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class="sidebarItemTitle_pO2u margin-bottom--md">All posts</div><div role=group><h3>2024</h3><div role=group><h4>Playing with fire</h4><ul><ul class="sidebarItemList_Yudw clean-list"><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2024/11/playing-with-fire>The fractal flame algorithm</a><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2024/11/playing-with-fire-transforms>Transforms and variations</a><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2024/11/playing-with-fire-log-density>Tone mapping and color</a></ul></ul></div></div><div role=group><h3>2022</h3><ul class="sidebarItemList_Yudw clean-list"><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2011/11/webpack-industrial-complex>The webpack industrial complex</a></ul></div><div role=group><h3>2019</h3><ul class="sidebarItemList_Yudw clean-list"><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2019/12/release-the-gil>Release the GIL</a></ul><ul class="sidebarItemList_Yudw clean-list"><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2019/09/binary-format-shootout>Binary format shootout</a></ul><ul class="sidebarItemList_Yudw clean-list"><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2019/06/high-performance-systems>On building high performance systems</a></ul><ul class="sidebarItemList_Yudw clean-list"><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2019/05/making-bread>Making bread</a></ul><div role=group><h4>Allocations in Rust</h4><ul><ul class="sidebarItemList_Yudw clean-list"><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2019/02/understanding-allocations-in-rust>Foreword</a><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2019/02/the-whole-world>Global memory</a><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2019/02/stacking-up>Fixed memory</a><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2019/02/a-heaping-helping>Dynamic memory</a><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2019/02/08/compiler-optimizations>Compiler optimizations</a><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2019/02/summary>Summary</a></ul></ul></div></div><div role=group><h3>2018</h3><ul class="sidebarItemList_Yudw clean-list"><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2018/12/allocation-safety>QADAPT - debug_assert! for allocations</a></ul><ul class="sidebarItemList_Yudw clean-list"><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2018/12/what-small-business-really-means>More "what companies really mean"</a></ul><ul class="sidebarItemList_Yudw clean-list"><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2018/10/case-study-optimization>A case study in heaptrack</a></ul><ul class="sidebarItemList_Yudw clean-list"><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2018/09/isomorphic-apps>Isomorphic desktop apps with Rust</a></ul><ul class="sidebarItemList_Yudw clean-list"><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2018/09/primitives-in-rust-are-weird>Primitives in Rust are weird (and cool)</a></ul><ul class="sidebarItemList_Yudw clean-list"><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2018/06/dateutil-parser-to-rust>What I learned porting dateutil to Rust</a></ul><ul class="sidebarItemList_Yudw clean-list"><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2018/05/hello>Hello!</a></ul><div role=group><h4>Captain's Cookbook</h4><ul><ul class="sidebarItemList_Yudw clean-list"><li class=sidebarItem__DBe><a aria-current=page class="sidebarItemLink_mo7H sidebarItemLinkActive_I1ZP" href=/2018/01/captains-cookbook-part-1>Project setup</a><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2018/01/captains-cookbook-part-2>Practical usage</a></ul></ul></div></div><div role=group><h3>2016</h3><ul class="sidebarItemList_Yudw clean-list"><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2016/11/pca-audio-compression>PCA audio compression</a></ul><ul class="sidebarItemList_Yudw clean-list"><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2016/10/rustic-repodcasting>A Rustic re-podcasting server</a></ul><ul class="sidebarItemList_Yudw clean-list"><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2016/06/event-studies-and-earnings-releases>Event studies and earnings releases</a></ul><ul class="sidebarItemList_Yudw clean-list"><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2016/05/the-unfair-casino>The unfair casino</a></ul><ul class="sidebarItemList_Yudw clean-list"><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2016/04/tick-tock>Tick tock...</a></ul><ul class="sidebarItemList_Yudw clean-list"><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2016/03/tweet-like-me>Tweet like me</a></ul><ul class="sidebarItemList_Yudw clean-list"><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2016/03/predicting-santander-customer-happiness>Predicting Santander customer happiness</a></ul><ul class="sidebarItemList_Yudw clean-list"><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2016/02/profitability-using-the-investment-formula>Profitability using the investment formula</a></ul><ul class="sidebarItemList_Yudw clean-list"><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2016/02/guaranteed-money-maker>Guaranteed money maker</a></ul><ul class="sidebarItemList_Yudw clean-list"><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2016/01/cloudy-in-seattle>Cloudy in Seattle</a></ul><ul class="sidebarItemList_Yudw clean-list"><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2016/01/complaining-about-the-weather>Complaining about the weather</a></ul></div><div role=group><h3>2015</h3><ul class="sidebarItemList_Yudw clean-list"><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2015/12/testing-cramer>Testing Cramer</a></ul><ul class="sidebarItemList_Yudw clean-list"><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2015/11/autocallable>Autocallable Bonds</a></ul><ul class="sidebarItemList_Yudw clean-list"><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2015/11/welcome>Welcome, and an algorithm</a></ul></div></nav></aside><main class="col col--7"><article><header><h1 class=title_f1Hy>Captain's Cookbook: Project setup</h1><div class="container_mt6G margin-vert--md"><time datetime=2018-01-16T12:00:00.000Z>January 16, 2018</time> · <!-- -->8 min read</div><div class="margin-top--md margin-bottom--sm row"><div class="col col--12 authorCol_Hf19"><div class="avatar margin-bottom--sm"><div class="avatar__intro authorDetails_lV9A"><div class=avatar__name><span class=authorName_yefp>Bradlee Speice</span></div><div class=authorSocials_rSDt><a href=https://github.com/bspeice target=_blank rel="noopener noreferrer" class=authorSocialLink_owbf title=GitHub><svg viewBox="0 0 256 250" width=1em height=1em class="authorSocialLink_owbf githubSvg_Uu4N" style=--dark:#000;--light:#fff preserveAspectRatio=xMidYMid><path d="M128.001 0C57.317 0 0 57.307 0 128.001c0 56.554 36.676 104.535 87.535 121.46 6.397 1.185 8.746-2.777 8.746-6.158 0-3.052-.12-13.135-.174-23.83-35.61 7.742-43.124-15.103-43.124-15.103-5.823-14.795-14.213-18.73-14.213-18.73-11.613-7.944.876-7.78.876-7.78 12.853.902 19.621 13.19 19.621 13.19 11.417 19.568 29.945 13.911 37.249 10.64 1.149-8.272 4.466-13.92 8.127-17.116-28.431-3.236-58.318-14.212-58.318-63.258 0-13.975 5-25.394 13.188-34.358-1.329-3.224-5.71-16.242 1.24-33.874 0 0 10.749-3.44 35.21 13.121 10.21-2.836 21.16-4.258 32.038-4.307 10.878.049 21.837 1.47 32.066 4.307 24.431-16.56 35.165-13.12 35.165-13.12 6.967 17.63 2.584 30.65 1.255 33.873 8.207 8.964 13.173 20.383 13.173 34.358 0 49.163-29.944 59.988-58.447 63.157 4.591 3.972 8.682 11.762 8.682 23.704 0 17.126-.148 30.91-.148 35.126 0 3.407 2.304 7.398 8.792 6.14C219.37 232.5 256 184.537 256 128.002 256 57.307 198.691 0 128.001 0Zm-80.06 182.34c-.282.636-1.283.827-2.194.39-.929-.417-1.45-1.284-1.15-1.922.276-.655 1.279-.838 2.205-.399.93.418 1.46 1.293 1.139 1.931Zm6.296 5.618c-.61.566-1.804.303-2.614-.591-.837-.892-.994-2.086-.375-2.66.63-.566 1.787-.301 2.626.591.838.903 1 2.088.363 2.66Zm4.32 7.188c-.785.545-2.067.034-2.86-1.104-.784-1.138-.784-2.503.017-3.05.795-.547 2.058-.055 2.861 1.075.782 1.157.782 2.522-.019 3.08Zm7.304 8.325c-.701.774-2.196.566-3.29-.49-1.119-1.032-1.43-2.496-.726-3.27.71-.776 2.213-.558 3.315.49 1.11 1.03 1.45 2.505.701 3.27Zm9.442 2.81c-.31 1.003-1.75 1.459-3.199 1.033-1.448-.439-2.395-1.613-2.103-2.626.301-1.01 1.747-1.484 3.207-1.028 1.446.436 2.396 1.602 2.095 2.622Zm10.744 1.193c.036 1.055-1.193 1.93-2.715 1.95-1.53.034-2.769-.82-2.786-1.86 0-1.065 1.202-1.932 2.733-1.958 1.522-.03 2.768.818 2.768 1.868Zm10.555-.405c.182 1.03-.875 2.088-2.387 2.37-1.485.271-2.861-.365-3.05-1.386-.184-1.056.893-2.114 2.376-2.387 1.514-.263 2.868.356 3.061 1.403Z"/></svg></a></div></div></div></div></div></header><div id=__blog-post-container class=markdown><p>A basic introduction to getting started with Cap'N Proto.</p>
<p>I've been working a lot with <a href=https://capnproto.org/ target=_blank rel="noopener noreferrer">Cap'N Proto</a> recently with Rust, but there's a real dearth of information
on how to set up and get going quickly. In the interest of trying to get more people using this (because I think it's
fantastic), I'm going to work through a couple of examples detailing what exactly should be done to get going.</p>
<p>So, what is Cap'N Proto? It's a data serialization library. It has contemporaries with <a href=https://developers.google.com/protocol-buffers/ target=_blank rel="noopener noreferrer">Protobuf</a>
and <a href=https://google.github.io/flatbuffers/ target=_blank rel="noopener noreferrer">FlatBuffers</a>, but is better compared with FlatBuffers. The whole point behind it
is to define a schema language and serialization format such that:</p>
<ol>
<li>Applications that do not share the same base programming language can communicate</li>
<li>The data and schema you use can naturally evolve over time as your needs change</li>
</ol>
<p>Accompanying this are typically code generators that take the schemas you define for your application and give you back
code for different languages to get data to and from that schema.</p>
<p>Now, what makes Cap'N Proto different from, say, Protobuf, is that there is no serialization/deserialization step the same way
as is implemented with Protobuf. Instead, the idea is that the message itself can be loaded in memory and used directly there.</p>
<p>We're going to take a look at a series of progressively more complex projects that use Cap'N Proto in an effort to provide some
examples of what idiomatic usage looks like, and shorten the startup time needed to make use of this library in Rust projects.
If you want to follow along, feel free. If not, I've posted <a href=https://github.com/bspeice/capnp_cookbook_1 target=_blank rel="noopener noreferrer">the final result</a>
for reference.</p>
<h2 class="anchor anchorWithStickyNavbar_LWe7" id=step-1-installing-capnp>Step 1: Installing <code>capnp</code><a href=#step-1-installing-capnp class=hash-link aria-label="Direct link to step-1-installing-capnp" title="Direct link to step-1-installing-capnp"></a></h2>
<p>The <code>capnp</code> binary itself is needed for taking the schema files you write and turning them into a format that can be used by the
code generation libraries. Don't ask me what that actually means, I just know that you need to make sure this is installed.</p>
<p>I'll refer you to <a href=https://capnproto.org/install.html target=_blank rel="noopener noreferrer">Cap'N Proto's installation instructions</a> here. As a quick TLDR though:</p>
<ul>
<li>Linux users will likely have a binary shipped by their package manager - On Ubuntu, <code>apt install capnproto</code> is enough</li>
<li>OS X users can use <a href=https://brew.sh/ target=_blank rel="noopener noreferrer">Homebrew</a> as an easy install path. Just <code>brew install capnp</code></li>
<li>Windows users are a bit more complicated. If you're using <a href=https://chocolatey.org/ target=_blank rel="noopener noreferrer">Chocolatey</a>, there's <a href=https://chocolatey.org/packages/capnproto/ target=_blank rel="noopener noreferrer">a package</a> available. If that doesn't work however, you need to download <a href=https://capnproto.org/capnproto-c++-win32-0.6.1.zip target=_blank rel="noopener noreferrer">a release zip</a> and make sure that the <code>capnp.exe</code> binary is in your <code>%PATH%</code> environment variable</li>
</ul>
<p>The way you know you're done with this step is if the following command works in your shell:</p>
<div class="language-bash codeBlockContainer_Ckt0 theme-code-block" style="--prism-background-color:hsl(230, 1%, 98%);--prism-color:hsl(230, 8%, 24%)"><div class=codeBlockContent_biex><pre tabindex=0 class="prism-code language-bash codeBlock_bY9V thin-scrollbar" style="background-color:hsl(230, 1%, 98%);color:hsl(230, 8%, 24%)"><code class=codeBlockLines_e6Vv><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain">capnp </span><span class="token function" style="color:hsl(221, 87%, 60%)">id</span><br></span></code></pre><div class=buttonGroup__atx><button type=button aria-label="Copy code to clipboard" title=Copy class=clean-btn><span class=copyButtonIcons_eSgA aria-hidden=true><svg viewBox="0 0 24 24" class=copyButtonIcon_y97N><path fill=currentColor d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"/></svg><svg viewBox="0 0 24 24" class=copyButtonSuccessIcon_LjdS><path fill=currentColor d=M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z /></svg></span></button></div></div></div>
<h2 class="anchor anchorWithStickyNavbar_LWe7" id=step-2-starting-a-capn-proto-rust-project>Step 2: Starting a Cap'N Proto Rust project<a href=#step-2-starting-a-capn-proto-rust-project class=hash-link aria-label="Direct link to Step 2: Starting a Cap'N Proto Rust project" title="Direct link to Step 2: Starting a Cap'N Proto Rust project"></a></h2>
<p>After the <code>capnp</code> binary is set up, it's time to actually create our Rust project. Nothing terribly complex here, just a simple</p>
<div class="language-bash codeBlockContainer_Ckt0 theme-code-block" style="--prism-background-color:hsl(230, 1%, 98%);--prism-color:hsl(230, 8%, 24%)"><div class=codeBlockContent_biex><pre tabindex=0 class="prism-code language-bash codeBlock_bY9V thin-scrollbar" style="background-color:hsl(230, 1%, 98%);color:hsl(230, 8%, 24%)"><code class=codeBlockLines_e6Vv><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token function" style="color:hsl(221, 87%, 60%)">mkdir</span><span class="token plain"> capnp_cookbook_1</span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"></span><span class="token builtin class-name" style="color:hsl(35, 99%, 36%)">cd</span><span class="token plain"> capnp_cookbook_1</span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"></span><span class="token function" style="color:hsl(221, 87%, 60%)">cargo</span><span class="token plain"> init </span><span class="token parameter variable" style="color:hsl(221, 87%, 60%)">--bin</span><br></span></code></pre><div class=buttonGroup__atx><button type=button aria-label="Copy code to clipboard" title=Copy class=clean-btn><span class=copyButtonIcons_eSgA aria-hidden=true><svg viewBox="0 0 24 24" class=copyButtonIcon_y97N><path fill=currentColor d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"/></svg><svg viewBox="0 0 24 24" class=copyButtonSuccessIcon_LjdS><path fill=currentColor d=M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z /></svg></span></button></div></div></div>
<p>We'll put the following content into <code>Cargo.toml</code>:</p>
<div class="codeBlockContainer_Ckt0 theme-code-block" style="--prism-background-color:hsl(230, 1%, 98%);--prism-color:hsl(230, 8%, 24%)"><div class=codeBlockContent_biex><pre tabindex=0 class="prism-code language-text codeBlock_bY9V thin-scrollbar" style="background-color:hsl(230, 1%, 98%);color:hsl(230, 8%, 24%)"><code class=codeBlockLines_e6Vv><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain">[package]</span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain">name = "capnp_cookbook_1"</span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain">version = "0.1.0"</span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain">authors = ["Bradlee Speice &lt;bspeice@kcg.com>"]</span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain" style=display:inline-block></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain">[build-dependencies]</span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain">capnpc = "0.8" # 1</span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain" style=display:inline-block></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain">[dependencies]</span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain">capnp = "0.8" # 2</span><br></span></code></pre><div class=buttonGroup__atx><button type=button aria-label="Copy code to clipboard" title=Copy class=clean-btn><span class=copyButtonIcons_eSgA aria-hidden=true><svg viewBox="0 0 24 24" class=copyButtonIcon_y97N><path fill=currentColor d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"/></svg><svg viewBox="0 0 24 24" class=copyButtonSuccessIcon_LjdS><path fill=currentColor d=M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z /></svg></span></button></div></div></div>
<p>This sets up:</p>
<ol>
<li>The Rust code generator (CAPNProto Compiler)</li>
<li>The Cap'N Proto runtime library (CAPNProto runtime)</li>
</ol>
<p>We've now got everything prepared that we need for writing a Cap'N Proto project.</p>
<h2 class="anchor anchorWithStickyNavbar_LWe7" id=step-3-writing-a-basic-schema>Step 3: Writing a basic schema<a href=#step-3-writing-a-basic-schema class=hash-link aria-label="Direct link to Step 3: Writing a basic schema" title="Direct link to Step 3: Writing a basic schema"></a></h2>
<p>We're going to start with writing a pretty trivial data schema that we can extend later. This is just intended to make sure
you get familiar with how to start from a basic project.</p>
<p>First, we're going to create a top-level directory for storing the schema files in:</p>
<div class="language-bash codeBlockContainer_Ckt0 theme-code-block" style="--prism-background-color:hsl(230, 1%, 98%);--prism-color:hsl(230, 8%, 24%)"><div class=codeBlockContent_biex><pre tabindex=0 class="prism-code language-bash codeBlock_bY9V thin-scrollbar" style="background-color:hsl(230, 1%, 98%);color:hsl(230, 8%, 24%)"><code class=codeBlockLines_e6Vv><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token comment" style="color:hsl(230, 4%, 64%)"># Assuming we're starting from the `capnp_cookbook_1` directory created earlier</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain" style=display:inline-block></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"></span><span class="token function" style="color:hsl(221, 87%, 60%)">mkdir</span><span class="token plain"> schema</span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"></span><span class="token builtin class-name" style="color:hsl(35, 99%, 36%)">cd</span><span class="token plain"> schema</span><br></span></code></pre><div class=buttonGroup__atx><button type=button aria-label="Copy code to clipboard" title=Copy class=clean-btn><span class=copyButtonIcons_eSgA aria-hidden=true><svg viewBox="0 0 24 24" class=copyButtonIcon_y97N><path fill=currentColor d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"/></svg><svg viewBox="0 0 24 24" class=copyButtonSuccessIcon_LjdS><path fill=currentColor d=M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z /></svg></span></button></div></div></div>
<p>Now, we're going to put the following content in <code>point.capnp</code>:</p>
<div class="codeBlockContainer_Ckt0 theme-code-block" style="--prism-background-color:hsl(230, 1%, 98%);--prism-color:hsl(230, 8%, 24%)"><div class=codeBlockContent_biex><pre tabindex=0 class="prism-code language-text codeBlock_bY9V thin-scrollbar" style="background-color:hsl(230, 1%, 98%);color:hsl(230, 8%, 24%)"><code class=codeBlockLines_e6Vv><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain">@0xab555145c708dad2;</span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain" style=display:inline-block></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain">struct Point {</span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> x @0 :Int32;</span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> y @1 :Int32;</span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain">}</span><br></span></code></pre><div class=buttonGroup__atx><button type=button aria-label="Copy code to clipboard" title=Copy class=clean-btn><span class=copyButtonIcons_eSgA aria-hidden=true><svg viewBox="0 0 24 24" class=copyButtonIcon_y97N><path fill=currentColor d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"/></svg><svg viewBox="0 0 24 24" class=copyButtonSuccessIcon_LjdS><path fill=currentColor d=M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z /></svg></span></button></div></div></div>
<p>Pretty easy, we've now got structure for an object we'll be able to quickly encode in a binary format.</p>
<h2 class="anchor anchorWithStickyNavbar_LWe7" id=step-4-setting-up-the-build-process>Step 4: Setting up the build process<a href=#step-4-setting-up-the-build-process class=hash-link aria-label="Direct link to Step 4: Setting up the build process" title="Direct link to Step 4: Setting up the build process"></a></h2>
<p>Now it's time to actually set up the build process to make sure that Cap'N Proto generates the Rust code we'll eventually be using.
This is typically done through a <code>build.rs</code> file to invoke the schema compiler.</p>
<p>In the same folder as your <code>Cargo.toml</code> file, please put the following content in <code>build.rs</code>:</p>
<div class="language-rust codeBlockContainer_Ckt0 theme-code-block" style="--prism-background-color:hsl(230, 1%, 98%);--prism-color:hsl(230, 8%, 24%)"><div class=codeBlockContent_biex><pre tabindex=0 class="prism-code language-rust codeBlock_bY9V thin-scrollbar" style="background-color:hsl(230, 1%, 98%);color:hsl(230, 8%, 24%)"><code class=codeBlockLines_e6Vv><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token keyword" style="color:hsl(301, 63%, 40%)">extern</span><span class="token plain"> </span><span class="token keyword" style="color:hsl(301, 63%, 40%)">crate</span><span class="token plain"> </span><span class="token module-declaration namespace">capnpc</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">;</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain" style=display:inline-block></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"></span><span class="token keyword" style="color:hsl(301, 63%, 40%)">fn</span><span class="token plain"> </span><span class="token function-definition function" style="color:hsl(221, 87%, 60%)">main</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">(</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">)</span><span class="token plain"> </span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">{</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">::</span><span class="token namespace">capnpc</span><span class="token namespace punctuation" style="color:hsl(119, 34%, 47%)">::</span><span class="token class-name" style="color:hsl(35, 99%, 36%)">CompilerCommand</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">::</span><span class="token function" style="color:hsl(221, 87%, 60%)">new</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">(</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">)</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">.</span><span class="token function" style="color:hsl(221, 87%, 60%)">src_prefix</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">(</span><span class="token string" style="color:hsl(119, 34%, 47%)">"schema"</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">)</span><span class="token plain"> </span><span class="token comment" style="color:hsl(230, 4%, 64%)">// 1</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">.</span><span class="token function" style="color:hsl(221, 87%, 60%)">file</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">(</span><span class="token string" style="color:hsl(119, 34%, 47%)">"schema/point.capnp"</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">)</span><span class="token plain"> </span><span class="token comment" style="color:hsl(230, 4%, 64%)">// 2</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">.</span><span class="token function" style="color:hsl(221, 87%, 60%)">run</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">(</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">)</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">.</span><span class="token function" style="color:hsl(221, 87%, 60%)">expect</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">(</span><span class="token string" style="color:hsl(119, 34%, 47%)">"compiling schema"</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">)</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">;</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"></span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">}</span><br></span></code></pre><div class=buttonGroup__atx><button type=button aria-label="Copy code to clipboard" title=Copy class=clean-btn><span class=copyButtonIcons_eSgA aria-hidden=true><svg viewBox="0 0 24 24" class=copyButtonIcon_y97N><path fill=currentColor d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"/></svg><svg viewBox="0 0 24 24" class=copyButtonSuccessIcon_LjdS><path fill=currentColor d=M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z /></svg></span></button></div></div></div>
<p>This sets up the protocol compiler (<code>capnpc</code> from earlier) to compile the schema we've built so far.</p>
<ol>
<li>Because Cap'N Proto schema files can re-use types specified in other files, the <code>src_prefix()</code> tells the compiler
where to look for those extra files at.</li>
<li>We specify the schema file we're including by hand. In a much larger project, you could presumably build the <code>CompilerCommand</code>
dynamically, but we won't worry too much about that one for now.</li>
</ol>
<h2 class="anchor anchorWithStickyNavbar_LWe7" id=step-5-running-the-build>Step 5: Running the build<a href=#step-5-running-the-build class=hash-link aria-label="Direct link to Step 5: Running the build" title="Direct link to Step 5: Running the build"></a></h2>
<p>If you've done everything correctly so far, you should be able to actually build the project and see the auto-generated code.
Run a <code>cargo build</code> command, and if you don't see <code>cargo</code> complaining, you're doing just fine!</p>
<p>So where exactly does the generated code go to? I think it's critically important for people to be able to see what the generated
code looks like, because you need to understand what you're actually programming against. The short answer is: the generated code lives
somewhere in the <code>target/</code> directory.</p>
<p>The long answer is that you're best off running a <code>find</code> command to get the actual file path:</p>
<div class="language-bash codeBlockContainer_Ckt0 theme-code-block" style="--prism-background-color:hsl(230, 1%, 98%);--prism-color:hsl(230, 8%, 24%)"><div class=codeBlockContent_biex><pre tabindex=0 class="prism-code language-bash codeBlock_bY9V thin-scrollbar" style="background-color:hsl(230, 1%, 98%);color:hsl(230, 8%, 24%)"><code class=codeBlockLines_e6Vv><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token comment" style="color:hsl(230, 4%, 64%)"># Assuming we're running from the capnp_cookbook_1 project folder</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"></span><span class="token function" style="color:hsl(221, 87%, 60%)">find</span><span class="token plain"> </span><span class="token builtin class-name" style="color:hsl(35, 99%, 36%)">.</span><span class="token plain"> </span><span class="token parameter variable" style="color:hsl(221, 87%, 60%)">-name</span><span class="token plain"> point_capnp.rs</span><br></span></code></pre><div class=buttonGroup__atx><button type=button aria-label="Copy code to clipboard" title=Copy class=clean-btn><span class=copyButtonIcons_eSgA aria-hidden=true><svg viewBox="0 0 24 24" class=copyButtonIcon_y97N><path fill=currentColor d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"/></svg><svg viewBox="0 0 24 24" class=copyButtonSuccessIcon_LjdS><path fill=currentColor d=M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z /></svg></span></button></div></div></div>
<p>Alternately, if the <code>find</code> command isn't available, the path will look something like:</p>
<div class="codeBlockContainer_Ckt0 theme-code-block" style="--prism-background-color:hsl(230, 1%, 98%);--prism-color:hsl(230, 8%, 24%)"><div class=codeBlockContent_biex><pre tabindex=0 class="prism-code language-text codeBlock_bY9V thin-scrollbar" style="background-color:hsl(230, 1%, 98%);color:hsl(230, 8%, 24%)"><code class=codeBlockLines_e6Vv><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain">./target/debug/build/capnp_cookbook_1-c6e2990393c32fe6/out/point_capnp.rs</span><br></span></code></pre><div class=buttonGroup__atx><button type=button aria-label="Copy code to clipboard" title=Copy class=clean-btn><span class=copyButtonIcons_eSgA aria-hidden=true><svg viewBox="0 0 24 24" class=copyButtonIcon_y97N><path fill=currentColor d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"/></svg><svg viewBox="0 0 24 24" class=copyButtonSuccessIcon_LjdS><path fill=currentColor d=M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z /></svg></span></button></div></div></div>
<p>See if there are any paths in your target directory that look similar.</p>
<p>Now, the file content looks pretty nasty. I've included an example <a href=https://github.com/bspeice/capnp_cookbook_1/blob/master/target/debug/build/capnp_cookbook_1-c6e2990393c32fe6/out/point_capnp.rs target=_blank rel="noopener noreferrer">here</a>
if you aren't following along at home. There are a couple things I'll try and point out though so you can get an idea of how
the schema we wrote for the "Point" message is tied to the generated code.</p>
<p>First, the Cap'N Proto library splits things up into <code>Builder</code> and <code>Reader</code> structs. These are best thought of the same way
Rust separates <code>mut</code> from non-<code>mut</code> code. <code>Builder</code>s are <code>mut</code> versions of your message, and <code>Reader</code>s are immutable versions.</p>
<p>For example, the <a href=https://github.com/bspeice/capnp_cookbook_1/blob/master/target/debug/build/capnp_cookbook_1-c6e2990393c32fe6/out/point_capnp.rs#L90 target=_blank rel="noopener noreferrer"><code>Builder</code> impl</a> for <code>point</code> defines <a href=https://github.com/bspeice/capnp_cookbook_1/blob/master/target/debug/build/capnp_cookbook_1-c6e2990393c32fe6/out/point_capnp.rs#L105 target=_blank rel="noopener noreferrer"><code>get_x()</code></a>, <a href=https://github.com/bspeice/capnp_cookbook_1/blob/master/target/debug/build/capnp_cookbook_1-c6e2990393c32fe6/out/point_capnp.rs#L109 target=_blank rel="noopener noreferrer"><code>set_x()</code></a>, <a href=https://github.com/bspeice/capnp_cookbook_1/blob/master/target/debug/build/capnp_cookbook_1-c6e2990393c32fe6/out/point_capnp.rs#L113 target=_blank rel="noopener noreferrer"><code>get_y()</code></a>, and <a href=https://github.com/bspeice/capnp_cookbook_1/blob/master/target/debug/build/capnp_cookbook_1-c6e2990393c32fe6/out/point_capnp.rs#L117 target=_blank rel="noopener noreferrer"><code>set_y()</code></a> methods.
In comparison, the <a href=https://github.com/bspeice/capnp_cookbook_1/blob/master/target/debug/build/capnp_cookbook_1-c6e2990393c32fe6/out/point_capnp.rs#L38 target=_blank rel="noopener noreferrer"><code>Reader</code> impl</a> only defines <a href=https://github.com/bspeice/capnp_cookbook_1/blob/master/target/debug/build/capnp_cookbook_1-c6e2990393c32fe6/out/point_capnp.rs#L47 target=_blank rel="noopener noreferrer"><code>get_x()</code></a> and <a href=https://github.com/bspeice/capnp_cookbook_1/blob/master/target/debug/build/capnp_cookbook_1-c6e2990393c32fe6/out/point_capnp.rs#L51 target=_blank rel="noopener noreferrer"><code>get_y()</code></a> methods.</p>
<p>So now we know that there are some <code>get</code> and <code>set</code> methods available for our <code>x</code> and <code>y</code> coordinates;
but what do we actually do with those?</p>
<h2 class="anchor anchorWithStickyNavbar_LWe7" id=step-6-making-a-point>Step 6: Making a point<a href=#step-6-making-a-point class=hash-link aria-label="Direct link to Step 6: Making a point" title="Direct link to Step 6: Making a point"></a></h2>
<p>So we've install Cap'N Proto, gotten a project set up, and can generate schema code now. It's time to actually start building
Cap'N Proto messages! I'm going to put the code you need here because it's small, and put some extra long comments inline. This code
should go in <a href=https://github.com/bspeice/capnp_cookbook_1/blob/master/src/main.rs target=_blank rel="noopener noreferrer"><code>src/main.rs</code></a>:</p>
<div class="language-rust codeBlockContainer_Ckt0 theme-code-block" style="--prism-background-color:hsl(230, 1%, 98%);--prism-color:hsl(230, 8%, 24%)"><div class=codeBlockContent_biex><pre tabindex=0 class="prism-code language-rust codeBlock_bY9V thin-scrollbar" style="background-color:hsl(230, 1%, 98%);color:hsl(230, 8%, 24%)"><code class=codeBlockLines_e6Vv><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token comment" style="color:hsl(230, 4%, 64%)">// Note that we use `capnp` here, NOT `capnpc`</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"></span><span class="token keyword" style="color:hsl(301, 63%, 40%)">extern</span><span class="token plain"> </span><span class="token keyword" style="color:hsl(301, 63%, 40%)">crate</span><span class="token plain"> </span><span class="token module-declaration namespace">capnp</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">;</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain" style=display:inline-block></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"></span><span class="token comment" style="color:hsl(230, 4%, 64%)">// We create a module here to define how we are to access the code</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"></span><span class="token comment" style="color:hsl(230, 4%, 64%)">// being included.</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"></span><span class="token keyword" style="color:hsl(301, 63%, 40%)">pub</span><span class="token plain"> </span><span class="token keyword" style="color:hsl(301, 63%, 40%)">mod</span><span class="token plain"> </span><span class="token module-declaration namespace">point_capnp</span><span class="token plain"> </span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">{</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token comment" style="color:hsl(230, 4%, 64%)">// The environment variable OUT_DIR is set by Cargo, and</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token comment" style="color:hsl(230, 4%, 64%)">// is the location of all the code that was built as part</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token comment" style="color:hsl(230, 4%, 64%)">// of the codegen step.</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token comment" style="color:hsl(230, 4%, 64%)">// point_capnp.rs is the actual file to include</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token macro property" style="color:hsl(5, 74%, 59%)">include!</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">(</span><span class="token macro property" style="color:hsl(5, 74%, 59%)">concat!</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">(</span><span class="token macro property" style="color:hsl(5, 74%, 59%)">env!</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">(</span><span class="token string" style="color:hsl(119, 34%, 47%)">"OUT_DIR"</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">)</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">,</span><span class="token plain"> </span><span class="token string" style="color:hsl(119, 34%, 47%)">"/point_capnp.rs"</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">)</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">)</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">;</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"></span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">}</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain" style=display:inline-block></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"></span><span class="token keyword" style="color:hsl(301, 63%, 40%)">fn</span><span class="token plain"> </span><span class="token function-definition function" style="color:hsl(221, 87%, 60%)">main</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">(</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">)</span><span class="token plain"> </span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">{</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain" style=display:inline-block></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token comment" style="color:hsl(230, 4%, 64%)">// The process of building a Cap'N Proto message is a bit tedious.</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token comment" style="color:hsl(230, 4%, 64%)">// We start by creating a generic Builder; it acts as the message</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token comment" style="color:hsl(230, 4%, 64%)">// container that we'll later be filling with content of our `Point`</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token keyword" style="color:hsl(301, 63%, 40%)">let</span><span class="token plain"> </span><span class="token keyword" style="color:hsl(301, 63%, 40%)">mut</span><span class="token plain"> builder </span><span class="token operator" style="color:hsl(221, 87%, 60%)">=</span><span class="token plain"> </span><span class="token namespace">capnp</span><span class="token namespace punctuation" style="color:hsl(119, 34%, 47%)">::</span><span class="token namespace">message</span><span class="token namespace punctuation" style="color:hsl(119, 34%, 47%)">::</span><span class="token class-name" style="color:hsl(35, 99%, 36%)">Builder</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">::</span><span class="token function" style="color:hsl(221, 87%, 60%)">new_default</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">(</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">)</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">;</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain" style=display:inline-block></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token comment" style="color:hsl(230, 4%, 64%)">// Because we need a mutable reference to the `builder` later,</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token comment" style="color:hsl(230, 4%, 64%)">// we fence off this part of the code to allow sequential mutable</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token comment" style="color:hsl(230, 4%, 64%)">// borrows. As I understand it, non-lexical lifetimes:</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token comment" style="color:hsl(230, 4%, 64%)">// https://github.com/rust-lang/rust-roadmap/issues/16</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token comment" style="color:hsl(230, 4%, 64%)">// will make this no longer necessary</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">{</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token comment" style="color:hsl(230, 4%, 64%)">// And now we can set up the actual message we're trying to create</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token keyword" style="color:hsl(301, 63%, 40%)">let</span><span class="token plain"> </span><span class="token keyword" style="color:hsl(301, 63%, 40%)">mut</span><span class="token plain"> point_msg </span><span class="token operator" style="color:hsl(221, 87%, 60%)">=</span><span class="token plain"> builder</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">.</span><span class="token function" style="color:hsl(221, 87%, 60%)">init_root</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">::</span><span class="token operator" style="color:hsl(221, 87%, 60%)">&lt;</span><span class="token namespace">point_capnp</span><span class="token namespace punctuation" style="color:hsl(119, 34%, 47%)">::</span><span class="token namespace">point</span><span class="token namespace punctuation" style="color:hsl(119, 34%, 47%)">::</span><span class="token class-name" style="color:hsl(35, 99%, 36%)">Builder</span><span class="token operator" style="color:hsl(221, 87%, 60%)">></span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">(</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">)</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">;</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain" style=display:inline-block></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token comment" style="color:hsl(230, 4%, 64%)">// Stuff our message with some content</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> point_msg</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">.</span><span class="token function" style="color:hsl(221, 87%, 60%)">set_x</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">(</span><span class="token number" style="color:hsl(35, 99%, 36%)">12</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">)</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">;</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain" style=display:inline-block></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> point_msg</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">.</span><span class="token function" style="color:hsl(221, 87%, 60%)">set_y</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">(</span><span class="token number" style="color:hsl(35, 99%, 36%)">14</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">)</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">;</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">}</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain" style=display:inline-block></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token comment" style="color:hsl(230, 4%, 64%)">// It's now time to serialize our message to binary. Let's set up a buffer for that:</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token keyword" style="color:hsl(301, 63%, 40%)">let</span><span class="token plain"> </span><span class="token keyword" style="color:hsl(301, 63%, 40%)">mut</span><span class="token plain"> buffer </span><span class="token operator" style="color:hsl(221, 87%, 60%)">=</span><span class="token plain"> </span><span class="token class-name" style="color:hsl(35, 99%, 36%)">Vec</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">::</span><span class="token function" style="color:hsl(221, 87%, 60%)">new</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">(</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">)</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">;</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain" style=display:inline-block></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token comment" style="color:hsl(230, 4%, 64%)">// And actually fill that buffer with our data</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token namespace">capnp</span><span class="token namespace punctuation" style="color:hsl(119, 34%, 47%)">::</span><span class="token namespace">serialize</span><span class="token namespace punctuation" style="color:hsl(119, 34%, 47%)">::</span><span class="token function" style="color:hsl(221, 87%, 60%)">write_message</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">(</span><span class="token operator" style="color:hsl(221, 87%, 60%)">&</span><span class="token keyword" style="color:hsl(301, 63%, 40%)">mut</span><span class="token plain"> buffer</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">,</span><span class="token plain"> </span><span class="token operator" style="color:hsl(221, 87%, 60%)">&</span><span class="token plain">builder</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">)</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">.</span><span class="token function" style="color:hsl(221, 87%, 60%)">unwrap</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">(</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">)</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">;</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain" style=display:inline-block></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token comment" style="color:hsl(230, 4%, 64%)">// Finally, let's deserialize the data</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token keyword" style="color:hsl(301, 63%, 40%)">let</span><span class="token plain"> deserialized </span><span class="token operator" style="color:hsl(221, 87%, 60%)">=</span><span class="token plain"> </span><span class="token namespace">capnp</span><span class="token namespace punctuation" style="color:hsl(119, 34%, 47%)">::</span><span class="token namespace">serialize</span><span class="token namespace punctuation" style="color:hsl(119, 34%, 47%)">::</span><span class="token function" style="color:hsl(221, 87%, 60%)">read_message</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">(</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token operator" style="color:hsl(221, 87%, 60%)">&</span><span class="token keyword" style="color:hsl(301, 63%, 40%)">mut</span><span class="token plain"> buffer</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">.</span><span class="token function" style="color:hsl(221, 87%, 60%)">as_slice</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">(</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">)</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">,</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token namespace">capnp</span><span class="token namespace punctuation" style="color:hsl(119, 34%, 47%)">::</span><span class="token namespace">message</span><span class="token namespace punctuation" style="color:hsl(119, 34%, 47%)">::</span><span class="token class-name" style="color:hsl(35, 99%, 36%)">ReaderOptions</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">::</span><span class="token function" style="color:hsl(221, 87%, 60%)">new</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">(</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">)</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">)</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">.</span><span class="token function" style="color:hsl(221, 87%, 60%)">unwrap</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">(</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">)</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">;</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain" style=display:inline-block></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token comment" style="color:hsl(230, 4%, 64%)">// `deserialized` is currently a generic reader; it understands</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token comment" style="color:hsl(230, 4%, 64%)">// the content of the message we gave it (i.e. that there are two</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token comment" style="color:hsl(230, 4%, 64%)">// int32 values) but doesn't really know what they represent (the Point).</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token comment" style="color:hsl(230, 4%, 64%)">// This is where we map the generic data back into our schema.</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token keyword" style="color:hsl(301, 63%, 40%)">let</span><span class="token plain"> point_reader </span><span class="token operator" style="color:hsl(221, 87%, 60%)">=</span><span class="token plain"> deserialized</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">.</span><span class="token function" style="color:hsl(221, 87%, 60%)">get_root</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">::</span><span class="token operator" style="color:hsl(221, 87%, 60%)">&lt;</span><span class="token namespace">point_capnp</span><span class="token namespace punctuation" style="color:hsl(119, 34%, 47%)">::</span><span class="token namespace">point</span><span class="token namespace punctuation" style="color:hsl(119, 34%, 47%)">::</span><span class="token class-name" style="color:hsl(35, 99%, 36%)">Reader</span><span class="token operator" style="color:hsl(221, 87%, 60%)">></span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">(</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">)</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">.</span><span class="token function" style="color:hsl(221, 87%, 60%)">unwrap</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">(</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">)</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">;</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain" style=display:inline-block></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token comment" style="color:hsl(230, 4%, 64%)">// We can now get our x and y values back, and make sure they match</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token macro property" style="color:hsl(5, 74%, 59%)">assert_eq!</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">(</span><span class="token plain">point_reader</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">.</span><span class="token function" style="color:hsl(221, 87%, 60%)">get_x</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">(</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">)</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">,</span><span class="token plain"> </span><span class="token number" style="color:hsl(35, 99%, 36%)">12</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">)</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">;</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"> </span><span class="token macro property" style="color:hsl(5, 74%, 59%)">assert_eq!</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">(</span><span class="token plain">point_reader</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">.</span><span class="token function" style="color:hsl(221, 87%, 60%)">get_y</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">(</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">)</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">,</span><span class="token plain"> </span><span class="token number" style="color:hsl(35, 99%, 36%)">14</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">)</span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">;</span><span class="token plain"></span><br></span><span class=token-line style="color:hsl(230, 8%, 24%)"><span class="token plain"></span><span class="token punctuation" style="color:hsl(119, 34%, 47%)">}</span><br></span></code></pre><div class=buttonGroup__atx><button type=button aria-label="Copy code to clipboard" title=Copy class=clean-btn><span class=copyButtonIcons_eSgA aria-hidden=true><svg viewBox="0 0 24 24" class=copyButtonIcon_y97N><path fill=currentColor d="M19,21H8V7H19M19,5H8A2,2 0 0,0 6,7V21A2,2 0 0,0 8,23H19A2,2 0 0,0 21,21V7A2,2 0 0,0 19,5M16,1H4A2,2 0 0,0 2,3V17H4V3H16V1Z"/></svg><svg viewBox="0 0 24 24" class=copyButtonSuccessIcon_LjdS><path fill=currentColor d=M21,7L9,19L3.5,13.5L4.91,12.09L9,16.17L19.59,5.59L21,7Z /></svg></span></button></div></div></div>
<p>And with that, we've now got a functioning project. Here's the content I'm planning to go over next as we build up
some practical examples of Cap'N Proto in action:</div></article><nav class="pagination-nav docusaurus-mt-lg" aria-label="Blog post page navigation"><a class="pagination-nav__link pagination-nav__link--prev" href=/2016/11/pca-audio-compression><div class=pagination-nav__sublabel>Older post</div><div class=pagination-nav__label>PCA audio compression</div></a><a class="pagination-nav__link pagination-nav__link--next" href=/2018/01/captains-cookbook-part-2><div class=pagination-nav__sublabel>Newer post</div><div class=pagination-nav__label>Captain's Cookbook: Practical usage</div></a></nav></main><div class="col col--2"><div class="tableOfContents_bqdL thin-scrollbar"><ul class="table-of-contents table-of-contents__left-border"><li><a href=#step-1-installing-capnp class="table-of-contents__link toc-highlight">Step 1: Installing <code>capnp</code></a><li><a href=#step-2-starting-a-capn-proto-rust-project class="table-of-contents__link toc-highlight">Step 2: Starting a Cap'N Proto Rust project</a><li><a href=#step-3-writing-a-basic-schema class="table-of-contents__link toc-highlight">Step 3: Writing a basic schema</a><li><a href=#step-4-setting-up-the-build-process class="table-of-contents__link toc-highlight">Step 4: Setting up the build process</a><li><a href=#step-5-running-the-build class="table-of-contents__link toc-highlight">Step 5: Running the build</a><li><a href=#step-6-making-a-point class="table-of-contents__link toc-highlight">Step 6: Making a point</a></ul></div></div></div></div></div><footer class=footer><div class="container container-fluid"><div class="footer__bottom text--center"><div class=footer__copyright>Copyright © 2024 Bradlee Speice</div></div></div></footer></div>