50 lines
1.5 KiB
Go
50 lines
1.5 KiB
Go
// 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. A `Context` carries deadlines,
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// cancellation signals, and other request-scoped values
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// across API boundaries and goroutines.
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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 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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// `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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// The context's `Err()` method returns an error
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// that explains why the `Done()` channel was
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// closed.
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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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