system/Error: helper library for constructing std::system_error

Makefile.am

@@ -464,6 +464,7 @@ libnet_a_SOURCES = \
 
 libsystem_a_SOURCES = \
 	src/system/ByteOrder.hxx \
+	src/system/Error.hxx \
 	src/system/FatalError.cxx src/system/FatalError.hxx \
 	src/system/FileDescriptor.cxx src/system/FileDescriptor.hxx \
 	src/system/fd_util.c src/system/fd_util.h \

src/system/Error.hxx

@@ -0,0 +1,109 @@
+/*
+ * Copyright (C) 2013-2015 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 SYSTEM_ERROR_HXX
+#define SYSTEM_ERROR_HXX
+
+#include "util/StringUtil.hxx"
+
+#include <system_error>
+#include <utility>
+
+template<typename... Args>
+static inline std::system_error
+FormatSystemError(std::error_code code, const char *fmt, Args&&... args)
+{
+	char buffer[1024];
+	snprintf(buffer, sizeof(buffer), fmt, std::forward<Args>(args)...);
+	return std::system_error(code, buffer);
+}
+
+#ifdef WIN32
+
+#include <windows.h>
+
+template<typename... Args>
+static inline std::system_error
+FormatLastError(DWORD code, const char *fmt, Args&&... args)
+{
+	char buffer[512];
+	const auto end = buffer + sizeof(buffer);
+	size_t length = snprintf(buffer, sizeof(buffer) - 128,
+				 fmt, std::forward<Args>(args)...);
+	char *p = buffer + length;
+	*p++ = ':';
+	*p++ = ' ';
+
+	FormatMessageA(FORMAT_MESSAGE_FROM_SYSTEM |
+		       FORMAT_MESSAGE_IGNORE_INSERTS,
+		       nullptr, code, 0, p, end - p, nullptr);
+	return std::system_error(std::error_code(code, std::system_category()),
+				 buffer);
+}
+
+template<typename... Args>
+static inline std::system_error
+FormatLastError(const char *fmt, Args&&... args)
+{
+	return FormatLastError(GetLastError(), fmt,
+			       std::forward<Args>(args)...);
+}
+
+#else
+
+#include <errno.h>
+#include <string.h>
+
+template<typename... Args>
+static inline std::system_error
+FormatErrno(int code, const char *fmt, Args&&... args)
+{
+	char buffer[512];
+	const auto end = buffer + sizeof(buffer);
+	size_t length = snprintf(buffer, sizeof(buffer) - 128,
+				 fmt, std::forward<Args>(args)...);
+	char *p = buffer + length;
+	*p++ = ':';
+	*p++ = ' ';
+
+	CopyString(p, strerror(code), end - p);
+	return std::system_error(std::error_code(code, std::system_category()),
+				 buffer);
+}
+
+template<typename... Args>
+static inline std::system_error
+FormatErrno(const char *fmt, Args&&... args)
+{
+	return FormatErrno(errno, fmt, std::forward<Args>(args)...);
+}
+
+#endif
+
+#endif