
       +++ exited with 0 +++
       

  • Reference

    • https://man7.org/linux/man-pages/man3/getaddrinfo.3.html
    • https://www.cnblogs.com/Iflyinsky/p/17520932.html

socket #

• http impl #

  Server

  public class Server {
      public static void main(String[] args) {
          // You can use print statements as follows for debugging, they'll be visible when running tests.
          System.out.println("Logs from your program will appear here!");
          ServerSocket serverSocket = null;
          Socket clientSocket = null;
  
          try {
              serverSocket = new ServerSocket(4221);
              serverSocket.setReuseAddress(true);
  
              while(true) {
                  clientSocket = serverSocket.accept(); // Wait for connection from client.
                  System.out.println("accepted new connection");
  
                  Socket finalClientSocket = clientSocket;
                  new Thread(() -> {
                      // 必须关闭，不关闭的话，容易资源泄露，并且curl 会等待。
                      try(finalClientSocket;
                          InputStream input = finalClientSocket.getInputStream();
                          OutputStream output = finalClientSocket.getOutputStream()){
  
                          BufferedReader in = new BufferedReader(new InputStreamReader(input));
                          String startLine = in.lines().findFirst().get();
                          String path = startLine.split(" ")[1];
  
                          StringBuilder response = new StringBuilder();
                          if ("/".equals(path)) {
                              response.append("HTTP/1.1 200 OK\n");
                          } else {
                              response.append("HTTP/1.1 404 Not Found\n");
                          }
  
                          response.append("Content-Type: text/plain\n");
                          //response.append("Connection: keep-alive\n");
                          response.append("Connection: close\n");
  
                          response.append("\n");
                          response.append("hello world");
  
                          String responseStr = response.toString();
                          output.write(responseStr.getBytes(StandardCharsets.UTF_8));
                          output.flush();
  
                          System.out.println("This message is sent to the client: \n" + responseStr);
                      }catch (Exception e){e.printStackTrace();}
                  }).start();
              }
          } catch (Exception e) {
              System.out.println("IOException: " + e.getMessage());
          } finally {
              if (serverSocket != null) {
                  try {
                      serverSocket.close();
                  } catch (IOException e) {
                      throw new RuntimeException(e);
                  }
              }
          }
      }
  }
  

  Client

  public class Client {
      public static void main(String[] args) throws Exception {
  
          //Instantiate a new socket
          try (Socket s = new Socket("localhost", 4221);
              OutputStream outputStream = s.getOutputStream();
              InputStream inputStream = s.getInputStream()) {
              //Prints the request string to the output stream
              StringBuilder req = new StringBuilder();
              req.append("GET / HTTP/1.1\r\n");
              req.append("Host: localhost\r\n");
              req.append("\r\n");
  
              outputStream.write(req.toString().getBytes(StandardCharsets.UTF_8));
  
              //Creates a BufferedReader that contains the server response
              BufferedReader bufRead = new BufferedReader(new InputStreamReader(inputStream));
              String outStr;
  
              //Prints each line of the response
              while((outStr = bufRead.readLine()) != null){
                  System.out.println(outStr);
              }
          }catch (Exception e){e.printStackTrace();}
      }
  }
  

channelsocket #

Reference #

• https://stackoverflow.com/questions/23184845/dont-understand-character-digit-in-java
• https://stackoverflow.com/questions/27014955/socket-connect-vs-bind