7e4533640b
* Add embed-directive example and rename embedding to struct-embedding Signed-off-by: peterzhu1992 <peterzhu1992@gmail.com> * Minor tweaks Signed-off-by: peterzhu1992 <peterzhu1992@gmail.com> * Add some improvements Signed-off-by: peterzhu1992 <peterzhu1992@gmail.com> * Add isDir() checks for measure.go and generate.go in tools Signed-off-by: peterzhu1992 <peterzhu1992@gmail.com>
227 lines
8.9 KiB
Plaintext
Generated
227 lines
8.9 KiB
Plaintext
Generated
<!DOCTYPE html>
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<html>
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<head>
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<meta charset="utf-8">
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<title>Go by Example: Embed Directive</title>
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<link rel=stylesheet href="site.css">
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</head>
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<script>
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onkeydown = (e) => {
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if (e.key == "ArrowLeft") {
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window.location.href = 'temporary-files-and-directories';
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}
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if (e.key == "ArrowRight") {
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window.location.href = 'testing-and-benchmarking';
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}
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}
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</script>
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<body>
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<div class="example" id="embed-directive">
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<h2><a href="./">Go by Example</a>: Embed Directive</h2>
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<table>
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<tr>
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<td class="docs">
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<p><code>//go:embed</code> is a compiler directive that allows programs to include arbitrary
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files/folders in the binary. Read more about go directive
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<a href="https://dave.cheney.net/2018/01/08/gos-hidden-pragmas">here</a>.</p>
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</td>
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<td class="code leading">
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<a href="http://play.golang.org/p/-EXJc75EbN-"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
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<pre class="chroma">
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<span class="kn">package</span> <span class="nx">main</span>
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</pre>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>If no exported identifiers is directly used from <code>embed</code> package,
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you can add an underscore <code>_</code> before the package name. In this example, we simply
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import it as we need to use the <code>embed.FS</code> type from the package.</p>
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</td>
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<td class="code leading">
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<pre class="chroma">
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<span class="kn">import</span> <span class="p">(</span>
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<span class="c1">//_ "embed"
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</span><span class="c1"></span> <span class="s">"embed"</span>
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<span class="p">)</span>
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</pre>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>Since one file is defined after the directive, the compiler will only include
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this single file, followed by variable <code>single_file_string</code> to access as <code>string</code> type.</p>
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</td>
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<td class="code leading">
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<pre class="chroma">
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<span class="c1">//go:embed example_folder/single_file.txt
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</span><span class="c1"></span><span class="kd">var</span> <span class="nx">single_file_string</span> <span class="kt">string</span>
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</pre>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>Here is a similar example but include single file as <code>[]byte</code>.</p>
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</td>
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<td class="code leading">
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<pre class="chroma">
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<span class="c1">//go:embed example_folder/single_file.txt
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</span><span class="c1"></span><span class="kd">var</span> <span class="nx">single_file_byte</span> <span class="p">[]</span><span class="kt">byte</span>
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</pre>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>We can also embed multiple files or even folders with wildcard.</p>
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</td>
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<td class="code leading">
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<pre class="chroma">
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<span class="c1">//go:embed example_folder/single_file.txt
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</span><span class="c1">//go:embed example_folder/*.hash
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</span><span class="c1"></span><span class="kd">var</span> <span class="nx">folder_FS</span> <span class="nx">embed</span><span class="p">.</span><span class="nx">FS</span>
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</pre>
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</td>
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</tr>
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<tr>
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<td class="docs">
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</td>
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<td class="code leading">
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<pre class="chroma"><span class="kd">func</span> <span class="nf">main</span><span class="p">()</span> <span class="p">{</span>
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</pre>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>Print out content of <code>example_single_file.txt</code> as <code>string</code>.</p>
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</td>
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<td class="code leading">
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<pre class="chroma">
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<span class="nb">print</span><span class="p">(</span><span class="nx">single_file_string</span><span class="p">)</span>
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</pre>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>Now handle <code>[]byte</code>.</p>
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</td>
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<td class="code leading">
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<pre class="chroma">
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<span class="nb">print</span><span class="p">(</span><span class="nb">string</span><span class="p">(</span><span class="nx">single_file_byte</span><span class="p">))</span>
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</pre>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>Retrieve file(s) matching <code>*.hash</code> pattern by reading from variable <code>folder_FS</code> first,
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then print out.</p>
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</td>
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<td class="code leading">
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<pre class="chroma">
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<span class="nx">hash_file1</span> <span class="o">:=</span> <span class="s">"example_folder/multi_file1.hash"</span>
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<span class="nx">hash_file2</span> <span class="o">:=</span> <span class="s">"example_folder/multi_file2.hash"</span>
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<span class="nx">hash_content1</span><span class="p">,</span> <span class="nx">_</span> <span class="o">:=</span> <span class="nx">folder_FS</span><span class="p">.</span><span class="nf">ReadFile</span><span class="p">(</span><span class="nx">hash_file1</span><span class="p">)</span>
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<span class="nx">hash_content2</span><span class="p">,</span> <span class="nx">_</span> <span class="o">:=</span> <span class="nx">folder_FS</span><span class="p">.</span><span class="nf">ReadFile</span><span class="p">(</span><span class="nx">hash_file2</span><span class="p">)</span>
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<span class="nb">print</span><span class="p">(</span><span class="nb">string</span><span class="p">(</span><span class="nx">hash_content1</span><span class="p">))</span>
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<span class="nb">print</span><span class="p">(</span><span class="nb">string</span><span class="p">(</span><span class="nx">hash_content2</span><span class="p">))</span>
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</pre>
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</td>
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</tr>
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<tr>
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<td class="docs">
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</td>
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<td class="code">
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<pre class="chroma"><span class="p">}</span>
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</pre>
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</td>
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</tr>
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</table>
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<table>
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<tr>
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<td class="docs">
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<p>Use these commands to run the example.
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(Note: due to limitation on go playground,
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this example can only be run on your local machine.)</p>
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</td>
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<td class="code leading">
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<pre class="chroma">
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<span class="gp">$</span> mkdir -p example_folder
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<span class="gp">$</span> echo "hello go" > example_folder/single_file.txt
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<span class="gp">$</span> echo "123" > example_folder/multi_file1.hash
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<span class="gp">$</span> echo "456" > example_folder/multi_file2.hash</pre>
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</td>
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</tr>
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<tr>
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<td class="docs">
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</td>
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<td class="code">
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<pre class="chroma"><span class="gp">$</span> go run embed-directive.go
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<span class="go">hello go
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</span><span class="go">hello go
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</span><span class="go">123
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</span><span class="go">456</span></pre>
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</td>
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</tr>
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</table>
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<p class="next">
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Next example: <a href="testing-and-benchmarking">Testing and Benchmarking</a>.
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</p>
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<p class="footer">
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by <a href="https://markmcgranaghan.com">Mark McGranaghan</a> and <a href="https://eli.thegreenplace.net">Eli Bendersky</a> | <a href="https://github.com/mmcgrana/gobyexample">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a>
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</p>
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</div>
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<script>
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var codeLines = [];
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codeLines.push('package main\u000A');codeLines.push('import (\u000A //_ \"embed\"\u000A \"embed\"\u000A)\u000A');codeLines.push('//go:embed example_folder/single_file.txt\u000Avar single_file_string string\u000A');codeLines.push('//go:embed example_folder/single_file.txt\u000Avar single_file_byte []byte\u000A');codeLines.push('//go:embed example_folder/single_file.txt\u000A//go:embed example_folder/*.hash\u000Avar folder_FS embed.FS\u000A');codeLines.push('func main() {\u000A');codeLines.push(' print(single_file_string)\u000A');codeLines.push(' print(string(single_file_byte))\u000A');codeLines.push(' hash_file1 :\u003D \"example_folder/multi_file1.hash\"\u000A hash_file2 :\u003D \"example_folder/multi_file2.hash\"\u000A hash_content1, _ :\u003D folder_FS.ReadFile(hash_file1)\u000A hash_content2, _ :\u003D folder_FS.ReadFile(hash_file2)\u000A print(string(hash_content1))\u000A print(string(hash_content2))\u000A');codeLines.push('}\u000A');codeLines.push('');codeLines.push('');
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</script>
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<script src="site.js" async></script>
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</body>
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</html>
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