command/{Player,Error}: extract messages from nested exceptions

Makefile.am

@@ -388,6 +388,7 @@ endif
 # Generic utility library
 
 libutil_a_SOURCES = \
+	src/util/Exception.cxx src/util/Exception.hxx \
 	src/util/RuntimeError.hxx \
 	src/util/Macros.hxx \
 	src/util/BindMethod.hxx \

src/command/CommandError.cxx

@@ -23,6 +23,7 @@
 #include "db/DatabaseError.hxx"
 #include "client/Response.hxx"
 #include "Log.hxx"
+#include "util/Exception.hxx"
 
 #include <system_error>
 
@@ -122,12 +123,6 @@ ToAck(std::exception_ptr ep)
 void
 PrintError(Response &r, std::exception_ptr ep)
 {
-	try {
+	LogError(ep);
-		std::rethrow_exception(ep);
+	r.Error(ToAck(ep), FullMessage(ep).c_str());
-	} catch (const std::exception &e) {
-		LogError(e);
-		r.Error(ToAck(ep), e.what());
-	} catch (...) {
-		r.Error(ACK_ERROR_UNKNOWN, "Unknown error");
-	}
 }

src/command/PlayerCommands.cxx

@@ -31,6 +31,7 @@
 #include "Idle.hxx"
 #include "AudioFormat.hxx"
 #include "util/ScopeExit.hxx"
+#include "util/Exception.hxx"
 
 #ifdef ENABLE_DATABASE
 #include "db/update/Service.hxx"
@@ -192,10 +193,9 @@ handle_status(Client &client, gcc_unused Request args, Response &r)
 
 	try {
 		client.player_control.LockCheckRethrowError();
-	} catch (const std::exception &e) {
-		r.Format(COMMAND_STATUS_ERROR ": %s\n", e.what());
 	} catch (...) {
-		r.Format(COMMAND_STATUS_ERROR ": unknown\n");
+		r.Format(COMMAND_STATUS_ERROR ": %s\n",
+			 FullMessage(std::current_exception()).c_str());
 	}
 
 	song = playlist.GetNextPosition();

src/util/Exception.cxx

@@ -0,0 +1,50 @@
+/*
+ * Copyright (C) 2016 Max Kellermann <max@duempel.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
+ * FOUNDATION OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "Exception.hxx"
+
+#include <stdexcept>
+
+std::string
+FullMessage(std::exception_ptr ep)
+{
+	try {
+		std::rethrow_exception(ep);
+	} catch (const std::exception &e) {
+		try {
+			std::rethrow_if_nested(e);
+			return e.what();
+		} catch (...) {
+			return std::string(e.what()) + "; " +
+				FullMessage(std::current_exception());
+		}
+	}
+
+	return std::string("Unknown error");
+}

src/util/Exception.hxx

@@ -0,0 +1,43 @@
+/*
+ * Copyright (C) 2016 Max Kellermann <max@duempel.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
+ * FOUNDATION OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
+ * OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef EXCEPTION_HXX
+#define EXCEPTION_HXX
+
+#include <exception>
+#include <string>
+
+/**
+ * Extract the full message of a C++ exception, considering its nested
+ * exceptions (if any).
+ */
+std::string
+FullMessage(std::exception_ptr ep);
+
+#endif