9e216da9ef
After go1.16, go will use module mode by default, even when the repository is checked out under GOPATH or in a one-off directory. Add go.mod, go.sum to keep this repo buildable without opting out of the module mode. > go mod init github.com/mmcgrana/gobyexample > go mod tidy > go mod vendor In module mode, the 'vendor' directory is special and its contents will be actively maintained by the go command. pygments aren't the dependency the go will know about, so it will delete the contents from vendor directory. Move it to `third_party` directory now. And, vendor the blackfriday package. Note: the tutorial contents are not affected by the change in go1.16 because all the examples in this tutorial ask users to run the go command with the explicit list of files to be compiled (e.g. `go run hello-world.go` or `go build command-line-arguments.go`). When the source list is provided, the go command does not have to compute the build list and whether it's running in GOPATH mode or module mode becomes irrelevant.
213 lines
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213 lines
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<!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: Context</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 = 'http-servers';
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}
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if (e.key == "ArrowRight") {
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window.location.href = 'spawning-processes';
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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="context">
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<h2><a href="./">Go by Example</a>: Context</h2>
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<table>
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<tr>
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<td class="docs">
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<p>In the previous example we looked at setting up a simple
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<a href="http-servers">HTTP server</a>. HTTP servers are useful for
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demonstrating the usage of <code>context.Context</code> for
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controlling cancellation. A <code>Context</code> carries deadlines,
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cancellation signals, and other request-scoped values
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across API boundaries and goroutines.</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/0_bu1o8rIBO"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
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<div class="highlight"><pre><span class="kn">package</span> <span class="nx">main</span>
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</pre></div>
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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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<div class="highlight"><pre><span class="kn">import</span> <span class="p">(</span>
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<span class="s">"fmt"</span>
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<span class="s">"net/http"</span>
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<span class="s">"time"</span>
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<span class="p">)</span>
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</pre></div>
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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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<div class="highlight"><pre><span class="kd">func</span> <span class="nx">hello</span><span class="p">(</span><span class="nx">w</span> <span class="nx">http</span><span class="p">.</span><span class="nx">ResponseWriter</span><span class="p">,</span> <span class="nx">req</span> <span class="o">*</span><span class="nx">http</span><span class="p">.</span><span class="nx">Request</span><span class="p">)</span> <span class="p">{</span>
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</pre></div>
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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>A <code>context.Context</code> is created for each request by
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the <code>net/http</code> machinery, and is available with
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the <code>Context()</code> method.</p>
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</td>
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<td class="code leading">
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<div class="highlight"><pre> <span class="nx">ctx</span> <span class="o">:=</span> <span class="nx">req</span><span class="p">.</span><span class="nx">Context</span><span class="p">()</span>
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<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">"server: hello handler started"</span><span class="p">)</span>
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<span class="k">defer</span> <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">"server: hello handler ended"</span><span class="p">)</span>
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</pre></div>
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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>Wait for a few seconds before sending a reply to the
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client. This could simulate some work the server is
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doing. While working, keep an eye on the context’s
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<code>Done()</code> channel for a signal that we should cancel
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the work and return as soon as possible.</p>
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</td>
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<td class="code leading">
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<div class="highlight"><pre> <span class="k">select</span> <span class="p">{</span>
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<span class="k">case</span> <span class="o"><-</span><span class="nx">time</span><span class="p">.</span><span class="nx">After</span><span class="p">(</span><span class="mi">10</span> <span class="o">*</span> <span class="nx">time</span><span class="p">.</span><span class="nx">Second</span><span class="p">):</span>
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<span class="nx">fmt</span><span class="p">.</span><span class="nx">Fprintf</span><span class="p">(</span><span class="nx">w</span><span class="p">,</span> <span class="s">"hello\n"</span><span class="p">)</span>
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<span class="k">case</span> <span class="o"><-</span><span class="nx">ctx</span><span class="p">.</span><span class="nx">Done</span><span class="p">():</span>
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</pre></div>
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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>The context’s <code>Err()</code> method returns an error
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that explains why the <code>Done()</code> channel was
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closed.</p>
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</td>
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<td class="code leading">
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<div class="highlight"><pre> <span class="nx">err</span> <span class="o">:=</span> <span class="nx">ctx</span><span class="p">.</span><span class="nx">Err</span><span class="p">()</span>
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<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">"server:"</span><span class="p">,</span> <span class="nx">err</span><span class="p">)</span>
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<span class="nx">internalError</span> <span class="o">:=</span> <span class="nx">http</span><span class="p">.</span><span class="nx">StatusInternalServerError</span>
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<span class="nx">http</span><span class="p">.</span><span class="nx">Error</span><span class="p">(</span><span class="nx">w</span><span class="p">,</span> <span class="nx">err</span><span class="p">.</span><span class="nx">Error</span><span class="p">(),</span> <span class="nx">internalError</span><span class="p">)</span>
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<span class="p">}</span>
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<span class="p">}</span>
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</pre></div>
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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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<div class="highlight"><pre><span class="kd">func</span> <span class="nx">main</span><span class="p">()</span> <span class="p">{</span>
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</pre></div>
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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>As before, we register our handler on the “/hello”
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route, and start serving.</p>
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</td>
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<td class="code">
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<div class="highlight"><pre> <span class="nx">http</span><span class="p">.</span><span class="nx">HandleFunc</span><span class="p">(</span><span class="s">"/hello"</span><span class="p">,</span> <span class="nx">hello</span><span class="p">)</span>
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<span class="nx">http</span><span class="p">.</span><span class="nx">ListenAndServe</span><span class="p">(</span><span class="s">":8090"</span><span class="p">,</span> <span class="kc">nil</span><span class="p">)</span>
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<span class="p">}</span>
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</pre></div>
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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>Run the server in the background.</p>
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</td>
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<td class="code leading">
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<div class="highlight"><pre><span class="gp">$</span> go run context-in-http-servers.go <span class="p">&</span>
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</pre></div>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>Simulate a client request to <code>/hello</code>, hitting
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Ctrl+C shortly after starting to signal
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cancellation.</p>
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</td>
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<td class="code">
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<div class="highlight"><pre><span class="gp">$</span> curl localhost:8090/hello
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<span class="go">server: hello handler started</span>
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<span class="go">^C</span>
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<span class="go">server: context canceled</span>
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<span class="go">server: hello handler ended</span>
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</pre></div>
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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="spawning-processes">Spawning Processes</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> | <a href="https://github.com/mmcgrana/gobyexample/blob/master/examples/context">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 \"fmt\"\u000A \"net/http\"\u000A \"time\"\u000A)\u000A');codeLines.push('func hello(w http.ResponseWriter, req *http.Request) {\u000A');codeLines.push(' ctx :\u003D req.Context()\u000A fmt.Println(\"server: hello handler started\")\u000A defer fmt.Println(\"server: hello handler ended\")\u000A');codeLines.push(' select {\u000A case \u003C-time.After(10 * time.Second):\u000A fmt.Fprintf(w, \"hello\\n\")\u000A case \u003C-ctx.Done():\u000A');codeLines.push(' err :\u003D ctx.Err()\u000A fmt.Println(\"server:\", err)\u000A internalError :\u003D http.StatusInternalServerError\u000A http.Error(w, err.Error(), internalError)\u000A }\u000A}\u000A');codeLines.push('func main() {\u000A');codeLines.push(' http.HandleFunc(\"/hello\", hello)\u000A http.ListenAndServe(\":8090\", nil)\u000A}\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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