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// The server program issues Google search requests and demonstrates the use of
// the go.net Context API. It serves on port 8080.
//
// The /search endpoint accepts these query params:
// q=the Google search query
// timeout=a timeout for the request, in time.Duration format
//
// For example, http://localhost:8080/search?q=golang&timeout=1s serves the
// first few Google search results for "golang" or a "deadline exceeded" error
// if the timeout expires.
package main
import (
"html/template"
"log"
"net/http"
"time"
"code.google.com/p/go.blog/content/context/google"
"code.google.com/p/go.blog/content/context/userip"
"code.google.com/p/go.net/context"
)
func main() {
http.HandleFunc("/search", handleSearch)
log.Fatal(http.ListenAndServe(":8080", nil))
}
// handleSearch handles URLs like /search?q=golang&timeout=1s by forwarding the
// query to google.Search. If the query param includes timeout, the search is
// canceled after that duration elapses.
func handleSearch(w http.ResponseWriter, req *http.Request) {
// ctx is the Context for this handler. Calling cancel closes the
// ctx.Done channel, which is the cancellation signal for requests
// started by this handler.
var (
ctx context.Context
cancel context.CancelFunc
)
timeout, err := time.ParseDuration(req.FormValue("timeout"))
if err == nil {
// The request has a timeout, so create a context that is
// canceled automatically when the timeout expires.
ctx, cancel = context.WithTimeout(context.Background(), timeout)
} else {
ctx, cancel = context.WithCancel(context.Background())
}
defer cancel() // Cancel ctx as soon as handleSearch returns.
// Check the search query.
query := req.FormValue("q")
if query == "" {
http.Error(w, "no query", http.StatusBadRequest)
return
}
// Store the user IP in ctx for use by code in other packages.
userIP, err := userip.FromRequest(req)
if err != nil {
http.Error(w, err.Error(), http.StatusBadRequest)
return
}
ctx = userip.NewContext(ctx, userIP)
// Run the Google search and print the results.
start := time.Now()
results, err := google.Search(ctx, query)
elapsed := time.Since(start)
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}
if err := resultsTemplate.Execute(w, struct {
Results google.Results
Timeout, Elapsed time.Duration
}{
Results: results,
Timeout: timeout,
Elapsed: elapsed,
}); err != nil {
log.Print(err)
return
}
}
var resultsTemplate = template.Must(template.New("results").Parse(`
<html>
<head/>
<body>
<ol>
{{range .Results}}
<li>{{.Title}} - <a href="{{.URL}}">{{.URL}}</a></li>
{{end}}
</ol>
<p>{{len .Results}} results in {{.Elapsed}}; timeout {{.Timeout}}</p>
</body>
</html>
`))
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