714 lines
48 KiB
HTML
714 lines
48 KiB
HTML
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<!doctype html>
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<html lang="en" class="no-js">
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<link rel="canonical" href="https://status-im.github.io/nim-libp2p/docs/tutorial_3_protobuf/">
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<link rel="prev" href="../tutorial_2_customproto/">
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<link rel="next" href="../tutorial_4_gossipsub/">
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<meta name="generator" content="mkdocs-1.4.3, mkdocs-material-9.1.15">
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<title>Protobuf - nim-libp2p</title>
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<link rel="stylesheet" href="../assets/stylesheets/main.26e3688c.min.css">
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<link rel="stylesheet" href="../assets/stylesheets/palette.ecc896b0.min.css">
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<link rel="preconnect" href="https://fonts.gstatic.com" crossorigin>
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<link rel="stylesheet" href="https://fonts.googleapis.com/css?family=Roboto:300,300i,400,400i,700,700i%7CRoboto+Mono:400,400i,700,700i&display=fallback">
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<style>:root{--md-text-font:"Roboto";--md-code-font:"Roboto Mono"}</style>
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<script>__md_scope=new URL("..",location),__md_hash=e=>[...e].reduce((e,_)=>(e<<5)-e+_.charCodeAt(0),0),__md_get=(e,_=localStorage,t=__md_scope)=>JSON.parse(_.getItem(t.pathname+"."+e)),__md_set=(e,_,t=localStorage,a=__md_scope)=>{try{t.setItem(a.pathname+"."+e,JSON.stringify(_))}catch(e){}}</script>
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<body dir="ltr" data-md-color-scheme="default" data-md-color-primary="blue-grey" data-md-color-accent="indigo">
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<script>var palette=__md_get("__palette");if(palette&&"object"==typeof palette.color)for(var key of Object.keys(palette.color))document.body.setAttribute("data-md-color-"+key,palette.color[key])</script>
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<label class="md-overlay" for="__drawer"></label>
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<div data-md-component="skip">
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<a href="#protobuf-usage" class="md-skip">
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Skip to content
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<div data-md-component="announce">
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<header class="md-header md-header--shadow" data-md-component="header">
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<nav class="md-header__inner md-grid" aria-label="Header">
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<a href=".." title="nim-libp2p" class="md-header__button md-logo" aria-label="nim-libp2p" data-md-component="logo">
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<img src="https://libp2p.io/img/logo_small.png" alt="logo">
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</a>
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<label class="md-header__button md-icon" for="__drawer">
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<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M3 6h18v2H3V6m0 5h18v2H3v-2m0 5h18v2H3v-2Z"/></svg>
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<div class="md-header__title" data-md-component="header-title">
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<div class="md-header__topic">
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<span class="md-ellipsis">
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nim-libp2p
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<div class="md-header__topic" data-md-component="header-topic">
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<span class="md-ellipsis">
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Protobuf
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<form class="md-header__option" data-md-component="palette">
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<input class="md-option" data-md-color-media="" data-md-color-scheme="default" data-md-color-primary="blue-grey" data-md-color-accent="indigo" aria-label="Switch to dark mode" type="radio" name="__palette" id="__palette_1">
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<label class="md-header__button md-icon" title="Switch to dark mode" for="__palette_2" hidden>
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<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M17 7H7a5 5 0 0 0-5 5 5 5 0 0 0 5 5h10a5 5 0 0 0 5-5 5 5 0 0 0-5-5m0 8a3 3 0 0 1-3-3 3 3 0 0 1 3-3 3 3 0 0 1 3 3 3 3 0 0 1-3 3Z"/></svg>
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<input class="md-option" data-md-color-media="" data-md-color-scheme="slate" data-md-color-primary="blue-grey" data-md-color-accent="indigo" aria-label="Switch to light mode" type="radio" name="__palette" id="__palette_2">
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<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M17 6H7c-3.31 0-6 2.69-6 6s2.69 6 6 6h10c3.31 0 6-2.69 6-6s-2.69-6-6-6zm0 10H7c-2.21 0-4-1.79-4-4s1.79-4 4-4h10c2.21 0 4 1.79 4 4s-1.79 4-4 4zM7 9c-1.66 0-3 1.34-3 3s1.34 3 3 3 3-1.34 3-3-1.34-3-3-3z"/></svg>
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<label class="md-header__button md-icon" for="__search">
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<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.516 6.516 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5Z"/></svg>
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<div class="md-search" data-md-component="search" role="dialog">
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<label class="md-search__overlay" for="__search"></label>
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<div class="md-search__inner" role="search">
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<form class="md-search__form" name="search">
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<input type="text" class="md-search__input" name="query" aria-label="Search" placeholder="Search" autocapitalize="off" autocorrect="off" autocomplete="off" spellcheck="false" data-md-component="search-query" required>
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<label class="md-search__icon md-icon" for="__search">
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<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M9.5 3A6.5 6.5 0 0 1 16 9.5c0 1.61-.59 3.09-1.56 4.23l.27.27h.79l5 5-1.5 1.5-5-5v-.79l-.27-.27A6.516 6.516 0 0 1 9.5 16 6.5 6.5 0 0 1 3 9.5 6.5 6.5 0 0 1 9.5 3m0 2C7 5 5 7 5 9.5S7 14 9.5 14 14 12 14 9.5 12 5 9.5 5Z"/></svg>
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<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M20 11v2H8l5.5 5.5-1.42 1.42L4.16 12l7.92-7.92L13.5 5.5 8 11h12Z"/></svg>
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</label>
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<nav class="md-search__options" aria-label="Search">
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<button type="reset" class="md-search__icon md-icon" title="Clear" aria-label="Clear" tabindex="-1">
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<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M19 6.41 17.59 5 12 10.59 6.41 5 5 6.41 10.59 12 5 17.59 6.41 19 12 13.41 17.59 19 19 17.59 13.41 12 19 6.41Z"/></svg>
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<div class="md-search__output">
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<div class="md-search__scrollwrap" data-md-scrollfix>
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<div class="md-search-result" data-md-component="search-result">
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<div class="md-search-result__meta">
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Initializing search
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<ol class="md-search-result__list" role="presentation"></ol>
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<div class="md-header__source">
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<a href="https://github.com/status-im/nim-libp2p" title="Go to repository" class="md-source" data-md-component="source">
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<div class="md-source__icon md-icon">
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<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 448 512"><!--! Font Awesome Free 6.4.0 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 2023 Fonticons, Inc.--><path d="M439.55 236.05 244 40.45a28.87 28.87 0 0 0-40.81 0l-40.66 40.63 51.52 51.52c27.06-9.14 52.68 16.77 43.39 43.68l49.66 49.66c34.23-11.8 61.18 31 35.47 56.69-26.49 26.49-70.21-2.87-56-37.34L240.22 199v121.85c25.3 12.54 22.26 41.85 9.08 55a34.34 34.34 0 0 1-48.55 0c-17.57-17.6-11.07-46.91 11.25-56v-123c-20.8-8.51-24.6-30.74-18.64-45L142.57 101 8.45 235.14a28.86 28.86 0 0 0 0 40.81l195.61 195.6a28.86 28.86 0 0 0 40.8 0l194.69-194.69a28.86 28.86 0 0 0 0-40.81z"/></svg>
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</div>
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<div class="md-source__repository">
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status-im/nim-libp2p
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</div>
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</a>
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</div>
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</nav>
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<div class="md-container" data-md-component="container">
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<main class="md-main" data-md-component="main">
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<div class="md-main__inner md-grid">
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<div class="md-sidebar md-sidebar--primary" data-md-component="sidebar" data-md-type="navigation" >
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<div class="md-sidebar__scrollwrap">
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<div class="md-sidebar__inner">
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<nav class="md-nav md-nav--primary" aria-label="Navigation" data-md-level="0">
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<label class="md-nav__title" for="__drawer">
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<a href=".." title="nim-libp2p" class="md-nav__button md-logo" aria-label="nim-libp2p" data-md-component="logo">
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<img src="https://libp2p.io/img/logo_small.png" alt="logo">
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</a>
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nim-libp2p
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</label>
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<div class="md-nav__source">
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<a href="https://github.com/status-im/nim-libp2p" title="Go to repository" class="md-source" data-md-component="source">
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<div class="md-source__icon md-icon">
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<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 448 512"><!--! Font Awesome Free 6.4.0 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 2023 Fonticons, Inc.--><path d="M439.55 236.05 244 40.45a28.87 28.87 0 0 0-40.81 0l-40.66 40.63 51.52 51.52c27.06-9.14 52.68 16.77 43.39 43.68l49.66 49.66c34.23-11.8 61.18 31 35.47 56.69-26.49 26.49-70.21-2.87-56-37.34L240.22 199v121.85c25.3 12.54 22.26 41.85 9.08 55a34.34 34.34 0 0 1-48.55 0c-17.57-17.6-11.07-46.91 11.25-56v-123c-20.8-8.51-24.6-30.74-18.64-45L142.57 101 8.45 235.14a28.86 28.86 0 0 0 0 40.81l195.61 195.6a28.86 28.86 0 0 0 40.8 0l194.69-194.69a28.86 28.86 0 0 0 0-40.81z"/></svg>
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</div>
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<div class="md-source__repository">
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status-im/nim-libp2p
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</div>
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</a>
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<ul class="md-nav__list" data-md-scrollfix>
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<li class="md-nav__item md-nav__item--active md-nav__item--nested">
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<input class="md-nav__toggle md-toggle " type="checkbox" id="__nav_1" checked>
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<label class="md-nav__link" for="__nav_1" id="__nav_1_label" tabindex="0">
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Tutorials
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<span class="md-nav__icon md-icon"></span>
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</label>
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<nav class="md-nav" data-md-level="1" aria-labelledby="__nav_1_label" aria-expanded="true">
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<label class="md-nav__title" for="__nav_1">
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<span class="md-nav__icon md-icon"></span>
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Tutorials
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<ul class="md-nav__list" data-md-scrollfix>
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<li class="md-nav__item">
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<a href=".." class="md-nav__link">
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Introduction
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</a>
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<li class="md-nav__item">
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<a href="../tutorial_1_connect/" class="md-nav__link">
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Simple connection
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</a>
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<li class="md-nav__item">
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<a href="../tutorial_2_customproto/" class="md-nav__link">
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Create a custom protocol
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</a>
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</li>
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<li class="md-nav__item md-nav__item--active">
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<input class="md-nav__toggle md-toggle" type="checkbox" id="__toc">
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<label class="md-nav__link md-nav__link--active" for="__toc">
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Protobuf
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<span class="md-nav__icon md-icon"></span>
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</label>
|
||
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<a href="./" class="md-nav__link md-nav__link--active">
|
||
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Protobuf
|
||
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</a>
|
||
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|
||
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|
||
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<nav class="md-nav md-nav--secondary" aria-label="Table of contents">
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<label class="md-nav__title" for="__toc">
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<span class="md-nav__icon md-icon"></span>
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Table of contents
|
||
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</label>
|
||
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<ul class="md-nav__list" data-md-component="toc" data-md-scrollfix>
|
||
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<li class="md-nav__item">
|
||
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<a href="#protobuf-encoding-decoding" class="md-nav__link">
|
||
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Protobuf encoding & decoding
|
||
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</a>
|
||
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</li>
|
||
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<li class="md-nav__item">
|
||
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<a href="#results-instead-of-exceptions" class="md-nav__link">
|
||
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Results instead of exceptions
|
||
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</a>
|
||
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</li>
|
||
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<li class="md-nav__item">
|
||
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<a href="#creating-the-protocol" class="md-nav__link">
|
||
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Creating the protocol
|
||
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</a>
|
||
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</li>
|
||
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</ul>
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</nav>
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<li class="md-nav__item">
|
||
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<a href="../tutorial_4_gossipsub/" class="md-nav__link">
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GossipSub
|
||
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</a>
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</li>
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<li class="md-nav__item">
|
||
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<a href="../tutorial_5_discovery/" class="md-nav__link">
|
||
|
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Discovery Manager
|
||
|
|
</a>
|
||
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</li>
|
||
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||
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<li class="md-nav__item">
|
||
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<a href="../tutorial_6_game/" class="md-nav__link">
|
||
|
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Game
|
||
|
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</a>
|
||
|
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</li>
|
||
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||
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<li class="md-nav__item">
|
||
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<a href="../circuitrelay/" class="md-nav__link">
|
||
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Circuit Relay
|
||
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</a>
|
||
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</li>
|
||
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</ul>
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</nav>
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</li>
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<li class="md-nav__item">
|
||
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<a href="/nim-libp2p/master/libp2p.html" class="md-nav__link">
|
||
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Reference
|
||
|
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</a>
|
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</li>
|
||
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</ul>
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||
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</nav>
|
||
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</div>
|
||
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</div>
|
||
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</div>
|
||
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|
||
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|
||
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|
||
|
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<div class="md-sidebar md-sidebar--secondary" data-md-component="sidebar" data-md-type="toc" >
|
||
|
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<div class="md-sidebar__scrollwrap">
|
||
|
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<div class="md-sidebar__inner">
|
||
|
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|
||
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|
||
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<nav class="md-nav md-nav--secondary" aria-label="Table of contents">
|
||
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|
||
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|
||
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|
||
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|
||
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|
||
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||
|
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<label class="md-nav__title" for="__toc">
|
||
|
|
<span class="md-nav__icon md-icon"></span>
|
||
|
|
Table of contents
|
||
|
|
</label>
|
||
|
|
<ul class="md-nav__list" data-md-component="toc" data-md-scrollfix>
|
||
|
|
|
||
|
|
<li class="md-nav__item">
|
||
|
|
<a href="#protobuf-encoding-decoding" class="md-nav__link">
|
||
|
|
Protobuf encoding & decoding
|
||
|
|
</a>
|
||
|
|
|
||
|
|
</li>
|
||
|
|
|
||
|
|
<li class="md-nav__item">
|
||
|
|
<a href="#results-instead-of-exceptions" class="md-nav__link">
|
||
|
|
Results instead of exceptions
|
||
|
|
</a>
|
||
|
|
|
||
|
|
</li>
|
||
|
|
|
||
|
|
<li class="md-nav__item">
|
||
|
|
<a href="#creating-the-protocol" class="md-nav__link">
|
||
|
|
Creating the protocol
|
||
|
|
</a>
|
||
|
|
|
||
|
|
</li>
|
||
|
|
|
||
|
|
</ul>
|
||
|
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|
||
|
|
</nav>
|
||
|
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</div>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
<div class="md-content" data-md-component="content">
|
||
|
|
<article class="md-content__inner md-typeset">
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
<h1 id="protobuf-usage">Protobuf usage</h1>
|
||
|
|
<p>In the <a href="../tutorial_2_customproto/">previous tutorial</a>, we created a simple "ping" protocol.
|
||
|
|
Most real protocol want their messages to be structured and extensible, which is why
|
||
|
|
most real protocols use <a href="https://developers.google.com/protocol-buffers">protobuf</a> to
|
||
|
|
define their message structures.</p>
|
||
|
|
<p>Here, we'll create a slightly more complex protocol, which parses & generate protobuf
|
||
|
|
messages. Let's start by importing our dependencies, as usual:
|
||
|
|
<div class="highlight"><pre><span></span><code><a id="__codelineno-0-1" name="__codelineno-0-1" href="#__codelineno-0-1"></a><span class="kn">import</span><span class="w"> </span><span class="n">chronos</span>
|
||
|
|
<a id="__codelineno-0-2" name="__codelineno-0-2" href="#__codelineno-0-2"></a><span class="kn">import</span><span class="w"> </span><span class="n">stew</span><span class="o">/</span><span class="n">results</span><span class="w"> </span><span class="c"># for Opt[T]</span>
|
||
|
|
<a id="__codelineno-0-3" name="__codelineno-0-3" href="#__codelineno-0-3"></a>
|
||
|
|
<a id="__codelineno-0-4" name="__codelineno-0-4" href="#__codelineno-0-4"></a><span class="kn">import</span><span class="w"> </span><span class="n">libp2p</span>
|
||
|
|
</code></pre></div></p>
|
||
|
|
<h2 id="protobuf-encoding-decoding">Protobuf encoding & decoding</h2>
|
||
|
|
<p>This will be the structure of our messages:
|
||
|
|
<div class="highlight"><pre><span></span><code><a id="__codelineno-1-1" name="__codelineno-1-1" href="#__codelineno-1-1"></a><span class="kd">message</span><span class="w"> </span><span class="nc">MetricList</span><span class="w"> </span><span class="p">{</span>
|
||
|
|
<a id="__codelineno-1-2" name="__codelineno-1-2" href="#__codelineno-1-2"></a><span class="w"> </span><span class="kd">message</span><span class="w"> </span><span class="nc">Metric</span><span class="w"> </span><span class="p">{</span>
|
||
|
|
<a id="__codelineno-1-3" name="__codelineno-1-3" href="#__codelineno-1-3"></a><span class="w"> </span><span class="kt">string</span><span class="w"> </span><span class="na">name</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">1</span><span class="p">;</span>
|
||
|
|
<a id="__codelineno-1-4" name="__codelineno-1-4" href="#__codelineno-1-4"></a><span class="w"> </span><span class="kt">float</span><span class="w"> </span><span class="na">value</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span>
|
||
|
|
<a id="__codelineno-1-5" name="__codelineno-1-5" href="#__codelineno-1-5"></a><span class="w"> </span><span class="p">}</span>
|
||
|
|
<a id="__codelineno-1-6" name="__codelineno-1-6" href="#__codelineno-1-6"></a>
|
||
|
|
<a id="__codelineno-1-7" name="__codelineno-1-7" href="#__codelineno-1-7"></a><span class="w"> </span><span class="k">repeated</span><span class="w"> </span><span class="n">Metric</span><span class="w"> </span><span class="na">metrics</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span>
|
||
|
|
<a id="__codelineno-1-8" name="__codelineno-1-8" href="#__codelineno-1-8"></a><span class="p">}</span>
|
||
|
|
</code></pre></div>
|
||
|
|
We'll create our protobuf types, encoders & decoders, according to this format.
|
||
|
|
To create the encoders & decoders, we are going to use minprotobuf
|
||
|
|
(included in libp2p).</p>
|
||
|
|
<p>While more modern technics
|
||
|
|
(such as <a href="https://github.com/status-im/nim-protobuf-serialization">nim-protobuf-serialization</a>)
|
||
|
|
exists, minprotobuf is currently the recommended method to handle protobuf, since it has
|
||
|
|
been used in production extensively, and audited.
|
||
|
|
<div class="highlight"><pre><span></span><code><a id="__codelineno-2-1" name="__codelineno-2-1" href="#__codelineno-2-1"></a><span class="k">type</span>
|
||
|
|
<a id="__codelineno-2-2" name="__codelineno-2-2" href="#__codelineno-2-2"></a><span class="w"> </span><span class="n">Metric</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">object</span>
|
||
|
|
<a id="__codelineno-2-3" name="__codelineno-2-3" href="#__codelineno-2-3"></a><span class="w"> </span><span class="n">name</span><span class="p">:</span><span class="w"> </span><span class="nb">string</span>
|
||
|
|
<a id="__codelineno-2-4" name="__codelineno-2-4" href="#__codelineno-2-4"></a><span class="w"> </span><span class="n">value</span><span class="p">:</span><span class="w"> </span><span class="nb">float</span>
|
||
|
|
<a id="__codelineno-2-5" name="__codelineno-2-5" href="#__codelineno-2-5"></a>
|
||
|
|
<a id="__codelineno-2-6" name="__codelineno-2-6" href="#__codelineno-2-6"></a><span class="w"> </span><span class="n">MetricList</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">object</span>
|
||
|
|
<a id="__codelineno-2-7" name="__codelineno-2-7" href="#__codelineno-2-7"></a><span class="w"> </span><span class="n">metrics</span><span class="p">:</span><span class="w"> </span><span class="nb">seq</span><span class="o">[</span><span class="n">Metric</span><span class="o">]</span>
|
||
|
|
<a id="__codelineno-2-8" name="__codelineno-2-8" href="#__codelineno-2-8"></a>
|
||
|
|
<a id="__codelineno-2-9" name="__codelineno-2-9" href="#__codelineno-2-9"></a><span class="sx">{.push</span><span class="w"> </span><span class="sx">raises</span>:<span class="w"> </span><span class="sx">[].}</span>
|
||
|
|
<a id="__codelineno-2-10" name="__codelineno-2-10" href="#__codelineno-2-10"></a>
|
||
|
|
<a id="__codelineno-2-11" name="__codelineno-2-11" href="#__codelineno-2-11"></a><span class="sx">proc</span><span class="w"> </span><span class="sx">encode(m</span>:<span class="w"> </span><span class="sx">Metric): ProtoBuffer</span><span class="w"> </span><span class="sx">=</span>
|
||
|
|
<a id="__codelineno-2-12" name="__codelineno-2-12" href="#__codelineno-2-12"></a><span class="sx"> result</span><span class="w"> </span><span class="sx">= initProtoBuffer()</span>
|
||
|
|
<a id="__codelineno-2-13" name="__codelineno-2-13" href="#__codelineno-2-13"></a><span class="sx"> result.write(1</span>,<span class="w"> </span><span class="sx">m.name)</span>
|
||
|
|
<a id="__codelineno-2-14" name="__codelineno-2-14" href="#__codelineno-2-14"></a><span class="sx"> result.write(2</span>,<span class="w"> </span><span class="sx">m.value)</span>
|
||
|
|
<a id="__codelineno-2-15" name="__codelineno-2-15" href="#__codelineno-2-15"></a><span class="sx"> result.finish()</span>
|
||
|
|
<a id="__codelineno-2-16" name="__codelineno-2-16" href="#__codelineno-2-16"></a>
|
||
|
|
<a id="__codelineno-2-17" name="__codelineno-2-17" href="#__codelineno-2-17"></a><span class="sx">proc</span><span class="w"> </span><span class="sx">decode(_</span>:<span class="w"> </span><span class="sx">type</span><span class="w"> </span><span class="sx">Metric</span>,<span class="w"> </span><span class="sx">buf</span>:<span class="w"> </span><span class="sx">seq[byte]): Result[Metric</span>,<span class="w"> </span><span class="sx">ProtoError] =</span>
|
||
|
|
<a id="__codelineno-2-18" name="__codelineno-2-18" href="#__codelineno-2-18"></a><span class="sx"> var</span><span class="w"> </span><span class="sx">res</span>:<span class="w"> </span><span class="sx">Metric</span>
|
||
|
|
<a id="__codelineno-2-19" name="__codelineno-2-19" href="#__codelineno-2-19"></a><span class="w"> </span><span class="sx">let</span><span class="w"> </span><span class="sx">pb</span><span class="w"> </span><span class="sx">= initProtoBuffer(buf)</span>
|
||
|
|
<a id="__codelineno-2-20" name="__codelineno-2-20" href="#__codelineno-2-20"></a><span class="sx"> # "getField" will</span><span class="w"> </span><span class="sx">return</span><span class="w"> </span><span class="sx">a</span><span class="w"> </span><span class="sx">Result[bool</span>,<span class="w"> </span><span class="sx">ProtoError].</span>
|
||
|
|
<a id="__codelineno-2-21" name="__codelineno-2-21" href="#__codelineno-2-21"></a><span class="sx"> # The</span><span class="w"> </span><span class="sx">Result</span><span class="w"> </span><span class="sx">will</span><span class="w"> </span><span class="sx">hold</span><span class="w"> </span><span class="sx">an</span><span class="w"> </span><span class="sx">error</span><span class="w"> </span><span class="sx">if</span><span class="w"> </span><span class="sx">the</span><span class="w"> </span><span class="sx">protobuf</span><span class="w"> </span><span class="sx">is</span><span class="w"> </span><span class="sx">invalid.</span>
|
||
|
|
<a id="__codelineno-2-22" name="__codelineno-2-22" href="#__codelineno-2-22"></a><span class="sx"> # The</span><span class="w"> </span><span class="sx">Result</span><span class="w"> </span><span class="sx">will</span><span class="w"> </span><span class="sx">hold</span><span class="w"> </span><span class="sx">"false" if</span><span class="w"> </span><span class="sx">the</span><span class="w"> </span><span class="sx">field</span><span class="w"> </span><span class="sx">is</span><span class="w"> </span><span class="sx">missing</span>
|
||
|
|
<a id="__codelineno-2-23" name="__codelineno-2-23" href="#__codelineno-2-23"></a><span class="w"> </span><span class="sx">#</span>
|
||
|
|
<a id="__codelineno-2-24" name="__codelineno-2-24" href="#__codelineno-2-24"></a><span class="sx"> # We</span><span class="w"> </span><span class="sx">are</span><span class="w"> </span><span class="sx">just</span><span class="w"> </span><span class="sx">checking</span><span class="w"> </span><span class="sx">the</span><span class="w"> </span><span class="sx">error</span>,<span class="w"> </span><span class="sx">and</span><span class="w"> </span><span class="sx">ignoring</span><span class="w"> </span><span class="sx">whether</span><span class="w"> </span><span class="sx">the</span><span class="w"> </span><span class="sx">value</span>
|
||
|
|
<a id="__codelineno-2-25" name="__codelineno-2-25" href="#__codelineno-2-25"></a><span class="w"> </span><span class="sx"># is</span><span class="w"> </span><span class="sx">present</span><span class="w"> </span><span class="sx">or</span><span class="w"> </span><span class="sx">not</span><span class="w"> </span><span class="sx">(default</span><span class="w"> </span><span class="sx">values</span><span class="w"> </span><span class="sx">are</span><span class="w"> </span><span class="sx">valid).</span>
|
||
|
|
<a id="__codelineno-2-26" name="__codelineno-2-26" href="#__codelineno-2-26"></a><span class="sx"> discard</span><span class="w"> </span><span class="sx">? pb.getField(1</span>,<span class="w"> </span><span class="sx">res.name)</span>
|
||
|
|
<a id="__codelineno-2-27" name="__codelineno-2-27" href="#__codelineno-2-27"></a><span class="sx"> discard</span><span class="w"> </span><span class="sx">? pb.getField(2</span>,<span class="w"> </span><span class="sx">res.value)</span>
|
||
|
|
<a id="__codelineno-2-28" name="__codelineno-2-28" href="#__codelineno-2-28"></a><span class="sx"> ok(res)</span>
|
||
|
|
<a id="__codelineno-2-29" name="__codelineno-2-29" href="#__codelineno-2-29"></a>
|
||
|
|
<a id="__codelineno-2-30" name="__codelineno-2-30" href="#__codelineno-2-30"></a><span class="sx">proc</span><span class="w"> </span><span class="sx">encode(m</span>:<span class="w"> </span><span class="sx">MetricList): ProtoBuffer</span><span class="w"> </span><span class="sx">=</span>
|
||
|
|
<a id="__codelineno-2-31" name="__codelineno-2-31" href="#__codelineno-2-31"></a><span class="sx"> result</span><span class="w"> </span><span class="sx">= initProtoBuffer()</span>
|
||
|
|
<a id="__codelineno-2-32" name="__codelineno-2-32" href="#__codelineno-2-32"></a><span class="sx"> for</span><span class="w"> </span><span class="sx">metric</span><span class="w"> </span><span class="sx">in</span><span class="w"> </span><span class="sx">m.metrics</span>:
|
||
|
|
<a id="__codelineno-2-33" name="__codelineno-2-33" href="#__codelineno-2-33"></a><span class="w"> </span><span class="sx">result.write(1</span>,<span class="w"> </span><span class="sx">metric.encode())</span>
|
||
|
|
<a id="__codelineno-2-34" name="__codelineno-2-34" href="#__codelineno-2-34"></a><span class="sx"> result.finish()</span>
|
||
|
|
<a id="__codelineno-2-35" name="__codelineno-2-35" href="#__codelineno-2-35"></a>
|
||
|
|
<a id="__codelineno-2-36" name="__codelineno-2-36" href="#__codelineno-2-36"></a><span class="sx">proc</span><span class="w"> </span><span class="sx">decode(_</span>:<span class="w"> </span><span class="sx">type</span><span class="w"> </span><span class="sx">MetricList</span>,<span class="w"> </span><span class="sx">buf</span>:<span class="w"> </span><span class="sx">seq[byte]): Result[MetricList</span>,<span class="w"> </span><span class="sx">ProtoError] =</span>
|
||
|
|
<a id="__codelineno-2-37" name="__codelineno-2-37" href="#__codelineno-2-37"></a><span class="sx"> var</span>
|
||
|
|
<a id="__codelineno-2-38" name="__codelineno-2-38" href="#__codelineno-2-38"></a><span class="w"> </span><span class="sx">res</span>:<span class="w"> </span><span class="sx">MetricList</span>
|
||
|
|
<a id="__codelineno-2-39" name="__codelineno-2-39" href="#__codelineno-2-39"></a><span class="w"> </span><span class="sx">metrics</span>:<span class="w"> </span><span class="sx">seq[seq[byte]]</span>
|
||
|
|
<a id="__codelineno-2-40" name="__codelineno-2-40" href="#__codelineno-2-40"></a><span class="sx"> let</span><span class="w"> </span><span class="sx">pb</span><span class="w"> </span><span class="sx">= initProtoBuffer(buf)</span>
|
||
|
|
<a id="__codelineno-2-41" name="__codelineno-2-41" href="#__codelineno-2-41"></a><span class="sx"> discard</span><span class="w"> </span><span class="sx">? pb.getRepeatedField(1</span>,<span class="w"> </span><span class="sx">metrics)</span>
|
||
|
|
<a id="__codelineno-2-42" name="__codelineno-2-42" href="#__codelineno-2-42"></a>
|
||
|
|
<a id="__codelineno-2-43" name="__codelineno-2-43" href="#__codelineno-2-43"></a><span class="sx"> for</span><span class="w"> </span><span class="sx">metric</span><span class="w"> </span><span class="sx">in</span><span class="w"> </span><span class="sx">metrics</span>:
|
||
|
|
<a id="__codelineno-2-44" name="__codelineno-2-44" href="#__codelineno-2-44"></a><span class="w"> </span><span class="sx">res.metrics</span><span class="w"> </span><span class="sx">&= ? Metric.decode(metric)</span>
|
||
|
|
<a id="__codelineno-2-45" name="__codelineno-2-45" href="#__codelineno-2-45"></a><span class="sx"> ok(res)</span>
|
||
|
|
</code></pre></div></p>
|
||
|
|
<h2 id="results-instead-of-exceptions">Results instead of exceptions</h2>
|
||
|
|
<p>As you can see, this part of the program also uses Results instead of exceptions for error handling.
|
||
|
|
We start by <code>{.push raises: [].}</code>, which will prevent every non-async function from raising
|
||
|
|
exceptions.</p>
|
||
|
|
<p>Then, we use <a href="https://github.com/arnetheduck/nim-result">nim-result</a> to convey
|
||
|
|
errors to function callers. A <code>Result[T, E]</code> will either hold a valid result of type
|
||
|
|
T, or an error of type E.</p>
|
||
|
|
<p>You can check if the call succeeded by using <code>res.isOk</code>, and then get the
|
||
|
|
value using <code>res.value</code> or the error by using <code>res.error</code>.</p>
|
||
|
|
<p>Another useful tool is <code>?</code>, which will unpack a Result if it succeeded,
|
||
|
|
or if it failed, exit the current procedure returning the error.</p>
|
||
|
|
<p>nim-result is packed with other functionalities that you'll find in the
|
||
|
|
nim-result repository.</p>
|
||
|
|
<p>Results and exception are generally interchangeable, but have different semantics
|
||
|
|
that you may or may not prefer.</p>
|
||
|
|
<h2 id="creating-the-protocol">Creating the protocol</h2>
|
||
|
|
<p>We'll next create a protocol, like in the last tutorial, to request these metrics from our host
|
||
|
|
<div class="highlight"><pre><span></span><code><a id="__codelineno-3-1" name="__codelineno-3-1" href="#__codelineno-3-1"></a><span class="k">type</span>
|
||
|
|
<a id="__codelineno-3-2" name="__codelineno-3-2" href="#__codelineno-3-2"></a><span class="w"> </span><span class="n">MetricCallback</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">proc</span><span class="p">:</span><span class="w"> </span><span class="n">Future</span><span class="o">[</span><span class="n">MetricList</span><span class="o">]</span><span class="w"> </span><span class="sx">{.raises</span>:<span class="w"> </span><span class="sx">[], gcsafe.}</span>
|
||
|
|
<a id="__codelineno-3-3" name="__codelineno-3-3" href="#__codelineno-3-3"></a><span class="w"> </span><span class="n">MetricProto</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">ref</span><span class="w"> </span><span class="k">object</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="n">LPProtocol</span>
|
||
|
|
<a id="__codelineno-3-4" name="__codelineno-3-4" href="#__codelineno-3-4"></a><span class="w"> </span><span class="n">metricGetter</span><span class="p">:</span><span class="w"> </span><span class="n">MetricCallback</span>
|
||
|
|
<a id="__codelineno-3-5" name="__codelineno-3-5" href="#__codelineno-3-5"></a>
|
||
|
|
<a id="__codelineno-3-6" name="__codelineno-3-6" href="#__codelineno-3-6"></a><span class="k">proc</span><span class="w"> </span><span class="nf">new</span><span class="p">(</span><span class="err">_: typedesc[MetricProto], cb: MetricCallback): MetricProto =</span>
|
||
|
|
<a id="__codelineno-3-7" name="__codelineno-3-7" href="#__codelineno-3-7"></a><span class="w"> </span><span class="kd">var</span><span class="w"> </span><span class="n">res</span><span class="p">:</span><span class="w"> </span><span class="n">MetricProto</span>
|
||
|
|
<a id="__codelineno-3-8" name="__codelineno-3-8" href="#__codelineno-3-8"></a><span class="w"> </span><span class="k">proc</span><span class="w"> </span><span class="nf">handle</span><span class="p">(</span><span class="n">conn</span><span class="p">:</span><span class="w"> </span><span class="n">Connection</span><span class="p">,</span><span class="w"> </span><span class="n">proto</span><span class="p">:</span><span class="w"> </span><span class="nb">string</span><span class="p">)</span><span class="w"> </span><span class="sx">{.async</span>,<span class="w"> </span><span class="sx">gcsafe.}</span><span class="w"> </span><span class="o">=</span>
|
||
|
|
<a id="__codelineno-3-9" name="__codelineno-3-9" href="#__codelineno-3-9"></a><span class="w"> </span><span class="k">let</span>
|
||
|
|
<a id="__codelineno-3-10" name="__codelineno-3-10" href="#__codelineno-3-10"></a><span class="w"> </span><span class="n">metrics</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">await</span><span class="w"> </span><span class="n">res</span><span class="p">.</span><span class="n">metricGetter</span><span class="p">()</span>
|
||
|
|
<a id="__codelineno-3-11" name="__codelineno-3-11" href="#__codelineno-3-11"></a><span class="w"> </span><span class="n">asProtobuf</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">metrics</span><span class="p">.</span><span class="n">encode</span><span class="p">()</span>
|
||
|
|
<a id="__codelineno-3-12" name="__codelineno-3-12" href="#__codelineno-3-12"></a><span class="w"> </span><span class="n">await</span><span class="w"> </span><span class="n">conn</span><span class="p">.</span><span class="n">writeLp</span><span class="p">(</span><span class="n">asProtobuf</span><span class="p">.</span><span class="n">buffer</span><span class="p">)</span>
|
||
|
|
<a id="__codelineno-3-13" name="__codelineno-3-13" href="#__codelineno-3-13"></a><span class="w"> </span><span class="n">await</span><span class="w"> </span><span class="n">conn</span><span class="p">.</span><span class="n">close</span><span class="p">()</span>
|
||
|
|
<a id="__codelineno-3-14" name="__codelineno-3-14" href="#__codelineno-3-14"></a>
|
||
|
|
<a id="__codelineno-3-15" name="__codelineno-3-15" href="#__codelineno-3-15"></a><span class="w"> </span><span class="n">res</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">MetricProto</span><span class="p">.</span><span class="n">new</span><span class="p">(</span><span class="o">@[</span><span class="s">"/metric-getter/1.0.0"</span><span class="o">]</span><span class="p">,</span><span class="w"> </span><span class="n">handle</span><span class="p">)</span>
|
||
|
|
<a id="__codelineno-3-16" name="__codelineno-3-16" href="#__codelineno-3-16"></a><span class="w"> </span><span class="n">res</span><span class="p">.</span><span class="n">metricGetter</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">cb</span>
|
||
|
|
<a id="__codelineno-3-17" name="__codelineno-3-17" href="#__codelineno-3-17"></a><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">res</span>
|
||
|
|
<a id="__codelineno-3-18" name="__codelineno-3-18" href="#__codelineno-3-18"></a>
|
||
|
|
<a id="__codelineno-3-19" name="__codelineno-3-19" href="#__codelineno-3-19"></a><span class="k">proc</span><span class="w"> </span><span class="nf">fetch</span><span class="p">(</span><span class="n">p</span><span class="p">:</span><span class="w"> </span><span class="n">MetricProto</span><span class="p">,</span><span class="w"> </span><span class="n">conn</span><span class="p">:</span><span class="w"> </span><span class="n">Connection</span><span class="p">):</span><span class="w"> </span><span class="n">Future</span><span class="o">[</span><span class="n">MetricList</span><span class="o">]</span><span class="w"> </span><span class="sx">{.async.}</span><span class="w"> </span><span class="o">=</span>
|
||
|
|
<a id="__codelineno-3-20" name="__codelineno-3-20" href="#__codelineno-3-20"></a><span class="w"> </span><span class="k">let</span><span class="w"> </span><span class="n">protobuf</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">await</span><span class="w"> </span><span class="n">conn</span><span class="p">.</span><span class="n">readLp</span><span class="p">(</span><span class="mi">2048</span><span class="p">)</span>
|
||
|
|
<a id="__codelineno-3-21" name="__codelineno-3-21" href="#__codelineno-3-21"></a><span class="w"> </span><span class="c"># tryGet will raise an exception if the Result contains an error.</span>
|
||
|
|
<a id="__codelineno-3-22" name="__codelineno-3-22" href="#__codelineno-3-22"></a><span class="w"> </span><span class="c"># It's useful to bridge between exception-world and result-world</span>
|
||
|
|
<a id="__codelineno-3-23" name="__codelineno-3-23" href="#__codelineno-3-23"></a><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">MetricList</span><span class="p">.</span><span class="n">decode</span><span class="p">(</span><span class="n">protobuf</span><span class="p">).</span><span class="n">tryGet</span><span class="p">()</span>
|
||
|
|
</code></pre></div>
|
||
|
|
We can now create our main procedure:
|
||
|
|
<div class="highlight"><pre><span></span><code><a id="__codelineno-4-1" name="__codelineno-4-1" href="#__codelineno-4-1"></a><span class="k">proc</span><span class="w"> </span><span class="nf">main</span><span class="p">()</span><span class="w"> </span><span class="sx">{.async</span>,<span class="w"> </span><span class="sx">gcsafe.}</span><span class="w"> </span><span class="o">=</span>
|
||
|
|
<a id="__codelineno-4-2" name="__codelineno-4-2" href="#__codelineno-4-2"></a><span class="w"> </span><span class="k">let</span><span class="w"> </span><span class="n">rng</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">newRng</span><span class="p">()</span>
|
||
|
|
<a id="__codelineno-4-3" name="__codelineno-4-3" href="#__codelineno-4-3"></a><span class="w"> </span><span class="k">proc</span><span class="w"> </span><span class="nf">randomMetricGenerator</span><span class="p">:</span><span class="w"> </span><span class="n">Future</span><span class="o">[</span><span class="n">MetricList</span><span class="o">]</span><span class="w"> </span><span class="sx">{.async.}</span><span class="w"> </span><span class="o">=</span>
|
||
|
|
<a id="__codelineno-4-4" name="__codelineno-4-4" href="#__codelineno-4-4"></a><span class="w"> </span><span class="k">let</span><span class="w"> </span><span class="n">metricCount</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">rng</span><span class="o">[]</span><span class="p">.</span><span class="n">generate</span><span class="p">(</span><span class="n">uint32</span><span class="p">)</span><span class="w"> </span><span class="ow">mod</span><span class="w"> </span><span class="mi">16</span>
|
||
|
|
<a id="__codelineno-4-5" name="__codelineno-4-5" href="#__codelineno-4-5"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="ow">in</span><span class="w"> </span><span class="mi">0</span><span class="w"> </span><span class="p">..</span><span class="o"><</span><span class="w"> </span><span class="n">metricCount</span><span class="w"> </span><span class="o">+</span><span class="w"> </span><span class="mi">1</span><span class="p">:</span>
|
||
|
|
<a id="__codelineno-4-6" name="__codelineno-4-6" href="#__codelineno-4-6"></a><span class="w"> </span><span class="n">result</span><span class="p">.</span><span class="n">metrics</span><span class="p">.</span><span class="n">add</span><span class="p">(</span><span class="n">Metric</span><span class="p">(</span>
|
||
|
|
<a id="__codelineno-4-7" name="__codelineno-4-7" href="#__codelineno-4-7"></a><span class="w"> </span><span class="n">name</span><span class="p">:</span><span class="w"> </span><span class="s">"metric_"</span><span class="w"> </span><span class="o">&</span><span class="w"> </span><span class="o">$</span><span class="n">i</span><span class="p">,</span>
|
||
|
|
<a id="__codelineno-4-8" name="__codelineno-4-8" href="#__codelineno-4-8"></a><span class="w"> </span><span class="n">value</span><span class="p">:</span><span class="w"> </span><span class="nb">float</span><span class="p">(</span><span class="n">rng</span><span class="o">[]</span><span class="p">.</span><span class="n">generate</span><span class="p">(</span><span class="n">uint16</span><span class="p">))</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="mf">1000.0</span>
|
||
|
|
<a id="__codelineno-4-9" name="__codelineno-4-9" href="#__codelineno-4-9"></a><span class="w"> </span><span class="p">))</span>
|
||
|
|
<a id="__codelineno-4-10" name="__codelineno-4-10" href="#__codelineno-4-10"></a><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">result</span>
|
||
|
|
<a id="__codelineno-4-11" name="__codelineno-4-11" href="#__codelineno-4-11"></a><span class="w"> </span><span class="k">let</span>
|
||
|
|
<a id="__codelineno-4-12" name="__codelineno-4-12" href="#__codelineno-4-12"></a><span class="w"> </span><span class="n">metricProto1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">MetricProto</span><span class="p">.</span><span class="n">new</span><span class="p">(</span><span class="n">randomMetricGenerator</span><span class="p">)</span>
|
||
|
|
<a id="__codelineno-4-13" name="__codelineno-4-13" href="#__codelineno-4-13"></a><span class="w"> </span><span class="n">metricProto2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">MetricProto</span><span class="p">.</span><span class="n">new</span><span class="p">(</span><span class="n">randomMetricGenerator</span><span class="p">)</span>
|
||
|
|
<a id="__codelineno-4-14" name="__codelineno-4-14" href="#__codelineno-4-14"></a><span class="w"> </span><span class="n">switch1</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">newStandardSwitch</span><span class="p">(</span><span class="n">rng</span><span class="o">=</span><span class="n">rng</span><span class="p">)</span>
|
||
|
|
<a id="__codelineno-4-15" name="__codelineno-4-15" href="#__codelineno-4-15"></a><span class="w"> </span><span class="n">switch2</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">newStandardSwitch</span><span class="p">(</span><span class="n">rng</span><span class="o">=</span><span class="n">rng</span><span class="p">)</span>
|
||
|
|
<a id="__codelineno-4-16" name="__codelineno-4-16" href="#__codelineno-4-16"></a>
|
||
|
|
<a id="__codelineno-4-17" name="__codelineno-4-17" href="#__codelineno-4-17"></a><span class="w"> </span><span class="n">switch1</span><span class="p">.</span><span class="n">mount</span><span class="p">(</span><span class="n">metricProto1</span><span class="p">)</span>
|
||
|
|
<a id="__codelineno-4-18" name="__codelineno-4-18" href="#__codelineno-4-18"></a>
|
||
|
|
<a id="__codelineno-4-19" name="__codelineno-4-19" href="#__codelineno-4-19"></a><span class="w"> </span><span class="n">await</span><span class="w"> </span><span class="n">switch1</span><span class="p">.</span><span class="n">start</span><span class="p">()</span>
|
||
|
|
<a id="__codelineno-4-20" name="__codelineno-4-20" href="#__codelineno-4-20"></a><span class="w"> </span><span class="n">await</span><span class="w"> </span><span class="n">switch2</span><span class="p">.</span><span class="n">start</span><span class="p">()</span>
|
||
|
|
<a id="__codelineno-4-21" name="__codelineno-4-21" href="#__codelineno-4-21"></a>
|
||
|
|
<a id="__codelineno-4-22" name="__codelineno-4-22" href="#__codelineno-4-22"></a><span class="w"> </span><span class="k">let</span>
|
||
|
|
<a id="__codelineno-4-23" name="__codelineno-4-23" href="#__codelineno-4-23"></a><span class="w"> </span><span class="n">conn</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">await</span><span class="w"> </span><span class="n">switch2</span><span class="p">.</span><span class="n">dial</span><span class="p">(</span><span class="n">switch1</span><span class="p">.</span><span class="n">peerInfo</span><span class="p">.</span><span class="n">peerId</span><span class="p">,</span><span class="w"> </span><span class="n">switch1</span><span class="p">.</span><span class="n">peerInfo</span><span class="p">.</span><span class="n">addrs</span><span class="p">,</span><span class="w"> </span><span class="n">metricProto2</span><span class="p">.</span><span class="n">codecs</span><span class="p">)</span>
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<a id="__codelineno-4-24" name="__codelineno-4-24" href="#__codelineno-4-24"></a><span class="w"> </span><span class="n">metrics</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">await</span><span class="w"> </span><span class="n">metricProto2</span><span class="p">.</span><span class="n">fetch</span><span class="p">(</span><span class="n">conn</span><span class="p">)</span>
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<a id="__codelineno-4-25" name="__codelineno-4-25" href="#__codelineno-4-25"></a><span class="w"> </span><span class="n">await</span><span class="w"> </span><span class="n">conn</span><span class="p">.</span><span class="n">close</span><span class="p">()</span>
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<a id="__codelineno-4-26" name="__codelineno-4-26" href="#__codelineno-4-26"></a>
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<a id="__codelineno-4-27" name="__codelineno-4-27" href="#__codelineno-4-27"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="n">metric</span><span class="w"> </span><span class="ow">in</span><span class="w"> </span><span class="n">metrics</span><span class="p">.</span><span class="n">metrics</span><span class="p">:</span>
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<a id="__codelineno-4-28" name="__codelineno-4-28" href="#__codelineno-4-28"></a><span class="w"> </span><span class="n">echo</span><span class="w"> </span><span class="n">metric</span><span class="p">.</span><span class="n">name</span><span class="p">,</span><span class="w"> </span><span class="s">" = "</span><span class="p">,</span><span class="w"> </span><span class="n">metric</span><span class="p">.</span><span class="n">value</span>
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<a id="__codelineno-4-29" name="__codelineno-4-29" href="#__codelineno-4-29"></a>
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<a id="__codelineno-4-30" name="__codelineno-4-30" href="#__codelineno-4-30"></a><span class="w"> </span><span class="n">await</span><span class="w"> </span><span class="n">allFutures</span><span class="p">(</span><span class="n">switch1</span><span class="p">.</span><span class="n">stop</span><span class="p">(),</span><span class="w"> </span><span class="n">switch2</span><span class="p">.</span><span class="n">stop</span><span class="p">())</span><span class="w"> </span><span class="c"># close connections and shutdown all transports</span>
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<a id="__codelineno-4-31" name="__codelineno-4-31" href="#__codelineno-4-31"></a>
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<a id="__codelineno-4-32" name="__codelineno-4-32" href="#__codelineno-4-32"></a><span class="n">waitFor</span><span class="p">(</span><span class="n">main</span><span class="p">())</span>
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</code></pre></div>
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If you run this program, you should see random metrics being sent from the switch1 to the switch2.</p>
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