<!DOCTYPE HTML>
< html lang = "zh-CN" class = "light sidebar-visible" dir = "ltr" >
< head >
<!-- Book generated using mdBook -->
< meta charset = "UTF-8" >
< title > 使用 tracing 记录日志 - Rust语言圣经(Rust Course)< / title >
<!-- Custom HTML head -->
< meta name = "description" content = "" >
< meta name = "viewport" content = "width=device-width, initial-scale=1" >
< meta name = "theme-color" content = "#ffffff" >
< link rel = "icon" href = "../favicon-de23e50b.svg" >
< link rel = "shortcut icon" href = "../favicon-8114d1fc.png" >
< link rel = "stylesheet" href = "../css/variables-8adf115d.css" >
< link rel = "stylesheet" href = "../css/general-2459343d.css" >
< link rel = "stylesheet" href = "../css/chrome-ae938929.css" >
< link rel = "stylesheet" href = "../css/print-9e4910d8.css" media = "print" >
<!-- Fonts -->
< link rel = "stylesheet" href = "../fonts/fonts-9644e21d.css" >
<!-- Highlight.js Stylesheets -->
< link rel = "stylesheet" id = "mdbook-highlight-css" href = "../highlight-493f70e1.css" >
< link rel = "stylesheet" id = "mdbook-tomorrow-night-css" href = "../tomorrow-night-4c0ae647.css" >
< link rel = "stylesheet" id = "mdbook-ayu-highlight-css" href = "../ayu-highlight-3fdfc3ac.css" >
<!-- Custom theme stylesheets -->
< link rel = "stylesheet" href = "../theme/style-78591068.css" >
<!-- Provide site root and default themes to javascript -->
< script >
const path_to_root = "../";
const default_light_theme = "light";
const default_dark_theme = "navy";
window.path_to_searchindex_js = "../searchindex-219e36e1.js";
< / script >
<!-- Start loading toc.js asap -->
< script src = "../toc-42887675.js" > < / script >
< / head >
< body >
< div id = "mdbook-help-container" >
< div id = "mdbook-help-popup" >
< h2 class = "mdbook-help-title" > Keyboard shortcuts< / h2 >
< div >
< p > Press < kbd > ←< / kbd > or < kbd > →< / kbd > to navigate between chapters< / p >
< p > Press < kbd > S< / kbd > or < kbd > /< / kbd > to search in the book< / p >
< p > Press < kbd > ?< / kbd > to show this help< / p >
< p > Press < kbd > Esc< / kbd > to hide this help< / p >
< / div >
< / div >
< / div >
< div id = "mdbook-body-container" >
<!-- Work around some values being stored in localStorage wrapped in quotes -->
< script >
try {
let theme = localStorage.getItem('mdbook-theme');
let sidebar = localStorage.getItem('mdbook-sidebar');
if (theme.startsWith('"') & & theme.endsWith('"')) {
localStorage.setItem('mdbook-theme', theme.slice(1, theme.length - 1));
}
if (sidebar.startsWith('"') & & sidebar.endsWith('"')) {
localStorage.setItem('mdbook-sidebar', sidebar.slice(1, sidebar.length - 1));
}
} catch (e) { }
< / script >
<!-- Set the theme before any content is loaded, prevents flash -->
< script >
const default_theme = window.matchMedia("(prefers-color-scheme: dark)").matches ? default_dark_theme : default_light_theme;
let theme;
try { theme = localStorage.getItem('mdbook-theme'); } catch(e) { }
if (theme === null || theme === undefined) { theme = default_theme; }
const html = document.documentElement;
html.classList.remove('light')
html.classList.add(theme);
html.classList.add("js");
< / script >
< input type = "checkbox" id = "mdbook-sidebar-toggle-anchor" class = "hidden" >
<!-- Hide / unhide sidebar before it is displayed -->
< script >
let sidebar = null;
const sidebar_toggle = document.getElementById("mdbook-sidebar-toggle-anchor");
if (document.body.clientWidth >= 1080) {
try { sidebar = localStorage.getItem('mdbook-sidebar'); } catch(e) { }
sidebar = sidebar || 'visible';
} else {
sidebar = 'hidden';
sidebar_toggle.checked = false;
}
if (sidebar === 'visible') {
sidebar_toggle.checked = true;
} else {
html.classList.remove('sidebar-visible');
}
< / script >
< nav id = "mdbook-sidebar" class = "sidebar" aria-label = "Table of contents" >
<!-- populated by js -->
< mdbook-sidebar-scrollbox class = "sidebar-scrollbox" > < / mdbook-sidebar-scrollbox >
< noscript >
< iframe class = "sidebar-iframe-outer" src = "../toc.html" > < / iframe >
< / noscript >
< div id = "mdbook-sidebar-resize-handle" class = "sidebar-resize-handle" >
< div class = "sidebar-resize-indicator" > < / div >
< / div >
< / nav >
< div id = "mdbook-page-wrapper" class = "page-wrapper" >
< div class = "page" >
< div id = "mdbook-menu-bar-hover-placeholder" > < / div >
< div id = "mdbook-menu-bar" class = "menu-bar sticky" >
< div class = "left-buttons" >
< label id = "mdbook-sidebar-toggle" class = "icon-button" for = "mdbook-sidebar-toggle-anchor" title = "Toggle Table of Contents" aria-label = "Toggle Table of Contents" aria-controls = "mdbook-sidebar" >
< span class = fa-svg > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 448 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M0 96C0 78.3 14.3 64 32 64H416c17.7 0 32 14.3 32 32s-14.3 32-32 32H32C14.3 128 0 113.7 0 96zM0 256c0-17.7 14.3-32 32-32H416c17.7 0 32 14.3 32 32s-14.3 32-32 32H32c-17.7 0-32-14.3-32-32zM448 416c0 17.7-14.3 32-32 32H32c-17.7 0-32-14.3-32-32s14.3-32 32-32H416c17.7 0 32 14.3 32 32z" / > < / svg > < / span >
< / label >
< button id = "mdbook-theme-toggle" class = "icon-button" type = "button" title = "Change theme" aria-label = "Change theme" aria-haspopup = "true" aria-expanded = "false" aria-controls = "mdbook-theme-list" >
< span class = fa-svg > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 576 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M371.3 367.1c27.3-3.9 51.9-19.4 67.2-42.9L600.2 74.1c12.6-19.5 9.4-45.3-7.6-61.2S549.7-4.4 531.1 9.6L294.4 187.2c-24 18-38.2 46.1-38.4 76.1L371.3 367.1zm-19.6 25.4l-116-104.4C175.9 290.3 128 339.6 128 400c0 3.9 .2 7.8 .6 11.6c1.8 17.5-10.2 36.4-27.8 36.4H96c-17.7 0-32 14.3-32 32s14.3 32 32 32H240c61.9 0 112-50.1 112-112c0-2.5-.1-5-.2-7.5z" / > < / svg > < / span >
< / button >
< ul id = "mdbook-theme-list" class = "theme-popup" aria-label = "Themes" role = "menu" >
< li role = "none" > < button role = "menuitem" class = "theme" id = "mdbook-theme-default_theme" > Auto< / button > < / li >
< li role = "none" > < button role = "menuitem" class = "theme" id = "mdbook-theme-light" > Light< / button > < / li >
< li role = "none" > < button role = "menuitem" class = "theme" id = "mdbook-theme-rust" > Rust< / button > < / li >
< li role = "none" > < button role = "menuitem" class = "theme" id = "mdbook-theme-coal" > Coal< / button > < / li >
< li role = "none" > < button role = "menuitem" class = "theme" id = "mdbook-theme-navy" > Navy< / button > < / li >
< li role = "none" > < button role = "menuitem" class = "theme" id = "mdbook-theme-ayu" > Ayu< / button > < / li >
< / ul >
< button id = "mdbook-search-toggle" class = "icon-button" type = "button" title = "Search (`/`)" aria-label = "Toggle Searchbar" aria-expanded = "false" aria-keyshortcuts = "/ s" aria-controls = "mdbook-searchbar" >
< span class = fa-svg > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 512 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M416 208c0 45.9-14.9 88.3-40 122.7L502.6 457.4c12.5 12.5 12.5 32.8 0 45.3s-32.8 12.5-45.3 0L330.7 376c-34.4 25.2-76.8 40-122.7 40C93.1 416 0 322.9 0 208S93.1 0 208 0S416 93.1 416 208zM208 352c79.5 0 144-64.5 144-144s-64.5-144-144-144S64 128.5 64 208s64.5 144 144 144z" / > < / svg > < / span >
< / button >
< / div >
< h1 class = "menu-title" > Rust语言圣经(Rust Course)< / h1 >
< div class = "right-buttons" >
< a href = "../print.html" title = "Print this book" aria-label = "Print this book" >
< span class = fa-svg id = "print-button" > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 512 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M128 0C92.7 0 64 28.7 64 64v96h64V64H354.7L384 93.3V160h64V93.3c0-17-6.7-33.3-18.7-45.3L400 18.7C388 6.7 371.7 0 354.7 0H128zM384 352v32 64H128V384 368 352H384zm64 32h32c17.7 0 32-14.3 32-32V256c0-35.3-28.7-64-64-64H64c-35.3 0-64 28.7-64 64v96c0 17.7 14.3 32 32 32H64v64c0 35.3 28.7 64 64 64H384c35.3 0 64-28.7 64-64V384zm-16-88c-13.3 0-24-10.7-24-24s10.7-24 24-24s24 10.7 24 24s-10.7 24-24 24z" / > < / svg > < / span >
< / a >
< a href = "https://github.com/sunface/rust-course" title = "Git repository" aria-label = "Git repository" >
< span class = fa-svg > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 496 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M165.9 397.4c0 2-2.3 3.6-5.2 3.6-3.3.3-5.6-1.3-5.6-3.6 0-2 2.3-3.6 5.2-3.6 3-.3 5.6 1.3 5.6 3.6zm-31.1-4.5c-.7 2 1.3 4.3 4.3 4.9 2.6 1 5.6 0 6.2-2s-1.3-4.3-4.3-5.2c-2.6-.7-5.5.3-6.2 2.3zm44.2-1.7c-2.9.7-4.9 2.6-4.6 4.9.3 2 2.9 3.3 5.9 2.6 2.9-.7 4.9-2.6 4.6-4.6-.3-1.9-3-3.2-5.9-2.9zM244.8 8C106.1 8 0 113.3 0 252c0 110.9 69.8 205.8 169.5 239.2 12.8 2.3 17.3-5.6 17.3-12.1 0-6.2-.3-40.4-.3-61.4 0 0-70 15-84.7-29.8 0 0-11.4-29.1-27.8-36.6 0 0-22.9-15.7 1.6-15.4 0 0 24.9 2 38.6 25.8 21.9 38.6 58.6 27.5 72.9 20.9 2.3-16 8.8-27.1 16-33.7-55.9-6.2-112.3-14.3-112.3-110.5 0-27.5 7.6-41.3 23.6-58.9-2.6-6.5-11.1-33.3 2.6-67.9 20.9-6.5 69 27 69 27 20-5.6 41.5-8.5 62.8-8.5s42.8 2.9 62.8 8.5c0 0 48.1-33.6 69-27 13.7 34.7 5.2 61.4 2.6 67.9 16 17.7 25.8 31.5 25.8 58.9 0 96.5-58.9 104.2-114.8 110.5 9.2 7.9 17 22.9 17 46.4 0 33.7-.3 75.4-.3 83.6 0 6.5 4.6 14.4 17.3 12.1C428.2 457.8 496 362.9 496 252 496 113.3 383.5 8 244.8 8zM97.2 352.9c-1.3 1-1 3.3.7 5.2 1.6 1.6 3.9 2.3 5.2 1 1.3-1 1-3.3-.7-5.2-1.6-1.6-3.9-2.3-5.2-1zm-10.8-8.1c-.7 1.3.3 2.9 2.3 3.9 1.6 1 3.6.7 4.3-.7.7-1.3-.3-2.9-2.3-3.9-2-.6-3.6-.3-4.3.7zm32.4 35.6c-1.6 1.3-1 4.3 1.3 6.2 2.3 2.3 5.2 2.6 6.5 1 1.3-1.3.7-4.3-1.3-6.2-2.2-2.3-5.2-2.6-6.5-1zm-11.4-14.7c-1.6 1-1.6 3.6 0 5.9 1.6 2.3 4.3 3.3 5.6 2.3 1.6-1.3 1.6-3.9 0-6.2-1.4-2.3-4-3.3-5.6-2z" / > < / svg > < / span >
< / a >
< a href = "https://github.com/sunface/rust-course/edit/main/src/logs/tracing.md" title = "Suggest an edit" aria-label = "Suggest an edit" rel = "edit" >
< span class = fa-svg id = "git-edit-button" > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 512 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M421.7 220.3l-11.3 11.3-22.6 22.6-205 205c-6.6 6.6-14.8 11.5-23.8 14.1L30.8 511c-8.4 2.5-17.5 .2-23.7-6.1S-1.5 489.7 1 481.2L38.7 353.1c2.6-9 7.5-17.2 14.1-23.8l205-205 22.6-22.6 11.3-11.3 33.9 33.9 62.1 62.1 33.9 33.9zM96 353.9l-9.3 9.3c-.9 .9-1.6 2.1-2 3.4l-25.3 86 86-25.3c1.3-.4 2.5-1.1 3.4-2l9.3-9.3H112c-8.8 0-16-7.2-16-16V353.9zM453.3 19.3l39.4 39.4c25 25 25 65.5 0 90.5l-14.5 14.5-22.6 22.6-11.3 11.3-33.9-33.9-62.1-62.1L314.3 67.7l11.3-11.3 22.6-22.6 14.5-14.5c25-25 65.5-25 90.5 0z" / > < / svg > < / span >
< / a >
< / div >
< / div >
< div id = "mdbook-search-wrapper" class = "hidden" >
< form id = "mdbook-searchbar-outer" class = "searchbar-outer" >
< div class = "search-wrapper" >
< input type = "search" id = "mdbook-searchbar" name = "searchbar" placeholder = "Search this book ..." aria-controls = "mdbook-searchresults-outer" aria-describedby = "searchresults-header" >
< div class = "spinner-wrapper" >
< span class = fa-svg id = "fa-spin" > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 512 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M304 48c0-26.5-21.5-48-48-48s-48 21.5-48 48s21.5 48 48 48s48-21.5 48-48zm0 416c0-26.5-21.5-48-48-48s-48 21.5-48 48s21.5 48 48 48s48-21.5 48-48zM48 304c26.5 0 48-21.5 48-48s-21.5-48-48-48s-48 21.5-48 48s21.5 48 48 48zm464-48c0-26.5-21.5-48-48-48s-48 21.5-48 48s21.5 48 48 48s48-21.5 48-48zM142.9 437c18.7-18.7 18.7-49.1 0-67.9s-49.1-18.7-67.9 0s-18.7 49.1 0 67.9s49.1 18.7 67.9 0zm0-294.2c18.7-18.7 18.7-49.1 0-67.9S93.7 56.2 75 75s-18.7 49.1 0 67.9s49.1 18.7 67.9 0zM369.1 437c18.7 18.7 49.1 18.7 67.9 0s18.7-49.1 0-67.9s-49.1-18.7-67.9 0s-18.7 49.1 0 67.9z" / > < / svg > < / span >
< / div >
< / div >
< / form >
< div id = "mdbook-searchresults-outer" class = "searchresults-outer hidden" >
< div id = "mdbook-searchresults-header" class = "searchresults-header" > < / div >
< ul id = "mdbook-searchresults" >
< / ul >
< / div >
< / div >
<!-- Apply ARIA attributes after the sidebar and the sidebar toggle button are added to the DOM -->
< script >
document.getElementById('mdbook-sidebar-toggle').setAttribute('aria-expanded', sidebar === 'visible');
document.getElementById('mdbook-sidebar').setAttribute('aria-hidden', sidebar !== 'visible');
Array.from(document.querySelectorAll('#mdbook-sidebar a')).forEach(function(link) {
link.setAttribute('tabIndex', sidebar === 'visible' ? 0 : -1);
});
< / script >
< div id = "mdbook-content" class = "content" >
< main >
< h1 id = "使用-tracing-记录日志" > < a class = "header" href = "#使用-tracing-记录日志" > 使用 tracing 记录日志< / a > < / h1 >
< p > 严格来说， ， < / p >
< p > 随着微服务的流行，现在一个产品有多个系统组成是非常常见的，这种情况下，一条用户请求可能会横跨几个甚至几十个服务。此时再用传统的日志方式去跟踪这条用户请求就变得较为困难，这就是分布式追踪在现代化监控系统中这么炽手可热的原因。< / p >
< p > 关于分布式追踪，在后面的监控章节进行详细介绍，大家只要知道：分布式追踪的核心就是在请求的开始生成一个 < code > trace_id< / code > ，然后将该 < code > trace_id< / code > 一直往后透传，请求经过的每个服务都会使用该 < code > trace_id< / code > 记录相关信息，最终将整个请求形成一个完整的链路予以记录下来。< / p >
< p > 那么后面当要查询这次请求的相关信息时，只要使用 < code > trace_id< / code > 就可以获取整个请求链路的所有信息了，非常简单好用。看到这里，相信大家也明白为什么这个库的名称叫 < code > tracing< / code > 了吧？< / p >
< p > 至于为何把它归到日志库的范畴呢？因为 < code > tracing< / code > 支持 < code > log< / code > 门面库的 API， ， < / p >
< blockquote >
< p > 在分布式追踪中， < / p >
< / blockquote >
< h2 id = "一个简单例子" > < a class = "header" href = "#一个简单例子" > 一个简单例子< / a > < / h2 >
< p > 开始之前，需要先将 < code > tracing< / code > 添加到项目的 < code > Cargo.toml< / code > 中:< / p >
< pre > < code class = "language-toml" > [dependencies]
tracing = "0.1"
< / code > < / pre >
< p > 注意，在写作本文时，< code > 0.2< / code > 版本已经快要出来了，所以具体使用的版本请大家以阅读时为准。< / p >
< p > 下面的例子中将同时使用 < code > log< / code > 和 < code > tracing< / code > :< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > use log;
use tracing_subscriber::{fmt, layer::SubscriberExt, util::SubscriberInitExt};
fn main() {
// 只有注册 subscriber 后， 才能在控制台上看到日志输出
tracing_subscriber::registry()
.with(fmt::layer())
.init();
// 调用 `log` 包的 `info!`
log::info!("Hello world");
let foo = 42;
// 调用 `tracing` 包的 `info!`
tracing::info!(foo, "Hello from tracing");
}< / code > < / pre >
< p > 可以看出，门面库的排场还是有的，< code > tracing< / code > 在 API 上明显是使用了 < code > log< / code > 的规范。< / p >
< p > 运行后，输出如下日志:< / p >
< pre > < code class = "language-shell" > 2022-04-09T14:34:28.965952Z INFO test_tracing: Hello world
2022-04-09T14:34:28.966011Z INFO test_tracing: Hello from tracing foo=42
< / code > < / pre >
< p > 还可以看出，< code > log< / code > 的日志格式跟 < code > tracing< / code > 一模一样，结合上一章节的知识，相信聪明的同学已经明白了这是为什么。< / p >
< p > 那么 < code > tracing< / code > 跟 < code > log< / code > 的具体日志实现框架有何区别呢？别急，我们再来接着看。< / p >
< h2 id = "异步编程中的挑战" > < a class = "header" href = "#异步编程中的挑战" > 异步编程中的挑战< / a > < / h2 >
< p > 除了分布式追踪，在异步编程中使用传统的日志也是存在一些问题的，最大的挑战就在于异步任务的执行没有确定的顺序，那么输出的日志也将没有确定的顺序并混在一起，无法按照我们想要的逻辑顺序串联起来。< / p >
< p > < strong > 归根到底，在于日志只能针对某个时间点进行记录，缺乏上下文信息，而线程间的执行顺序又是不确定的，因此日志就有些无能为力< / strong > 。而 < code > tracing< / code > 为了解决这个问题，引入了 < code > span< / code > 的概念( 这个概念也来自于分布式追踪 )，一个 < code > span< / code > 代表了一个时间段，拥有开始和结束时间，在此期间的所有类型数据、结构化数据、文本数据都可以记录其中。< / p >
< p > 大家发现了吗？ < code > span< / code > 是可以拥有上下文信息的，这样就能帮我们把信息按照所需的逻辑性串联起来了。< / p >
< h2 id = "核心概念" > < a class = "header" href = "#核心概念" > 核心概念< / a > < / h2 >
< p > < code > tracing< / code > 中最重要的三个概念是 < code > Span< / code > 、< code > Event< / code > 和 < code > Collector< / code > ，下面我们来一一简单介绍下。< / p >
< h3 id = "span" > < a class = "header" href = "#span" > Span< / a > < / h3 >
< p > 相比起日志只能记录在某个时间点发生的事件，< code > span< / code > 最大的意义就在于它可以记录一个过程，也就是在某一段时间内发生的事件流。既然是记录时间段，那自然有开始和结束:< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > use tracing::{span, Level};
fn main() {
let span = span!(Level::TRACE, "my_span");
// `enter` 返回一个 RAII ，当其被 drop 时，将自动结束该 span
let enter = span.enter();
// 这里开始进入 `my_span` 的上下文
// 下面执行一些任务，并记录一些信息到 `my_span` 中
// ...
} // 这里 enter 将被 drop， < / code > < / pre >
< h3 id = "event-事件" > < a class = "header" href = "#event-事件" > Event 事件< / a > < / h3 >
< p > < code > Event< / code > 代表了某个时间点发生的事件，这方面它跟日志类似，但是不同的是，< code > Event< / code > 还可以产生在 span 的上下文中。< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > use tracing::{event, span, Level};
use tracing_subscriber::{fmt, layer::SubscriberExt, util::SubscriberInitExt};
fn main() {
tracing_subscriber::registry().with(fmt::layer()).init();
// 在 span 的上下文之外记录一次 event 事件
event!(Level::INFO, "something happened");
let span = span!(Level::INFO, "my_span");
let _guard = span.enter();
// 在 "my_span" 的上下文中记录一次 event
event!(Level::DEBUG, "something happened inside my_span");
}< / code > < / pre >
< pre > < code class = "language-shell" > 2022-04-09T14:51:38.382987Z INFO test_tracing: something happened
2022-04-09T14:51:38.383111Z DEBUG my_span: test_tracing: something happened inside my_span
< / code > < / pre >
< p > 虽然 < code > event< / code > 在哪里都可以使用，< strong > 但是最好只在 span 的上下文中使用< / strong > ：用于代表一个时间点发生的事件，例如记录 HTTP 请求返回的状态码，从队列中获取一个对象，等等。< / p >
< h3 id = "collector-收集器" > < a class = "header" href = "#collector-收集器" > Collector 收集器< / a > < / h3 >
< p > 当 < code > Span< / code > 或 < code > Event< / code > 发生时，它们会被实现了 < code > Collect< / code > 特征的收集器所记录或聚合。这个过程是通过通知的方式实现的：当 < code > Event< / code > 发生或者 < code > Span< / code > 开始/结束时，会调用 < code > Collect< / code > 特征的< a href = "https://tracing-rs.netlify.app/tracing/trait.collect#tymethod.event" > 相应方法< / a > 通知 Collector。< / p >
< h4 id = "tracing-subscriber" > < a class = "header" href = "#tracing-subscriber" > tracing-subscriber< / a > < / h4 >
< p > 我们前面提到只有使用了 < a href = "https://docs.rs/tracing-subscriber/" > < code > tracing-subscriber< / code > < / a > 后，日志才能输出到控制台中。< / p >
< p > 之前大家可能还不理解，现在应该明白了，它是一个 Collector， ， < / p >
< h2 id = "使用方法" > < a class = "header" href = "#使用方法" > 使用方法< / a > < / h2 >
< h3 id = "span-宏" > < a class = "header" href = "#span-宏" > < code > span!< / code > 宏< / a > < / h3 >
< p > < code > span!< / code > 宏可以用于创建一个 < code > Span< / code > 结构体，然后通过调用结构体的 < code > enter< / code > 方法来开始，再通过超出作用域时的 < code > drop< / code > 来结束。< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > use tracing::{span, Level};
fn main() {
let span = span!(Level::TRACE, "my_span");
// `enter` 返回一个 RAII ，当其被 drop 时，将自动结束该 span
let enter = span.enter();
// 这里开始进入 `my_span` 的上下文
// 下面执行一些任务，并记录一些信息到 `my_span` 中
// ...
} // 这里 enter 将被 drop， < / code > < / pre >
< h3 id = "instrument" > < a class = "header" href = "#instrument" > #[instrument]< / a > < / h3 >
< p > 如果想要将某个函数的整个函数体都设置为 span 的范围，最简单的方法就是为函数标记上 < code > #[instrument]< / code > ，此时 tracing 会自动为函数创建一个 span， < / p >
< pre class = "playground" > < code class = "language-rust edition2021" > use tracing::{info, instrument};
use tracing_subscriber::{fmt, layer::SubscriberExt, util::SubscriberInitExt};
#[instrument]
fn foo(ans: i32) {
info!("in foo");
}
fn main() {
tracing_subscriber::registry().with(fmt::layer()).init();
foo(42);
}< / code > < / pre >
< pre > < code class = "language-shell" > 2022-04-10T02:44:12.885556Z INFO foo{ans=42}: test_tracing: in foo
< / code > < / pre >
< p > 关于 < code > #[instrument]< / code > 详细说明，请参见< a href = "https://tracing-rs.netlify.app/tracing/attr.instrument.html" > 官方文档< / a > 。< / p >
< h3 id = "in_scope" > < a class = "header" href = "#in_scope" > in_scope< / a > < / h3 >
< p > 对于没有内置 tracing 支持或者无法使用 < code > #instrument< / code > 的函数，例如外部库的函数，我们可以使用 < code > Span< / code > 结构体的 < code > in_scope< / code > 方法，它可以将同步代码包裹在一个 span 中：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > use tracing::info_span;
let json = info_span!("json.parse").in_scope(|| serde_json::from_slice(& buf))?;
< span class = "boring" > }< / span > < / code > < / pre >
< h3 id = "在-async-中使用-span" > < a class = "header" href = "#在-async-中使用-span" > 在 async 中使用 span< / a > < / h3 >
< p > 需要注意，如果是在异步编程时使用，要避免以下使用方式:< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > async fn my_async_function() {
let span = info_span!("my_async_function");
// WARNING: 该 span 直到 drop 后才结束，因此在 .await 期间，
let _enter = span.enter();
// 在这里 span 依然在记录，但是 .await 会让出当前任务的执行权，然后运行时会去运行其它任务，此时这个 span 可能会记录其它任务的执行信息，最终记录了不正确的 trace 信息
some_other_async_function().await
// ...
}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 我们建议使用以下方式，简单又有效:< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > use tracing::{info, instrument};
use tokio::{io::AsyncWriteExt, net::TcpStream};
use std::io;
#[instrument]
async fn write(stream: & mut TcpStream) -> io::Result< usize> {
let result = stream.write(b"hello world\n").await;
info!("wrote to stream; success={:?}", result.is_ok());
result
}
< span class = "boring" > }< / span > < / code > < / pre >
< p > 那有同学可能要问了，是不是我们无法在异步代码中使用 < code > span.enter< / code > 了，答案是：是也不是。< / p >
< p > 是，你无法直接使用 < code > span.enter< / code > 语法了，原因上面也说过，但是可以通过下面的方式来曲线使用：< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > use tracing::Instrument;
let my_future = async {
// ...
};
my_future
.instrument(tracing::info_span!("my_future"))
.await
< span class = "boring" > }< / span > < / code > < / pre >
< h3 id = "span-嵌套" > < a class = "header" href = "#span-嵌套" > span 嵌套< / a > < / h3 >
< p > < code > tracing< / code > 的 span 不仅仅是上面展示的基本用法，它们还可以进行嵌套！< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > use tracing::{debug, info, span, Level};
use tracing_subscriber::{fmt, layer::SubscriberExt, util::SubscriberInitExt};
fn main() {
tracing_subscriber::registry().with(fmt::layer()).init();
let scope = span!(Level::DEBUG, "foo");
let _enter = scope.enter();
info!("Hello in foo scope");
debug!("before entering bar scope");
{
let scope = span!(Level::DEBUG, "bar", ans = 42);
let _enter = scope.enter();
debug!("enter bar scope");
info!("In bar scope");
debug!("end bar scope");
}
debug!("end bar scope");
}< / code > < / pre >
< pre > < code class = "language-shell" > INFO foo: log_test: Hello in foo scope
DEBUG foo: log_test: before entering bar scope
DEBUG foo:bar{ans=42}: log_test: enter bar scope
INFO foo:bar{ans=42}: log_test: In bar scope
DEBUG foo:bar{ans=42}: log_test: end bar scope
DEBUG foo: log_test: end bar scope
< / code > < / pre >
< p > 在上面的日志中，< code > foo:bar< / code > 不仅包含了 < code > foo< / code > 和 < code > bar< / code > span 名，还显示了它们之间的嵌套关系。< / p >
< h2 id = "对宏进行配置" > < a class = "header" href = "#对宏进行配置" > 对宏进行配置< / a > < / h2 >
< h3 id = "日志级别和目标" > < a class = "header" href = "#日志级别和目标" > 日志级别和目标< / a > < / h3 >
< p > < code > span!< / code > 和 < code > event!< / code > 宏都需要设定相应的日志级别，而且它们支持可选的 < code > target< / code > 或 < code > parent< / code > 参数( 只能二者选其一 )，该参数用于描述事件发生的位置，如果父 span 没有设置，< code > target< / code > 参数也没有提供，那这个位置默认分别是当前的 span 和 当前的模块。< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > use tracing::{debug, info, span, Level,event};
use tracing_subscriber::{fmt, layer::SubscriberExt, util::SubscriberInitExt};
fn main() {
tracing_subscriber::registry().with(fmt::layer()).init();
let s = span!(Level::TRACE, "my span");
// 没进入 span，
event!(target: "app_events", Level::INFO, "something has happened 1!");
// 进入 span ( 开始 )
let _enter = s.enter();
// 没有设置 target 和 parent
// 这里的对象位置分别是当前的 span 名和模块名
event!(Level::INFO, "something has happened 2!");
// 设置了 target
// 这里的对象位置分别是当前的 span 名和 target
event!(target: "app_events",Level::INFO, "something has happened 3!");
let span = span!(Level::TRACE, "my span 1");
// 这里就更为复杂一些，留给大家作为思考题
event!(parent: & span, Level::INFO, "something has happened 4!");
}< / code > < / pre >
< h3 id = "记录字段" > < a class = "header" href = "#记录字段" > 记录字段< / a > < / h3 >
< p > 我们可以通过语法 < code > field_name = field_value< / code > 来输出结构化的日志< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > // 记录一个事件，带有两个字段:
// - "answer", 值是 42
// - "question", 值是 "life, the universe and everything"
event!(Level::INFO, answer = 42, question = "life, the universe, and everything");
// 日志输出 -> INFO test_tracing: answer=42 question="life, the universe, and everything"
< span class = "boring" > }< / span > < / code > < / pre >
< h4 id = "捕获环境变量" > < a class = "header" href = "#捕获环境变量" > 捕获环境变量< / a > < / h4 >
< p > 还可以捕获环境中的变量:< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > let user = "ferris";
// 下面的简写方式
span!(Level::TRACE, "login", user);
// 等价于:
span!(Level::TRACE, "login", user = user);
< span class = "boring" > }< / span > < / code > < / pre >
< pre class = "playground" > < code class = "language-rust edition2021" > use tracing::{info, span, Level};
use tracing_subscriber::{fmt, layer::SubscriberExt, util::SubscriberInitExt};
fn main() {
tracing_subscriber::registry().with(fmt::layer()).init();
let user = "ferris";
let s = span!(Level::TRACE, "login", user);
let _enter = s.enter();
info!(welcome="hello", user);
// 下面一行将报错，原因是这种写法是格式化字符串的方式，必须使用 info!("hello {}", user)
// info!("hello", user);
}
// 日志输出 -> INFO login{user="ferris"}: test_tracing: welcome="hello" user="ferris"< / code > < / pre >
< h4 id = "字段名的多种形式" > < a class = "header" href = "#字段名的多种形式" > 字段名的多种形式< / a > < / h4 >
< p > 字段名还可以包含 < code > .< / code > :< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > let user = "ferris";
let email = "ferris@rust-lang.org";
event!(Level::TRACE, user, user.email = email);
// 还可以使用结构体
let user = User {
name: "ferris",
email: "ferris@rust-lang.org",
};
// 直接访问结构体字段，无需赋值即可使用
span!(Level::TRACE, "login", user.name, user.email);
// 字段名还可以使用字符串
event!(Level::TRACE, "guid:x-request-id" = "abcdef", "type" = "request");
// 日志输出 ->
// TRACE test_tracing: user="ferris" user.email="ferris@rust-lang.org"
// TRACE test_tracing: user.name="ferris" user.email="ferris@rust-lang.org"
// TRACE test_tracing: guid:x-request-id="abcdef" type="request"
< span class = "boring" > }< / span > < / code > < / pre >
< h4 id = "" > < a class = "header" href = "#" > ?< / a > < / h4 >
< p > < code > ?< / code > 符号用于说明该字段将使用 < code > fmt::Debug< / code > 来格式化。< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > #[derive(Debug)]
struct MyStruct {
field: & 'static str,
}
let my_struct = MyStruct {
field: "Hello world!",
};
// `my_struct` 将使用 Debug 的形式输出
event!(Level::TRACE, greeting = ?my_struct);
// 等价于:
event!(Level::TRACE, greeting = tracing::field::debug(& my_struct));
// 下面代码将报错, my_struct 没有实现 Display
// event!(Level::TRACE, greeting = my_struct);
// 日志输出 -> TRACE test_tracing: greeting=MyStruct { field: "Hello world!" }
< span class = "boring" > }< / span > < / code > < / pre >
< h4 id = "-1" > < a class = "header" href = "#-1" > %< / a > < / h4 >
< p > < code > %< / code > 说明字段将用 < code > fmt::Display< / code > 来格式化。< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > // `my_struct.field` 将使用 `fmt::Display` 的格式化形式输出
event!(Level::TRACE, greeting = %my_struct.field);
// 等价于:
event!(Level::TRACE, greeting = tracing::field::display(& my_struct.field));
// 作为对比，大家可以看下 Debug 和正常的字段输出长什么样
event!(Level::TRACE, greeting = ?my_struct.field);
event!(Level::TRACE, greeting = my_struct.field);
// 下面代码将报错, my_struct 没有实现 Display
// event!(Level::TRACE, greeting = %my_struct);
< span class = "boring" > }< / span > < / code > < / pre >
< pre > < code class = "language-shell" > 2022-04-10T03:49:00.834330Z TRACE test_tracing: greeting=Hello world!
2022-04-10T03:49:00.834410Z TRACE test_tracing: greeting=Hello world!
2022-04-10T03:49:00.834422Z TRACE test_tracing: greeting="Hello world!"
2022-04-10T03:49:00.834433Z TRACE test_tracing: greeting="Hello world!"
< / code > < / pre >
< h4 id = "empty" > < a class = "header" href = "#empty" > Empty< / a > < / h4 >
< p > 字段还能标记为 < code > Empty< / code > ，用于说明该字段目前没有任何值，但是可以在后面进行记录。< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > use tracing::{trace_span, field};
let span = trace_span!("my_span", greeting = "hello world", parting = field::Empty);
// ...
// 现在，为 parting 记录一个值
span.record("parting", & "goodbye world!");
< span class = "boring" > }< / span > < / code > < / pre >
< h4 id = "格式化字符串" > < a class = "header" href = "#格式化字符串" > 格式化字符串< / a > < / h4 >
< p > 除了以字段的方式记录信息，我们还可以使用格式化字符串的方式( 同 < code > println!< / code > 、< code > format!< / code > )。< / p >
< blockquote >
< p > 注意，当字段跟格式化的方式混用时，必须把格式化放在最后，如下所示< / p >
< / blockquote >
< pre class = "playground" > < code class = "language-rust edition2021" > < span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > let question = "the ultimate question of life, the universe, and everything";
let answer = 42;
event!(
Level::DEBUG,
question.answer = answer,
question.tricky = true,
"the answer to {} is {}.", question, answer
);
// 日志输出 -> DEBUG test_tracing: the answer to the ultimate question of life, the universe, and everything is 42. question.answer=42 question.tricky=true
< span class = "boring" > }< / span > < / code > < / pre >
< h3 id = "文件输出" > < a class = "header" href = "#文件输出" > 文件输出< / a > < / h3 >
< p > 截至目前，我们上面的日志都是输出到控制台中。< / p >
< p > 针对文件输出，< code > tracing< / code > 提供了一个专门的库 < a href = "https://github.com/tokio-rs/tracing/tree/master/tracing-appender" > tracing-appender< / a > ，大家可以查看官方文档了解更多。< / p >
< h2 id = "一个综合例子" > < a class = "header" href = "#一个综合例子" > 一个综合例子< / a > < / h2 >
< p > 最后，再来看一个综合的例子，使用了 < a href = "https://github.com/yaahc/color-eyre" > color-eyre< / a > 和 文件输出，前者用于为输出的日志加上更易读的颜色。< / p >
< pre class = "playground" > < code class = "language-rust edition2021" > use color_eyre::{eyre::eyre, Result};
use tracing::{error, info, instrument};
use tracing_appender::{non_blocking, rolling};
use tracing_error::ErrorLayer;
use tracing_subscriber::{
filter::EnvFilter, fmt, layer::SubscriberExt, util::SubscriberInitExt, Registry,
};
#[instrument]
fn return_err() -> Result< ()> {
Err(eyre!("Something went wrong"))
}
#[instrument]
fn call_return_err() {
info!("going to log error");
if let Err(err) = return_err() {
// 推荐大家运行下，看看这里的输出效果
error!(?err, "error");
}
}
fn main() -> Result< ()> {
let env_filter = EnvFilter::try_from_default_env().unwrap_or_else(|_| EnvFilter::new("info"));
// 输出到控制台中
let formatting_layer = fmt::layer().pretty().with_writer(std::io::stderr);
// 输出到文件中
let file_appender = rolling::never("logs", "app.log");
let (non_blocking_appender, _guard) = non_blocking(file_appender);
let file_layer = fmt::layer()
.with_ansi(false)
.with_writer(non_blocking_appender);
// 注册
Registry::default()
.with(env_filter)
// ErrorLayer 可以让 color-eyre 获取到 span 的信息
.with(ErrorLayer::default())
.with(formatting_layer)
.with(file_layer)
.init();
// 安裝 color-eyre 的 panic 处理句柄
color_eyre::install()?;
call_return_err();
Ok(())
}< / code > < / pre >
< h2 id = "总结--推荐" > < a class = "header" href = "#总结--推荐" > 总结 & 推荐< / a > < / h2 >
< p > 至此，< code > tracing< / code > 的介绍就已结束，相信大家都看得出，它比上个章节的 < code > log< / code > 及兄弟们要更加复杂一些，一方面是因为它能更好的支持异步编程环境，另一方面就是它还是一个分布式追踪的库，对于后者，我们将在后续的监控章节进行讲解。< / p >
< p > 如果你让我推荐使用哪个，那我的建议是:< / p >
< ul >
< li > 对于简单的工程，例如用于 POC（ ） < code > log< / code > 即可< / li >
< li > 对于需要认真对待，例如生产级或优秀的开源项目，建议使用 tracing 的方式，一举解决日志和监控的后顾之忧< / li >
< / ul >
< / main >
< nav class = "nav-wrapper" aria-label = "Page navigation" >
<!-- Mobile navigation buttons -->
< a rel = "prev" href = "../logs/log.html" class = "mobile-nav-chapters previous" title = "Previous chapter" aria-label = "Previous chapter" aria-keyshortcuts = "Left" >
< span class = fa-svg > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 320 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M41.4 233.4c-12.5 12.5-12.5 32.8 0 45.3l160 160c12.5 12.5 32.8 12.5 45.3 0s12.5-32.8 0-45.3L109.3 256 246.6 118.6c12.5-12.5 12.5-32.8 0-45.3s-32.8-12.5-45.3 0l-160 160z" / > < / svg > < / span >
< / a >
< a rel = "next prefetch" href = "../logs/tracing-logger.html" class = "mobile-nav-chapters next" title = "Next chapter" aria-label = "Next chapter" aria-keyshortcuts = "Right" >
< span class = fa-svg > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 320 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M278.6 233.4c12.5 12.5 12.5 32.8 0 45.3l-160 160c-12.5 12.5-32.8 12.5-45.3 0s-12.5-32.8 0-45.3L210.7 256 73.4 118.6c-12.5-12.5-12.5-32.8 0-45.3s32.8-12.5 45.3 0l160 160z" / > < / svg > < / span >
< / a >
< div style = "clear: both" > < / div >
< / nav >
< / div >
< / div >
< nav class = "nav-wide-wrapper" aria-label = "Page navigation" >
< a rel = "prev" href = "../logs/log.html" class = "nav-chapters previous" title = "Previous chapter" aria-label = "Previous chapter" aria-keyshortcuts = "Left" >
< span class = fa-svg > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 320 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M41.4 233.4c-12.5 12.5-12.5 32.8 0 45.3l160 160c12.5 12.5 32.8 12.5 45.3 0s12.5-32.8 0-45.3L109.3 256 246.6 118.6c12.5-12.5 12.5-32.8 0-45.3s-32.8-12.5-45.3 0l-160 160z" / > < / svg > < / span >
< / a >
< a rel = "next prefetch" href = "../logs/tracing-logger.html" class = "nav-chapters next" title = "Next chapter" aria-label = "Next chapter" aria-keyshortcuts = "Right" >
< span class = fa-svg > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 320 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M278.6 233.4c12.5 12.5 12.5 32.8 0 45.3l-160 160c-12.5 12.5-32.8 12.5-45.3 0s-12.5-32.8 0-45.3L210.7 256 73.4 118.6c-12.5-12.5-12.5-32.8 0-45.3s32.8-12.5 45.3 0l160 160z" / > < / svg > < / span >
< / a >
< / nav >
< / div >
< template id = fa-eye > < span class = fa-svg > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 576 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M288 32c-80.8 0-145.5 36.8-192.6 80.6C48.6 156 17.3 208 2.5 243.7c-3.3 7.9-3.3 16.7 0 24.6C17.3 304 48.6 356 95.4 399.4C142.5 443.2 207.2 480 288 480s145.5-36.8 192.6-80.6c46.8-43.5 78.1-95.4 93-131.1c3.3-7.9 3.3-16.7 0-24.6c-14.9-35.7-46.2-87.7-93-131.1C433.5 68.8 368.8 32 288 32zM432 256c0 79.5-64.5 144-144 144s-144-64.5-144-144s64.5-144 144-144s144 64.5 144 144zM288 192c0 35.3-28.7 64-64 64c-11.5 0-22.3-3-31.6-8.4c-.2 2.8-.4 5.5-.4 8.4c0 53 43 96 96 96s96-43 96-96s-43-96-96-96c-2.8 0-5.6 .1-8.4 .4c5.3 9.3 8.4 20.1 8.4 31.6z" / > < / svg > < / span > < / template >
< template id = fa-eye-slash > < span class = fa-svg > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 640 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M38.8 5.1C28.4-3.1 13.3-1.2 5.1 9.2S-1.2 34.7 9.2 42.9l592 464c10.4 8.2 25.5 6.3 33.7-4.1s6.3-25.5-4.1-33.7L525.6 386.7c39.6-40.6 66.4-86.1 79.9-118.4c3.3-7.9 3.3-16.7 0-24.6c-14.9-35.7-46.2-87.7-93-131.1C465.5 68.8 400.8 32 320 32c-68.2 0-125 26.3-169.3 60.8L38.8 5.1zM223.1 149.5C248.6 126.2 282.7 112 320 112c79.5 0 144 64.5 144 144c0 24.9-6.3 48.3-17.4 68.7L408 294.5c5.2-11.8 8-24.8 8-38.5c0-53-43-96-96-96c-2.8 0-5.6 .1-8.4 .4c5.3 9.3 8.4 20.1 8.4 31.6c0 10.2-2.4 19.8-6.6 28.3l-90.3-70.8zm223.1 298L373 389.9c-16.4 6.5-34.3 10.1-53 10.1c-79.5 0-144-64.5-144-144c0-6.9 .5-13.6 1.4-20.2L83.1 161.5C60.3 191.2 44 220.8 34.5 243.7c-3.3 7.9-3.3 16.7 0 24.6c14.9 35.7 46.2 87.7 93 131.1C174.5 443.2 239.2 480 320 480c47.8 0 89.9-12.9 126.2-32.5z" / > < / svg > < / span > < / template >
< template id = fa-copy > < span class = fa-svg > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 512 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M502.6 70.63l-61.25-61.25C435.4 3.371 427.2 0 418.7 0H255.1c-35.35 0-64 28.66-64 64l.0195 256C192 355.4 220.7 384 256 384h192c35.2 0 64-28.8 64-64V93.25C512 84.77 508.6 76.63 502.6 70.63zM464 320c0 8.836-7.164 16-16 16H255.1c-8.838 0-16-7.164-16-16L239.1 64.13c0-8.836 7.164-16 16-16h128L384 96c0 17.67 14.33 32 32 32h47.1V320zM272 448c0 8.836-7.164 16-16 16H63.1c-8.838 0-16-7.164-16-16L47.98 192.1c0-8.836 7.164-16 16-16H160V128H63.99c-35.35 0-64 28.65-64 64l.0098 256C.002 483.3 28.66 512 64 512h192c35.2 0 64-28.8 64-64v-32h-47.1L272 448z" / > < / svg > < / span > < / template >
< template id = fa-play > < span class = fa-svg > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 384 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M73 39c-14.8-9.1-33.4-9.4-48.5-.9S0 62.6 0 80V432c0 17.4 9.4 33.4 24.5 41.9s33.7 8.1 48.5-.9L361 297c14.3-8.7 23-24.2 23-41s-8.7-32.2-23-41L73 39z" / > < / svg > < / span > < / template >
< template id = fa-clock-rotate-left > < span class = fa-svg > < svg xmlns = "http://www.w3.org/2000/svg" viewBox = "0 0 512 512" > <!-- ! Font Awesome Free 6.2.0 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license/free (Icons: CC BY 4.0, Fonts: SIL OFL 1.1, Code: MIT License) Copyright 2022 Fonticons, Inc. --> < path d = "M75 75L41 41C25.9 25.9 0 36.6 0 57.9V168c0 13.3 10.7 24 24 24H134.1c21.4 0 32.1-25.9 17-41l-30.8-30.8C155 85.5 203 64 256 64c106 0 192 86 192 192s-86 192-192 192c-40.8 0-78.6-12.7-109.7-34.4c-14.5-10.1-34.4-6.6-44.6 7.9s-6.6 34.4 7.9 44.6C151.2 495 201.7 512 256 512c141.4 0 256-114.6 256-256S397.4 0 256 0C185.3 0 121.3 28.7 75 75zm181 53c-13.3 0-24 10.7-24 24V256c0 6.4 2.5 12.5 7 17l72 72c9.4 9.4 24.6 9.4 33.9 0s9.4-24.6 0-33.9l-65-65V152c0-13.3-10.7-24-24-24z" / > < / svg > < / span > < / template >
< script >
window.playground_copyable = true;
< / script >
< script src = "../ace-2a3cd908.js" > < / script >
< script src = "../mode-rust-2c9d5c9a.js" > < / script >
< script src = "../editor-16ca416c.js" > < / script >
< script src = "../theme-dawn-4493f9c8.js" > < / script >
< script src = "../theme-tomorrow_night-9dbe62a9.js" > < / script >
< script src = "../elasticlunr-ef4e11c1.min.js" > < / script >
< script src = "../mark-09e88c2c.min.js" > < / script >
< script src = "../searcher-c2a407aa.js" > < / script >
< script src = "../clipboard-1626706a.min.js" > < / script >
< script src = "../highlight-abc7f01d.js" > < / script >
< script src = "../book-a0b12cfe.js" > < / script >
<!-- Custom JS scripts -->
< script src = "../assets/custom-7d8ae1df.js" > < / script >
< script src = "../assets/bigPicture-be03f9c8.js" > < / script >
< / div >
< / body >
< / html >
