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| <section id='main' class="content"> |
| <h1 class='fqn'><span class='in-band'>Crate <a class="mod" href=''>log</a></span><span class='out-of-band'><span id='render-detail'> |
| <a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs"> |
| [<span class='inner'>−</span>] |
| </a> |
| </span><a class='srclink' href='../src/log/lib.rs.html#11-1091' title='goto source code'>[src]</a></span></h1> |
| <div class='docblock'><p>A lightweight logging facade.</p> |
| |
| <p>A logging facade provides a single logging API that abstracts over the |
| actual logging implementation. Libraries can use the logging API provided |
| by this crate, and the consumer of those libraries can choose the logging |
| framework that is most suitable for its use case.</p> |
| |
| <p>If no logging implementation is selected, the facade falls back to a "noop" |
| implementation that ignores all log messages. The overhead in this case |
| is very small - just an integer load, comparison and jump.</p> |
| |
| <p>A log request consists of a target, a level, and a body. A target is a |
| string which defaults to the module path of the location of the log |
| request, though that default may be overridden. Logger implementations |
| typically use the target to filter requests based on some user |
| configuration.</p> |
| |
| <h1 id='use' class='section-header'><a href='#use'>Use</a></h1> |
| <h2 id='in-libraries' class='section-header'><a href='#in-libraries'>In libraries</a></h2> |
| <p>Libraries should link only to the <code>log</code> crate, and use the provided |
| macros to log whatever information will be useful to downstream consumers.</p> |
| |
| <h3 id='examples' class='section-header'><a href='#examples'>Examples</a></h3> |
| <pre class="rust rust-example-rendered"> |
| <span class="attribute">#[<span class="ident">macro_use</span>]</span> |
| <span class="kw">extern</span> <span class="kw">crate</span> <span class="ident">log</span>; |
| |
| <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">shave_the_yak</span>(<span class="ident">yak</span>: <span class="kw-2">&</span><span class="ident">Yak</span>) { |
| <span class="macro">info</span><span class="macro">!</span>(<span class="ident">target</span>: <span class="string">"yak_events"</span>, <span class="string">"Commencing yak shaving for {:?}"</span>, <span class="ident">yak</span>); |
| |
| <span class="kw">loop</span> { |
| <span class="kw">match</span> <span class="ident">find_a_razor</span>() { |
| <span class="prelude-val">Ok</span>(<span class="ident">razor</span>) <span class="op">=></span> { |
| <span class="macro">info</span><span class="macro">!</span>(<span class="string">"Razor located: {}"</span>, <span class="ident">razor</span>); |
| <span class="ident">yak</span>.<span class="ident">shave</span>(<span class="ident">razor</span>); |
| <span class="kw">break</span>; |
| } |
| <span class="prelude-val">Err</span>(<span class="ident">err</span>) <span class="op">=></span> { |
| <span class="macro">warn</span><span class="macro">!</span>(<span class="string">"Unable to locate a razor: {}, retrying"</span>, <span class="ident">err</span>); |
| } |
| } |
| } |
| }</pre> |
| |
| <h2 id='in-executables' class='section-header'><a href='#in-executables'>In executables</a></h2> |
| <p>Executables should choose a logging framework and initialize it early in the |
| runtime of the program. Logging frameworks will typically include a |
| function to do this. Any log messages generated before the framework is |
| initialized will be ignored.</p> |
| |
| <p>The executable itself may use the <code>log</code> crate to log as well.</p> |
| |
| <h3 id='warning' class='section-header'><a href='#warning'>Warning</a></h3> |
| <p>The logging system may only be initialized once.</p> |
| |
| <h3 id='examples-1' class='section-header'><a href='#examples-1'>Examples</a></h3> |
| <pre class="rust rust-example-rendered"> |
| <span class="attribute">#[<span class="ident">macro_use</span>]</span> |
| <span class="kw">extern</span> <span class="kw">crate</span> <span class="ident">log</span>; |
| <span class="kw">extern</span> <span class="kw">crate</span> <span class="ident">my_logger</span>; |
| |
| <span class="kw">fn</span> <span class="ident">main</span>() { |
| <span class="ident">my_logger</span>::<span class="ident">init</span>(); |
| |
| <span class="macro">info</span><span class="macro">!</span>(<span class="string">"starting up"</span>); |
| |
| <span class="comment">// ...</span> |
| }</pre> |
| |
| <h1 id='logger-implementations' class='section-header'><a href='#logger-implementations'>Logger implementations</a></h1> |
| <p>Loggers implement the <code>Log</code> trait. Here's a very basic example that simply |
| logs all messages at the <code>Error</code>, <code>Warn</code> or <code>Info</code> levels to stdout:</p> |
| |
| <pre class="rust rust-example-rendered"> |
| <span class="kw">extern</span> <span class="kw">crate</span> <span class="ident">log</span>; |
| |
| <span class="kw">use</span> <span class="ident">log</span>::{<span class="ident">LogRecord</span>, <span class="ident">LogLevel</span>, <span class="ident">LogMetadata</span>}; |
| |
| <span class="kw">struct</span> <span class="ident">SimpleLogger</span>; |
| |
| <span class="kw">impl</span> <span class="ident">log</span>::<span class="ident">Log</span> <span class="kw">for</span> <span class="ident">SimpleLogger</span> { |
| <span class="kw">fn</span> <span class="ident">enabled</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">metadata</span>: <span class="kw-2">&</span><span class="ident">LogMetadata</span>) <span class="op">-></span> <span class="ident">bool</span> { |
| <span class="ident">metadata</span>.<span class="ident">level</span>() <span class="op"><=</span> <span class="ident">LogLevel</span>::<span class="ident">Info</span> |
| } |
| |
| <span class="kw">fn</span> <span class="ident">log</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">record</span>: <span class="kw-2">&</span><span class="ident">LogRecord</span>) { |
| <span class="kw">if</span> <span class="self">self</span>.<span class="ident">enabled</span>(<span class="ident">record</span>.<span class="ident">metadata</span>()) { |
| <span class="macro">println</span><span class="macro">!</span>(<span class="string">"{} - {}"</span>, <span class="ident">record</span>.<span class="ident">level</span>(), <span class="ident">record</span>.<span class="ident">args</span>()); |
| } |
| } |
| } |
| </pre> |
| |
| <p>Loggers are installed by calling the <code>set_logger</code> function. It takes a |
| closure which is provided a <code>MaxLogLevel</code> token and returns a <code>Log</code> trait |
| object. The <code>MaxLogLevel</code> token controls the global maximum log level. The |
| logging facade uses this as an optimization to improve performance of log |
| messages at levels that are disabled. In the case of our example logger, |
| we'll want to set the maximum log level to <code>Info</code>, since we ignore any |
| <code>Debug</code> or <code>Trace</code> level log messages. A logging framework should provide a |
| function that wraps a call to <code>set_logger</code>, handling initialization of the |
| logger:</p> |
| |
| <pre class="rust rust-example-rendered"> |
| <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">init</span>() <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span>(), <span class="ident">SetLoggerError</span><span class="op">></span> { |
| <span class="ident">log</span>::<span class="ident">set_logger</span>(<span class="op">|</span><span class="ident">max_log_level</span><span class="op">|</span> { |
| <span class="ident">max_log_level</span>.<span class="ident">set</span>(<span class="ident">LogLevelFilter</span>::<span class="ident">Info</span>); |
| <span class="ident">Box</span>::<span class="ident">new</span>(<span class="ident">SimpleLogger</span>) |
| }) |
| }</pre> |
| |
| <h1 id='use-with-no_std' class='section-header'><a href='#use-with-no_std'>Use with <code>no_std</code></a></h1> |
| <p>To use the <code>log</code> crate without depending on <code>libstd</code>, you need to specify |
| <code>default-features = false</code> when specifying the dependency in <code>Cargo.toml</code>. |
| This makes no difference to libraries using <code>log</code> since the logging API |
| remains the same. However executables will need to use the <code>set_logger_raw</code> |
| function to initialize a logger and the <code>shutdown_logger_raw</code> function to |
| shut down the global logger before exiting:</p> |
| |
| <pre class="rust rust-example-rendered"> |
| <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">init</span>() <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span>(), <span class="ident">SetLoggerError</span><span class="op">></span> { |
| <span class="kw">unsafe</span> { |
| <span class="ident">log</span>::<span class="ident">set_logger_raw</span>(<span class="op">|</span><span class="ident">max_log_level</span><span class="op">|</span> { |
| <span class="kw">static</span> <span class="ident">LOGGER</span>: <span class="ident">SimpleLogger</span> <span class="op">=</span> <span class="ident">SimpleLogger</span>; |
| <span class="ident">max_log_level</span>.<span class="ident">set</span>(<span class="ident">LogLevelFilter</span>::<span class="ident">Info</span>); |
| <span class="kw-2">&</span><span class="ident">SimpleLogger</span> |
| }) |
| } |
| } |
| <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">shutdown</span>() <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span>(), <span class="ident">ShutdownLoggerError</span><span class="op">></span> { |
| <span class="ident">log</span>::<span class="ident">shutdown_logger_raw</span>().<span class="ident">map</span>(<span class="op">|</span><span class="ident">logger</span><span class="op">|</span> { |
| <span class="kw">let</span> <span class="ident">logger</span> <span class="op">=</span> <span class="kw">unsafe</span> { <span class="kw-2">&</span><span class="kw-2">*</span>(<span class="ident">logger</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw">const</span> <span class="ident">SimpleLogger</span>) }; |
| <span class="ident">logger</span>.<span class="ident">flush</span>(); |
| }) |
| }</pre> |
| </div><h2 id='macros' class='section-header'><a href="#macros">Macros</a></h2> |
| <table> |
| <tr class=' module-item'> |
| <td><a class="macro" href="macro.debug.html" |
| title='macro log::debug'>debug</a></td> |
| <td class='docblock-short'> |
| <p>Logs a message at the debug level.</p> |
| </td> |
| </tr> |
| <tr class=' module-item'> |
| <td><a class="macro" href="macro.error.html" |
| title='macro log::error'>error</a></td> |
| <td class='docblock-short'> |
| <p>Logs a message at the error level.</p> |
| </td> |
| </tr> |
| <tr class=' module-item'> |
| <td><a class="macro" href="macro.info.html" |
| title='macro log::info'>info</a></td> |
| <td class='docblock-short'> |
| <p>Logs a message at the info level.</p> |
| </td> |
| </tr> |
| <tr class=' module-item'> |
| <td><a class="macro" href="macro.log.html" |
| title='macro log::log'>log</a></td> |
| <td class='docblock-short'> |
| <p>The standard logging macro.</p> |
| </td> |
| </tr> |
| <tr class=' module-item'> |
| <td><a class="macro" href="macro.log_enabled.html" |
| title='macro log::log_enabled'>log_enabled</a></td> |
| <td class='docblock-short'> |
| <p>Determines if a message logged at the specified level in that module will |
| be logged.</p> |
| </td> |
| </tr> |
| <tr class=' module-item'> |
| <td><a class="macro" href="macro.trace.html" |
| title='macro log::trace'>trace</a></td> |
| <td class='docblock-short'> |
| <p>Logs a message at the trace level.</p> |
| </td> |
| </tr> |
| <tr class=' module-item'> |
| <td><a class="macro" href="macro.warn.html" |
| title='macro log::warn'>warn</a></td> |
| <td class='docblock-short'> |
| <p>Logs a message at the warn level.</p> |
| </td> |
| </tr></table><h2 id='structs' class='section-header'><a href="#structs">Structs</a></h2> |
| <table> |
| <tr class=' module-item'> |
| <td><a class="struct" href="struct.LogLocation.html" |
| title='struct log::LogLocation'>LogLocation</a></td> |
| <td class='docblock-short'> |
| <p>The location of a log message.</p> |
| </td> |
| </tr> |
| <tr class=' module-item'> |
| <td><a class="struct" href="struct.LogMetadata.html" |
| title='struct log::LogMetadata'>LogMetadata</a></td> |
| <td class='docblock-short'> |
| <p>Metadata about a log message.</p> |
| </td> |
| </tr> |
| <tr class=' module-item'> |
| <td><a class="struct" href="struct.LogRecord.html" |
| title='struct log::LogRecord'>LogRecord</a></td> |
| <td class='docblock-short'> |
| <p>The "payload" of a log message.</p> |
| </td> |
| </tr> |
| <tr class=' module-item'> |
| <td><a class="struct" href="struct.MaxLogLevelFilter.html" |
| title='struct log::MaxLogLevelFilter'>MaxLogLevelFilter</a></td> |
| <td class='docblock-short'> |
| <p>A token providing read and write access to the global maximum log level |
| filter.</p> |
| </td> |
| </tr> |
| <tr class=' module-item'> |
| <td><a class="struct" href="struct.SetLoggerError.html" |
| title='struct log::SetLoggerError'>SetLoggerError</a></td> |
| <td class='docblock-short'> |
| <p>The type returned by <code>set_logger</code> if <code>set_logger</code> has already been called.</p> |
| </td> |
| </tr> |
| <tr class=' module-item'> |
| <td><a class="struct" href="struct.ShutdownLoggerError.html" |
| title='struct log::ShutdownLoggerError'>ShutdownLoggerError</a></td> |
| <td class='docblock-short'> |
| <p>The type returned by <code>shutdown_logger_raw</code> if <code>shutdown_logger_raw</code> has |
| already been called or if <code>set_logger_raw</code> has not been called yet.</p> |
| </td> |
| </tr></table><h2 id='enums' class='section-header'><a href="#enums">Enums</a></h2> |
| <table> |
| <tr class=' module-item'> |
| <td><a class="enum" href="enum.LogLevel.html" |
| title='enum log::LogLevel'>LogLevel</a></td> |
| <td class='docblock-short'> |
| <p>An enum representing the available verbosity levels of the logging framework</p> |
| </td> |
| </tr> |
| <tr class=' module-item'> |
| <td><a class="enum" href="enum.LogLevelFilter.html" |
| title='enum log::LogLevelFilter'>LogLevelFilter</a></td> |
| <td class='docblock-short'> |
| <p>An enum representing the available verbosity level filters of the logging |
| framework.</p> |
| </td> |
| </tr></table><h2 id='traits' class='section-header'><a href="#traits">Traits</a></h2> |
| <table> |
| <tr class=' module-item'> |
| <td><a class="trait" href="trait.Log.html" |
| title='trait log::Log'>Log</a></td> |
| <td class='docblock-short'> |
| <p>A trait encapsulating the operations required of a logger</p> |
| </td> |
| </tr></table><h2 id='functions' class='section-header'><a href="#functions">Functions</a></h2> |
| <table> |
| <tr class=' module-item'> |
| <td><a class="fn" href="fn.max_log_level.html" |
| title='fn log::max_log_level'>max_log_level</a></td> |
| <td class='docblock-short'> |
| <p>Returns the current maximum log level.</p> |
| </td> |
| </tr> |
| <tr class=' module-item'> |
| <td><a class="fn" href="fn.set_logger.html" |
| title='fn log::set_logger'>set_logger</a></td> |
| <td class='docblock-short'> |
| <p>Sets the global logger.</p> |
| </td> |
| </tr> |
| <tr class=' module-item'> |
| <td><a class="fn" href="fn.set_logger_raw.html" |
| title='fn log::set_logger_raw'>set_logger_raw</a><a title='unsafe function' href='#'><sup>⚠</sup></a></td> |
| <td class='docblock-short'> |
| <p>Sets the global logger from a raw pointer.</p> |
| </td> |
| </tr> |
| <tr class=' module-item'> |
| <td><a class="fn" href="fn.shutdown_logger.html" |
| title='fn log::shutdown_logger'>shutdown_logger</a></td> |
| <td class='docblock-short'> |
| <p>Shuts down the global logger.</p> |
| </td> |
| </tr> |
| <tr class=' module-item'> |
| <td><a class="fn" href="fn.shutdown_logger_raw.html" |
| title='fn log::shutdown_logger_raw'>shutdown_logger_raw</a></td> |
| <td class='docblock-short'> |
| <p>Shuts down the global logger.</p> |
| </td> |
| </tr></table></section> |
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