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package manners
import (
"net"
"net/http"
"sync"
)
// Creates a new GracefulServer. The server will begin shutting down when
// a value is passed to the Shutdown channel.
func NewServer() *GracefulServer {
return &GracefulServer{
Shutdown: make(chan bool),
}
}
// A GracefulServer maintains a WaitGroup that counts how many in-flight
// requests the server is handling. When it receives a shutdown signal,
// it stops accepting new requests but does not actually shut down until
// all in-flight requests terminate.
type GracefulServer struct {
Shutdown chan bool
wg sync.WaitGroup
shutdownHandler func()
InnerServer http.Server
}
// A helper function that emulates the functionality of http.ListenAndServe.
func (s *GracefulServer) ListenAndServe(addr string, handler http.Handler) error {
oldListener, err := net.Listen("tcp", addr)
if err != nil {
return err
}
listener := NewListener(oldListener, s)
err = s.Serve(listener, handler)
return err
}
// Similar to http.Serve. The listener passed must wrap a GracefulListener.
func (s *GracefulServer) Serve(listener net.Listener, handler http.Handler) error {
s.shutdownHandler = func() { listener.Close() }
s.listenForShutdown()
s.InnerServer.Handler = handler
s.InnerServer.ConnState = func(conn net.Conn, newState http.ConnState) {
switch newState {
case http.StateNew:
s.StartRoutine()
case http.StateClosed, http.StateHijacked:
s.FinishRoutine()
}
}
err := s.InnerServer.Serve(listener)
// This block is reached when the server has received a shut down command.
if err == nil {
s.wg.Wait()
return nil
} else if _, ok := err.(listenerAlreadyClosed); ok {
s.wg.Wait()
return nil
}
return err
}
// Increments the server's WaitGroup. Use this if a web request starts more
// goroutines and these goroutines are not guaranteed to finish before the
// request.
func (s *GracefulServer) StartRoutine() {
s.wg.Add(1)
}
// Decrement the server's WaitGroup. Used this to complement StartRoutine().
func (s *GracefulServer) FinishRoutine() {
s.wg.Done()
}
func (s *GracefulServer) listenForShutdown() {
go func() {
<-s.Shutdown
s.shutdownHandler()
}()
}
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