使用C语言Curl程序通过Gmail发邮件遇SSL证书错误求助

我想用基于Curl的C语言程序通过Gmail发送邮件，但即便指定了SSL选项，运行时还是出现SSL错误。以下是相关代码、编译脚本和不同尝试下的错误信息：

错误信息 #

• 初始错误：SSL peer certificate or SSH remote key was not OK
• 将cacert.pem路径设置到CURLOPT_SSLCERT时，出现：Problem with the local SSL certificate 和 unable to set private key file: 'cacert.pem' type PEM
• 将curl-ca-bundle.crt路径设置到该选项时，出现类似的本地SSL证书问题和私钥文件错误

C语言代码 #

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

static size_t payload_source(char *ptr, size_t size, size_t nmemb, void *userp);

typedef struct {
  size_t bytes_read;
} upload_status;

char *from_addr = "<sender@gmail.com>";
char *to_addr = "<receiver@gmail.com>";

static const char *payload_text =
  "To: " "<receiver@gmail.com>" "\r\n"
  "From: " "<sender@gmail.com>" "\r\n"
  "Cc: " "" "\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 RFC 5322 */
  "This message is a test\r\n"
  "\r\n"
  "It could be a lot of lines, could be MIME encoded, whatever.\r\n"
  "Check RFC 5322.\r\n";

int main(void)
{
    CURL *curl;
    CURLcode res = CURLE_OK;
    struct curl_slist *recipients = NULL;
    upload_status upload = { 0 };
    printf("This is a curl program\n");
    
    curl = curl_easy_init();

    if(!curl)
    {
        printf("Curl wasn't initialized!\n");
        return 1;
    }

    printf("Curl was initialized!\n");

    curl_easy_setopt(curl, CURLOPT_URL, "smtps://smtp.gmail.com:465");

    curl_easy_setopt(curl, CURLOPT_VERBOSE, 1L);
    curl_easy_setopt(curl, CURLOPT_MAIL_FROM, from_addr);

    recipients = curl_slist_append(recipients, to_addr);
    curl_easy_setopt(curl, CURLOPT_MAIL_RCPT, recipients);

    curl_easy_setopt(curl, CURLOPT_USE_SSL, 1L);
    curl_easy_setopt(curl, CURLOPT_USERNAME, from_addr);
    curl_easy_setopt(curl, CURLOPT_PASSWORD, "password");

    curl_easy_setopt(curl, CURLOPT_READFUNCTION, payload_source);
    curl_easy_setopt(curl, CURLOPT_READDATA, &upload);
    curl_easy_setopt(curl, CURLOPT_UPLOAD, 1L);

    curl_easy_setopt(curl, CURLOPT_HTTPAUTH, (long)CURLAUTH_ANY);

    printf("Sending email...\n");
    res = curl_easy_perform(curl);
    printf("%d %d\n", (int)res, (int)CURLE_OK);

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

    curl_slist_free_all(recipients);
    curl_easy_cleanup(curl);

    return (int)res;
}

static size_t payload_source(char *ptr, size_t size, size_t nmemb, void *userp)
{
    upload_status *upload_ctx = (upload_status *)userp;
    const char *data;
    size_t room = size * nmemb;

    if((size == 0) || (nmemb == 0) || ((size*nmemb) < 1)) {
    return 0;
    }

    data = &payload_text[upload_ctx->bytes_read];

    if(data) {
    size_t len = strlen(data);
    if(room < len)
        len = room;
    memcpy(ptr, data, len);
    upload_ctx->bytes_read += len;

    return len;
    }

    return 0;
}

编译脚本run.bat #

@echo off
del main.exe
cls
gcc -I src/include -L src/lib -o main *.c -lcurl -lssl -lssh2 -lbrotlicommon -lbrotlidec -lcrypto -lnghttp2 -lnghttp3 -lngtcp2_crypto_quictls -lngtcp2 -lz -lzstd
main

内容的提问来源于stack exchange，提问作者Artiom Kvartiuk