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<h1 id="日志"><a class="header" href="#日志">日志</a></h1>
<h2 id="log-包"><a class="header" href="#log-包">log 包</a></h2>
<p><a href="https://docs.rs/crate/log/0.4.16">log</a> 提供了日志相关的实用工具。</p>
<h3 id="在控制台打印-debug-信息"><a class="header" href="#在控制台打印-debug-信息">在控制台打印 debug 信息</a></h3>
<p><code>env_logger</code> 通过环境变量来配置日志。<a href="https://docs.rs/log/0.4.16/log/macro.debug.html">log::debug!</a> 使用起来跟 <a href="https://doc.rust-lang.org/std/fmt/">std::fmt</a> 中的格式化字符串很像。</p>
<pre><pre class="playground"><code class="language-rust edition2021">fn execute_query(query: &amp;str) {
log::debug!(&quot;Executing query: {}&quot;, query);
}
fn main() {
env_logger::init();
execute_query(&quot;DROP TABLE students&quot;);
}
</code></pre></pre>
<p>如果大家运行代码,会发现没有任何日志输出,原因是默认的日志级别是 <code>error</code>,因此我们需要通过 <code>RUST_LOG</code> 环境变量来设置下新的日志级别:</p>
<pre><code class="language-shell">$ RUST_LOG=debug cargo run
</code></pre>
<p>然后你将成功看到以下输出:</p>
<pre><code class="language-shell">DEBUG:main: Executing query: DROP TABLE students
</code></pre>
<h3 id="将错误日志输出到控制台"><a class="header" href="#将错误日志输出到控制台">将错误日志输出到控制台</a></h3>
<p>下面我们通过 <a href="https://docs.rs/log/0.4.16/log/macro.error.html">log::error!</a> 将错误日志输出到标准错误 <code>stderr</code></p>
<pre><pre class="playground"><code class="language-rust edition2021">fn execute_query(_query: &amp;str) -&gt; Result&lt;(), &amp;'static str&gt; {
Err(&quot;I'm afraid I can't do that&quot;)
}
fn main() {
env_logger::init();
let response = execute_query(&quot;DROP TABLE students&quot;);
if let Err(err) = response {
log::error!(&quot;Failed to execute query: {}&quot;, err);
}
}
</code></pre></pre>
<h3 id="将错误输出到标准输出-stdout"><a class="header" href="#将错误输出到标准输出-stdout">将错误输出到标准输出 stdout</a></h3>
<p>默认的错误会输出到标准错误输出 <code>stderr</code>,下面我们通过自定的配置来让错误输出到标准输出 <code>stdout</code></p>
<pre><pre class="playground"><code class="language-rust editable edition2021">use env_logger::{Builder, Target};
fn main() {
Builder::new()
.target(Target::Stdout)
.init();
log::error!(&quot;This error has been printed to Stdout&quot;);
}
</code></pre></pre>
<h3 id="使用自定义-logger"><a class="header" href="#使用自定义-logger">使用自定义 logger</a></h3>
<p>下面的代码将实现一个自定义 logger <code>ConsoleLogger</code>,输出到标准输出 <code>stdout</code>。为了使用日志宏,<code>ConsoleLogger</code> 需要实现 <a href="https://docs.rs/log/*/log/trait.Log.html">log::Log</a> 特征,然后使用 <a href="https://docs.rs/log/*/log/fn.set_logger.html">log::set_logger</a> 来安装使用。</p>
<pre><pre class="playground"><code class="language-rust editable edition2021">use log::{Record, Level, Metadata, LevelFilter, SetLoggerError};
static CONSOLE_LOGGER: ConsoleLogger = ConsoleLogger;
struct ConsoleLogger;
impl log::Log for ConsoleLogger {
fn enabled(&amp;self, metadata: &amp;Metadata) -&gt; bool {
metadata.level() &lt;= Level::Info
}
fn log(&amp;self, record: &amp;Record) {
if self.enabled(record.metadata()) {
println!(&quot;Rust says: {} - {}&quot;, record.level(), record.args());
}
}
fn flush(&amp;self) {}
}
fn main() -&gt; Result&lt;(), SetLoggerError&gt; {
log::set_logger(&amp;CONSOLE_LOGGER)?;
log::set_max_level(LevelFilter::Info);
log::info!(&quot;hello log&quot;);
log::warn!(&quot;warning&quot;);
log::error!(&quot;oops&quot;);
Ok(())
}
</code></pre></pre>
<h3 id="输出到-unix-syslog"><a class="header" href="#输出到-unix-syslog">输出到 Unix syslog</a></h3>
<p>下面的代码将使用 <a href="https://docs.rs/crate/syslog/6.0.1">syslog</a> 包将日志输出到 <a href="https://www.gnu.org/software/libc/manual/html_node/Overview-of-Syslog.html">Unix Syslog</a>.</p>
<pre><pre class="playground"><code class="language-rust editable edition2021">#[cfg(target_os = &quot;linux&quot;)]
#[cfg(target_os = &quot;linux&quot;)]
use syslog::{Facility, Error};
#[cfg(target_os = &quot;linux&quot;)]
fn main() -&gt; Result&lt;(), Error&gt; {
// 初始化 logger
syslog::init(Facility::LOG_USER,
log::LevelFilter::Debug,
// 可选的应用名称
Some(&quot;My app name&quot;))?;
log::debug!(&quot;this is a debug {}&quot;, &quot;message&quot;);
log::error!(&quot;this is an error!&quot;);
Ok(())
}
#[cfg(not(target_os = &quot;linux&quot;))]
fn main() {
println!(&quot;So far, only Linux systems are supported.&quot;);
}
</code></pre></pre>
<h2 id="tracing"><a class="header" href="#tracing">tracing</a></h2>
<p>@todo</p>
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