Add helper functions to build queries and stream resolvers

Author: tstenner

src/lsl_resolver_c.cpp

@@ -17,17 +17,7 @@ using namespace lsl;
 *					  The recommended default value is 5.0.
 */
 LIBLSL_C_API lsl_continuous_resolver lsl_create_continuous_resolver(double forget_after) {
-	try {
-		// create a new resolver
-		resolver_impl *resolver = new resolver_impl();
-		// start it with the given query
-		std::ostringstream os; os << "session_id='" << api_config::get_instance()->session_id() << "'";
-		resolver->resolve_continuous(os.str(),forget_after);
-		return resolver;
-	} catch(std::exception &e) {
-		LOG_F(ERROR, "Error while creating a continuous_resolver: %s", e.what());
-		return nullptr;
-	}
+	return resolver_impl::create_resolver(forget_after);
 }
 
 /**
@@ -40,17 +30,7 @@ LIBLSL_C_API lsl_continuous_resolver lsl_create_continuous_resolver(double forge
 *					  The recommended default value is 5.0.
 */
 LIBLSL_C_API lsl_continuous_resolver lsl_create_continuous_resolver_byprop(const char *prop, const char *value, double forget_after) {
-	try {
-		// create a new resolver
-		resolver_impl *resolver = new resolver_impl();
-		// start it with the given query
-		std::ostringstream os; os << "session_id='" << api_config::get_instance()->session_id() << "' and " << prop << "='" << value << "'";
-		resolver->resolve_continuous(os.str(),forget_after);
-		return resolver;
-	} catch(std::exception &e) {
-		LOG_F(ERROR, "Error while creating a continuous_resolver: %s", e.what());
-		return nullptr;
-	}
+	return resolver_impl::create_resolver(forget_after, prop, value);
 }
 
 /**
@@ -62,17 +42,7 @@ LIBLSL_C_API lsl_continuous_resolver lsl_create_continuous_resolver_byprop(const
 *					  The recommended default value is 5.0.
 */
 LIBLSL_C_API lsl_continuous_resolver lsl_create_continuous_resolver_bypred(const char *pred, double forget_after) {
-	try {
-		// create a new resolver
-		resolver_impl *resolver = new resolver_impl();
-		// start it with the given query
-		std::ostringstream os; os << "session_id='" << api_config::get_instance()->session_id() << "' and " << pred;
-		resolver->resolve_continuous(os.str(),forget_after);
-		return resolver;
-	} catch(std::exception &e) {
-		LOG_F(ERROR, "Error while creating a continuous_resolver: %s", e.what());
-		return nullptr;
-	}
+	return resolver_impl::create_resolver(forget_after, pred, nullptr);
 }
 
 /**
@@ -159,12 +129,8 @@ LIBLSL_C_API int32_t lsl_resolve_all(lsl_streaminfo *buffer, uint32_t buffer_ele
 */
 LIBLSL_C_API int32_t lsl_resolve_byprop(lsl_streaminfo *buffer, uint32_t buffer_elements, const char *prop, const char *value, int32_t minimum, double timeout) {
 	try {
-		// create a new resolver
-		resolver_impl resolver;
-		// build a new query.
-		std::ostringstream os; os << "session_id='" << api_config::get_instance()->session_id() << "' and " << prop << "='" << value << "'";
-		// invoke it
-		std::vector<stream_info_impl> tmp = resolver.resolve_oneshot(os.str(),minimum,timeout);
+		std::string query{resolver_impl::build_query(prop, value)};
+		auto tmp = resolver_impl().resolve_oneshot(query, minimum, timeout);
 		// allocate new stream_info_impl's and assign to the buffer
 		uint32_t result = buffer_elements<tmp.size() ? buffer_elements : (uint32_t)tmp.size();
 		for (uint32_t k = 0; k < result; k++) buffer[k] = new stream_info_impl(tmp[k]);
@@ -192,12 +158,8 @@ LIBLSL_C_API int32_t lsl_resolve_byprop(lsl_streaminfo *buffer, uint32_t buffer_
 */
 LIBLSL_C_API int32_t lsl_resolve_bypred(lsl_streaminfo *buffer, uint32_t buffer_elements, const char *pred, int32_t minimum, double timeout) {
 	try {
-		// create a new resolver
-		resolver_impl resolver;
-		// build a new query.
-		std::ostringstream os; os << "session_id='" << api_config::get_instance()->session_id() << "' and " << pred;
-		// invoke it
-		std::vector<stream_info_impl> tmp = resolver.resolve_oneshot(os.str(),minimum,timeout);
+		std::string query{resolver_impl::build_query(pred)};
+		auto tmp = resolver_impl().resolve_oneshot(query, minimum, timeout);
 		// allocate new stream_info_impl's and assign to the buffer
 		uint32_t result = buffer_elements<tmp.size() ? buffer_elements : (uint32_t)tmp.size();
 		for (uint32_t k = 0; k < result; k++) buffer[k] = new stream_info_impl(tmp[k]);

src/resolver_impl.cpp

@@ -70,6 +70,28 @@ void check_query(const std::string& query) {
 	}
 }
 
+std::string resolver_impl::build_query(const char* pred_or_prop, const char* value)
+{
+	std::string query("session_id='");
+	query += api_config::get_instance()->session_id();
+	query += '\'';
+	if (pred_or_prop) (query += " and ") += pred_or_prop;
+	if (value) ((query += "='") += value) += '\'';
+	return query;
+}
+
+resolver_impl *resolver_impl::create_resolver(
+	double forget_after, const char *pred_or_prop, const char *value) noexcept {
+	try {
+		auto *resolver = new resolver_impl();
+		resolver->resolve_continuous(build_query(pred_or_prop, value), forget_after);
+		return resolver;
+	} catch (std::exception &e) {
+		LOG_F(ERROR, "Error while creating a continuous_resolver: %s", e.what());
+		return nullptr;
+	}
+}
+
 // === resolve functions ===
 
 /**

src/resolver_impl.h

@@ -44,6 +44,25 @@ namespace lsl {
 		*/
 		resolver_impl();
 
+		/** Build a query string
+		 *
+		 * @param pred_or_prop an entire predicate if value isn't set or the
+		 * name of the property, e.g. "foo='bar'" / "foo" (+value set as "bar")
+		 * @param value the value for the property parameter
+		 */
+		static std::string build_query(
+			const char *pred_or_prop = nullptr, const char *value = nullptr);
+
+		/** Create a resolver object with optionally a predicate or property + value
+		 *
+		 * @param pred_or_prop an entire predicate of value isn't set or the
+		 * name of the property, e.g. "foo='bar'" / "foo" (+value set as "bar")
+		 * @param value the value for the property parameter
+		 * @return A pointer to the resolver on success or nullptr on error
+		 */
+		static resolver_impl *create_resolver(double forget_after,
+			const char *pred_or_prop = nullptr, const char *value = nullptr) noexcept;
+
 		/// Destructor.
 		/// Cancels any ongoing processes and waits until they finish.
 		~resolver_impl();