How to add timeout to an XMLRPC-C client

XMLRPC-C is very efficient if you need a remote process call protocol.

I happen to need to add timeout limit to an XMLRPC client based on C, but I went into a problem: the timeout does not work as expected.

I started with an example code in the xmlrpc-c package located at:
xmlrpc-c-1.42.99/src/examples/cpp/sample_add_client_complex.cpp (as shown in the Reference at the end of this post)
, but found that when I set the timeout less than 1000, the timeout basically does not work at all, i.e., no timeout could happen.

After looking into the codes of xmlrpc-c, I found the trick. The xmlrpc-c has a source file at:
xmlrpc-c-1.42.99/lib/curl_transport/curltransaction.c
which actually sets the timeout in the following function:

static void
setCurlTimeout(CURL *       const curlSessionP ATTR_UNUSED,
               unsigned int const timeoutMs ATTR_UNUSED) {

#if HAVE_CURL_NOSIGNAL
    unsigned int const timeoutSec = (timeoutMs + 999)/1000;

    assert((long)timeoutSec == (int)timeoutSec);
        /* Calling requirement */
    curl_easy_setopt(curlSessionP, CURLOPT_TIMEOUT, (long)timeoutSec);
#else
    /* Caller should not have called us */
    abort();
#endif
}

You can see that it actually sets the CURLOPT_TIMEOUT option of a curl connection, while CURLOPT_TIMEOUT is in seconds not milliseconds. If I originally set the timeout of xmlrpc client as 600ms, this function would convert it into 1 second, which is definitely not what I want.

One quick fix is to use my another post as follows:

static void
setCurlTimeout(CURL *       const curlSessionP ATTR_UNUSED,
               unsigned int const timeoutMs ATTR_UNUSED) {

#if HAVE_CURL_NOSIGNAL
    curl_easy_setopt(curlSessionP, CURLOPT_NOSIGNAL, 1);
    curl_easy_setopt(curlSessionP, CURLOPT_TIMEOUT_MS, timeoutMs);
#else
    /* Caller should not have called us */
    abort();
#endif
}

Reference:

// taken from xmlrpc-c-1.42.99/examples/cpp/sample_add_client_complex.cp
/*=============================================================================
                        sample_add_client_complex.cpp
===============================================================================
  This is an example of an XML-RPC client that uses XML-RPC for C/C++
  (Xmlrpc-c).

  In particular, it uses the complex lower-level interface that gives you
  lots of flexibility but requires lots of code.  Also see
  xmlrpc_sample_add_server, which does the same thing as this program,
  but with much simpler code because it uses a simpler facility of
  Xmlrpc-c.

  This program actually gains nothing from using the more difficult
  facility.  It is for demonstration purposes.
=============================================================================*/

#include
#include
#include
#include

using namespace std;

#include
#include
#include

int
main(int argc, char **) {

    if (argc-1 > 0) {
        cerr << "This program has no arguments" << endl;
        exit(1);
    }

    try {
        xmlrpc_c::clientXmlTransport_curl myTransport(
            xmlrpc_c::clientXmlTransport_curl::constrOpt()
            .timeout(10000)  // milliseconds
            .user_agent("sample_add/1.0"));

        xmlrpc_c::client_xml myClient(&myTransport);

        string const methodName("sample.add");

        xmlrpc_c::paramList sampleAddParms;
        sampleAddParms.add(xmlrpc_c::value_int(5));
        sampleAddParms.add(xmlrpc_c::value_int(7));

        xmlrpc_c::rpcPtr myRpcP(methodName, sampleAddParms);

        string const serverUrl("http://localhost:8080/RPC2");

        xmlrpc_c::carriageParm_curl0 myCarriageParm(serverUrl);

        myRpcP->call(&myClient, &myCarriageParm);

        assert(myRpcP->isFinished());

        int const sum(xmlrpc_c::value_int(myRpcP->getResult()));
            // Assume the method returned an integer; throws error if not

        cout << "Result of RPC (sum of 5 and 7): " << sum << endl;

    } catch (exception const& e) {
        cerr << "Client threw error: " << e.what() << endl;
    } catch (...) {
        cerr << "Client threw unexpected error." << endl;
    }

    return 0;
}