Merge branch 'context1'
This commit is contained in:
Mark McGranaghan
commit
acc5c0365c
@ -68,6 +68,7 @@ Command-Line Subcommands
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Environment Variables
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HTTP Clients
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HTTP Servers
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Context
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Spawning Processes
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Exec'ing Processes
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Signals
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44
examples/context/context.go
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44
examples/context/context.go
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@ -0,0 +1,44 @@
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// In the previous example we looked at setting up a simple
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// [HTTP server](http-servers). HTTP servers are useful for
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// demonstrating the usage of `context.Context` for
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// controlling cancellation.
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package main
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import (
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"fmt"
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"net/http"
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"time"
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)
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func hello(w http.ResponseWriter, req *http.Request) {
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// A `context.Context` is created for each request by
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// the `net/http` machinery, and is available with
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// the `Context()` method.
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ctx := req.Context()
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fmt.Println("server: hello handler started")
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defer fmt.Println("server: hello handler ended")
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// Wait for 3 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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// `Done()` channel for a signal that we should cancel
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// the work and return as soon as possible.
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select {
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case <-time.After(10 * time.Second):
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fmt.Fprintf(w, "hello\n")
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case <-ctx.Done():
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err := ctx.Err()
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fmt.Println("server:", err)
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internalError := http.StatusInternalServerError
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http.Error(w, err.Error(), internalError)
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}
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}
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func main() {
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// As before, we register our handler on the "/hello"
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// route, and start serving.
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http.HandleFunc("/hello", hello)
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http.ListenAndServe(":8090", nil)
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}
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2
examples/context/context.hash
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2
examples/context/context.hash
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@ -0,0 +1,2 @@
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a899a68d131b0f8cf3ae846ef728877d2407d219
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9fUzFC2uyFk
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11
examples/context/context.sh
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11
examples/context/context.sh
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@ -0,0 +1,11 @@
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# Run the server in the background.
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$ go run context-in-http-servers.go &
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# Simulate a client request to `/hello`, hitting
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# Ctrl+C shortly after starting to signal
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# cancellation.
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$ curl localhost:8090/hello
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server: hello handler started
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^C
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server: context canceled
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server: hello handler ended
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196
public/context
generated
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196
public/context
generated
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@ -0,0 +1,196 @@
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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.</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/9fUzFC2uyFk"><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 3 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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<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 := req.Context()\u000A fmt.Println(\"server: hello handler started\")\u000A defer fmt.Println(\"server: hello handler ended\")\u000A');codeLines.push(' select {\u000A case \x3C-time.After(10 * time.Second):\u000A fmt.Fprintf(w, \"hello\\n\")\u000A case \x3C-ctx.Done():\u000A err := ctx.Err()\u000A fmt.Println(\"server:\", err)\u000A internalError := 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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4
public/http-servers
generated
4
public/http-servers
generated
@ -14,7 +14,7 @@
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if (e.key == "ArrowRight") {
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window.location.href = 'spawning-processes';
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window.location.href = 'context';
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}
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}
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@ -201,7 +201,7 @@ router we’ve just set up.</p>
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<p class="next">
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Next example: <a href="spawning-processes">Spawning Processes</a>.
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Next example: <a href="context">Context</a>.
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</p>
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<p class="footer">
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2
public/index.html
generated
2
public/index.html
generated
@ -163,6 +163,8 @@
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<li><a href="http-servers">HTTP Servers</a></li>
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<li><a href="context">Context</a></li>
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<li><a href="spawning-processes">Spawning Processes</a></li>
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<li><a href="execing-processes">Exec'ing Processes</a></li>
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2
public/spawning-processes
generated
2
public/spawning-processes
generated
@ -9,7 +9,7 @@
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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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window.location.href = 'context';
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}
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