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.