Issue #41 - Bring method of determining IE version up to date

src/shared/IE_version.cpp

+#include "IE_version.h"
+#include "Registry.h"
+
+using namespace AdblockPlus;
+
+/**
+ * Internal implementation of the IE version string.
+ *
+ * This version throws exceptions for its errors, relying on its caller to handle them.
+ *
+ * Quoting http://support.microsoft.com/kb/969393:
+ *   "Note The version string value for Internet Explorer 10 is 9.10.9200.16384, and the svcVersion string value is 10.0.9200.16384."
+ * [EH 2014-06-20] My current version of IE 11 is reporting these values:
+ *   Version 9.11.9600.17041
+ *   svcVersion 11.0.9600.17041
+ *
+ * Warning: IE version 12 and later might not behave the same, so this function should be reviewed with each new release.
+ */
+std::wstring IE_version_string()
+{
+  Registry_Key IE_key(Registry_Key::Predefined::HKLM, L"Software\\Microsoft\\Internet Explorer");
+  std::wstring version(IE_key.value_wstring(L"Version"));
+  /*
+    * We're expecting a version string that matches the regex "^[1-9]\.".
+    * Since IE versions 10 and 11 use a version string that begins with "9.", this simplistic parsing method works adequately.
+    */
+  if (version[1] != '.' || version[0] < L'0' || version[0] > L'9')
+  {
+    throw std::runtime_error("IE version string has unexpected format");
+  }
+  if (version[0] != L'9')
+  {
+    return version;
+  }
+  // Assert the major version in the "Version" value is 9.
+  /*
+    * Version 9 might either be an actual version 9 or it might represent a version >= 10
+    * If the value named "svcVersion" exists, we'll report that instead.
+    */
+  try
+  {
+    return IE_key.value_wstring(L"svcVersion");
+  }
+  catch (...)
+  {
+    return version;
+  }
+}
+
+std::wstring AdblockPlus::IE::installed_version_string()
+{
+  try
+  {
+    return IE_version_string();
+  }
+  catch (...)
+  {
+    return L"";
+  }
+}
+
+int AdblockPlus::IE::installed_major_version()
+{
+  try
+  {
+    std::wstring version = IE_version_string();
+    /*
+     * If the second character is a period, we assume that the major version is a single digit.
+     */
+    if (version[ 1 ] == L'.')
+    {
+      return version[ 0 ] - L'0';
+    }
+    // Assert IE_version_string() did not verify the syntax of the version string.
+    /*
+     * In this case, we'll assume that the version returned is two digits followed by a period.
+     * If not, we'll assume an error.
+     */
+    if (version[ 0 ] < L'0' || version[ 0 ] > L'9' || version[ 1 ] < L'0' || version[ 1 ] > L'9' || version[ 2 ] != L'.')
+    {
+      return 0;
+    }
+    return 10 * (version[ 0 ] - L'0') + (version[ 1 ] - L'0');
+  }
+  catch (...)
+  {
+    return 0;
+  }
+}