libcurl example - smtp-mail.c extended

date.c

/*
 * https://tools.ietf.org/html/rfc5322#section-3.3
 *
 * gcc -Wall -Wextra -Werror -o date date.c; ./date
 */
#include <stdio.h>
#include <string.h>
#include <time.h>

int main(void)
{
        struct tm *tm_info;
        time_t timer;
        char date[36];

        time(&timer);
        tm_info = localtime(&timer);
        /* RFC 822 POSIX time stamp */
        strftime(date, 36, "%a, %d %b %Y %H:%M:%S %z", tm_info);
        printf("Date: %s\n", date);

        return 0;
}

message_id.c

/*
 * https://tools.ietf.org/html/rfc5322#section-3.6.4
 *
 * gcc -Wall -Wextra -Werror -o message_id message_id.c -luuid; ./message_id
 */
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <uuid/uuid.h>

int main(void)
{
        char domainname[64],
             hostname[64],
             msg_id[37];
        size_t i;
        uuid_t uuid;

        uuid_generate(uuid);

        for (i = 0; i < sizeof(uuid); i++) {
                if(i == 0) {
                        snprintf(msg_id, sizeof(msg_id) - strlen(msg_id), "%02x", uuid[i]);
                } else if(i == 3 || i == 5 || i == 7 || i == 9) {
                        snprintf(msg_id + strlen(msg_id), sizeof(msg_id) - strlen(msg_id) + 1, "%02x-", uuid[i]);
                } else {
                        snprintf(msg_id + strlen(msg_id), sizeof(msg_id) - strlen(msg_id), "%02x", uuid[i]);
                }
        }

        getdomainname(domainname, sizeof(domainname));
        gethostname(hostname, sizeof(hostname));
        printf("Message-ID: %s@%s.%s\n", msg_id, hostname, domainname);
        return 0;
}

payload.c

/*
 * https://curl.haxx.se/libcurl/c/smtp-mail.html
 *
 * gcc -Wall -Wextra -Werror -o payload payload.c; ./payload
 */
#include <stdio.h>
#include <string.h>

#define FROM_ADDR    "<[email protected]>"
#define TO_ADDR      "<[email protected]>"

#define FROM_MAIL "Sender Person " FROM_ADDR
#define TO_MAIL   "A Receiver " TO_ADDR

static const char *payload_text[] = {
        "Date: Mon, 29 Nov 2010 21:54:29 +1100\r\n",
        "To: " TO_MAIL "\r\n",
        "From: " FROM_MAIL "\r\n",
        "Message-ID: <dcd7cb36-11db-487a-9f3a-e652a9458efd@"
                "rfcpedant.example.org>\r\n",
        "Subject: SMTP example message\r\n",
        "\r\n", /* empty line to divide headers from body, see RFC5322 */
        "The body of the message starts here.\r\n",
        "\r\n",
        "It could be a lot of lines, could be MIME encoded, whatever.\r\n",
        "Check RFC5322.\r\n",
        NULL
};

int main(void)
{
        const char *data;

        for (size_t i = 0; i < (sizeof(payload_text) / sizeof(payload_text[0])); i++)
        {
                data = payload_text[i];
                if(data) {
                        printf("%s", data);
                }
        }

        return 0;
}

send_email.c

/*
 * https://curl.haxx.se/libcurl/c/smtp-mail.html
 *
 * gcc -o send_email send_email.c -luuid -lcurl; ./send_email
 */
#include <curl/curl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
#include <uuid/uuid.h>

#define FROM_ADDR    "<[email protected]>"
#define TO_ADDR      "<[email protected]>"

#define FROM_MAIL "Sender Person " FROM_ADDR
#define TO_MAIL   "A Receiver " TO_ADDR
#define SMTP_SERVER "smtp://mail.example.com"

struct message {
  size_t lines_read;
  char *data[];
};

static size_t read_callback(void *ptr, size_t size, size_t nmemb, void *userp)
{
  struct message *msg = (struct message*)userp;
  char *data;

  if((size == 0) || (nmemb == 0) || ((size*nmemb) < 1)) {
    return 0;
  }
  printf("lines_read: %d\n", msg->lines_read);

  data = msg->data[msg->lines_read];

  if(data) {
    size_t len = strlen(data);
    memcpy(ptr, data, len);
    msg->lines_read++;

    return len;
  }

  return 0;
}

static char *get_date(void)
{
  char *date;
  int len = 56;
  struct tm *tm_info;
  time_t timer;

  date = (char *) malloc(len * sizeof(char));
  time(&timer);
  tm_info = localtime(&timer);
  /* RFC 822 POSIX time stamp */
  strftime(date, len, "Date: %a, %d %b %Y %H:%M:%S %z\r\n", tm_info);
  return date;
}

static char *get_message_id(void)
{
  char domainname[64], hostname[64], msg_id[37], *message_id;
  int len = 192;
  size_t i;
  uuid_t uuid;

  message_id = (char *) malloc(len * sizeof(char));
  uuid_generate(uuid);

  for (i = 0; i < sizeof(uuid); i++) {
    if(i == 0) {
      snprintf(msg_id, sizeof(msg_id) - strlen(msg_id), "%02x", uuid[i]);
    } else if(i == 3 || i == 5 || i == 7 || i == 9) {
      snprintf(msg_id + strlen(msg_id), sizeof(msg_id) - strlen(msg_id) + 1, "%02x-", uuid[i]);
    } else {
      snprintf(msg_id + strlen(msg_id), sizeof(msg_id) - strlen(msg_id), "%02x", uuid[i]);
    }
  }

  getdomainname(domainname, sizeof(domainname));
  gethostname(hostname, sizeof(hostname));
  snprintf(message_id, len, "Message-ID: <%s@%s.%s>\r\n", msg_id, hostname, domainname);
  return message_id;
}

int main(void)
{
  CURL *curl;
  CURLcode res = CURLE_OK;
  struct curl_slist *recipients = NULL;
  int msg_len = 9;
  struct message *msg;

  msg = malloc(sizeof(struct message) + (msg_len * sizeof(char*)));
  msg->lines_read = 0;
  msg->data[0] = get_date();
  msg->data[1] = "To: " TO_MAIL "\r\n";
  msg->data[2] = "From: " FROM_MAIL "\r\n";
  msg->data[3] = get_message_id();
  msg->data[4] = "Subject: SMTP example message\r\n";
  msg->data[5] = "\r\n";
  msg->data[6] = "The body of the message starts here.\r\n";
  msg->data[7] = "\r\n";
  msg->data[8] = NULL;

  curl = curl_easy_init();
  if(curl) {
    curl_easy_setopt(curl, CURLOPT_USE_SSL, (long) CURLUSESSL_ALL);
    curl_easy_setopt(curl, CURLOPT_URL, SMTP_SERVER);
    curl_easy_setopt(curl, CURLOPT_MAIL_FROM, FROM_ADDR);
    recipients = curl_slist_append(recipients, TO_ADDR);
    curl_easy_setopt(curl, CURLOPT_MAIL_RCPT, recipients);
    curl_easy_setopt(curl, CURLOPT_READFUNCTION, read_callback);
    curl_easy_setopt(curl, CURLOPT_READDATA, msg);
    curl_easy_setopt(curl, CURLOPT_UPLOAD, 1L);
    curl_easy_setopt(curl, CURLOPT_VERBOSE, 1L);

    res = curl_easy_perform(curl);

    if(res != CURLE_OK)
      fprintf(stderr, "curl_easy_perform() failed: %s\n",
              curl_easy_strerror(res));

    curl_slist_free_all(recipients);
    curl_easy_cleanup(curl);
  }

  free(msg->data[0]);
  free(msg->data[3]);
  free(msg);
  return (int)res;
}