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Short article about a misunderstanding I had with fstest.mapfs that
broke my tests.
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| <!DOCTYPE html> | ||
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| <head> | ||
| <script type="text/javascript" src="/main.js"></script> | ||
| <title>fstest mapfs file does not exist error</title> | ||
| <meta name="andrew-published-at" content="2024-03-27" </head> | ||
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| <body> | ||
| <nav class="navigation"> | ||
| <a href="/" class="link">front page</a> | ||
| <a href="/articles/index.html" class="link">articles</a> | ||
| <a href="/projects/index.html" class="link">projects</a> | ||
| </nav> | ||
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| <link rel="stylesheet" href="/styles.css"> | ||
| <div id="header"></div> | ||
| <main> | ||
| <article> | ||
| <section id="introduction"> | ||
| <p> | ||
| In my tests, I defined an <code>fstest.MapFS</code> like this | ||
| <code> | ||
| <pre> | ||
| contentRoot := fstest.MapFS{ | ||
| "/parentDir/index.html": &fstest.MapFile{Data: []byte("content"), Mode: 0o755}, | ||
| "/parentDir/childDir/1-2-3.html": &fstest.MapFile{Data: []byte("other content"`), Mode: 0o755}, | ||
| } | ||
| </pre> | ||
| </code> | ||
| Simple, and yet when I ran a test against it, I received this error: | ||
| <code> | ||
| <pre> | ||
| 2024/03/27 19:42:59 http: panic serving [::1]:57135: open parentDir: file does not exist | ||
| </pre> | ||
| </code> | ||
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| </p> | ||
| </section> | ||
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| <section id="resolution"> | ||
| <h1>What's the misunderstanding?</h1> | ||
| <p> | ||
| This one took me a couple of hours to finally understand. | ||
| </p> | ||
| <p> | ||
| An <code>fstest.MapFS</code> is pretty much a hash map. <i>If you don't have a precise match for the key in the map | ||
| then you get a <code>file does not exist</code> error.</i> Here's the implementation that shows that: | ||
| <code> | ||
| <pre> | ||
| file := fsys[name] | ||
| </pre> | ||
| - reference in <a href="https://cs.opensource.google/go/go/+/refs/tags/go1.22.1:src/testing/fstest/mapfs.go;l=51">the go source code</a>. | ||
| </code> | ||
| </p> | ||
| <h1>What's the fix?</h1> | ||
| <p> | ||
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| In my case, I was performing some path munging in my logic so that I was searching for paths relatively, not absolutely | ||
| using a leading "/", so my search string was "parentDir/index.html". | ||
| </p> | ||
| <p> | ||
| Once I understood that <i>the path in the <code>fstest.MapFS</code> does not need to be an absolute path</i>, because <i>it is only | ||
| a key in a hash map</i>, I redefined my structure like this and got my tests passing: | ||
| <code> | ||
| <pre> | ||
| contentRoot := fstest.MapFS{ | ||
| "/parentDir/index.html": &fstest.MapFile{Data: []byte("content"), Mode: 0o755}, | ||
| "/parentDir/childDir/1-2-3.html": &fstest.MapFile{Data: []byte("other content"`), Mode: 0o755}, | ||
| } | ||
| </pre> | ||
| </code> | ||
| </p> | ||
| </section> | ||
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| </article> | ||
| </main> | ||
| </body> | ||
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