Writers - Zend_Log


A Writer is an object that inherits from Zend_Log_Writer_Abstract. A Writer's responsibility is to record log data to a storage backend.

Writing to Streams

Zend_Log_Writer_Stream sends log data to a » PHP stream.

To write log data to the PHP output buffer, use the URL php://output. Alternatively, you can send log data directly to a stream like STDERR (php://stderr).

  1. $writer = new Zend_Log_Writer_Stream('php://output');
  2. $logger = new Zend_Log($writer);
  4. $logger->info('Informational message');

To write data to a file, use one of the » Filesystem URLs:

  1. $writer = new Zend_Log_Writer_Stream('/path/to/logfile');
  2. $logger = new Zend_Log($writer);
  4. $logger->info('Informational message');

By default, the stream opens in the append mode ("a"). To open it with a different mode, the Zend_Log_Writer_Stream constructor accepts an optional second parameter for the mode.

The constructor of Zend_Log_Writer_Stream also accepts an existing stream resource:

  1. $stream = @fopen('/path/to/logfile', 'a', false);
  2. if (! $stream) {
  3.     throw new Exception('Failed to open stream');
  4. }
  6. $writer = new Zend_Log_Writer_Stream($stream);
  7. $logger = new Zend_Log($writer);
  9. $logger->info('Informational message');

You cannot specify the mode for existing stream resources. Doing so causes a Zend_Log_Exception to be thrown.

Writing to Databases

Zend_Log_Writer_Db writes log information to a database table using Zend_Db. The constructor of Zend_Log_Writer_Db receives a Zend_Db_Adapter instance, a table name, and a mapping of database columns to event data items:

  1. $params = array ('host'     => '',
  2.                  'username' => 'malory',
  3.                  'password' => '******',
  4.                  'dbname'   => 'camelot');
  5. $db = Zend_Db::factory('PDO_MYSQL', $params);
  7. $columnMapping = array('lvl' => 'priority', 'msg' => 'message');
  8. $writer = new Zend_Log_Writer_Db($db, 'log_table_name', $columnMapping);
  10. $logger = new Zend_Log($writer);
  12. $logger->info('Informational message');

The example above writes a single row of log data to the database table named 'log_table_name' table. The database column named 'lvl' receives the priority number and the column named 'msg' receives the log message.

Writing to Firebug

Zend_Log_Writer_Firebug sends log data to the » Firebug » Console.


All data is sent via the Zend_Wildfire_Channel_HttpHeaders component which uses HTTP headers to ensure the page content is not disturbed. Debugging AJAX requests that require clean JSON and XML responses is possible with this approach.


Example #1 Logging with Zend_Controller_Front

  1. // Place this in your bootstrap file before dispatching your front controller
  2. $writer = new Zend_Log_Writer_Firebug();
  3. $logger = new Zend_Log($writer);
  5. // Use this in your model, view and controller files
  6. $logger->log('This is a log message!', Zend_Log::INFO);

Example #2 Logging without Zend_Controller_Front

  1. $writer = new Zend_Log_Writer_Firebug();
  2. $logger = new Zend_Log($writer);
  4. $request = new Zend_Controller_Request_Http();
  5. $response = new Zend_Controller_Response_Http();
  6. $channel = Zend_Wildfire_Channel_HttpHeaders::getInstance();
  7. $channel->setRequest($request);
  8. $channel->setResponse($response);
  10. // Start output buffering
  12. // Now you can make calls to the logger
  14. $logger->log('This is a log message!', Zend_Log::INFO);
  16. // Flush log data to browser
  17. $channel->flush();
  18. $response->sendHeaders();

Setting Styles for Priorities

Built-in and user-defined priorities can be styled with the setPriorityStyle() method.

  1. $logger->addPriority('FOO', 8);
  2. $writer->setPriorityStyle(8, 'TRACE');
  3. $logger->foo('Foo Message');

The default style for user-defined priorities can be set with the setDefaultPriorityStyle() method.

  1. $writer->setDefaultPriorityStyle('TRACE');

The supported styles are as follows:

Firebug Logging Styles
Style Description
LOG Displays a plain log message
INFO Displays an info log message
WARN Displays a warning log message
ERROR Displays an error log message that increments Firebug's error count
TRACE Displays a log message with an expandable stack trace
EXCEPTION Displays an error long message with an expandable stack trace
TABLE Displays a log message with an expandable table

Preparing data for Logging

While any PHP variable can be logged with the built-in priorities, some special formatting is required if using some of the more specialized log styles.

The LOG, INFO, WARN, ERROR and TRACE styles require no special formatting.

Exception Logging

To log a Zend_Exception simply pass the exception object to the logger. It does not matter which priority or style you have set as the exception is automatically recognized.

  1. $exception = new Zend_Exception('Test exception');
  2. $logger->err($exception);

Table Logging

You can also log data and format it in a table style. Columns are automatically recognized and the first row of data automatically becomes the header.

  1. $writer->setPriorityStyle(8, 'TABLE');
  2. $logger->addPriority('TABLE', 8);
  4. $table = array('Summary line for the table',
  5.              array(
  6.                  array('Column 1', 'Column 2'),
  7.                  array('Row 1 c 1',' Row 1 c 2'),
  8.                  array('Row 2 c 1',' Row 2 c 2')
  9.              )
  10.             );
  11. $logger->table($table);

Writing to Email

Zend_Log_Writer_Mail writes log entries in an email message by using Zend_Mail. The Zend_Log_Writer_Mail constructor takes a Zend_Mail object, and an optional Zend_Layout object.

The primary use case for Zend_Log_Writer_Mail is notifying developers, systems administrators, or any concerned parties of errors that might be occurring with PHP-based scripts. Zend_Log_Writer_Mail was born out of the idea that if something is broken, a human being needs to be alerted of it immediately so they can take corrective action.

Basic usage is outlined below:

  1. $mail = new Zend_Mail();
  2. $mail->setFrom('')
  3.      ->addTo('');
  5. $writer = new Zend_Log_Writer_Mail($mail);
  7. // Set subject text for use; summary of number of errors is appended to the
  8. // subject line before sending the message.
  9. $writer->setSubjectPrependText('Errors with script foo.php');
  11. // Only email warning level entries and higher.
  12. $writer->addFilter(Zend_Log::WARN);
  14. $log = new Zend_Log();
  15. $log->addWriter($writer);
  17. // Something bad happened!
  18. $log->error('unable to connect to database');
  20. // On writer shutdown, Zend_Mail::send() is triggered to send an email with
  21. // all log entries at or above the Zend_Log filter level.

Zend_Log_Writer_Mail will render the email body as plain text by default.

One email is sent containing all log entries at or above the filter level. For example, if warning-level entries an up are to be emailed, and two warnings and five errors occur, the resulting email will contain a total of seven log entries.

Zend_Layout Usage

A Zend_Layout instance may be used to generate the HTML portion of a multipart email. If a Zend_Layout instance is in use, Zend_Log_Writer_Mail assumes that it is being used to render HTML and sets the body HTML for the message as the Zend_Layout-rendered value.

When using Zend_Log_Writer_Mail with a Zend_Layout instance, you have the option to set a custom formatter by using the setLayoutFormatter() method. If no Zend_Layout-specific entry formatter was specified, the formatter currently in use will be used. Full usage of Zend_Layout with a custom formatter is outlined below.

  1. $mail = new Zend_Mail();
  2. $mail->setFrom('')
  3.      ->addTo('');
  4. // Note that a subject line is not being set on the Zend_Mail instance!
  6. // Use a simple Zend_Layout instance with its defaults.
  7. $layout = new Zend_Layout();
  9. // Create a formatter that wraps the entry in a listitem tag.
  10. $layoutFormatter = new Zend_Log_Formatter_Simple(
  11.     '<li>' . Zend_Log_Formatter_Simple::DEFAULT_FORMAT . '</li>'
  12. );
  14. $writer = new Zend_Log_Writer_Mail($mail, $layout);
  16. // Apply the formatter for entries as rendered with Zend_Layout.
  17. $writer->setLayoutFormatter($layoutFormatter);
  18. $writer->setSubjectPrependText('Errors with script foo.php');
  19. $writer->addFilter(Zend_Log::WARN);
  21. $log = new Zend_Log();
  22. $log->addWriter($writer);
  24. // Something bad happened!
  25. $log->error('unable to connect to database');
  27. // On writer shutdown, Zend_Mail::send() is triggered to send an email with
  28. // all log entries at or above the Zend_Log filter level. The email will
  29. // contain both plain text and HTML parts.

Subject Line Error Level Summary

The setSubjectPrependText() method may be used in place of Zend_Mail::setSubject() to have the email subject line dynamically written before the email is sent. For example, if the subject prepend text reads "Errors from script", the subject of an email generated by Zend_Log_Writer_Mail with two warnings and five errors would be "Errors from script (warn = 2; error = 5)". If subject prepend text is not in use via Zend_Log_Writer_Mail, the Zend_Mail subject line, if any, is used.


Sending log entries via email can be dangerous. If error conditions are being improperly handled by your script, or if you're misusing the error levels, you might find yourself in a situation where you are sending hundreds or thousands of emails to the recipients depending on the frequency of your errors.

At this time, Zend_Log_Writer_Mail does not provide any mechanism for throttling or otherwise batching up the messages. Such functionality should be implemented by the consumer if necessary.

Again, Zend_Log_Writer_Mail's primary goal is to proactively notify a human being of error conditions. If those errors are being handled in a timely fashion, and safeguards are being put in place to prevent those circumstances in the future, then email-based notification of errors can be a valuable tool.

Writing to the System Log

Zend_Log_Writer_Syslog writes log entries to the system log (syslog). Internally, it proxies to PHP's openlog(), closelog(), and syslog() functions.

One useful case for Zend_Log_Writer_Syslog is for aggregating logs from clustered machines via the system log functionality. Many systems allow remote logging of system events, which allows system administrators to monitor a cluster of machines from a single log file.

By default, all syslog messages generated are prefixed with the string "Zend_Log". You may specify a different "application" name by which to identify such log messages by either passing the application name to the constructor or the application accessor:

  1. // At instantiation, pass the "application" key in the options:
  2. $writer = new Zend_Log_Writer_Syslog(array('application' => 'FooBar'));
  4. // Any other time:
  5. $writer->setApplicationName('BarBaz');

The system log also allows you to identify the "facility," or application type, logging the message; many system loggers will actually generate different log files per facility, which again aids administrators monitoring server activity.

You may specify the log facility either in the constructor or via an accessor. It should be one of the openlog() constants defined on the » openlog() manual page.

  1. // At instantiation, pass the "facility" key in the options:
  2. $writer = new Zend_Log_Writer_Syslog(array('facility' => LOG_AUTH));
  4. // Any other time:
  5. $writer->setFacility(LOG_USER);

When logging, you may continue to use the default Zend_Log priority constants; internally, they are mapped to the appropriate syslog() priority constants.

Writing to the Zend Server Monitor

Zend_Log_Writer_ZendMonitor allows you to log events via Zend Server's Monitor API. This allows you to aggregate log messages for your entire application environment in a single location. Internally, it simply uses the monitor_custom_event() function from the Zend Monitor API.

One particularly useful feature of the Monitor API is that it allows you to specify arbitrary custom information alongside the log message. For instance, if you wish to log an exception, you can log not just the exception message, but pass the entire exception object to the function, and then inspect the object within the Zend Server event monitor.

Note: Zend Monitor must be installed and enabled
In order to use this log writer, Zend Monitor must be both installed and enabled. However, it is designed such that if Zend Monitor is not detected, it will simply act as a NULL logger.

Instantiating the ZendMonitor log writer is trivial:

  1. $writer = new Zend_Log_Writer_ZendMonitor();
  2. $log    = new Zend_Log($writer);

Then, simply log messages as usual:

  1. $log->info('This is a message');

If you want to specify additional information to log with the event, pass that information in a second parameter:

  1. $log->info('Exception occurred', $e);

The second parameter may be a scalar, object, or array; if you need to pass multiple pieces of information, the best way to do so is to pass an associative array.

  1. $log->info('Exception occurred', array(
  2.     'request'   => $request,
  3.     'exception' => $e,
  4. ));

Within Zend Server, your event is logged as a "custom event". From the "Monitor" tab, select the "Events" sub-item, and then filter on "Custom" to see custom events.


Events in Zend Server's Monitor dashboard

In this screenshot, the first two events listed are custom events logged via the ZendMonitor log writer. You may then click on an event to view all information related to it.


Event detail in Zend Server's Monitor

Clicking on the "Custom" sub tab will detail any extra information you logged by passing the second argument to the logging method. This information will be logged as the info subkey; you can see that the request object was logged in this example.

Note: Integration with Zend_Application
By default, the and zf.bat commands add configuration for the Zend_Application log resource, which includes configuration for the ZendMonitor log writer. Additionally, the ErrorController uses the configured logger to log application exceptions -- providing you with Zend Monitor event integration by default.
As noted previously, if the Monitor API is not detected in your PHP installation, the logger will simply act as a NULL logger.

Stubbing Out the Writer

The Zend_Log_Writer_Null is a stub that does not write log data to anything. It is useful for disabling logging or stubbing out logging during tests:

  1. $writer = new Zend_Log_Writer_Null;
  2. $logger = new Zend_Log($writer);
  4. // goes nowhere
  5. $logger->info('Informational message');

Testing with the Mock

The Zend_Log_Writer_Mock is a very simple writer that records the raw data it receives in an array exposed as a public property.

  1. $mock = new Zend_Log_Writer_Mock;
  2. $logger = new Zend_Log($mock);
  4. $logger->info('Informational message');
  6. var_dump($mock->events[0]);
  8. // Array
  9. // (
  10. //    [timestamp] => 2007-04-06T07:16:37-07:00
  11. //    [message] => Informational message
  12. //    [priority] => 6
  13. //    [priorityName] => INFO
  14. // )

To clear the events logged by the mock, simply set $mock->events = array().

Compositing Writers

There is no composite Writer object. However, a Log instance can write to any number of Writers. To do this, use the addWriter() method:

  1. $writer1 = new Zend_Log_Writer_Stream('/path/to/first/logfile');
  2. $writer2 = new Zend_Log_Writer_Stream('/path/to/second/logfile');
  4. $logger = new Zend_Log();
  5. $logger->addWriter($writer1);
  6. $logger->addWriter($writer2);
  8. // goes to both writers
  9. $logger->info('Informational message');


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