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<li><a href="#top-level-gomod-template">Top-level go.mod template</a></li>
<li><a href="#building-local-code-the-replace-directive">Building local code: the replace directive</a></li>
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<h1 id="working-with-go-modules">Working with Go modules</h1>
<p>If you are not yet familiar with Go modules in general (outside of gokrazy),
please <a href="https://github.com/golang/go/wiki/Modules" rel="external">read the Go wiki page on
Modules</a> first.</p>
<p><a href="https://github.com/gokrazy/tools/commit/c3979e1ceb3ea4fe02b78b2c1493c8128a5dc3f9" rel="external">Since September
2022</a>,
the gokrazy packer builds each package in its own build directory, with its own
<code>go.mod</code> and <code>go.sum</code> files. This is done for isolation: if you update one
program, that will not have any effect on the other programs you include in your
gokrazy instance.</p>
<h2 id="example-setup">Example setup<span class="btn cstyle anchor copyanchor scrollanchor link noborder notitle interactive"><button type="button" title="Copy link to clipboard"><i class="fa-fw fas fa-link fa-lg"></i></button></span></h2>
<p>Throughout this page, lets assume your gokrazy instance is named <code>scanner</code>, and
will hence store its files in <code>~/gokrazy/scanner</code>. A single additional program,
<code>scan2drive</code>, is included:</p>
<div class="highlight actionbar-wrapper wrap-code" dir="auto"><pre tabindex="0" style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4;-webkit-text-size-adjust:none;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span>gok -i scanner new
</span></span><span style="display:flex;"><span>gok -i scanner add github.com/stapelberg/scan2drive/cmd/scan2drive</span></span></code></pre></div>
<p>When building this instance (using <code>gok overwrite</code> initially, or <code>gok update</code>
afterwards), the <code>gok</code> CLI will create the following build directory structure:</p>
<div class="highlight actionbar-wrapper wrap-code" dir="auto"><pre tabindex="0" style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4;-webkit-text-size-adjust:none;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span>% cd ~/gokrazy/scanner
</span></span><span style="display:flex;"><span>% find . -name go.mod
</span></span><span style="display:flex;"><span>./builddir/init/go.mod
</span></span><span style="display:flex;"><span>./builddir/github.com/stapelberg/scan2drive/cmd/scan2drive/go.mod
</span></span><span style="display:flex;"><span>./builddir/github.com/gokrazy/serial-busybox/go.mod
</span></span><span style="display:flex;"><span>./builddir/github.com/gokrazy/hello/go.mod
</span></span><span style="display:flex;"><span>./builddir/github.com/gokrazy/fbstatus/go.mod
</span></span><span style="display:flex;"><span>./builddir/github.com/gokrazy/gokrazy/go.mod
</span></span><span style="display:flex;"><span>./builddir/github.com/gokrazy/gokrazy/cmd/randomd/go.mod
</span></span><span style="display:flex;"><span>./builddir/github.com/gokrazy/gokrazy/cmd/ntp/go.mod
</span></span><span style="display:flex;"><span>./builddir/github.com/gokrazy/gokrazy/cmd/dhcp/go.mod
</span></span><span style="display:flex;"><span>./builddir/github.com/gokrazy/rpi-eeprom/go.mod
</span></span><span style="display:flex;"><span>./builddir/github.com/gokrazy/firmware/go.mod
</span></span><span style="display:flex;"><span>./builddir/github.com/gokrazy/kernel/go.mod</span></span></code></pre></div>
<p>You can see that there is one subdirectory for each package listed in the
<code>Packages</code> field of your instances <code>config.json</code> (see <code>gok edit</code>), which
includes the explicitly added <code>scan2drive</code>, plus a couple extra ones that
gokrazy always installs, e.g. <code>github.com/gokrazy/gokrazy/cmd/dhcp</code>.</p>
<h2 id="top-level-gomod-template">Top-level go.mod template<span class="btn cstyle anchor copyanchor scrollanchor link noborder notitle interactive"><button type="button" title="Copy link to clipboard"><i class="fa-fw fas fa-link fa-lg"></i></button></span></h2>
<p>If you want to influence the content of any <em>newly created</em> <code>go.mod</code> (no effect
on existing <code>go.mod</code> files), you can create a <code>go.mod</code> template in your instance
directory: <code>~/gokrazy/scanner/go.mod</code>.</p>
<h2 id="building-local-code-the-replace-directive">Building local code: the replace directive<span class="btn cstyle anchor copyanchor scrollanchor link noborder notitle interactive"><button type="button" title="Copy link to clipboard"><i class="fa-fw fas fa-link fa-lg"></i></button></span></h2>
<p>Go modules are loaded from the internet by default and are stored read-only on
disk.</p>
<p>If you want to make the gokrazy packer pick up a local working copy with
not-yet-published code, or a working copy with local changes to existing code,
use <code>gok add</code> with a directory name:</p>
<div class="highlight actionbar-wrapper wrap-code" dir="auto"><pre tabindex="0" style="color:#f8f8f2;background-color:#272822;-moz-tab-size:4;-o-tab-size:4;tab-size:4;-webkit-text-size-adjust:none;"><code class="language-bash" data-lang="bash"><span style="display:flex;"><span><span style="color:#75715e"># Create a local working copy in whichever directory you like.</span>
</span></span><span style="display:flex;"><span>% cd ~/projects
</span></span><span style="display:flex;"><span>% git clone https://github.com/stapelberg/scan2drive
</span></span><span style="display:flex;"><span>% cd scan2drive
</span></span><span style="display:flex;"><span><span style="color:#75715e"># make some changes</span>
</span></span><span style="display:flex;"><span>
</span></span><span style="display:flex;"><span>% gok -i scan2drive add ./cmd/scan2drive</span></span></code></pre></div>
<p>The <code>gok</code> CLI will set up the <code>replace</code> directive for you. For more details on
<code>replace</code>, see <a href="https://github.com/golang/go/wiki/Modules#when-should-i-use-the-replace-directive" rel="external">the Go
wiki</a>.</p>
<p>To undo a local override, either manually delete the <code>replace</code> directive in the
relevant <code>builddir/.../go.mod</code> file, or use <code>go mod edit</code> with
<code>-dropreplace=path/to/pkg</code>. See this
<a href="https://github.com/gokrazy/gokrazy/discussions/352#discussioncomment-15404080" rel="external">comment</a>
for a worked example.</p>
<h2 id="influencing-the-granularity">Influencing the granularity<span class="btn cstyle anchor copyanchor scrollanchor link noborder notitle interactive"><button type="button" title="Copy link to clipboard"><i class="fa-fw fas fa-link fa-lg"></i></button></span></h2>
<p>Often, one Go <em>package</em> will be the only package you use from a certain Go
<em>module</em>. But this isnt always the case: for example, the system packages
<code>github.com/gokrazy/gokrazy/cmd/dhcp</code> and <code>github.com/gokrazy/gokrazy/cmd/ntp</code>
both come from the <code>github.com/gokrazy/gokrazy</code> module.</p>
<p>The packer will by default create a separate builddir, including a separate
<code>go.mod</code> and <code>go.sum</code>, for each package, even when they come from the same
module.</p>
<p>If you want to add module-wide replace directives to your <code>go.mod</code> file, you can
influence the granularity at which gokr-packer works as follows.</p>
<p>Move the <code>go.mod</code>/<code>go.sum</code> files to the directory level within the <code>builddir/</code>
hierarchy at which you would like to work. gokr-packer will look for
<code>go.mod</code>/<code>go.sum</code> files at the package level, going one level up until it finds
the files.</p>
<p>Hence, you can use the following locations, ordered from finest to coarsest
granularity:</p>
<ol>
<li>
<p>per-package builddir (default), e.g.:
<code>builddir/github.com/gokrazy/gokrazy/cmd/dhcp/go.mod</code></p>
</li>
<li>
<p>per-module builddir (convenient when working with replace directives), e.g.:
<code>builddir/github.com/gokrazy/gokrazy/go.mod</code></p>
</li>
<li>
<p>per-org builddir (convenient for wide-reaching replace directives), e.g.:
<code>builddir/github.com/gokrazy/go.mod</code></p>
</li>
<li>
<p>single builddir, preserving the previous behavior, e.g.:
<code>builddir/go.mod</code></p>
</li>
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