Hello World To Web Services With C And C++

Once you have a web service, you can write clients to invoke that service from any language, mostly with the help of a framework written in to that particular language. When it comes to C, the most popular choice is Apache Axis2/C framework. When you are using Axis2/C to write web service clients, you need to learn about AXIOM which is a easy to use high performing XML model and the service client API which can be used to actually invoke the service. Lets look at the code.

#include <stdio.h>
#include <axiom.h>
#include <axis2_util.h>
#include <axiom_soap.h>
#include <axis2_client.h>

axiom_node_t *build_om_payload_for_helloworld_svc(
    const axutil_env_t * env);

int
main()
{
    const axutil_env_t *env = NULL;
    const axis2_char_t *address = NULL;
    axis2_endpoint_ref_t *endpoint_ref = NULL;
    axis2_options_t *options = NULL;
    const axis2_char_t *client_home = NULL;
    axis2_svc_client_t *svc_client = NULL;
    axiom_node_t *payload = NULL;
    axiom_node_t *ret_node = NULL;

    /* Set up the environment */
    env = axutil_env_create_all("helloworld.log", AXIS2_LOG_LEVEL_TRACE);

    /* Set end point reference of helloworld service */
    address = "http://localhost:9090/axis2/services/helloworld";

    /* Create EPR with given address */
    endpoint_ref = axis2_endpoint_ref_create(env, address);

    /* Setup options */
    options = axis2_options_create(env);
    axis2_options_set_to(options, env, endpoint_ref);
    axis2_options_set_action(options, env,
                             "http://ws.apache.org/axis2/c/samples/helloworldString");

    /* Set up deploy folder. It is from the deploy folder, the configuration is picked up
     * using the axis2.xml file. You need to set the AXIS2C_HOME variable to the axis2/c
     * installed dir.
     */
    client_home = AXIS2_GETENV("AXIS2C_HOME");
    if (!client_home || !strcmp(client_home, ""))
        client_home = "../..";

    /* Create service client */
    svc_client = axis2_svc_client_create(env, client_home);
    if (!svc_client)
    {
        /* reporting the error */
        printf
            ("Error creating service client, Please check AXIS2C_HOME again\\n");
        AXIS2_LOG_ERROR(env->log, AXIS2_LOG_SI,
                        "Stub invoke FAILED: Error code:" " %d :: %s",
                        env->error->error_number,
                        AXIS2_ERROR_GET_MESSAGE(env->error));
        return -1;
    }

    /* Set service client options */
    axis2_svc_client_set_options(svc_client, env, options);

    /* Build the SOAP request message payload using OM API. */
    payload = build_om_payload_for_helloworld_svc(env);

    /* Send request */
    ret_node = axis2_svc_client_send_receive(svc_client, env, payload);

    if (ret_node)
    {
        /* extracting out the content from the response */
        axis2_char_t *om_str = NULL;
        om_str = axiom_node_to_string(ret_node, env);
        if (om_str)
            printf("\\nReceived OM : %s\\n", om_str);
        printf("\\nhelloworld client invoke SUCCESSFUL!\\n");

        AXIS2_FREE(env->allocator, om_str);
        ret_node = NULL;
    }
    else
    {
        AXIS2_LOG_ERROR(env->log, AXIS2_LOG_SI,
                        "Stub invoke FAILED: Error code:" " %d :: %s",
                        env->error->error_number,
                        AXIS2_ERROR_GET_MESSAGE(env->error));
        printf("helloworld client invoke FAILED!\\n");
    }

    /* freeing the allocated memory */
    if (svc_client)
    {
        axis2_svc_client_free(svc_client, env);
        svc_client = NULL;
    }

    if (env)
    {
        axutil_env_free((axutil_env_t *) env);
        env = NULL;
    }

    return 0;
}

Here is the implementation of the “build_om_payload_for_helloworld_svc” function that build the request SOAP message using Axiom/C. Note that axiom_element and axiom_node has one to one association. We use node to to navigate the XML, where as axiom_element to store the data.

/* build SOAP request message content using OM
           <ns1:greet xmlns:ns1="http://ws.apache.org/axis2/services/helloworld">
                <text>Hello World</text>
           </ns1:greet>
*/
axiom_node_t *
build_om_payload_for_helloworld_svc(
    const axutil_env_t * env)
{
    axiom_node_t *helloworld_om_node = NULL;
    axiom_element_t *helloworld_om_ele = NULL;
    axiom_node_t *text_om_node = NULL;
    axiom_element_t *text_om_ele = NULL;
    axiom_namespace_t *ns1 = NULL;
    axis2_char_t *om_str = NULL;

    ns1 =
       axiom_namespace_create(env, "http://ws.apache.org/axis2/services/helloworld",
                               "ns1");
    helloworld_om_ele =
        axiom_element_create(env, NULL, "greet", ns1, &helloworld_om_node);
    text_om_ele =
        axiom_element_create(env, helloworld_om_node, "text", NULL, &text_om_node);
    axiom_element_set_text(text_om_ele, env, "Hello World!", text_om_node);
    om_str = axiom_node_to_string(helloworld_om_node, env);

    if (om_str)
    {
        printf("\\nSending OM : %s\\n", om_str);
        AXIS2_FREE(env->allocator, om_str);
        om_str = NULL;
    }
    return helloworld_om_node;
}

So lets see how the same thing is done with C++. For C++ we use WSO2 WSF/C++

#include <stdio.h>
#include <WSSOAPClient.h>
#include <OMElement.h>
#include <iostream>
#include <AxisFault.h>
using namespace std;
using namespace wso2wsf;

OMElement build_om_payload_for_helloworld_svc();

int main()
{
    WSSOAPClient * sc = new WSSOAPClient("http://localhost:9090/axis2/services/helloworld");
    sc->initializeClient("helloworld_blocking.log", AXIS2_LOG_LEVEL_TRACE);
    {
        /* generating the payload */
        OMElement * payload = build_om_payload_for_helloworld_svc();

        OMElement * response;
        try
        {
            /* invoking the web service */
            response = sc->request(payload, "http://ws.apache.org/axis2/c/samples/helloworldString");

            /* printing the response */
            if (response)
            {
                cout << endl << "Response: " << response << endl;
            }
        }

        /* handling the fault */
        catch (AxisFault & e)
        {
            if (sc->getLastSOAPFault())
            {
                cout << endl << "Response: " << sc->getLastSOAPFault() << endl;
            }
            else
            {
                cout << endl << "Response: " << e << endl;
            }
        }
        delete payload;
    }
    delete sc;
}

You can see lines of code is reduced a lot. And you can see it from the code to build the request XML as well.

/* building the request soap message
   <ns1:greet xmlns:ns1="http://ws.apache.org/axis2/services/helloworld">
        <text>Hello World</text>
   </ns1:greet>
 */
OMElement build_om_payload_for_helloworld_svc()
{
    OMNamespace * ns = new OMNamespace("http://ws.apache.org/axis2/services/helloworld", "ns1");
    OMElement * payload = new OMElement(NULL,"greet", ns);
    OMElement * child = new OMElement(payload,"text", NULL);
    child->setText("Hello World!");

    return payload;
}

WSF/C++ is build on top of Axis2/C. You can see the WSF/C++ API is designed very carefully to make it easy to use without breaking the flexibility provided in the C API. So C++ developers can straightaway use WSF/C++ to develop their web service consumers. Anyway Axis2/C API still has the power of embedding easily in to scripting languages (Like it is done in WSF/PHP, WSF/Ruby) and probably deploy in legacy systems that doesn’t support C++ compiled binaries. So you have the options to select the most sutiable one for your application.