curl_easy_perform（）：： SSL_connect_error-如何解决？

Question

Sending messages to curl via multiple threads, and once a while I get one of the following errors.

curl_easy_perform(): failed ssl connect error. sschannel: next initializesecuritycontext failed: SEC_E_MESSAGE_ALTERED

curl_easy_perform(): failed ssl connect error. sschannel: next initializesecuritycontext failed: SEC_E_BUFFER_SMALL

As of now, I'm resolving this by re-sending the request. But why does this error happen ( Same request in the next 40 seconds works) and what can be done to avoid this.

Source code is written in C++. LibCurl was built using Microsoft visual studio 2010. Following is the code that invokes the curl library.

CURL *curl = curl_easy_init();
if (curl) {
    curl_easy_setopt(curl, CURLOPT_URL, "connection-page");
    curl_easy_setopt(curl, CURLOPT_POST, 1);
    curl_easy_setopt(curl, CURLOPT_POSTFIELDS, requestToPost.c_str());
    curl_easy_setopt(curl, CURLOPT_POSTFIELDSIZE, (long)strlen(requestToPost.c_str()));
    curl_easy_setopt(curl, CURLOPT_VERBOSE, 0L);
    curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headerInfo);
    curl_easy_setopt(curl, CURLOPT_HEADERFUNCTION, header_data);
    curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_data);
    curl_easy_setopt(curl, CURLOPT_ERRORBUFFER, curlErrorbuffer);
    std::stringstream resPonseInfo;
    std::stringstream headerResponse;
    curl_easy_setopt(curl, CURLOPT_WRITEDATA, &resPonseInfo);
    curl_easy_setopt(curl, CURLOPT_HEADERDATA, &headerResponse);
    curl_easy_setopt(curl, CURLOPT_HTTPAUTH, (long)CURLAUTH_ANY);
    res = curl_easy_perform(curl);
    if ((res != CURLE_OK))
    {
        fprintf(stderr, "curl_easy_perform() failed: %s\n", curl_easy_strerror(res));
        std::cout << "Request === " << std::endl;
        std::cout << requestToPost << std::endl;
        std::cout << "Error === " << std::endl;
        std::cout << curlErrorbuffer << std::endl;
        std::cout << "Header == " << std::endl << headerResponse.str() << std::endl;
        std::cout << "Response == " << std::endl << resPonseInfo.str() << std::endl;
    }
    else // if(res == CURLE_OK)
    {
        std::cout << "Response from the http post was successful " << std::endl;
        responseInfo = resPonseInfo.str();
    }
    curl_easy_cleanup(curl);
    curl = NULL;
}

Answer 1

"Sending messages to curl via multiple threads..." - given described symptoms most logical would be to assume a multi-threading related issue

• libcurl itself a thread safe, but not the shared data and handles used. You might want to consult this page: https://curl.haxx.se/libcurl/c/threadsafe.html and ensure your threads are not stepping each other toes

• one (possibly) easy way to confirm above hypothesis - try running your program in a single thread mode (if you can) and see if the issue reoccurs. If it does then it's definitely not threading.

• another way to verify (if above is not an option) put a thread mutex on your curl operation (even before you start setting up curl options) - see if that help avoiding those errors