c/c++ curl smtp 发送邮件太长导致段错误的问题

在Linux下，使用
libcurl 库发送邮件，当邮件长度超过16000字节时（具体应该为 16000 ~ 17000之间），

 执行到 curl_easy_perform(curl); 会发生段错误 Segmentation fault

下面看一下 curl 提供的 smtp 示例：

#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 example 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;
}

段错误原因：payload_text 数组其中任一个指针指向的字符串长度大于16000（之前程序在组合邮件内容时，其中一个指针指向了整个内容）
解决方法：把过长的邮件内容拆成多个字符串

深层原因：可能和 curl 实现有关系（需要深入研究）