apiserver.go

package agent

import (
	"context"
	"fmt"
	"net"
	"net/http"
	"sync"
	"time"

	"github.com/hashicorp/go-hclog"
	"golang.org/x/sync/errgroup"
)

// apiServers is a wrapper around errgroup.Group for managing go routines for
// long running agent components (ex: http server, dns server). If any of the
// servers fail, the failed channel will be closed, which will cause the agent
// to be shutdown instead of running in a degraded state.
//
// This struct exists as a shim for using errgroup.Group without making major
// changes to Agent. In the future it may be removed and replaced with more
// direct usage of errgroup.Group.
type apiServers struct {
	logger  hclog.Logger
	group   *errgroup.Group
	servers []apiServer
	// failed channel is closed when the first server goroutines exit with a
	// non-nil error.
	failed <-chan struct{}
}

type apiServer struct {
	// Protocol supported by this server. One of: dns, http, https
	Protocol string
	// Addr the server is listening on
	Addr net.Addr
	// Run will be called in a goroutine to run the server. When any Run exits
	// with a non-nil error, the failed channel will be closed.
	Run func() error
	// Shutdown function used to stop the server
	Shutdown func(context.Context) error
}

// NewAPIServers returns an empty apiServers that is ready to Start servers.
func NewAPIServers(logger hclog.Logger) *apiServers {
	group, ctx := errgroup.WithContext(context.TODO())
	return &apiServers{
		logger: logger,
		group:  group,
		failed: ctx.Done(),
	}
}

func (s *apiServers) Start(srv apiServer) {
	srv.logger(s.logger).Info("Starting server")
	s.servers = append(s.servers, srv)
	s.group.Go(srv.Run)
}

func (s apiServer) logger(base hclog.Logger) hclog.Logger {
	return base.With(
		"protocol", s.Protocol,
		"address", s.Addr.String(),
		"network", s.Addr.Network())
}

// Shutdown all the servers and log any errors as warning. Each server is given
// 1 second, or until ctx is cancelled, to shutdown gracefully.
func (s *apiServers) Shutdown(ctx context.Context) {
	shutdownGroup := new(sync.WaitGroup)

	for i := range s.servers {
		server := s.servers[i]
		shutdownGroup.Add(1)

		go func() {
			defer shutdownGroup.Done()
			logger := server.logger(s.logger)
			logger.Info("Stopping server")

			ctx, cancel := context.WithTimeout(ctx, time.Second)
			defer cancel()
			if err := server.Shutdown(ctx); err != nil {
				logger.Warn("Failed to stop server")
			}
		}()
	}
	s.servers = nil
	shutdownGroup.Wait()
}

// WaitForShutdown waits until all server goroutines have exited. Shutdown
// must be called before WaitForShutdown, otherwise it will block forever.
func (s *apiServers) WaitForShutdown() error {
	return s.group.Wait()
}

func newAPIServerHTTP(proto string, l net.Listener, httpServer *http.Server) apiServer {
	return apiServer{
		Protocol: proto,
		Addr:     l.Addr(),
		Shutdown: httpServer.Shutdown,
		Run: func() error {
			err := httpServer.Serve(l)
			if err == nil || err == http.ErrServerClosed {
				return nil
			}
			return fmt.Errorf("%s server %s failed: %w", proto, l.Addr(), err)
		},
	}
}