diff --git a/src/csoap/common.cc b/src/csoap/common.cc
index 8f49afc..f616075 100644
--- a/src/csoap/common.cc
+++ b/src/csoap/common.cc
@@ -18,8 +18,8 @@ const std::string kTextXmlUtf8 = "text/xml; charset=utf-8";
 
 ////////////////////////////////////////////////////////////////////////////////
 
-const char* GetErrorMessage(ErrorCode error_code) {
-  switch (error_code) {
+const char* GetErrorMessage(Error error) {
+  switch (error) {
     case kHostResolveError:
       return "Cannot resolve the host.";
 
diff --git a/src/csoap/common.h b/src/csoap/common.h
index f1042f1..d9e4bbc 100644
--- a/src/csoap/common.h
+++ b/src/csoap/common.h
@@ -35,7 +35,8 @@ const std::size_t kInvalidLength = std::string::npos;
 
 ////////////////////////////////////////////////////////////////////////////////
 
-enum ErrorCode {
+// Error codes.
+enum Error {
   kNoError = 0,  // OK
 
   kHostResolveError,
@@ -59,7 +60,7 @@ enum ErrorCode {
 };
 
 // Return a descriptive message for the given error code.
-const char* GetErrorMessage(ErrorCode error_code);
+const char* GetErrorMessage(Error error);
 
 ////////////////////////////////////////////////////////////////////////////////
 
diff --git a/src/csoap/connection.cc b/src/csoap/connection.cc
index 292cbf4..e8a6b28 100644
--- a/src/csoap/connection.cc
+++ b/src/csoap/connection.cc
@@ -50,7 +50,7 @@ void Connection::HandleRead(boost::system::error_code ec,
     return;
   }
 
-  ErrorCode error = request_parser_.Parse(buffer_.data(), bytes_transferred);
+  Error error = request_parser_.Parse(buffer_.data(), bytes_transferred);
 
   if (error != kNoError) {
     // Bad request.
diff --git a/src/csoap/http_client.cc b/src/csoap/http_client.cc
index 1908536..5ff893a 100644
--- a/src/csoap/http_client.cc
+++ b/src/csoap/http_client.cc
@@ -56,8 +56,8 @@ HttpClient::HttpClient()
     : timeout_seconds_(15) {
 }
 
-ErrorCode HttpClient::SendRequest(const HttpRequest& request,
-                                  HttpResponse* response) {
+Error HttpClient::SendRequest(const HttpRequest& request,
+                              HttpResponse* response) {
   assert(response != NULL);
 
   using boost::asio::ip::tcp;
@@ -71,6 +71,7 @@ ErrorCode HttpClient::SendRequest(const HttpRequest& request,
     port = "80";
   }
 
+  // TODO: IPv4 or both IPv4 and IPv6
   boost::system::error_code ec;
   tcp::resolver::results_type endpoints =
       resolver.resolve(/*tcp::v4(), */request.host(), port, ec);
@@ -130,7 +131,7 @@ ErrorCode HttpClient::SendRequest(const HttpRequest& request,
     // Parse the response piece just read.
     // If the content has been fully received, next time flag "finished_"
     // will be set.
-    ErrorCode error = parser.Parse(buffer_.data(), length);
+    Error error = parser.Parse(buffer_.data(), length);
 
     if (error != kNoError) {
       return error;
diff --git a/src/csoap/http_client.h b/src/csoap/http_client.h
index dec69c1..a1cb911 100644
--- a/src/csoap/http_client.h
+++ b/src/csoap/http_client.h
@@ -25,8 +25,8 @@ public:
   }
 
   // Send an HTTP request, wait until the response is received.
-  ErrorCode SendRequest(const HttpRequest& request,
-                        HttpResponse* response);
+  Error SendRequest(const HttpRequest& request,
+                    HttpResponse* response);
 
 private:
   boost::asio::io_context io_context_;
diff --git a/src/csoap/http_parser.cc b/src/csoap/http_parser.cc
index 1abdab7..0dd883e 100644
--- a/src/csoap/http_parser.cc
+++ b/src/csoap/http_parser.cc
@@ -18,7 +18,7 @@ void HttpParser::Reset() {
   // TODO: Reset parsing state.
 }
 
-ErrorCode HttpParser::Parse(const char* data, size_t len) {
+Error HttpParser::Parse(const char* data, size_t len) {
   if (header_parsed_) {
     // Add the data to the content.
     message_->AppendContent(data, len);
@@ -50,7 +50,7 @@ ErrorCode HttpParser::Parse(const char* data, size_t len) {
 
     if (!start_line_parsed_) {
       start_line_parsed_ = true;
-      ErrorCode error = ParseStartLine(line);
+      Error error = ParseStartLine(line);
       if (error != kNoError) {
         return error;
       }
diff --git a/src/csoap/http_parser.h b/src/csoap/http_parser.h
index fc7bc05..8ae093e 100644
--- a/src/csoap/http_parser.h
+++ b/src/csoap/http_parser.h
@@ -21,11 +21,11 @@ public:
   // Reset parsing state.
   void Reset();
 
-  ErrorCode Parse(const char* data, size_t len);
+  Error Parse(const char* data, size_t len);
 
 protected:
   // Parse HTTP start line.
-  virtual ErrorCode ParseStartLine(const std::string& line) = 0;
+  virtual Error ParseStartLine(const std::string& line) = 0;
 
   void ParseContentLength(const std::string& line);
 
@@ -33,7 +33,7 @@ protected:
   // The result HTTP message.
   HttpMessage* message_;
 
-  ErrorCode error_;
+  Error error_;
 
   // Data waiting to be parsed.
   std::string pending_data_;
diff --git a/src/csoap/http_request_parser.cc b/src/csoap/http_request_parser.cc
index 4560332..83e65b3 100644
--- a/src/csoap/http_request_parser.cc
+++ b/src/csoap/http_request_parser.cc
@@ -12,7 +12,7 @@ HttpRequestParser::HttpRequestParser(HttpRequest* request)
   , request_(request) {
 }
 
-ErrorCode HttpRequestParser::ParseStartLine(const std::string& line) {
+Error HttpRequestParser::ParseStartLine(const std::string& line) {
   // Example: POST / HTTP/1.1
 
   std::vector<std::string> strs;
diff --git a/src/csoap/http_request_parser.h b/src/csoap/http_request_parser.h
index 7bcbce5..53a7b62 100644
--- a/src/csoap/http_request_parser.h
+++ b/src/csoap/http_request_parser.h
@@ -12,7 +12,7 @@ public:
   explicit HttpRequestParser(HttpRequest* request);
 
 private:
-  ErrorCode ParseStartLine(const std::string& line) override;
+  Error ParseStartLine(const std::string& line) override;
 
 private:
   HttpRequest* request_;
diff --git a/src/csoap/http_response_parser.cc b/src/csoap/http_response_parser.cc
index 279c6a5..77f0fcf 100644
--- a/src/csoap/http_response_parser.cc
+++ b/src/csoap/http_response_parser.cc
@@ -10,7 +10,7 @@ HttpResponseParser::HttpResponseParser(HttpResponse* response)
 }
 
 // TODO: Use split.
-ErrorCode HttpResponseParser::ParseStartLine(const std::string& line) {
+Error HttpResponseParser::ParseStartLine(const std::string& line) {
   size_t off = 0;
 
   size_t pos = line.find(' ');
diff --git a/src/csoap/http_response_parser.h b/src/csoap/http_response_parser.h
index a5d8352..c6e6f51 100644
--- a/src/csoap/http_response_parser.h
+++ b/src/csoap/http_response_parser.h
@@ -13,7 +13,7 @@ public:
 
 private:
   // Parse HTTP start line; E.g., "HTTP/1.1 200 OK".
-  ErrorCode ParseStartLine(const std::string& line) override;
+  Error ParseStartLine(const std::string& line) override;
 
 private:
   // The result response message.
diff --git a/src/csoap/soap_client.cc b/src/csoap/soap_client.cc
index ba8384f..36e774d 100644
--- a/src/csoap/soap_client.cc
+++ b/src/csoap/soap_client.cc
@@ -13,63 +13,57 @@
 
 namespace csoap {
 
-bool SoapClient::Call(const std::string& operation,
-                      const csoap::Parameter* parameters,
-                      size_t count,
-                      std::string* result) {
+Error SoapClient::Call(const std::string& operation,
+                       const Parameter* parameters,
+                       std::size_t count,
+                       std::string* result) {
   assert(!url_.empty() &&
          !host_.empty() &&
          !result_name_.empty() &&
          service_ns_.IsValid());
 
-  csoap::SoapRequest soap_request;
+  SoapRequest soap_request;
 
-  soap_request.set_soapenv_ns(kSoapEnvNamespace);
+  soap_request.set_soapenv_ns(kSoapEnvNamespace);  // TODO: Configurable
   soap_request.set_service_ns(service_ns_);
 
   soap_request.set_operation(operation);
 
-  for (size_t i = 0; i < count; ++i) {
+  for (std::size_t i = 0; i < count; ++i) {
     soap_request.AddParameter(parameters[i]);
   }
 
   std::string http_request_body;
   soap_request.ToXml(&http_request_body);
 
-  csoap::HttpRequest http_request;
+  HttpRequest http_request;
 
-  http_request.set_version(csoap::kHttpV11);
+  http_request.set_version(kHttpV11);  // TODO
   http_request.set_url(url_);
   http_request.set_content_length(http_request_body.size());
   http_request.set_content(http_request_body);  // TODO: move
   http_request.set_host(host_, port_);
   http_request.set_soap_action(operation);
 
-  csoap::HttpResponse http_response;
+  HttpResponse http_response;
 
-  csoap::HttpClient http_client;
-  csoap::ErrorCode ec = http_client.SendRequest(http_request, &http_response);
-  if (ec != csoap::kNoError) {
-    std::cerr << csoap::GetErrorMessage(ec) << std::endl;
+  HttpClient http_client;
+  Error error = http_client.SendRequest(http_request, &http_response);
 
-    if (ec == csoap::kHttpStatusError) {
-      //std::cerr << "\t"
-      //  << http_response.status() << ", "
-      //  << http_response.reason() << std::endl;
-    }
-
-    return false;
+  if (error != kNoError) {
+    return error;
   }
 
-  csoap::SoapResponse soap_response;
+  SoapResponse soap_response;
   soap_response.set_result_name(result_name_);
 
-  if (soap_response.FromXml(http_response.content())) {
-    *result = soap_response.result();
-    return true;
+  if (!soap_response.FromXml(http_response.content())) {
+    return kXmlError;  // TODO: Some SOAP error?
   }
 
-  return false;
+  *result = soap_response.result();
+
+  return kNoError;
 }
 
 }  // namespace csoap
diff --git a/src/csoap/soap_client.h b/src/csoap/soap_client.h
index 4c973af..17713e2 100644
--- a/src/csoap/soap_client.h
+++ b/src/csoap/soap_client.h
@@ -19,10 +19,10 @@ protected:
   }
 
   // A generic wrapper to make a call.
-  bool Call(const std::string& operation,
-            const csoap::Parameter* parameters,
-            size_t count,
-            std::string* result);
+  Error Call(const std::string& operation,
+             const Parameter* parameters,
+             std::size_t count,
+             std::string* result);
 
 protected:
   // Request URL.
diff --git a/src/demo/calculator_client/calculator_client.cc b/src/demo/calculator_client/calculator_client.cc
index 04661b2..3c831b7 100644
--- a/src/demo/calculator_client/calculator_client.cc
+++ b/src/demo/calculator_client/calculator_client.cc
@@ -55,7 +55,11 @@ bool CalculatorClient::Calc(const std::string& operation,
   };
 
   std::string result_str;
-  if (!Call(operation, parameters, 2, &result_str)) {
+  csoap::Error error = Call(operation, parameters, 2, &result_str);
+
+  if (error != csoap::kNoError) {
+    std::cerr << "Error: " << error;
+    std::cerr << ", " << csoap::GetErrorMessage(error) << std::endl;
     return false;
   }
 
diff --git a/src/demo/csdm_client/csdm_client.cc b/src/demo/csdm_client/csdm_client.cc
index 83a7749..b2a2377 100644
--- a/src/demo/csdm_client/csdm_client.cc
+++ b/src/demo/csdm_client/csdm_client.cc
@@ -9,7 +9,7 @@ CsdmClient::CsdmClient() {
 }
 
 bool CsdmClient::GetVersion(std::string* result_xml) {
-  return Call("getVersion", NULL, 0, result_xml);
+  return Call0("getVersion", result_xml);
 }
 
 void CsdmClient::Init() {
@@ -20,7 +20,12 @@ void CsdmClient::Init() {
   host_ = "127.0.0.1";
   port_ = "52540";
 
-  result_name_ = "Result";
+  result_name_ = "return";
+}
+
+bool CsdmClient::Call0(const std::string& operation,
+                       std::string* result_xml) {
+  return CallEx(operation, NULL, 0, result_xml);
 }
 
 bool CsdmClient::Call1(const std::string& operation,
@@ -31,5 +36,27 @@ bool CsdmClient::Call1(const std::string& operation,
     { name, value },
   };
 
-  return Call(operation, parameters, 1, result_xml);
+  return CallEx(operation, parameters, 1, result_xml);
+}
+
+bool CsdmClient::Call2(const std::string& operation,
+                       const std::string& name1,
+                       const std::string& value1,
+                       const std::string& name2,
+                       const std::string& value2,
+                       std::string* result_xml) {
+  csoap::Parameter parameters[] = {
+    { name1, value1 },
+    { name2, value2 },
+  };
+
+  return CallEx(operation, parameters, 2, result_xml);
+}
+
+bool CsdmClient::CallEx(const std::string& operation,
+                        const csoap::Parameter* parameters,
+                        std::size_t count,
+                        std::string* result) {
+  csoap::Error error = Call(operation, parameters, count, result);
+  return error == csoap::kNoError;
 }
diff --git a/src/demo/csdm_client/csdm_client.h b/src/demo/csdm_client/csdm_client.h
index 5b23d6f..28785ae 100644
--- a/src/demo/csdm_client/csdm_client.h
+++ b/src/demo/csdm_client/csdm_client.h
@@ -15,11 +15,29 @@ public:
 protected:
   void Init();
 
+  // Call CSDM API with NO parameter.
+  bool Call0(const std::string& operation,
+             std::string* result_xml);
+
   // Call CSDM API with one parameter.
   bool Call1(const std::string& operation,
              const std::string& name,
              const std::string& value,
              std::string* result_xml);
+
+  // Call CSDM API with two parameters.
+  bool Call2(const std::string& operation,
+             const std::string& name1,
+             const std::string& value1,
+             const std::string& name2,
+             const std::string& value2,
+             std::string* result_xml);
+
+  // A wrapper of CSoapClient::Call().
+  bool CallEx(const std::string& operation,
+              const csoap::Parameter* parameters,
+              std::size_t count,
+              std::string* result);
 };
 
 #endif  // CSDM_CLIENT_H_