fix flaky server input test

cmd/dependabot/internal/cmd/update.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"io"
 	"log"
+	"net"
 	"os"
 
 	"github.com/MakeNowJust/heredoc"
@@ -140,7 +141,11 @@ func extractInput(cmd *cobra.Command, flags *UpdateFlags) (*model.Input, error)
 	}
 
 	if hasServer {
-		return server.Input(flags.inputServerPort)
+		l, err := net.Listen("tcp", fmt.Sprintf("127.0.0.1:%d", flags.inputServerPort))
+		if err != nil {
+			return nil, fmt.Errorf("failed to create listener: %w", err)
+		}
+		return server.Input(l)
 	}
 
 	if hasStdin {

internal/server/input.go

@@ -1,19 +1,17 @@
 package server
 
 import (
-	"context"
 	"encoding/json"
-	"fmt"
+	"errors"
+	"github.com/dependabot/cli/internal/model"
 	"log"
+	"net"
 	"net/http"
-	"time"
-
-	"github.com/dependabot/cli/internal/model"
 )
 
 type credServer struct {
-	server *http.Server
-	data   *model.Input
+	listener net.Listener
+	data     *model.Input
 }
 
 // the server receives one payload and shuts itself down
@@ -24,22 +22,19 @@ func (s *credServer) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	w.WriteHeader(200)
 	_ = r.Body.Close()
 	go func() {
-		_ = s.server.Shutdown(context.Background())
+		_ = s.listener.Close()
 	}()
 }
 
 // Input receives configuration via HTTP on the port and returns it decoded
-func Input(port int) (*model.Input, error) {
-	server := &http.Server{
-		Addr:              fmt.Sprintf("127.0.0.1:%d", port),
-		ReadHeaderTimeout: time.Second,
+func Input(listener net.Listener) (*model.Input, error) {
+	handler := &credServer{
+		listener: listener,
 	}
-	s := &credServer{server: server}
-	server.Handler = s
 	// printing so the user doesn't think the cli is hanging
-	log.Println("waiting for input on port", port)
-	if err := server.ListenAndServe(); err != nil && err != http.ErrServerClosed {
+	log.Println("waiting for input on", listener.Addr())
+	if err := http.Serve(listener, handler); err != nil && !errors.Is(err, net.ErrClosed) {
 		return nil, err
 	}
-	return s.data, nil
+	return handler.data, nil
 }

internal/server/input_test.go

@@ -2,33 +2,43 @@ package server
 
 import (
 	"bytes"
+	"fmt"
+	"github.com/dependabot/cli/internal/model"
+	"net"
 	"net/http"
 	"sync"
 	"testing"
-	"time"
-
-	"github.com/dependabot/cli/internal/model"
 )
 
 func TestInput(t *testing.T) {
 	wg := sync.WaitGroup{}
 	wg.Add(1)
 	var input *model.Input
+
+	l, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatal("Failed to create listener: ", err.Error())
+	}
+
 	go func() {
-		input, _ = Input(8080)
+		input, err = Input(l)
+		if err != nil {
+			t.Errorf(err.Error())
+		}
 		wg.Done()
 	}()
-	// give the server time to start
-	time.Sleep(10 * time.Millisecond)
 
+	url := fmt.Sprintf("http://%s", l.Addr().String())
 	data := `{"job":{"package-manager":"test"},"credentials":[{"credential":"value"}]}`
-	resp, err := http.Post("http://localhost:8080", "application/json", bytes.NewReader([]byte(data)))
+	resp, err := http.Post(url, "application/json", bytes.NewReader([]byte(data)))
 	if err != nil {
 		t.Fatal(err.Error())
 	}
 	if resp.StatusCode != 200 {
 		t.Errorf("expected status code 200, got %d", resp.StatusCode)
 	}
+
+	// Test will hang here if the server does not shut down
 	wg.Wait()
 
 	if input.Job.PackageManager != "test" {