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FGJ: Create:2022/10/19 Update: (2024-10-24)

  • 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

socket #

  • http impl #

    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);
                }
            }
        }
    }
}

    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 #

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