dbus: dbuswrite: use factory to catch errors

Add factories for creating DbusWrite and DbusWritePercent objects and
use these factories.

Change-Id: Iad222d4bf6c1fdf561daa4ba9d88a6644c0a5965
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/dbus/dbuswrite.cpp b/dbus/dbuswrite.cpp
index 714580b..b691b66 100644
--- a/dbus/dbuswrite.cpp
+++ b/dbus/dbuswrite.cpp
@@ -17,13 +17,36 @@
 #include "dbus/dbuswrite.hpp"
 
 #include <iostream>
+#include <memory>
 #include <sdbusplus/bus.hpp>
+#include <string>
+
+constexpr const char* pwmInterface = "xyz.openbmc_project.Control.FanPwm";
 
 // this bus object is treated as a singleton because the class is constructed in
 // a different thread than it is used, and as bus objects are relatively
 // expensive we'd prefer to only have one
 std::unique_ptr<sdbusplus::bus::bus> writeBus = nullptr;
 
+std::unique_ptr<WriteInterface>
+    DbusWritePercent::createDbusWrite(const std::string& path, int64_t min,
+                                      int64_t max, DbusHelperInterface& helper)
+{
+    auto tempBus = sdbusplus::bus::new_default();
+    std::string connectionName;
+
+    try
+    {
+        connectionName = helper.getService(tempBus, pwmInterface, path);
+    }
+    catch (const std::exception& e)
+    {
+        return nullptr;
+    }
+
+    return std::make_unique<DbusWritePercent>(path, min, max, connectionName);
+}
+
 void initBus()
 {
     if (writeBus == nullptr)
@@ -61,6 +84,25 @@
     return;
 }
 
+std::unique_ptr<WriteInterface>
+    DbusWrite::createDbusWrite(const std::string& path, int64_t min,
+                               int64_t max, DbusHelperInterface& helper)
+{
+    auto tempBus = sdbusplus::bus::new_default();
+    std::string connectionName;
+
+    try
+    {
+        connectionName = helper.getService(tempBus, pwmInterface, path);
+    }
+    catch (const std::exception& e)
+    {
+        return nullptr;
+    }
+
+    return std::make_unique<DbusWrite>(path, min, max, connectionName);
+}
+
 void DbusWrite::write(double value)
 {
     if (oldValue == static_cast<int64_t>(value))