Start test servers on a port the system picks (closes #211)

The internal/server and internal/ircserver tests picked a port by
opening a listener, reading its port and closing it. They then started
a server on that number. Another process could take the port in
between, and a test failed with "address already in use".

The IRC server tests now start the server on 127.0.0.1:0 and read the
port back from its listener. The HTTP server tests start the app with
port 0. The stop test cannot read that port, so it serves the same HTTP
server on a listener it opened and keeps open.

Only test files change.

Model: opus-5-5

internal/server/export_test.go

@@ -15,12 +15,6 @@ func NewTestSPAServer() *Server {
 	return srv
 }
 
-// Listener returns the listener the start hook bound for the
-// HTTP server.
-func (srv *Server) Listener() net.Listener {
-	return srv.listener
-}
-
 // ServeUntilShutdown runs serveUntilShutdown, which serves the
 // HTTP server on listener, and returns when it does.
 func (srv *Server) ServeUntilShutdown(listener net.Listener) {

internal/server/server.go

@@ -50,7 +50,6 @@ type Server struct {
 	sentryEnabled bool
 	log           *slog.Logger
 	httpServer    *http.Server
-	listener      net.Listener
 	router        *chi.Mux
 	params        Params
 	mw            *middleware.Middleware
@@ -180,8 +179,6 @@ func (srv *Server) startHTTP(ctx context.Context) error {
 		return fmt.Errorf("http listen: %w", err)
 	}
 
-	srv.listener = listener
-
 	srv.httpServer = &http.Server{ //nolint:exhaustruct // optional fields
 		Addr:           listenAddr,
 		ReadTimeout:    httpReadTimeout,

internal/server/server_test.go

@@ -8,7 +8,6 @@ import (
 	"fmt"
 	"net"
 	"net/http"
-	"strconv"
 	"strings"
 	"testing"
 	"time"
@@ -56,12 +55,20 @@ func TestStopWaitsForRequestInProgress(t *testing.T) {
 		t.Fatalf("create session: %v", err)
 	}
 
-	tcpAddr, ok := srv.Listener().Addr().(*net.TCPAddr)
-	if !ok {
-		t.Fatalf("listener address %v is not TCP", srv.Listener().Addr())
+	// The test cannot read the port the system gave the app, so
+	// it serves the same HTTP server on a listener of its own.
+	var listenConfig net.ListenConfig
+
+	listener, err := listenConfig.Listen(
+		t.Context(), "tcp", "127.0.0.1:0",
+	)
+	if err != nil {
+		t.Fatalf("listen: %v", err)
 	}
 
-	addr := net.JoinHostPort("127.0.0.1", strconv.Itoa(tcpAddr.Port))
+	go srv.ServeUntilShutdown(listener)
+
+	addr := listener.Addr().String()
 
 	statuses := make(chan int, 1)