kea/src/lib/log/logger.h

// Copyright (C) 2011  Internet Systems Consortium, Inc. ("ISC")
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice appear in all copies.
//
// THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
// AND FITNESS.  IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
// OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
// PERFORMANCE OF THIS SOFTWARE.

#ifndef __LOGGER_H
#define __LOGGER_H

#include <cstdlib>
#include <string>

#include <log/logger_level.h>
#include <log/message_types.h>
#include <log/log_formatter.h>

namespace isc {
namespace log {

/// \page LoggingApi Logging API
/// \section LoggingApiOverview Overview
/// BIND 10 logging uses the concepts of the widely-used Java logging
/// package log4j (http://logging.apache.log/log4j), albeit implemented 
/// in C++ using an open-source port.  Features of the system are:
/// 
/// - Within the code objects - known as loggers - can be created and
/// used to log messages.  These loggers have names; those with the
/// same name share characteristics (such as output destination).
/// - Loggers have a hierarchical relationship, with each logger being
/// the child of another logger, except for the top of the hierarchy, the
/// root logger.  If a logger does not log a message, it is passed to the
/// parent logger.
/// - Messages can be logged at severity levels of FATAL, ERROR, WARN, INFO
/// or DEBUG.  The DEBUG level has further sub-levels numbered 0 (least
/// informative) to 99 (most informative).
/// - Each logger has a severity level set associated with it.  When a
/// message is logged, it is output only if it is logged at a level equal
/// to the logger severity level or greater, e.g. if the logger's severity
/// is WARN, only messages logged at WARN, ERROR or FATAL will be output.
/// 
/// \section LoggingApiLoggerNames BIND 10 Logger Names
/// Within BIND 10, the root logger root logger is given the name of the
/// program (via the stand-along function setRootLoggerName()). Other loggers
/// are children of the root logger and are named "<program>.<sublogger>".
/// This name appears in logging output, allowing users to identify both
/// the BIND 10 program and the component within the program that generated
/// the message.
/// 
/// When creating a logger, the abbreviated name "<sublogger>" can be used;
/// the program name will be prepended to it when the logger is created.
/// In this way, individual libraries can have their own loggers without
/// worrying about the program in which they are used, but:
/// - The origin of the message will be clearly identified.
/// - The same component can have different options (e.g. logging severity)
/// in different programs at the same time.
/// 
/// \section LoggingApiLoggingMessages Logging Messages
/// Instead of embedding the text of messages within the code, each message
/// is referred to using a symbolic name.  The logging code uses this name as
/// a key in a dictionary from which the message text is obtained.  Such a
/// system allows for the optional replacement of message text at run time.
/// More details about the message disction (and the compiler used to create
/// the symbol definitions) can be found in other modules in the src/lib/log
/// directory.

class LoggerImpl;   // Forward declaration of the implementation class

/// \brief Logger Class
///
/// This class is the main class used for logging.  Use comprises:
///
/// 1. Constructing a logger by instantiating it with a specific name.  As
/// well as instantiating it when needed, the logger can also be declared
/// outside a program using.
///
/// 2. Using the error(), info() etc. methods to log an error.  (Although it is
/// recommended to use the LOG_ERROR, LOG_INFO etc. macros defined in macros.h.
/// These will avoid the potentially-expensive evaluation of arguments if the
/// severity is such that the message will be suppressed.)

class Logger {
public:

    /// \brief Constructor
    ///
    /// Creates/attaches to a logger of a specific name.
    ///
    /// \param name Name of the logger.  If the name is that of the root name,
    /// this creates an instance of the root logger; otherwise it creates a
    /// child of the root logger.
    Logger(const std::string& name) : loggerptr_(NULL), name_(name)
    {}

    /// \brief Destructor
    virtual ~Logger();

    /// \brief The formatter used to replace placeholders
    typedef isc::log::Formatter<Logger> Formatter;

    /// \brief Get Name of Logger
    ///
    /// \return The full name of the logger (including the root name)
    virtual std::string getName();

    /// \brief Set Severity Level for Logger
    ///
    /// Sets the level at which this logger will log messages.  If none is set,
    /// the level is inherited from the parent.
    ///
    /// \param severity Severity level to log
    /// \param dbglevel If the severity is DEBUG, this is the debug level.
    /// This can be in the range 1 to 100 and controls the verbosity.  A value
    /// outside these limits is silently coerced to the nearest boundary.
    virtual void setSeverity(isc::log::Severity severity, int dbglevel = 1);

    /// \brief Get Severity Level for Logger
    ///
    /// \return The current logging level of this logger.  In most cases though,
    /// the effective logging level is what is required.
    virtual isc::log::Severity getSeverity();

    /// \brief Get Effective Severity Level for Logger
    ///
    /// \return The effective severity level of the logger.  This is the same
    /// as getSeverity() if the logger has a severity level set, but otherwise
    /// is the severity of the parent.
    virtual isc::log::Severity getEffectiveSeverity();

    /// \brief Return DEBUG Level
    ///
    /// \return Current setting of debug level.  This is returned regardless of
    /// whether the severity is set to debug.
    virtual int getDebugLevel();

    /// \brief Returns if Debug Message Should Be Output
    ///
    /// \param dbglevel Level for which debugging is checked.  Debugging is
    /// enabled only if the logger has DEBUG enabled and if the dbglevel
    /// checked is less than or equal to the debug level set for the logger.
    virtual bool isDebugEnabled(int dbglevel = MIN_DEBUG_LEVEL);

    /// \brief Is INFO Enabled?
    virtual bool isInfoEnabled();

    /// \brief Is WARNING Enabled?
    virtual bool isWarnEnabled();

    /// \brief Is ERROR Enabled?
    virtual bool isErrorEnabled();

    /// \brief Is FATAL Enabled?
    virtual bool isFatalEnabled();

    /// \brief Output Debug Message
    ///
    /// \param dbglevel Debug level, ranging between 0 and 99.  Higher numbers
    /// are used for more verbose output.
    /// \param ident Message identification.
    Formatter debug(int dbglevel, const MessageID& ident);

    /// \brief Output Informational Message
    ///
    /// \param ident Message identification.
    Formatter info(const MessageID& ident);

    /// \brief Output Warning Message
    ///
    /// \param ident Message identification.
    Formatter warn(const MessageID& ident);

    /// \brief Output Error Message
    ///
    /// \param ident Message identification.
    Formatter error(const MessageID& ident);

    /// \brief Output Fatal Message
    ///
    /// \param ident Message identification.
    Formatter fatal(const MessageID& ident);

    /// \brief Equality
    ///
    /// Check if two instances of this logger refer to the same stream.
    ///
    /// \return true if the logger objects are instances of the same logger.
    bool operator==(Logger& other);

private:
    friend class isc::log::Formatter<Logger>;

    /// \brief Raw output function
    ///
    /// This is used by the formatter to output formatted output.
    ///
    /// \param severity Severity of the message being output.
    /// \param message Text of the message to be output.
    void output(const Severity& severity, const std::string& message);

    /// \brief Copy Constructor
    ///
    /// Disabled (marked private) as it makes no sense to copy the logger -
    /// just create another one of the same name.
    Logger(const Logger&);

    /// \brief Assignment Operator
    ///
    /// Disabled (marked private) as it makes no sense to copy the logger -
    /// just create another one of the same name.
    Logger& operator=(const Logger&);

    /// \brief Initialize Implementation
    ///
    /// Returns the logger pointer.  If not yet set, the underlying
    /// implementation class is initialized.\n
    /// \n
    /// The reason for this indirection is to avoid the "static initialization
    /// fiacso", whereby we cannot rely on the order of static initializations.
    /// The main problem is the root logger name - declared statically - which
    /// is referenced by various loggers.  By deferring a reference to it until
    /// after the program starts executing - by which time the root name object
    /// will be initialized - we avoid this problem.
    ///
    /// \return Returns pointer to implementation
    LoggerImpl* getLoggerPtr() {
        if (!loggerptr_) {
            initLoggerImpl();
        }
        return (loggerptr_);
    }

    /// \brief Initialize Underlying Implementation and Set loggerptr_
    void initLoggerImpl();

    LoggerImpl*     loggerptr_;     ///< Pointer to the underlying logger
    std::string     name_;          ///< Copy of the logger name
};

} // namespace log
} // namespace isc


#endif // __LOGGER_H