util/Exception: add GetFullMessage(std::exception)

src/util/Exception.cxx

@@ -30,13 +30,10 @@
 #include "Exception.hxx"
 
 std::string
-GetFullMessage(std::exception_ptr ep,
+GetFullMessage(const std::exception &e,
 	       const char *fallback, const char *separator) noexcept
 {
 	try {
-		std::rethrow_exception(ep);
-	} catch (const std::exception &e) {
-		try {
 		std::rethrow_if_nested(e);
 		return e.what();
 	} catch (...) {
@@ -44,6 +41,16 @@ GetFullMessage(std::exception_ptr ep,
 			GetFullMessage(std::current_exception(),
 				       fallback, separator);
 	}
+}
+
+std::string
+GetFullMessage(std::exception_ptr ep,
+	       const char *fallback, const char *separator) noexcept
+{
+	try {
+		std::rethrow_exception(ep);
+	} catch (const std::exception &e) {
+		return GetFullMessage(e, fallback, separator);
 	} catch (const std::nested_exception &ne) {
 		return GetFullMessage(ne.nested_ptr(), fallback, separator);
 	}

src/util/Exception.hxx

@@ -34,6 +34,15 @@
 #include <string>
 
 /**
+ * Obtain the full concatenated message of an exception and its nested
+ * chain.
+ */
+std::string
+GetFullMessage(const std::exception &e,
+	       const char *fallback="Unknown exception",
+	       const char *separator="; ") noexcept;
+
+/**
  * Extract the full message of a C++ exception, considering its nested
  * exceptions (if any).
  */