Using libcurl to send an email in C++ - c++

Question

I'm following a libcurl sample code and trying to use it to send an email to myself, but there's a few things I'm not quite understanding...
#include <stdio.h>
#include <string.h>
#include <curl/curl.h>
/*
* For an SMTP example using the multi interface please see smtp-multi.c.
*/
/* The libcurl options want plain addresses, the viewable headers in the mail
* can very well get a full name as well.
*/
#define FROM_ADDR "<sender#example.org>"
#define TO_ADDR "<addressee#example.net>"
#define CC_ADDR "<info#example.org>"
#define FROM_MAIL "Sender Person " FROM_ADDR
#define TO_MAIL "A Receiver " TO_ADDR
#define CC_MAIL "John CC Smith " CC_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",
"Cc: " CC_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
};
struct upload_status {
int lines_read;
};
static size_t payload_source(void *ptr, size_t size, size_t nmemb, void *userp)
{
struct upload_status *upload_ctx = (struct upload_status *)userp;
const char *data;
if((size == 0) || (nmemb == 0) || ((size*nmemb) < 1)) {
return 0;
}
data = payload_text[upload_ctx->lines_read];
if(data) {
size_t len = strlen(data);
memcpy(ptr, data, len);
upload_ctx->lines_read++;
return len;
}
return 0;
}
int main(void)
{
CURL *curl;
CURLcode res = CURLE_OK;
struct curl_slist *recipients = NULL;
struct upload_status upload_ctx;
upload_ctx.lines_read = 0;
curl = curl_easy_init();
if(curl) {
/* This is the URL for your mailserver */
curl_easy_setopt(curl, CURLOPT_URL, "smtp://mail.example.com");
/* Note that this option isn't strictly required, omitting it will result
* in libcurl sending the MAIL FROM command with empty sender data. All
* autoresponses should have an empty reverse-path, and should be directed
* to the address in the reverse-path which triggered them. Otherwise,
* they could cause an endless loop. See RFC 5321 Section 4.5.5 for more
* details.
*/
curl_easy_setopt(curl, CURLOPT_MAIL_FROM, FROM_ADDR);
/* Add two recipients, in this particular case they correspond to the
* To: and Cc: addressees in the header, but they could be any kind of
* recipient. */
recipients = curl_slist_append(recipients, TO_ADDR);
recipients = curl_slist_append(recipients, CC_ADDR);
curl_easy_setopt(curl, CURLOPT_MAIL_RCPT, recipients);
/* We're using a callback function to specify the payload (the headers and
* body of the message). You could just use the CURLOPT_READDATA option to
* specify a FILE pointer to read from. */
curl_easy_setopt(curl, CURLOPT_READFUNCTION, payload_source);
curl_easy_setopt(curl, CURLOPT_READDATA, &upload_ctx);
curl_easy_setopt(curl, CURLOPT_UPLOAD, 1L);
/* Send the message */
res = curl_easy_perform(curl);
/* Check for errors */
if(res != CURLE_OK)
fprintf(stderr, "curl_easy_perform() failed: %s\n",
curl_easy_strerror(res));
/* Free the list of recipients */
curl_slist_free_all(recipients);
/* curl won't send the QUIT command until you call cleanup, so you should
* be able to re-use this connection for additional messages (setting
* CURLOPT_MAIL_FROM and CURLOPT_MAIL_RCPT as required, and calling
* curl_easy_perform() again. It may not be a good idea to keep the
* connection open for a very long time though (more than a few minutes
* may result in the server timing out the connection), and you do want to
* clean up in the end.
*/
curl_easy_cleanup(curl);
}
return (int)res;
}
Now it looks like for the first curl_easy line, I'd need to change it to
curl_easy_setopt(curl, CURLOPT_URL, "smtp.gmail.com");
If I was using gmail, right? And since this is for outgoing mail, I don't need to worry about what the user is using as long as my outgoing mail address is a gmail address?
Going a little out of order...
recipients = curl_slist_append(recipients, useremail);
In this case, it would be my email. All I need to do is replace this with the receiving email correct? Well what about the sender?
curl_easy_setopt(curl, CURLOPT_MAIL_FROM, myemail);
I'm guessing that likewise, I would need to change this to my email. But it feels like it's missing something. Surely I can't just tell this program to send an email with my address without some sort of authorization, right? But I don't see anywhere on the code where I would need to supply my password (obviously I wouldn't want it hard coded, but that's an issue for later), so how would this work?
For the time being, these are the only lines I would need to change (besides a specific message), right? Am I going about this the right way? Is there more I would need to do for this to work? And how does the authorization work?
EDIT: I have made updates based on what I think would work, as well as the suggestion given for a username and password. I currently have this error:
curl_easy_perform() failed: Failed sending data to the peer
Unfortunately, it's not too specific on what went wrong. This is the new version:
#include <stdio.h>
#include <string.h>
#include <curl/curl.h>
/*
* For an SMTP example using the multi interface please see smtp-multi.c.
*/
/* The libcurl options want plain addresses, the viewable headers in the mail
* can very well get a full name as well.
*/
#define FROM_ADDR "<sender#example.org>"
#define TO_ADDR "<addressee#example.net>"
#define CC_ADDR "<info#example.org>"
#define FROM_MAIL "Sender Person " FROM_ADDR
#define TO_MAIL "A Receiver " TO_ADDR
#define CC_MAIL "John CC Smith " CC_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",
"Cc: " CC_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
};
struct upload_status {
int lines_read;
};
static size_t payload_source(void *ptr, size_t size, size_t nmemb, void *userp)
{
struct upload_status *upload_ctx = (struct upload_status *)userp;
const char *data;
if((size == 0) || (nmemb == 0) || ((size*nmemb) < 1)) {
return 0;
}
data = payload_text[upload_ctx->lines_read];
if(data) {
size_t len = strlen(data);
memcpy(ptr, data, len);
upload_ctx->lines_read++;
return len;
}
return 0;
}
int main(void)
{
CURL *curl;
CURLcode res = CURLE_OK;
struct curl_slist *recipients = NULL;
struct upload_status upload_ctx;
upload_ctx.lines_read = 0;
curl = curl_easy_init();
if(curl) {
/* This is the URL for your mailserver */
curl_easy_setopt(curl, CURLOPT_URL, "smtp.gmail.com");
/* Note that this option isn't strictly required, omitting it will result
* in libcurl sending the MAIL FROM command with empty sender data. All
* autoresponses should have an empty reverse-path, and should be directed
* to the address in the reverse-path which triggered them. Otherwise,
* they could cause an endless loop. See RFC 5321 Section 4.5.5 for more
* details.
*/
curl_easy_setopt(curl, CURLOPT_MAIL_FROM, "myemail#gmail.com");
/* Add two recipients, in this particular case they correspond to the
* To: and Cc: addressees in the header, but they could be any kind of
* recipient. */
recipients = curl_slist_append(recipients, "myemail#gmail.com");
recipients = curl_slist_append(recipients, CC_ADDR);
curl_easy_setopt(curl, CURLOPT_USERNAME, "myemail#gmail.com");
curl_easy_setopt(curl, CURLOPT_PASSWORD, "mypassword");
curl_easy_setopt(curl, CURLOPT_MAIL_RCPT, recipients);
/* We're using a callback function to specify the payload (the headers and
* body of the message). You could just use the CURLOPT_READDATA option to
* specify a FILE pointer to read from. */
curl_easy_setopt(curl, CURLOPT_READFUNCTION, payload_source);
curl_easy_setopt(curl, CURLOPT_READDATA, &upload_ctx);
curl_easy_setopt(curl, CURLOPT_UPLOAD, 1L);
/* Send the message */
res = curl_easy_perform(curl);
/* Check for errors */
if(res != CURLE_OK)
fprintf(stderr, "curl_easy_perform() failed: %s\n",
curl_easy_strerror(res));
/* Free the list of recipients */
curl_slist_free_all(recipients);
/* curl won't send the QUIT command until you call cleanup, so you should
* be able to re-use this connection for additional messages (setting
* CURLOPT_MAIL_FROM and CURLOPT_MAIL_RCPT as required, and calling
* curl_easy_perform() again. It may not be a good idea to keep the
* connection open for a very long time though (more than a few minutes
* may result in the server timing out the connection), and you do want to
* clean up in the end.
*/
curl_easy_cleanup(curl);
}
return (int)res;
}
I haven't filled in CC_MAIL, but is this truly necessary? The actual name of the personal is generally automatically filled out by Google when you send an email.

Answer 1

You can set it below
curl_easy_setopt(curl, CURLOPT_USERNAME, USERNAME);
curl_easy_setopt(curl, CURLOPT_PASSWORD, PASSWORD);
Please refer to the example on curl (tag: curl-7_34_0)
https://github.com/curl/curl/blob/curl-7_34_0/docs/examples/smtp-multi.c
Recommended reference smtp-tls.c, using TLS
https://github.com/curl/curl/blob/master/docs/examples/smtp-tls.c

Answer 2

I am also confused whether we have to use that "<" sign or not while defining that
#define CC_ADDR "<info#example.org>"
section for eg.
Do I have to use #define CC_ADDR "anything" or I have to use #define CC_ADDR "<anything>"
I have one information regarding writing the server mail, we can use smtp.gmail.com:587 and it will work. Note that : used here is used to specify the specific port address to the mail server.