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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Go by Example: Recover</title>
<link rel=stylesheet href="site.css">
</head>
<script>
onkeydown = (e) => {
if (e.key == "ArrowLeft") {
window.location.href = 'defer';
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<body>
<div class="example" id="recover">
<h2><a href="./">Go by Example</a>: Recover</h2>
<table>
<tr>
<td class="docs">
<p>Go makes it possible to <em>recover</em> from a panic, by
using the <code>recover</code> built-in function. A <code>recover</code> can
stop a <code>panic</code> from aborting the program and let it
continue with execution instead.</p>
</td>
<td class="code empty leading">
</td>
</tr>
<tr>
<td class="docs">
<p>An example of where this can be useful: a server
wouldn’t want to crash if one of the client connections
exhibits a critical error. Instead, the server would
want to close that connection and continue serving
other clients. In fact, this is what Go’s <code>net/http</code>
does by default for HTTP servers.</p>
</td>
<td class="code empty leading">
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<a href="http://play.golang.org/p/Sk-SVdofEIZ"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
<pre class="chroma"><span class="kn">package</span> <span class="nx">main</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"><span class="kn">import</span> <span class="s">"fmt"</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>This function panics.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="kd">func</span> <span class="nf">mayPanic</span><span class="p">()</span> <span class="p">{</span>
<span class="nb">panic</span><span class="p">(</span><span class="s">"a problem"</span><span class="p">)</span>
<span class="p">}</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p><code>recover</code> must be called within a deferred function.
When the enclosing function panics, the defer will
activate and a <code>recover</code> call within it will catch
the panic.</p>
</td>
<td class="code leading">
<pre class="chroma"><span class="kd">func</span> <span class="nf">main</span><span class="p">()</span> <span class="p">{</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>The return value of <code>recover</code> is the error raised in
the call to <code>panic</code>.</p>
</td>
<td class="code leading">
<pre class="chroma"> <span class="k">defer</span> <span class="kd">func</span><span class="p">()</span> <span class="p">{</span>
<span class="k">if</span> <span class="nx">r</span> <span class="o">:=</span> <span class="nb">recover</span><span class="p">();</span> <span class="nx">r</span> <span class="o">!=</span> <span class="kc">nil</span> <span class="p">{</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"> <span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"Recovered. Error:\n"</span><span class="p">,</span> <span class="nx">r</span><span class="p">)</span>
<span class="p">}</span>
<span class="p">}()</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"> <span class="nf">mayPanic</span><span class="p">()</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>This code will not run, because <code>mayPanic</code> panics.
The execution of <code>main</code> stops at the point of the
panic and resumes in the deferred closure.</p>
</td>
<td class="code">
<pre class="chroma">
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"After mayPanic()"</span><span class="p">)</span>
<span class="p">}</span>
</pre>
</td>
</tr>
</table>
<table>
<tr>
<td class="docs">
</td>
<td class="code">
<pre class="chroma"><span class="go">Recovered. Error:
</span><span class="go"> a problem</span></pre>
</td>
</tr>
</table>
<p class="next">
Next example: <a href="collection-functions">Collection Functions</a>.
</p>
<p class="footer">
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>
</p>
</div>
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codeLines.push('');codeLines.push('');codeLines.push('package main\u000A');codeLines.push('import \"fmt\"\u000A');codeLines.push('func mayPanic() {\u000A panic(\"a problem\")\u000A}\u000A');codeLines.push('func main() {\u000A');codeLines.push(' defer func() {\u000A if r :\u003D recover(); r !\u003D nil {\u000A');codeLines.push(' fmt.Println(\"Recovered. Error:\\n\", r)\u000A }\u000A }()\u000A');codeLines.push(' mayPanic()\u000A');codeLines.push(' fmt.Println(\"After mayPanic()\")\u000A}\u000A');codeLines.push('');
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</body>
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