在C中更改libcurl中的主机名

Question

我尝试使用libcurl SMTP，这个例子一切正常：http://curl.haxx.se/libcurl/c/smtp-mail.html

#include <stdio.h>
#include <string.h>
#include <curl/curl.h>

/* This is a simple example showing how to send mail using libcurl's SMTP
 * capabilities. For an exmaple of using the multi interface please see
 * smtp-multi.c.
 *
 * Note that this example requires libcurl 7.20.0 or above.
 */ 

#define FROM    "<sender@example.org>"
#define TO      "<addressee@example.net>"
#define CC      "<info@example.org>"

static const char *payload_text[] = {
  "Date: Mon, 29 Nov 2010 21:54:29 +1100\r\n",
  "To: " TO "\r\n",
  "From: " FROM "(Example User)\r\n",
  "Cc: " CC "(Another example User)\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);

    /* 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);
    recipients = curl_slist_append(recipients, CC);
    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;
}

我发送的电子邮件如下：

Return-Path: ...
Received: from Hostname (ip)
...
Date:...
Subject:...
...

但是我如何从libcurl更改自己的主机名。是否可以在标题中发送它或类似的东西？或者我只能通过添加/ etc / hostname文件中的行来改变它？