~~ ====================================================================
~~ Licensed to the Apache Software Foundation (ASF) under one
~~ or more contributor license agreements.  See the NOTICE file
~~ distributed with this work for additional information
~~ regarding copyright ownership.  The ASF licenses this file
~~ to you under the Apache License, Version 2.0 (the
~~ "License"); you may not use this file except in compliance
~~ with the License.  You may obtain a copy of the License at
~~
~~   http://www.apache.org/licenses/LICENSE-2.0
~~
~~ Unless required by applicable law or agreed to in writing,
~~ software distributed under the License is distributed on an
~~ "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
~~ KIND, either express or implied.  See the License for the
~~ specific language governing permissions and limitations
~~ under the License.
~~ ====================================================================
~~
~~ This software consists of voluntary contributions made by many
~~ individuals on behalf of the Apache Software Foundation.  For more
~~ information on the Apache Software Foundation, please see
~~ <http://www.apache.org/>.

    ----------
    HttpClient Logging Practices
    ----------
    ----------
    ----------

Logging Practices

    Being a library HttpClient is not to dictate which logging framework the user has to use. 
    Therefore  HttpClient utilizes the logging facade provided by the 
    {{{https://logging.apache.org/log4j/2.x/manual/api.html}Apache Log4j 2}} package. 
    <<<Log4j 2>>> provides a simple and generalized 
    {{{https://logging.apache.org/log4j/2.x/log4j-api/apidocs/index.html?org/apache/logging/log4j/package-summary.html}log interface}} to 
    various logging packages. By using <<<Log4j>>>, HttpClient can be configured for a 
    variety of different logging behaviours. That means the user will have to make a choice which 
    logging implementation to use. By default <<<Log4j 2>>> supports the following logging 
    implementation:

    * {{{https://logging.apache.org/log4j/2.x/}Log4J 2}}

    * {{{https://logging.apache.org/log4j/2.x/log4j-to-slf4j/index.html}SLF4J}}

    * {{{https://logging.apache.org/log4j/2.x/log4j-api/apidocs/org/apache/logging/log4j/simple/SimpleLogger.html}
      SimpleLog}} (internal to <<<Log4J 2>>>)

    * {{{https://logging.apache.org/log4j/2.x/log4j-jul/index.html}
      java.util.logging}}
      
    By implementing some simple interfaces <<<Log4J 2>>> can be extended to support 
    basically any other custom logging framework. <<<Log4J 2>>> tries to automatically 
    discover the logging framework to use. If it fails to select the expected one, you must 
    configure <<<Log4J 2>>> by hand. Please refer to the <<<Log4J 2>>> 
    documentation for more information.

    HttpClient performs three different kinds of logging: the standard context logging used within 
    each class, HTTP header logging and full wire logging.            

* {Understanding Logger Names}

    Most logging implementations use a hierarchical scheme for matching logger names with logging
    configuration. In this scheme, the logger name hierarchy is represented by <<<'.'>>> characters 
    in the logger name, in a fashion very similar to the hierarchy used for Java package names. For example,
    <<<org.apache.logging.appender>>> and <<<org.apache.logging.filter>>> both have 
    <<<org.apache.logging>>> as their parent. In most cases, applications name their loggers by 
    passing the current class's name to <<<LogManager.getLogger(...)>>>. 
              
* {Context Logging}

    Context logging contains information about the internal operation of HttpClient as it performs 
    HTTP requests.  Each class has its own logger named according to the class's fully qualified name. 
    For example the class <<<DefaultHttpClient>>> has a logger named 
    <<<org.apache.http.impl.client.DefaultHttpClient>>>. Since all classes follow this convention 
    it is possible to configure context logging for all classes using the single logger named 
    <<<org.apache.hc.client5.http>>>.

* {Wire Logging}

    The wire logger is used to log all data transmitted to and from servers when executing HTTP 
    requests. The wire logger uses the <<<org.apache.hc.client5.http.wire>>> logger name. This logger should 
    only be enabled to debug problems, as it will produce an extremely large amount of log data.
    
* {HTTP header Logging}

    Because the content of HTTP requests is usually less important for debugging than the HTTP 
    headers, use the <<<org.apache.hc.client5.http.headers>>> logger for capturing HTTP headers only.

* {Configuration Examples}

    <<<Log4j 2>>> can delegate to a variety of logging implementations for processing the actual output. 
    Below are configuration examples for <<<Log4j 2>>>, <<<Commons Logging>>>, and 
    <<<java.util.logging>>>.

** {Log4j 2 Examples}

    The simplest way to {{{https://logging.apache.org/log4j/2.x/manual/configuration.html}configure}} <<<Log4j 2>>> 
    is via a <<<log4j2.xml>>> file. <<<Log4j 2>>> will 
    {{{https://logging.apache.org/log4j/2.x/manual/configuration.html#AutomaticConfiguration}automatically}}
    configure itself using a file named <<<log4j2.xml>>> when  it's present at the root of the  application 
    classpath. Below are some <<<Log4j>>> configuration examples.

    <<Note:>> The <<<Log4j 2>>> implementation a.k.a "core" is not included in the <<<HttpClient>>> distribution.
    You can include it in your project using 
    {{{https://logging.apache.org/log4j/2.x/maven-artifacts.html}Maven, Ivy, Gradle, or SBT}}.              
    
    * Enable header wire + context logging - <<Best for Debugging>>

--------------------------------------
<Configuration>
  <Appenders>
    <Console name="STDOUT">
      <PatternLayout pattern="%d %-5level [%logger] %msg%n%xThrowable" />
    </Console>
  </Appenders>
  <Loggers>
    <Logger name="org.apache.hc.client5.http" level="DEBUG">
      <AppenderRef ref="Console"/>
    </Logger>
    <Logger name="org.apache.hc.client5.http.wire" level="DEBUG">
      <AppenderRef ref="Console"/>
    </Logger>
    <Root level="INFO">
      <AppenderRef ref="STDOUT" />
    </Root>
  </Loggers>
</Configuration>
--------------------------------------
 
    * Enable full wire + context logging

--------------------------------------
<Configuration>
  <Appenders>
    <Console name="STDOUT">
      <PatternLayout pattern="%d %-5level [%logger] %msg%n%xThrowable" />
    </Console>
  </Appenders>
  <Loggers>
    <Logger name="org.apache.hc.client5.http" level="DEBUG">
      <AppenderRef ref="Console"/>
    </Logger>
    <Root level="INFO">
      <AppenderRef ref="STDOUT" />
    </Root>
  </Loggers>
</Configuration>
--------------------------------------
 
    * Enable context logging for connection management

--------------------------------------
<Configuration>
  <Appenders>
    <Console name="STDOUT">
      <PatternLayout pattern="%d %-5level [%logger] %msg%n%xThrowable" />
    </Console>
  </Appenders>
  <Loggers>
    <Logger name="org.apache.hc.client5.http.impl.io" level="DEBUG">
      <AppenderRef ref="Console"/>
    </Logger>
    <Logger name="org.apache.hc.client5.http.impl.nio" level="DEBUG">
      <AppenderRef ref="Console"/>
    </Logger>
    <Root level="INFO">
      <AppenderRef ref="STDOUT" />
    </Root>
  </Loggers>
</Configuration>
--------------------------------------
 
    * Enable context logging for connection management / request execution

--------------------------------------
<Configuration>
  <Appenders>
    <Console name="STDOUT">
      <PatternLayout pattern="%d %-5level [%logger] %msg%n%xThrowable" />
    </Console>
  </Appenders>
  <Loggers>
    <Logger name="org.apache.hc.client5.http.impl" level="DEBUG">
      <AppenderRef ref="Console"/>
    </Logger>
    <Root level="INFO">
      <AppenderRef ref="STDOUT" />
    </Root>
  </Loggers>
</Configuration>
--------------------------------------

    []

    The <<<Log4J 2>>> manual is the best reference for how to configure <<<Log4J 2>>>. It is available at 
    {{{https://logging.apache.org/log4j/2.x/manual/}
    https://logging.apache.org/log4j/2.x/manual/}}.