Bind the app port deliberately and document the proxy deployment (closes #268) (closes #226)

internal/server/http.go

@@ -2,8 +2,9 @@ package server
 
 import (
 	"errors"
-	"fmt"
+	"net"
 	"net/http"
+	"strconv"
 	"time"
 )
 
@@ -24,21 +25,47 @@ const (
 	httpMaxHeaderBytes = 1 << 20
 )
 
-func (s *Server) serveUntilShutdown() {
-	listenAddr := fmt.Sprintf(":%d", s.params.Config.Port)
-	s.httpServer = &http.Server{
-		Addr:           listenAddr,
+// listenAddr renders the address the HTTP listener binds.
+//
+// The host half is always present: an empty host would be the
+// wildcard, and the whole point of BIND_ADDRESS is that binding every
+// interface is a choice the operator makes rather than one the
+// process makes for them. Config guarantees a literal, so
+// JoinHostPort's bracketing is enough to make IPv6 well formed.
+func (s *Server) listenAddr() string {
+	return net.JoinHostPort(
+		s.params.Config.BindAddress,
+		strconv.Itoa(s.params.Config.Port),
+	)
+}
+
+// newHTTPServer builds the HTTP server for this Server's
+// configuration.
+//
+// It is called from New, on the constructing goroutine, rather than
+// from the serving goroutine that used to assign s.httpServer
+// directly. Two goroutines reach that field — the serving goroutine
+// and the fx stop hook, which calls Shutdown on it — with nothing
+// ordering them. Constructing it during New puts the write before
+// every hook fx will later run, which both removes the race and rules
+// out the nil dereference a stop that arrived before the serving
+// goroutine had run would have caused.
+func (s *Server) newHTTPServer() *http.Server {
+	return &http.Server{
+		Addr:           s.listenAddr(),
 		ReadTimeout:    httpReadTimeout,
 		WriteTimeout:   httpWriteTimeout,
 		MaxHeaderBytes: httpMaxHeaderBytes,
 		Handler:        s,
 	}
+}
 
+func (s *Server) serveUntilShutdown() {
 	// add routes
 	// this does any necessary setup in each handler
 	s.SetupRoutes()
 
-	s.log.Info("http begin listen", "listenaddr", listenAddr)
+	s.log.Info("http begin listen", "listenaddr", s.httpServer.Addr)
 
 	err := s.httpServer.ListenAndServe()
 	if err != nil && !errors.Is(err, http.ErrServerClosed) {