UNP 简介

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// 以下代码与 UNP intro/daytimetcpcli.c 等价
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

// inet_pton/3, htons/1
#include <arpa/inet.h>

// struct sockaddr_in
#include <netinet/in.h>

// errno
#include <errno.h>

// socket/3, connect/3
#include <sys/socket.h>
#include <sys/types.h>

// read/3
#include <unistd.h>

#define MAXLINE 4096

void err_sys(const char* fmt, ...) {
  va_list ap;
  va_start(ap, fmt);
  char buffer[MAXLINE + 1] = {0};
  vsnprintf(buffer, MAXLINE, fmt, ap);
  int n = strlen(buffer);
  snprintf(buffer + n, MAXLINE - n, ":%s", strerror(errno));
  strcat(buffer, "\n");
  fflush(stdout);
  fputs(buffer, stderr);
  fflush(stderr);
  va_end(ap);
  exit(1);
}

void err_quit(const char* fmt, ...) {
  va_list ap;
  va_start(ap, fmt);
  char buffer[MAXLINE + 1] = {0};
  vsnprintf(buffer, MAXLINE, fmt, ap);
  strcat(buffer, "\n");
  fflush(stdout);
  fputs(buffer, stderr);
  fflush(stderr);
  va_end(ap);
  exit(1);
}

int main(int argc, char** argv) {
  if (argc != 2) {
    err_quit("usage: a.out <IPaddress>");
  }
  int sockfd;
  if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
    err_sys("socket error");
  }
  struct sockaddr_in servaddr = {
    .sin_family = AF_INET,
    .sin_port = htons(13),
  };
  if (inet_pton(AF_INET, argv[1], &servaddr.sin_addr) <= 0) {
    err_quit("inet_pton error for %s", argv[1]);
  }
  if (connect(sockfd, (struct sockaddr*) &servaddr, sizeof(servaddr)) < 0) {
    err_sys("connect error");
  }
  int n;
  char recvline[MAXLINE + 1];
  while ((n = read(sockfd, recvline, MAXLINE)) > 0) {
    recvline[n] = 0;
    if (fputs(recvline, stdout) == EOF) {
      err_sys("read error");
    }
  }
  if (n < 0) {
    err_sys("read error");
  }
  return 0;
}

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// 构建 IPv4 socket
tcp_socket = socket(AF_INET, SOCK_STREAM, 0);
udp_socket = socket(AF_INET, SOCK_DGRAM, 0);
raw_socket = socket(AF_INET, SOCK_RAW, protocol);
// 构建 IPv6 socket
tcp6_socket = socket(AF_INET6, SOCK_STREAM, 0);
raw6_socket = socket(AF_INET6, SOCK_RAW, protocol);
udp6_socket = socket(AF_INET6, SOCK_DGRAM, protocol);

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// IPv4
struct sockaddr_in {
    sa_family_t    sin_family; /* address family: AF_INET */
    in_port_t      sin_port;   /* port in network byte order */
    struct in_addr sin_addr;   /* internet address */
};
/* Internet address. */
typedef uint32_t in_addr_t;
struct in_addr {
    in_addr_t      s_addr;     /* address in network byte order */
};

// Ipv6
struct sockaddr_in6 {
    sa_family_t     sin6_family;   /* AF_INET6 */
    in_port_t       sin6_port;     /* port number */
    uint32_t        sin6_flowinfo; /* IPv6 flow information */
    struct in6_addr sin6_addr;     /* IPv6 address */
    uint32_t        sin6_scope_id; /* Scope ID (new in 2.4) */
};

struct in6_addr {
    unsigned char   s6_addr[16];   /* IPv6 address */
};

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uint32_t htonl(uint32_t hostlong);   // 将 unsigned int 类型 host to network
uint16_t htons(uint16_t hostshort);  // 将 unsigned short 类型 host to network
uint32_t ntohl(uint32_t netlong);    // 将 unsigned int 类型 network to host
uint16_t ntohs(uint16_t netshort);   // 将 unsigned short 类型 network to host

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#include <arpa/inet.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main(int argc, char *argv[]) {
    unsigned char buf[sizeof(struct in6_addr)];
    int domain, s;
    char str[INET6_ADDRSTRLEN];
    if (argc != 3) {
        fprintf(stderr, "Usage: %s {i4|i6|<num>} string\n", argv[0]);
        exit(EXIT_FAILURE);
    }
    domain = (strcmp(argv[1], "i4") == 0) ? AF_INET :
             (strcmp(argv[1], "i6") == 0) ? AF_INET6 : atoi(argv[1]);
    s = inet_pton(domain, argv[2], buf);
    if (s <= 0) {
        if (s == 0) {
            fprintf(stderr, "Not in presentation format");
        } else {
            perror("inet_pton");
        }
        exit(EXIT_FAILURE);
    }
    if (inet_ntop(domain, buf, str, INET6_ADDRSTRLEN) == NULL) {
        perror("inet_ntop");
        exit(EXIT_FAILURE);
    }
    printf("%s\n", str);
    exit(EXIT_SUCCESS);
}
// ./a.out i4 127.0.0.1
// 127.0.0.1
// ./a.out i6 0:0:0:0:0:0:0:0
// ::
// ./a.out i6 1:0:0:0:0:0:0:8
// 1::8
// ./a.out i6 0:0:0:0:0:FFFF:204.152.189.116
// ::ffff:204.152.189.116

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// #include <sys/socket.h>
// #include <sys/types.h>
int connect(int sockfd, const struct sockaddr *addr, socklen_t addrlen);

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// 以下代码与 UNP intro/daytimetcpsrv.c 等价
#include <stdbool.h>
#include <stdio.h>
#include <time.h>

#include <arpa/inet.h>
#include <netinet/in.h>
#include <unistd.h>

#include <sys/socket.h>
#include <sys/types.h>

#define LISTENQ 1024
#define MAXLINE 4096

int main(int argc, const char* argv[]) {
  int listenfd = socket(AF_INET, SOCK_STREAM, 0);
  if (listenfd == -1) {
    err_sys("listen error");
  }
  struct sockaddr_in servaddr = {
    .sin_family = AF_INET,
    .sin_port = htons(13),
    .sin_addr.s_addr = htonl(INADDR_ANY),
  };
  if (bind(listenfd, (struct sockaddr*) &servaddr, sizeof(servaddr)) == -1) {
    err_sys("bind error");
  }
  if (listen(listenfd, LISTENQ) == -1) {
    err_sys("listen error");
  }
  while (true) {
    int connfd = accept(listenfd, (struct sockaddr*) NULL, NULL);
    if (connfd == -1) {
      err_ret("connect error");
      continue;
    }
    time_t ticks = time(NULL);
    char buffer[MAXLINE + 1] = {0};
    snprintf(buffer, sizeof(buffer), "%.24s\r\n", ctime(&ticks));
    if (write(connfd, buffer, strlen(buffer)) == -1) {
      err_ret("write error");
    }
    if (close(connfd) == -1) {
      err_ret("close error");
    }
  }
}