使用c发送GET请求

参考地址：http://www.wangafu.net/~nickm/libevent-book/01_intro.html#_footnote_1

在阅读libevent文档时发现这个例子，文档列出这个例子的重点是说明阻塞式编程。因为对C网络编程还不太懂，这里添加了一些注释。

/* For sockaddr_in */#include <netinet/in.h>/* For socket functions */#include <sys/socket.h>/* For gethostbyname */#include <netdb.h>#include <unistd.h>#include <string.h>#include <stdio.h>int main(int c, char **v){//\r表示回车，\n表示换行//发送这些信息，应该相当于发送了一个GET请求。利用socket来发送get请求    const char query[] =        "GET / HTTP/1.0\r\n"        "Host: www.baidu.com\r\n"        "\r\n";    const char hostname[] = "www.baidu.com";    //套接字地址结构，在Unix网络编程中有描述    struct sockaddr_in socketAddr_in;    //对一个主机的描述，有地址，主机名等    struct hostent *baiduhost;    const char *cp;    int fd;    ssize_t n_written, remaining;    char buf[1024];    /* Look up the IP address for the hostname.   Watch out; this isn't       threadsafe on most platforms. */    baiduhost = gethostbyname(hostname);//gethostbyname是阻塞的，得不到地址不返回    if (!baiduhost) {        fprintf(stderr, "Couldn't lookup %s: %s", hostname, hstrerror(h_errno));        return 1;    }    if (baiduhost->h_addrtype != AF_INET) {        fprintf(stderr, "No ipv6 support, sorry.");        return 1;    }    /* Allocate a new socket，Returns a file descriptor for the new socket, or -1 for errors.  */    //the first is the address domain of the socket. recall that there are two possile address domains    //the unic domain for two processes which share a common file system, and the internet domain for    //any two hosts on the Internet. The symbol constant AF_UNIX is used for the former, and    //AF_INET is used for the latter    //第二个参数表示类型，SOCK_STREAM表示TCP，SOCK_DGRAM表示UDP    //这个函数返回an entry into the file descriptor table (i.e. a small integer)，this value is used for all    // subsequent references to this socket    fd = socket(AF_INET, SOCK_STREAM, 0);    printf("fd-----> %d\n",fd);    if (fd < 0) {        perror("socket");        return 1;    }    /* Connect to the remote host. */    socketAddr_in.sin_family = AF_INET;    socketAddr_in.sin_port = htons(80);    socketAddr_in.sin_addr = *(struct in_addr*)baiduhost->h_addr;    //connect函数，从进程到内核传递套接字地址结构的函数，第二个参数为socket指针，第三个参数为大小    if (connect(fd, (struct sockaddr*) &socketAddr_in, sizeof(socketAddr_in))) {        perror("connect");        close(fd);        return 1;    }    /* Write the query. */    /* XXX Can send succeed partially? */    //使用send和recv发送和接收数据时，都使用无限循环    cp = query;    remaining = strlen(query);    while (remaining) {      n_written = send(fd, cp, remaining, 0); //send函数，成功则返回实际传送出去的字符数，失败返回-1      if (n_written <= 0) {        perror("send");        return 1;      }      remaining -= n_written;   //remaining 不为0表明还没有发送完数据      cp += n_written;    }    /* Get an answer back. */    //将返回结果读入到buf中，利用循环来实现读取所有的数据    while (1) {        ssize_t result = recv(fd, buf, sizeof(buf), 0);        if (result == 0) { //result返回0,表示读入完毕，跳出循环            break;        } else if (result < 0) {            perror("recv");            close(fd);            return 1;        }        fwrite(buf, 1, result, stdout); //写入文件或者标准输出    }    close(fd);    return 0;}