curl - send email

#include <ctime>
#include <cstring>
#include <curl/curl.h>

std::string dateTimeNow();
std::string generateMessageId();

std::string setPayloadText(const std::string &to,
                           const std::string &from,
                           const std::string &cc,
                           const std::string &nameFrom,
                           const std::string &subject,
                           const std::string &body)
{
    std::string ret;

    ret += "Date: "  + dateTimeNow() + ">\r\n";
    ret += "To: <"   + to   + ">\r\n";
    ret += "From: <" + from + "> (" + nameFrom + ")\r\n";
    ret += "Cc: <"   + cc   + "> (" + nameFrom + ")\r\n";
    ret += "Message-ID: <"  + generateMessageId() + "@" + from.substr(from.find('@') + 1) + ">\r\n";
    ret += "Subject: "      + subject + "\r\n";
    ret += "\r\n";
    ret += body + "\r\n";
    ret += "\r\n";
    ret += "\r\n"; // "It could be a lot of lines, could be MIME encoded, whatever.\r\n";
    ret += "\r\n"; // "Check RFC5322.\r\n";

    return ret;
}

std::string dateTimeNow()
{
    static const char *DAY_NAMES  [] = { "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat" };
    static const char *MONTH_NAMES[] = { "Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec" };

    const int RFC1123_TIME_LEN = 29;
    time_t t;
    struct tm tm;

    std::string ret;
    ret.resize(RFC1123_TIME_LEN);

    time(&t);
    gmtime_s(&tm, &t);

    strftime(&ret[0], RFC1123_TIME_LEN + 1, "---, %d --- %Y %H:%M:%S GMT", &tm);
    memcpy(&ret[0], DAY_NAMES  [tm.tm_wday], 3);
    memcpy(&ret[8], MONTH_NAMES[tm.tm_mon],  3);

    return ret;
}

std::string generateMessageId()
{
    const int MESSAGE_ID_LEN = 37;
    time_t t;
    struct tm tm;

    std::string ret;
    ret.resize(15);

    time(&t);
    gmtime_s(&tm, &t);

    strftime(const_cast<char *>(ret.c_str()),
             MESSAGE_ID_LEN,
             "%Y%m%d%H%M%S.",
             &tm);

    ret.reserve(MESSAGE_ID_LEN);

    static const char alphanum[] =
            "0123456789"
            "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
            "abcdefghijklmnopqrstuvwxyz";

    while (ret.size() < MESSAGE_ID_LEN) {
        ret += alphanum[rand() % (sizeof(alphanum) - 1)];
    }

    return ret;
}

struct uploadStatus { int linesRead; };

struct StringData
{
    std::string msg;
    size_t bytesleft;

    StringData(std::string &&m) : msg{ m }, bytesleft{ msg.size() } {}
    StringData(std::string  &m) = delete;
};

size_t payloadSource(void *ptr, size_t size, size_t nmemb, void *userp)
{
    StringData *text = reinterpret_cast<StringData *>(userp);

    if ((size == 0) || (nmemb == 0) || ((size*nmemb) < 1) || (text->bytesleft == 0)) {
        return 0;
    }

    if ((nmemb * size) >= text->msg.size()) {
        text->bytesleft = 0;
        return text->msg.copy(reinterpret_cast<char *>(ptr), text->msg.size());
    }

    return 0;
}


CURLcode sendEmail(const std::string &to,
                   const std::string &from,
                   const std::string &cc,
                   const std::string &nameFrom,
                   const std::string &subject,
                   const std::string &body,
                   const std::string &url,
                   const std::string &password)
{
    CURLcode ret = CURLE_OK;

    struct curl_slist *recipients = NULL;

    CURL *curl = curl_easy_init();

    StringData textData { setPayloadText(to, from, cc, nameFrom, subject, body) };

    if (curl) {
        curl_easy_setopt(curl, CURLOPT_USERNAME,     from    .c_str());
        curl_easy_setopt(curl, CURLOPT_PASSWORD,     password.c_str());
        curl_easy_setopt(curl, CURLOPT_URL,          url     .c_str());

        curl_easy_setopt(curl, CURLOPT_USE_SSL,      (long)CURLUSESSL_ALL);
        //curl_easy_setopt(curl, CURLOPT_CAINFO, "/path/to/certificate.pem");

        curl_easy_setopt(curl, CURLOPT_MAIL_FROM,    ("<" + from + ">").c_str());
        recipients = curl_slist_append(recipients,   ("<" + to   + ">").c_str());
        recipients = curl_slist_append(recipients,   ("<" + cc   + ">").c_str());

        curl_easy_setopt(curl, CURLOPT_MAIL_RCPT,    recipients);
        curl_easy_setopt(curl, CURLOPT_READFUNCTION, payloadSource);
        curl_easy_setopt(curl, CURLOPT_READDATA,     &textData);
        curl_easy_setopt(curl, CURLOPT_UPLOAD,       1L);
        curl_easy_setopt(curl, CURLOPT_VERBOSE,      1L);

        ret = curl_easy_perform(curl);

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

        curl_slist_free_all(recipients);
        curl_easy_cleanup(curl);
    }

    return ret;
}