Extract logging logic

Previously logging logic was scattered over OS class implementations
with plenty of duplication. Major changes in this commit:

 - Extracted logging logic into a separate Logger hierarchy. It allows
   easy configuration of logging mechanism depending on compile-time or
   run-time configuration.

 - Implemented RotatedFileLogger which is usually used with StdLogger,
   providing persistency of logs. It is often important to be able to
   obtain logs of the game even in production to be able to understand
   what happened prior to some problem. On mobile there previously was
   no way to obtain the logs aside from having the device connected to
   your machine.

 - flush() is not performed in release mode for every logged line. It
   is only performed for errors.

20 files changed, 433 insertions, 29 deletions

diff --git a/core/error_macros.cpp b/core/error_macros.cpp
index 5919d3837..170a22e8d 100644
--- a/core/error_macros.cpp
+++ b/core/error_macros.cpp
@@ -29,6 +29,7 @@
 /*************************************************************************/
 #include "error_macros.h"
 
+#include "io/logger.h"
 #include "os/os.h"
 
 bool _err_error_exists = false;
@@ -79,7 +80,7 @@ void remove_error_handler(ErrorHandlerList *p_handler) {
 
 void _err_print_error(const char *p_function, const char *p_file, int p_line, const char *p_error, ErrorHandlerType p_type) {
 
-	OS::get_singleton()->print_error(p_function, p_file, p_line, p_error, _err_error_exists ? OS::get_singleton()->get_last_error() : "", (OS::ErrorType)p_type);
+	OS::get_singleton()->print_error(p_function, p_file, p_line, p_error, _err_error_exists ? OS::get_singleton()->get_last_error() : "", (Logger::ErrorType)p_type);
 
 	_global_lock();
 	ErrorHandlerList *l = error_handler_list;
diff --git a/core/io/file_access_buffered_fa.h b/core/io/file_access_buffered_fa.h
index 9e4183456..309fc16d0 100644
--- a/core/io/file_access_buffered_fa.h
+++ b/core/io/file_access_buffered_fa.h
@@ -76,6 +76,11 @@ protected:
 	};
 
 public:
+	void flush() {
+
+		f.flush();
+	};
+
 	void store_8(uint8_t p_dest) {
 
 		f.store_8(p_dest);
diff --git a/core/io/file_access_compressed.cpp b/core/io/file_access_compressed.cpp
index 475094585..514e3c65f 100644
--- a/core/io/file_access_compressed.cpp
+++ b/core/io/file_access_compressed.cpp
@@ -338,6 +338,13 @@ Error FileAccessCompressed::get_error() const {
 	return read_eof ? ERR_FILE_EOF : OK;
 }
 
+void FileAccessCompressed::flush() {
+	ERR_FAIL_COND(!f);
+	ERR_FAIL_COND(!writing);
+
+	// compressed files keep data in memory till close()
+}
+
 void FileAccessCompressed::store_8(uint8_t p_dest) {
 
 	ERR_FAIL_COND(!f);
diff --git a/core/io/file_access_compressed.h b/core/io/file_access_compressed.h
index 1a57e2d4e..1d99e5bfd 100644
--- a/core/io/file_access_compressed.h
+++ b/core/io/file_access_compressed.h
@@ -84,6 +84,7 @@ public:
 
 	virtual Error get_error() const; ///< get last error
 
+	virtual void flush();
 	virtual void store_8(uint8_t p_dest); ///< store a byte
 
 	virtual bool file_exists(const String &p_name); ///< return true if a file exists
diff --git a/core/io/file_access_encrypted.cpp b/core/io/file_access_encrypted.cpp
index 461c5bafe..c93e12f7d 100644
--- a/core/io/file_access_encrypted.cpp
+++ b/core/io/file_access_encrypted.cpp
@@ -268,6 +268,12 @@ void FileAccessEncrypted::store_buffer(const uint8_t *p_src, int p_length) {
 	}
 }
 
+void FileAccessEncrypted::flush() {
+	ERR_FAIL_COND(!writing);
+
+	// encrypted files keep data in memory till close()
+}
+
 void FileAccessEncrypted::store_8(uint8_t p_dest) {
 
 	ERR_FAIL_COND(!writing);
diff --git a/core/io/file_access_encrypted.h b/core/io/file_access_encrypted.h
index 82f60ac65..d83fed3e0 100644
--- a/core/io/file_access_encrypted.h
+++ b/core/io/file_access_encrypted.h
@@ -71,6 +71,7 @@ public:
 
 	virtual Error get_error() const; ///< get last error
 
+	virtual void flush();
 	virtual void store_8(uint8_t p_dest); ///< store a byte
 	virtual void store_buffer(const uint8_t *p_src, int p_length); ///< store an array of bytes
 
diff --git a/core/io/file_access_memory.cpp b/core/io/file_access_memory.cpp
index b94839438..0a5815fca 100644
--- a/core/io/file_access_memory.cpp
+++ b/core/io/file_access_memory.cpp
@@ -170,6 +170,10 @@ Error FileAccessMemory::get_error() const {
 	return pos >= length ? ERR_FILE_EOF : OK;
 }
 
+void FileAccessMemory::flush() {
+	ERR_FAIL_COND(!data);
+}
+
 void FileAccessMemory::store_8(uint8_t p_byte) {
 
 	ERR_FAIL_COND(!data);
diff --git a/core/io/file_access_memory.h b/core/io/file_access_memory.h
index b7b843008..23392719b 100644
--- a/core/io/file_access_memory.h
+++ b/core/io/file_access_memory.h
@@ -62,6 +62,7 @@ public:
 
 	virtual Error get_error() const; ///< get last error
 
+	virtual void flush();
 	virtual void store_8(uint8_t p_byte); ///< store a byte
 	virtual void store_buffer(const uint8_t *p_src, int p_length); ///< store an array of bytes
 
diff --git a/core/io/file_access_network.cpp b/core/io/file_access_network.cpp
index 8c624226a..a224abd9e 100644
--- a/core/io/file_access_network.cpp
+++ b/core/io/file_access_network.cpp
@@ -456,6 +456,10 @@ Error FileAccessNetwork::get_error() const {
 	return pos == total_size ? ERR_FILE_EOF : OK;
 }
 
+void FileAccessNetwork::flush() {
+	ERR_FAIL();
+}
+
 void FileAccessNetwork::store_8(uint8_t p_dest) {
 
 	ERR_FAIL();
diff --git a/core/io/file_access_network.h b/core/io/file_access_network.h
index abbe378b6..20614476d 100644
--- a/core/io/file_access_network.h
+++ b/core/io/file_access_network.h
@@ -155,6 +155,7 @@ public:
 
 	virtual Error get_error() const; ///< get last error
 
+	virtual void flush();
 	virtual void store_8(uint8_t p_dest); ///< store a byte
 
 	virtual bool file_exists(const String &p_path); ///< return true if a file exists
diff --git a/core/io/file_access_pack.cpp b/core/io/file_access_pack.cpp
index ff4c28ec3..a7eb8ce6a 100644
--- a/core/io/file_access_pack.cpp
+++ b/core/io/file_access_pack.cpp
@@ -293,6 +293,11 @@ Error FileAccessPack::get_error() const {
 	return OK;
 }
 
+void FileAccessPack::flush() {
+
+	ERR_FAIL();
+}
+
 void FileAccessPack::store_8(uint8_t p_dest) {
 
 	ERR_FAIL();
diff --git a/core/io/file_access_pack.h b/core/io/file_access_pack.h
index 3deb0d2bd..12187a353 100644
--- a/core/io/file_access_pack.h
+++ b/core/io/file_access_pack.h
@@ -161,6 +161,7 @@ public:
 
 	virtual Error get_error() const;
 
+	virtual void flush();
 	virtual void store_8(uint8_t p_dest);
 
 	virtual void store_buffer(const uint8_t *p_src, int p_length);
diff --git a/core/io/file_access_zip.cpp b/core/io/file_access_zip.cpp
index 73b23ac70..ec809011a 100644
--- a/core/io/file_access_zip.cpp
+++ b/core/io/file_access_zip.cpp
@@ -353,6 +353,11 @@ Error FileAccessZip::get_error() const {
 	return OK;
 };
 
+void FileAccessZip::flush() {
+
+	ERR_FAIL();
+}
+
 void FileAccessZip::store_8(uint8_t p_dest) {
 
 	ERR_FAIL();
diff --git a/core/io/file_access_zip.h b/core/io/file_access_zip.h
index a40e1a753..0977b241e 100644
--- a/core/io/file_access_zip.h
+++ b/core/io/file_access_zip.h
@@ -108,6 +108,7 @@ public:
 
 	virtual Error get_error() const; ///< get last error
 
+	virtual void flush();
 	virtual void store_8(uint8_t p_dest); ///< store a byte
 	virtual bool file_exists(const String &p_name); ///< return true if a file exists
 
diff --git a/core/io/logger.cpp b/core/io/logger.cpp
new file mode 100644
index 000000000..7ea5f06d7
--- /dev/null
+++ b/core/io/logger.cpp
@@ -0,0 +1,252 @@
+/*************************************************************************/
+/*  logger.cpp                                                           */
+/*************************************************************************/
+/*                       This file is part of:                           */
+/*                           GODOT ENGINE                                */
+/*                      https://godotengine.org                          */
+/*************************************************************************/
+/* Copyright (c) 2007-2017 Juan Linietsky, Ariel Manzur.                 */
+/* Copyright (c) 2014-2017 Godot Engine contributors (cf. AUTHORS.md)    */
+/*                                                                       */
+/* Permission is hereby granted, free of charge, to any person obtaining */
+/* a copy of this software and associated documentation files (the       */
+/* "Software"), to deal in the Software without restriction, including   */
+/* without limitation the rights to use, copy, modify, merge, publish,   */
+/* distribute, sublicense, and/or sell copies of the Software, and to    */
+/* permit persons to whom the Software is furnished to do so, subject to */
+/* the following conditions:                                             */
+/*                                                                       */
+/* The above copyright notice and this permission notice shall be        */
+/* included in all copies or substantial portions of the Software.       */
+/*                                                                       */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,       */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF    */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY  */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,  */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
+/*************************************************************************/
+
+#include "logger.h"
+#include "os/dir_access.h"
+#include "os/os.h"
+#include "print_string.h"
+
+bool Logger::should_log(bool p_err) {
+	return (!p_err || _print_error_enabled) && (p_err || _print_line_enabled);
+}
+
+void Logger::log_error(const char *p_function, const char *p_file, int p_line, const char *p_code, const char *p_rationale, ErrorType p_type) {
+	if (!should_log(true)) {
+		return;
+	}
+
+	const char *err_type = "**ERROR**";
+	switch (p_type) {
+		case ERR_ERROR: err_type = "**ERROR**"; break;
+		case ERR_WARNING: err_type = "**WARNING**"; break;
+		case ERR_SCRIPT: err_type = "**SCRIPT ERROR**"; break;
+		case ERR_SHADER: err_type = "**SHADER ERROR**"; break;
+		default: ERR_PRINT("Unknown error type"); break;
+	}
+
+	const char *err_details;
+	if (p_rationale && *p_rationale)
+		err_details = p_rationale;
+	else
+		err_details = p_code;
+
+	logf_error("%s: %s\n", err_type, err_details);
+	logf_error("   At: %s:%i:%s() - %s\n", p_file, p_line, p_function, p_code);
+}
+
+void Logger::logf(const char *p_format, ...) {
+	if (!should_log(false)) {
+		return;
+	}
+
+	va_list argp;
+	va_start(argp, p_format);
+
+	logv(p_format, argp, false);
+
+	va_end(argp);
+}
+
+void Logger::logf_error(const char *p_format, ...) {
+	if (!should_log(true)) {
+		return;
+	}
+
+	va_list argp;
+	va_start(argp, p_format);
+
+	logv(p_format, argp, true);
+
+	va_end(argp);
+}
+
+Logger::~Logger() {}
+
+void RotatedFileLogger::close_file() {
+	if (file) {
+		memdelete(file);
+		file = NULL;
+	}
+}
+
+void RotatedFileLogger::clear_old_backups() {
+	int max_backups = max_files - 1; // -1 for the current file
+
+	String basename = base_path.get_basename();
+	String extension = "." + base_path.get_extension();
+
+	DirAccess *da = DirAccess::open(base_path.get_base_dir());
+	if (!da) {
+		return;
+	}
+
+	da->list_dir_begin();
+	String f = da->get_next();
+	Set<String> backups;
+	while (f != String()) {
+		if (!da->current_is_dir() && f.begins_with(basename) && f.ends_with(extension) && f != base_path) {
+			backups.insert(f);
+		}
+		f = da->get_next();
+	}
+	da->list_dir_end();
+
+	if (backups.size() > max_backups) {
+		// since backups are appended with timestamp and Set iterates them in sorted order,
+		// first backups are the oldest
+		int to_delete = backups.size() - max_backups;
+		for (Set<String>::Element *E = backups.front(); E && to_delete > 0; E = E->next(), --to_delete) {
+			da->remove(E->get());
+		}
+	}
+
+	memdelete(da);
+}
+
+void RotatedFileLogger::rotate_file() {
+	close_file();
+
+	if (FileAccess::exists(base_path)) {
+		if (max_files > 1) {
+			char timestamp[21];
+			OS::Date date = OS::get_singleton()->get_date();
+			OS::Time time = OS::get_singleton()->get_time();
+			sprintf(timestamp, "-%04d-%02d-%02d-%02d-%02d-%02d", date.year, date.month, date.day + 1, time.hour, time.min, time.sec);
+
+			String backup_name = base_path.get_basename() + timestamp + "." + base_path.get_extension();
+
+			DirAccess *da = DirAccess::open(base_path.get_base_dir());
+			if (da) {
+				da->copy(base_path, backup_name);
+				memdelete(da);
+			}
+			clear_old_backups();
+		}
+	} else {
+		DirAccess *da = DirAccess::create(DirAccess::ACCESS_USERDATA);
+		if (da) {
+			da->make_dir_recursive(base_path.get_base_dir());
+			memdelete(da);
+		}
+	}
+
+	file = FileAccess::open(base_path, FileAccess::WRITE);
+}
+
+RotatedFileLogger::RotatedFileLogger(const String &p_base_path, int p_max_files) {
+	file = NULL;
+	base_path = p_base_path.simplify_path();
+	max_files = p_max_files > 0 ? p_max_files : 1;
+
+	rotate_file();
+}
+
+void RotatedFileLogger::logv(const char *p_format, va_list p_list, bool p_err) {
+	if (!should_log(p_err)) {
+		return;
+	}
+
+	if (file) {
+		const int static_buf_size = 512;
+		char static_buf[static_buf_size];
+		char *buf = static_buf;
+		int len = vsnprintf(buf, static_buf_size, p_format, p_list);
+		if (len >= static_buf_size) {
+			buf = (char *)Memory::alloc_static(len + 1);
+			vsnprintf(buf, len + 1, p_format, p_list);
+		}
+		file->store_buffer((uint8_t *)buf, len);
+		if (len >= static_buf_size) {
+			Memory::free_static(buf);
+		}
+#ifdef DEBUG_ENABLED
+		const bool need_flush = true;
+#else
+		bool need_flush = p_err;
+#endif
+		if (need_flush) {
+			file->flush();
+		}
+	}
+}
+
+RotatedFileLogger::~RotatedFileLogger() {
+	close_file();
+}
+
+void StdLogger::logv(const char *p_format, va_list p_list, bool p_err) {
+	if (!should_log(p_err)) {
+		return;
+	}
+
+	if (p_err) {
+		vfprintf(stderr, p_format, p_list);
+	} else {
+		vprintf(p_format, p_list);
+#ifdef DEBUG_ENABLED
+		fflush(stdout);
+#endif
+	}
+}
+
+StdLogger::~StdLogger() {}
+
+CompositeLogger::CompositeLogger(Vector<Logger *> p_loggers) {
+	loggers = p_loggers;
+}
+
+void CompositeLogger::logv(const char *p_format, va_list p_list, bool p_err) {
+	if (!should_log(p_err)) {
+		return;
+	}
+
+	for (int i = 0; i < loggers.size(); ++i) {
+		va_list list_copy;
+		va_copy(list_copy, p_list);
+		loggers[i]->logv(p_format, list_copy, p_err);
+		va_end(list_copy);
+	}
+}
+
+void CompositeLogger::log_error(const char *p_function, const char *p_file, int p_line, const char *p_code, const char *p_rationale, ErrorType p_type) {
+	if (!should_log(true)) {
+		return;
+	}
+
+	for (int i = 0; i < loggers.size(); ++i) {
+		loggers[i]->log_error(p_function, p_file, p_line, p_code, p_rationale, p_type);
+	}
+}
+
+CompositeLogger::~CompositeLogger() {
+	for (int i = 0; i < loggers.size(); ++i) {
+		memdelete(loggers[i]);
+	}
+}
diff --git a/core/io/logger.h b/core/io/logger.h
new file mode 100644
index 000000000..cf0cc7699
--- /dev/null
+++ b/core/io/logger.h
@@ -0,0 +1,107 @@
+/*************************************************************************/
+/*  logger.h                                                             */
+/*************************************************************************/
+/*                       This file is part of:                           */
+/*                           GODOT ENGINE                                */
+/*                      https://godotengine.org                          */
+/*************************************************************************/
+/* Copyright (c) 2007-2017 Juan Linietsky, Ariel Manzur.                 */
+/* Copyright (c) 2014-2017 Godot Engine contributors (cf. AUTHORS.md)    */
+/*                                                                       */
+/* Permission is hereby granted, free of charge, to any person obtaining */
+/* a copy of this software and associated documentation files (the       */
+/* "Software"), to deal in the Software without restriction, including   */
+/* without limitation the rights to use, copy, modify, merge, publish,   */
+/* distribute, sublicense, and/or sell copies of the Software, and to    */
+/* permit persons to whom the Software is furnished to do so, subject to */
+/* the following conditions:                                             */
+/*                                                                       */
+/* The above copyright notice and this permission notice shall be        */
+/* included in all copies or substantial portions of the Software.       */
+/*                                                                       */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,       */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF    */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY  */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,  */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
+/*************************************************************************/
+
+#ifndef LOGGER_H
+#define LOGGER_H
+
+#include "os/file_access.h"
+#include "ustring.h"
+#include "vector.h"
+#include <stdarg.h>
+
+class Logger {
+protected:
+	bool should_log(bool p_err);
+
+public:
+	enum ErrorType {
+		ERR_ERROR,
+		ERR_WARNING,
+		ERR_SCRIPT,
+		ERR_SHADER
+	};
+
+	virtual void logv(const char *p_format, va_list p_list, bool p_err) = 0;
+	virtual void log_error(const char *p_function, const char *p_file, int p_line, const char *p_code, const char *p_rationale, ErrorType p_type = ERR_ERROR);
+
+	void logf(const char *p_format, ...);
+	void logf_error(const char *p_format, ...);
+
+	virtual ~Logger();
+};
+
+/**
+ * Writes messages to stdout/stderr.
+ */
+class StdLogger : public Logger {
+
+public:
+	virtual void logv(const char *p_format, va_list p_list, bool p_err);
+	virtual ~StdLogger();
+};
+
+/**
+ * Writes messages to the specified file. If the file already exists, creates a copy (backup)
+ * of it with timestamp appended to the file name. Maximum number of backups is configurable.
+ * When maximum is reached, the oldest backups are erased. With the maximum being equal to 1,
+ * it acts as a simple file logger.
+ */
+class RotatedFileLogger : public Logger {
+	String base_path;
+	int max_files;
+
+	FileAccess *file;
+
+	void rotate_file_without_closing();
+	void close_file();
+	void clear_old_backups();
+	void rotate_file();
+
+public:
+	RotatedFileLogger(const String &p_base_path, int p_max_files = 10);
+
+	virtual void logv(const char *p_format, va_list p_list, bool p_err);
+
+	virtual ~RotatedFileLogger();
+};
+
+class CompositeLogger : public Logger {
+	Vector<Logger *> loggers;
+
+public:
+	CompositeLogger(Vector<Logger *> p_loggers);
+
+	virtual void logv(const char *p_format, va_list p_list, bool p_err);
+	virtual void log_error(const char *p_function, const char *p_file, int p_line, const char *p_code, const char *p_rationale, ErrorType p_type = ERR_ERROR);
+
+	virtual ~CompositeLogger();
+};
+
+#endif
\ No newline at end of file
diff --git a/core/os/file_access.cpp b/core/os/file_access.cpp
index b969b58bf..fcb3b58fe 100644
--- a/core/os/file_access.cpp
+++ b/core/os/file_access.cpp
@@ -55,7 +55,7 @@ FileAccess *FileAccess::create(AccessType p_access) {
 
 bool FileAccess::exists(const String &p_name) {
 
-	if (PackedData::get_singleton()->has_path(p_name))
+	if (PackedData::get_singleton() && PackedData::get_singleton()->has_path(p_name))
 		return true;
 
 	FileAccess *f = open(p_name, READ);
diff --git a/core/os/file_access.h b/core/os/file_access.h
index 34e7549fa..455dd1ea9 100644
--- a/core/os/file_access.h
+++ b/core/os/file_access.h
@@ -119,6 +119,7 @@ public:
 
 	virtual Error get_error() const = 0; ///< get last error
 
+	virtual void flush() = 0;
 	virtual void store_8(uint8_t p_dest) = 0; ///< store a byte
 	virtual void store_16(uint16_t p_dest); ///< store 16 bits uint
 	virtual void store_32(uint32_t p_dest); ///< store 32 bits uint
diff --git a/core/os/os.cpp b/core/os/os.cpp
index 437ce01a5..ff17cdb50 100644
--- a/core/os/os.cpp
+++ b/core/os/os.cpp
@@ -62,20 +62,20 @@ void OS::debug_break(){
 	// something
 };
 
-void OS::print_error(const char *p_function, const char *p_file, int p_line, const char *p_code, const char *p_rationale, ErrorType p_type) {
-
-	const char *err_type = "**ERROR**";
-	switch (p_type) {
-		case ERR_ERROR: err_type = "**ERROR**"; break;
-		case ERR_WARNING: err_type = "**WARNING**"; break;
-		case ERR_SCRIPT: err_type = "**SCRIPT ERROR**"; break;
-		case ERR_SHADER: err_type = "**SHADER ERROR**"; break;
-		default: ERR_PRINT("Unknown error type"); break;
+void OS::_set_logger(Logger *p_logger) {
+	if (_logger) {
+		memdelete(_logger);
 	}
+	_logger = p_logger;
+}
+
+void OS::initialize_logger() {
+	_set_logger(memnew(StdLogger));
+}
 
-	if (p_rationale && *p_rationale)
-		print("%s: %s\n ", err_type, p_rationale);
-	print("%s: At: %s:%i:%s() - %s\n", err_type, p_file, p_line, p_function, p_code);
+void OS::print_error(const char *p_function, const char *p_file, int p_line, const char *p_code, const char *p_rationale, Logger::ErrorType p_type) {
+
+	_logger->log_error(p_function, p_file, p_line, p_code, p_rationale, p_type);
 }
 
 void OS::print(const char *p_format, ...) {
@@ -83,17 +83,16 @@ void OS::print(const char *p_format, ...) {
 	va_list argp;
 	va_start(argp, p_format);
 
-	vprint(p_format, argp);
+	_logger->logv(p_format, argp, false);
 
 	va_end(argp);
 };
 
 void OS::printerr(const char *p_format, ...) {
-
 	va_list argp;
 	va_start(argp, p_format);
 
-	vprint(p_format, argp, true);
+	_logger->logv(p_format, argp, true);
 
 	va_end(argp);
 };
@@ -533,9 +532,12 @@ OS::OS() {
 
 	_allow_hidpi = true;
 	_stack_bottom = (void *)(&stack_bottom);
+
+	_logger = NULL;
+	_set_logger(memnew(StdLogger));
 }
 
 OS::~OS() {
-
+	memdelete(_logger);
 	singleton = NULL;
 }
diff --git a/core/os/os.h b/core/os/os.h
index 38bbbc0a5..0b6229054 100644
--- a/core/os/os.h
+++ b/core/os/os.h
@@ -32,6 +32,7 @@
 
 #include "engine.h"
 #include "image.h"
+#include "io/logger.h"
 #include "list.h"
 #include "os/main_loop.h"
 #include "ustring.h"
@@ -61,6 +62,11 @@ class OS {
 
 	void *_stack_bottom;
 
+	Logger *_logger;
+
+protected:
+	void _set_logger(Logger *p_logger);
+
 public:
 	typedef void (*ImeCallback)(void *p_inp, String p_text, Point2 p_selection);
 
@@ -108,6 +114,7 @@ protected:
 	virtual int get_audio_driver_count() const = 0;
 	virtual const char *get_audio_driver_name(int p_driver) const = 0;
 
+	virtual void initialize_logger();
 	virtual void initialize_core() = 0;
 	virtual void initialize(const VideoMode &p_desired, int p_video_driver, int p_audio_driver) = 0;
 
@@ -127,18 +134,10 @@ public:
 
 	static OS *get_singleton();
 
-	enum ErrorType {
-		ERR_ERROR,
-		ERR_WARNING,
-		ERR_SCRIPT,
-		ERR_SHADER
-	};
-
-	virtual void print_error(const char *p_function, const char *p_file, int p_line, const char *p_code, const char *p_rationale, ErrorType p_type = ERR_ERROR);
+	void print_error(const char *p_function, const char *p_file, int p_line, const char *p_code, const char *p_rationale, Logger::ErrorType p_type = Logger::ERR_ERROR);
+	void print(const char *p_format, ...);
+	void printerr(const char *p_format, ...);
 
-	virtual void print(const char *p_format, ...);
-	virtual void printerr(const char *p_format, ...);
-	virtual void vprint(const char *p_format, va_list p_list, bool p_stderr = false) = 0;
 	virtual void alert(const String &p_alert, const String &p_title = "ALERT!") = 0;
 	virtual String get_stdin_string(bool p_block = true) = 0;