应用层常见协议及其实现库
DNS
利用C语言实现DNS查询和DNS响应包的解析。
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HTTP
利用C语言实现HTTP请求，可以采用原生Socket往端口发包，根据HTTP协议自行构造请求的方式。
但更方便的方式是使用libcurl库。自行构造Socket请求的方式既不能保证性能，又无法保证安全。
libcurl库至少是相对完善的第三方库。
详细用法，参考libcurl官方文档以及libcurl官方样例。
SMTP
SMTP一例1
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235/*
* 源码出处：https://blog.csdn.net/zx824/article/details/7387418
*/
#ifdef WIN32
#include <windows.h>
#include <stdio.h>
#else
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/types.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <errno.h>
#include <unistd.h>
#include <sys/time.h>
#endif
struct data6{
unsigned int d4:6;
unsigned int d3:6;
unsigned int d2:6;
unsigned int d1:6;
};
// 协议中加密部分使用的是base64方法
char con628(char c6);
void base64(char *dbuf,char *buf128,int len);
void sendemail(char *email,char *body);
int open_socket(struct sockaddr *addr);
int main()
{
char email[] = "[email protected]";
char body[] = "From: \"yyy\"<[email protected]>\r\n"
"To: \"xxx\"<[email protected]>\r\n"
"Subject: Hello\r\n\r\n"
"Hello World, Hello Email!";
sendemail(email, body);
return 0;
}
char con628(char c6)
{
char rtn = '\0';
if (c6 < 26) rtn = c6 + 65;
else if (c6 < 52) rtn = c6 + 71;
else if (c6 < 62) rtn = c6 - 4;
else if (c6 == 62) rtn = 43;
else rtn = 47;
return rtn;
}
// base64的实现
void base64(char *dbuf, char *buf128, int len)
{
struct data6 *ddd = NULL;
int i = 0;
char buf[256] = {0};
char *tmp = NULL;
char cc = '\0';
memset(buf, 0, 256);
strcpy(buf, buf128);
for(i = 1; i <= len/3; i++)
{
tmp = buf+(i-1)*3;
cc = tmp[2];
tmp[2] = tmp[0];
tmp[0] = cc;
ddd = (struct data6 *)tmp;
dbuf[(i-1)*4+0] = con628((unsigned int)ddd->d1);
dbuf[(i-1)*4+1] = con628((unsigned int)ddd->d2);
dbuf[(i-1)*4+2] = con628((unsigned int)ddd->d3);
dbuf[(i-1)*4+3] = con628((unsigned int)ddd->d4);
}
if(len%3 == 1)
{
tmp = buf+(i-1)*3;
cc = tmp[2];
tmp[2] = tmp[0];
tmp[0] = cc;
ddd = (struct data6 *)tmp;
dbuf[(i-1)*4+0] = con628((unsigned int)ddd->d1);
dbuf[(i-1)*4+1] = con628((unsigned int)ddd->d2);
dbuf[(i-1)*4+2] = '=';
dbuf[(i-1)*4+3] = '=';
}
if(len%3 == 2)
{
tmp = buf+(i-1)*3;
cc = tmp[2];
tmp[2] = tmp[0];
tmp[0] = cc;
ddd = (struct data6 *)tmp;
dbuf[(i-1)*4+0] = con628((unsigned int)ddd->d1);
dbuf[(i-1)*4+1] = con628((unsigned int)ddd->d2);
dbuf[(i-1)*4+2] = con628((unsigned int)ddd->d3);
dbuf[(i-1)*4+3] = '=';
}
return;
}
// 发送邮件
void sendemail(char *email, char *body)
{
int sockfd = 0;
struct sockaddr_in their_addr = {0};
char buf[1500] = {0};
char rbuf[1500] = {0};
char login[128] = {0};
char pass[128] = {0};
#ifdef WIN32
WSADATA WSAData;
WSAStartup(MAKEWORD(2, 2), &WSAData);
#endif
memset(&their_addr, 0, sizeof(their_addr));
their_addr.sin_family = AF_INET;
their_addr.sin_port = htons(25);
their_addr.sin_addr.s_addr = inet_addr("123.58.177.49");//qq smtp 服务器
// 连接邮件服务器，如果连接后没有响应，则2 秒后重新连接
sockfd = open_socket((struct sockaddr *)&their_addr);
memset(rbuf,0,1500);
while(recv(sockfd, rbuf, 1500, 0) == 0)
{
printf("reconnect...\n");
//Sleep(2);
//close(sockfd);
sockfd = open_socket((struct sockaddr *)&their_addr);
memset(rbuf,0,1500);
}
printf("%s\n", rbuf);
// EHLO
memset(buf, 0, 1500);
sprintf(buf, "EHLO abcdefg-PC\r\n");
send(sockfd, buf, strlen(buf), 0);
memset(rbuf, 0, 1500);
recv(sockfd, rbuf, 1500, 0);
printf("%s\n", rbuf);
// AUTH LOGIN
memset(buf, 0, 1500);
sprintf(buf, "AUTH LOGIN\r\n");
send(sockfd, buf, strlen(buf), 0);
printf("%s\n", buf);
memset(rbuf, 0, 1500);
recv(sockfd, rbuf, 1500, 0);
printf("%s\n", rbuf);
// USER
memset(buf, 0, 1500);
sprintf(buf,"[email protected]");
memset(login, 0, 128);
base64(login, buf, strlen(buf));
sprintf(buf, "%s\r\n", login);
send(sockfd, buf, strlen(buf), 0);
printf("%s\n", buf);
memset(rbuf, 0, 1500);
recv(sockfd, rbuf, 1500, 0);
printf("%s\n", rbuf);
// PASSWORD
sprintf(buf, "password");
memset(pass, 0, 128);
base64(pass, buf, strlen(buf));
sprintf(buf, "%s\r\n", pass);
send(sockfd, buf, strlen(buf), 0);
printf("%s\n", buf);
memset(rbuf, 0, 1500);
recv(sockfd, rbuf, 1500, 0);
printf("%s\n", rbuf);
// MAIL FROM
memset(buf, 0, 1500);
sprintf(buf, "MAIL FROM: <[email protected]>\r\n");
send(sockfd, buf, strlen(buf), 0);
memset(rbuf, 0, 1500);
recv(sockfd, rbuf, 1500, 0);
printf("%s\n", rbuf);
// RCPT TO 第一个收件人
sprintf(buf, "RCPT TO:<%s>\r\n", email);
send(sockfd, buf, strlen(buf), 0);
memset(rbuf, 0, 1500);
recv(sockfd, rbuf, 1500, 0);
printf("%s\n", rbuf);
// DATA 准备开始发送邮件内容
sprintf(buf, "DATA\r\n");
send(sockfd, buf, strlen(buf), 0);
memset(rbuf, 0, 1500);
recv(sockfd, rbuf, 1500, 0);
printf("%s\n", rbuf);
// 发送邮件内容，\r\n.\r\n内容结束标记
sprintf(buf, "%s\r\n.\r\n", body);
send(sockfd, buf, strlen(buf), 0);
memset(rbuf, 0, 1500);
recv(sockfd, rbuf, 1500, 0);
printf("%s\n", rbuf);
// QUIT
sprintf(buf, "QUIT\r\n");
send(sockfd, buf, strlen(buf), 0);
memset(rbuf, 0, 1500);
recv(sockfd, rbuf, 1500, 0);
printf("%s\n", rbuf);
// VC2005 需要使用
//closesocket(sockfd);
close(sockfd);
#ifdef WIN32
WSACleanup();
#endif
return;
}
// 打开TCP Socket连接
int open_socket(struct sockaddr *addr)
{
int sockfd = 0;
sockfd=socket(PF_INET, SOCK_STREAM, 0);
if(sockfd < 0)
{
fprintf(stderr, "Open sockfd(TCP) error!\n");
exit(-1);
}
if(connect(sockfd, addr, sizeof(struct sockaddr)) < 0)
{
fprintf(stderr, "Connect sockfd(TCP) error!\n");
exit(-1);
}
return sockfd;
}
其他协议，后续学到再补充。
