今天做了一個簡單的stmp郵件傳送的客戶端demo，可以支援帶附件傳送，希望將實現分享一下， 目前測試環境是公司的內部郵箱， 

有gmail郵箱測試沒有成功， 可能gmail郵箱需要ssl加密，後續再進行完善吧， 這個demo實現的非常簡單的阻塞的傳送傳送郵件， 在後續的工作中需要

改成非阻塞的方式， 原理就是這樣的。 你可以在網上stmp的原理，網上資料很多，在這裡就不羅嗦了，本人水平有限， 如有問題，大家可以相互交流，共同

進步。

下面是原始碼：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <errno.h>
#include <unistd.h>
#include <sys/time.h>
#include <netdb.h>


#define TEST_IMG     ("test.jpg")
static char base64_table[64] =
{
	'A', 'B', 'C', 'D', 'E', 'F', 'G',
	'H', 'I', 'J', 'K', 'L', 'M', 'N',
	'O', 'P', 'Q', 'R', 'S', 'T',
	'U', 'V', 'W', 'X', 'Y', 'Z',
	'a', 'b', 'c', 'd', 'e', 'f', 'g',
	'h', 'i', 'j', 'k', 'l', 'm', 'n',
	'o', 'p', 'q', 'r', 's', 't',
	'u', 'v', 'w', 'x', 'y', 'z',
	'0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
	'+', '/'
};


int base64_encode(unsigned char *buf, int nLen, char *pOutBuf, int nBufSize);

void sendemail(char *stmpServer, char *body);
int open_socket(struct sockaddr *addr);

int main()
{
    FILE * fp = NULL;
    char buf[128] = {0};
    char outbuf[256] = {0};
    char *body = NULL;
    char email[] = "smtp.**.com";
#if 0
    char body[] = "From: \"********\"<****@qq.com>\r\n"
        "To:  \"horst\"<>\r\n"
        "Subject: Hello\r\n\r\n"
        "this is a test!\n"
        "good bye!"
        "MIME-Version:1.0\r\n"
        "Content-Type:multipart/mixed;boundary=\"---=_NextPart_000_0050_01C\"\r\n"
        "Subject:=?gb2312?B?TU1NRdCt0unLtcP308q8/g==?=\r\n";
#endif
    char bodyHead[] = "From: \"****\"<***@**.com>\r\n"
        "To:  \"**\"<**>\r\n"
        "MIME-Version:1.0\r\n"
        "Content-Type:multipart/mixed;boundary=\"---=_NextPart_000_0050_01C\"\r\n"
        "Subject:test\r\n"
        "\r\n"
        "-----=_NextPart_000_0050_01C\r\n"
        "Content-Type:text/plain;charset=\"gb2312\"\r\n"
        "\r\n"
        "hello \r\n"
        "-----=_NextPart_000_0050_01C\r\n"
        "\r\n\r\n"
        "Content-Type:application/octet-stream;name=\"test.jpg\"\r\n"
        "Content-Transfer-Encoding:base64\r\n"
        "Content-Disposion:attachment;filename=\"test.jpg\""
        "\r\n\r\n";
        
    char bodyend[] = "\r\n-----=_NextPart_000_0050_01C\r\n";

    body = malloc(8 * 1024 * 1024);
    if(NULL == body)
    {
        perror("malloc(): ");
        return -1;
    }

    memset(body, 0x0, 8*1024*1024);

    sprintf(body, bodyHead);
    
    fp = fopen(TEST_IMG, "rb");
    if(fp == NULL)
    {
        perror("fopen(): ");
        return -1;
    }

    memset(buf, 0x0, 128);
    memset(outbuf, 0x0, 256);
    int len = 0;
    char *ptr = NULL;
    ptr = body + strlen(body);
    while((len = fread(buf, sizeof(char), 60, fp)) > 0)
    {
        base64_encode(buf, len, outbuf, sizeof(outbuf));
        len = sprintf(outbuf, "%s\r\n", outbuf);
        printf("len :  %d\n", len);
        sprintf(ptr, outbuf);
        memset(buf, 0x0, 128);
        memset(outbuf, 0x0, 256);
        ptr += len;
    }

    sprintf(ptr, "\r\n\r\n");
    ptr += strlen("\r\n\r\n");
    sprintf(ptr, bodyend);

    sendemail(email, body);

    fclose(fp);
    free(body);

    return 0;




}

int base64_encode(unsigned char* pBase64, int nLen, char* pOutBuf, int nBufSize)
{
	int i = 0;
	int j = 0;
	int nOutStrLen = 0;

	/* nOutStrLen does not contain null terminator. */
	nOutStrLen = nLen / 3 * 4 + (0 == (nLen % 3) ? 0 : 4);
	if ( pOutBuf && nOutStrLen < nBufSize )
	{
		char cTmp = 0;
		for ( i = 0, j = 0; i < nLen; i += 3, j += 4 )
		{
			/* the first character: from the first byte. */
			pOutBuf[j] = base64_table[pBase64[i] >> 2];

			/* the second character: from the first & second byte. */
			cTmp = (char)((pBase64[i] & 0x3) << 4);
			if ( i + 1 < nLen )
			{
				cTmp |= ((pBase64[i + 1] & 0xf0) >> 4);
			}
			pOutBuf[j+1] = base64_table[(int)cTmp];

			/* the third character: from the second & third byte. */
			cTmp = '=';
			if ( i + 1 < nLen )
			{
				cTmp = (char)((pBase64[i + 1] & 0xf) << 2);
				if ( i + 2 < nLen )
				{
					cTmp |= (pBase64[i + 2] >> 6);
				}
				cTmp = base64_table[(int)cTmp];
			}
			pOutBuf[j + 2] = cTmp;

			/* the fourth character: from the third byte. */
			cTmp = '=';
			if ( i + 2 < nLen )
			{
				cTmp = base64_table[pBase64[i + 2] & 0x3f];
			}
			pOutBuf[j + 3] = cTmp;
		}

		pOutBuf[j] = '\0';
	}

	return nOutStrLen + 1;
}

/** 
 * @func  sendemail
 * @brief send email in blocking-mode
 * @param smtpServer 
 * @param body 
 */
void sendemail(char *smtpServer, 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};
    struct hostent *host = NULL;

    if((host = gethostbyname(smtpServer))==NULL)/*取得主機IP地址*/
    {
        fprintf(stderr,"Gethostname error, %s\n", strerror(errno));
        exit(1);
    }


    memset(&their_addr, 0, sizeof(their_addr));
    their_addr.sin_family = AF_INET;
    their_addr.sin_port = htons(25);
    their_addr.sin_addr = *((struct in_addr *)host->h_addr);

    sockfd = open_socket((struct sockaddr *)&their_addr);

    memset(rbuf, 0, 1500);

    while(recv(sockfd, rbuf, 1500, 0) == 0)
    {
        printf("reconnect..\n");

        close(sockfd);
        sleep(2);
        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, "********");
    memset(login, 0, 128);

    base64_encode(buf, strlen(buf), login, 128);                   /* base64 */

    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 */
    memset(buf, 0, 1500);
    sprintf(buf, "******");
    memset(pass, 0, 128);

    base64_encode(buf, strlen(buf), pass, 128);
    memset(buf, 0, 1500);
    sprintf(buf, "%s\r\n", pass);
    send(sockfd, buf, strlen(buf), 0);

    printf("%s, %d\n", buf, __LINE__);

    memset(rbuf, 0, 1500);
    recv(sockfd, rbuf, 1500, 0);
    printf("%s, %d\n", rbuf, __LINE__);

    /* MAIL FROM */

    memset(buf, 0, 1500);
    sprintf(buf, "MAIL FROM: <****@**.com>\r\n");
    send(sockfd, buf, strlen(buf), 0);

    memset(rbuf, 0, 1500);
    recv(sockfd, rbuf, 1500, 0);

    printf("%s\n", rbuf);

    /* rcpt to 第一個收件人 */
    sprintf(buf, "RCPT TO:<***@***.com>\r\n");
    send(sockfd, buf, strlen(buf), 0);

    memset(rbuf, 0, 1500);
    recv(sockfd, rbuf, 1500, 0);

    printf("%s\n", rbuf);

    /* DATA email connext ready  */

    sprintf(buf, "DATA\r\n");
    send(sockfd, buf, strlen(buf), 0);

    memset(rbuf, 0, 1500);
    recv(sockfd, rbuf, 1500, 0);
    printf("%s\n", rbuf);

    /* send email connext \r\n.\r\n end*/

    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);

    return ;

}

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)
    {
        close(sockfd);

        fprintf(stderr, "Connect sockfd(TCP ) error!\n");
        exit(-1);
    }

    return sockfd;

}