C/C++：libcurl smtp 邮件客户端（MUA）

客户端（MUA）"/>

C/C++：libcurl smtp 邮件客户端（MUA）

C/C++：libcurl smtp 邮件客户端（MUA）

最近在研究关于邮件的一些东西，需要实现个自己的邮件客户端，也就是类似于Foxmail那样的东西。

网上找了下感觉使用libcurl比较便捷靠谱（当然，还有esmtp等库）。

先放几个主要的libcurl官方的Sample，然后相关内容我晚点再整理下。

Sample 1：（最常用的最简单的，模拟MUA发送邮件到MTA）

/****************************************************************************                                  _   _ ____  _*  Project                     ___| | | |  _ \| |*                             / __| | | | |_) | |*                            | (__| |_| |  _ <| |___*                             \___|\___/|_| \_\_____|** Copyright (C) 1998 - 2017, Daniel Stenberg, <daniel@haxx.se>, et al.** This software is licensed as described in the file COPYING, which* you should have received as part of this distribution. The terms* are also available at .html.** You may opt to use, copy, modify, merge, publish, distribute and/or sell* copies of the Software, and permit persons to whom the Software is* furnished to do so, under the terms of the COPYING file.** This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY* KIND, either express or implied.****************************************************************************//* <DESC>* Send e-mail with SMTP* </DESC>*/#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>"
#define TO_ADDR      "<addressee@example>"
#define CC_ADDR      "<info@example>"#define FROM_MAIL "Sender Person " FROM_ADDR
#define TO_MAIL   "A Receiver " TO_ADDR
#define CC_MAIL   "John CC Smith " CC_ADDRstatic 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>\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");/* 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;
}

Sample 2：（+SSL）

/****************************************************************************                                  _   _ ____  _*  Project                     ___| | | |  _ \| |*                             / __| | | | |_) | |*                            | (__| |_| |  _ <| |___*                             \___|\___/|_| \_\_____|** Copyright (C) 1998 - 2016, Daniel Stenberg, <daniel@haxx.se>, et al.** This software is licensed as described in the file COPYING, which* you should have received as part of this distribution. The terms* are also available at .html.** You may opt to use, copy, modify, merge, publish, distribute and/or sell* copies of the Software, and permit persons to whom the Software is* furnished to do so, under the terms of the COPYING file.** This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY* KIND, either express or implied.****************************************************************************//* <DESC>* SMTP example using SSL* </DESC>*/#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. It builds on the smtp-mail.c example to add authentication* and, more importantly, transport security to protect the authentication* details from being snooped.** Note that this example requires libcurl 7.20.0 or above.*/#define FROM    "<sender@example>"
#define TO      "<addressee@example>"
#define CC      "<info@example>"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>\r\n","Subject: SMTP SSL 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) {/* Set username and password */curl_easy_setopt(curl, CURLOPT_USERNAME, "user");curl_easy_setopt(curl, CURLOPT_PASSWORD, "secret");/* This is the URL for your mailserver. Note the use of smtps:// rather* than smtp:// to request a SSL based connection. */curl_easy_setopt(curl, CURLOPT_URL, "smtps://mainserver.example");/* If you want to connect to a site who isn't using a certificate that is* signed by one of the certs in the CA bundle you have, you can skip the* verification of the server's certificate. This makes the connection* A LOT LESS SECURE.** If you have a CA cert for the server stored someplace else than in the* default bundle, then the CURLOPT_CAPATH option might come handy for* you. */
#ifdef SKIP_PEER_VERIFICATIONcurl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER, 0L);
#endif/* If the site you're connecting to uses a different host name that what* they have mentioned in their server certificate's commonName (or* subjectAltName) fields, libcurl will refuse to connect. You can skip* this check, but this will make the connection less secure. */
#ifdef SKIP_HOSTNAME_VERIFICATIONcurl_easy_setopt(curl, CURLOPT_SSL_VERIFYHOST, 0L);
#endif/* 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);/* Since the traffic will be encrypted, it is very useful to turn on debug* information within libcurl to see what is happening during the* transfer */curl_easy_setopt(curl, CURLOPT_VERBOSE, 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);/* Always cleanup */curl_easy_cleanup(curl);}return (int)res;
}

Sample 3：（+TLS）

/****************************************************************************                                  _   _ ____  _*  Project                     ___| | | |  _ \| |*                             / __| | | | |_) | |*                            | (__| |_| |  _ <| |___*                             \___|\___/|_| \_\_____|** Copyright (C) 1998 - 2016, Daniel Stenberg, <daniel@haxx.se>, et al.** This software is licensed as described in the file COPYING, which* you should have received as part of this distribution. The terms* are also available at .html.** You may opt to use, copy, modify, merge, publish, distribute and/or sell* copies of the Software, and permit persons to whom the Software is* furnished to do so, under the terms of the COPYING file.** This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY* KIND, either express or implied.****************************************************************************//* <DESC>* SMTP example using TLS* </DESC>*/#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. It builds on the smtp-mail.c example to add authentication* and, more importantly, transport security to protect the authentication* details from being snooped.** Note that this example requires libcurl 7.20.0 or above.*/#define FROM    "<sender@example>"
#define TO      "<addressee@example>"
#define CC      "<info@example>"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>\r\n","Subject: SMTP TLS 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) {/* Set username and password */curl_easy_setopt(curl, CURLOPT_USERNAME, "user");curl_easy_setopt(curl, CURLOPT_PASSWORD, "secret");/* This is the URL for your mailserver. Note the use of port 587 here,* instead of the normal SMTP port (25). Port 587 is commonly used for* secure mail submission (see RFC4403), but you should use whatever* matches your server configuration. */curl_easy_setopt(curl, CURLOPT_URL, "smtp://mainserver.example:587");/* In this example, we'll start with a plain text connection, and upgrade* to Transport Layer Security (TLS) using the STARTTLS command. Be careful* of using CURLUSESSL_TRY here, because if TLS upgrade fails, the transfer* will continue anyway - see the security discussion in the libcurl* tutorial for more details. */curl_easy_setopt(curl, CURLOPT_USE_SSL, (long)CURLUSESSL_ALL);/* If your server doesn't have a valid certificate, then you can disable* part of the Transport Layer Security protection by setting the* CURLOPT_SSL_VERIFYPEER and CURLOPT_SSL_VERIFYHOST options to 0 (false).*   curl_easy_setopt(curl, CURLOPT_SSL_VERIFYPEER, 0L);*   curl_easy_setopt(curl, CURLOPT_SSL_VERIFYHOST, 0L);* That is, in general, a bad idea. It is still better than sending your* authentication details in plain text though.  Instead, you should get* the issuer certificate (or the host certificate if the certificate is* self-signed) and add it to the set of certificates that are known to* libcurl using CURLOPT_CAINFO and/or CURLOPT_CAPATH. See docs/SSLCERTS* for more information. */curl_easy_setopt(curl, CURLOPT_CAINFO, "/path/to/certificate.pem");/* 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);/* Since the traffic will be encrypted, it is very useful to turn on debug* information within libcurl to see what is happening during the transfer.*/curl_easy_setopt(curl, CURLOPT_VERBOSE, 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);/* Always cleanup */curl_easy_cleanup(curl);}return (int)res;
}

官方资料：

1）.html
2）.html
3）.html
4）.html

源文件：

1）.c
2）.c
3）.c

资料搬运工~

今天晚点我再整理下具体遇到的问题~