galaxy-game/game/internal/router/router_test.go

package router_test

import (
	"context"
	"encoding/json"
	"fmt"
	"net/http"
	"net/http/httptest"
	"strings"
	"sync"
	"sync/atomic"
	"testing"
	"time"

	"galaxy/model/rest"

	"galaxy/game/internal/router"

	"github.com/gin-gonic/gin"
	"github.com/google/uuid"
	"github.com/stretchr/testify/assert"
)

func TestLimitConnections(t *testing.T) {
	r := limitTestingRouter()

	wg := sync.WaitGroup{}
	lock := sync.WaitGroup{}
	lock.Add(1)
	for range 1000 {
		wg.Go(func() {
			w := httptest.NewRecorder()
			lock.Wait()
			req, _ := http.NewRequest("GET", "/limited", nil)
			r.ServeHTTP(w, req)
			assert.Equal(t, 200, w.Code, w.Body)
		})
	}
	lock.Done()
	wg.Wait()
}

// TestLimitSharedInstanceSerialisesRoutes pins the property the engine relies
// on to serialise state mutations: a single LimitMiddleware(1) instance shared
// across several routes admits at most one request across all of them at a
// time. The handler tracks the high-water concurrency and asserts it never
// exceeds one.
func TestLimitSharedInstanceSerialisesRoutes(t *testing.T) {
	gin.SetMode(gin.ReleaseMode)
	r := gin.New()
	r.Use(gin.Recovery())

	shared := router.LimitMiddleware(1)

	var inFlight, maxSeen atomic.Int32
	handler := func(c *gin.Context) {
		n := inFlight.Add(1)
		for {
			cur := maxSeen.Load()
			if n <= cur || maxSeen.CompareAndSwap(cur, n) {
				break
			}
		}
		time.Sleep(time.Millisecond) // widen the overlap window
		inFlight.Add(-1)
		c.Status(http.StatusOK)
	}
	r.GET("/a", shared, handler)
	r.PUT("/b", shared, handler)

	wg := sync.WaitGroup{}
	for i := range 200 {
		method, path := http.MethodGet, "/a"
		if i%2 == 1 {
			method, path = http.MethodPut, "/b"
		}
		wg.Go(func() {
			w := httptest.NewRecorder()
			req, _ := http.NewRequest(method, path, nil)
			r.ServeHTTP(w, req)
			assert.Equal(t, http.StatusOK, w.Code, w.Body)
		})
	}
	wg.Wait()
	assert.Equal(t, int32(1), maxSeen.Load(), "a shared limiter must serialise across every route it guards")
}

// TestLimitReleasesOnContextCancel verifies the wait path: while one request
// holds the only slot, a second request blocked on the limiter answers 503
// once its request context is cancelled, instead of hanging.
func TestLimitReleasesOnContextCancel(t *testing.T) {
	gin.SetMode(gin.ReleaseMode)
	r := gin.New()
	r.Use(gin.Recovery())

	shared := router.LimitMiddleware(1)
	entered := make(chan struct{})
	release := make(chan struct{})
	r.GET("/hold", shared, func(c *gin.Context) {
		close(entered)
		<-release
		c.Status(http.StatusOK)
	})

	// First request grabs and holds the only slot.
	go func() {
		w := httptest.NewRecorder()
		req, _ := http.NewRequest(http.MethodGet, "/hold", nil)
		r.ServeHTTP(w, req)
	}()
	<-entered

	// Second request blocks on the limiter, then loses its context.
	ctx, cancel := context.WithCancel(context.Background())
	w := httptest.NewRecorder()
	req, _ := http.NewRequestWithContext(ctx, http.MethodGet, "/hold", nil)
	done := make(chan struct{})
	go func() {
		r.ServeHTTP(w, req)
		close(done)
	}()
	cancel()
	<-done

	assert.Equal(t, http.StatusServiceUnavailable, w.Code)
	close(release)
}

func asBody(body any) *strings.Reader {
	commandJson, _ := json.Marshal(body)
	return strings.NewReader(string(commandJson))
}

func limitTestingRouter() *gin.Engine {
	gin.SetMode(gin.ReleaseMode)
	r := gin.New()
	r.Use(gin.Recovery())

	counter := atomic.Int32{}
	r.GET("/limited",
		// limiting all ingoing connections
		router.LimitMiddleware(1),
		// storing counter value and testing increment after executing Next handlers
		func(c *gin.Context) {
			expected := counter.Load() + 1
			c.Next()
			current := counter.Load()
			if current != expected {
				c.String(http.StatusConflict, "expected: %d, got: %d", expected, current)
			}
		},
		// increment counter
		func(c *gin.Context) {
			counter.Add(1)
			c.Status(http.StatusOK)
		})
	return r
}

func generateInitRequest(races int) rest.InitRequest {
	request := rest.InitRequest{
		GameID: uuid.New(),
		Races:  make([]rest.InitRace, races),
	}
	for i := range request.Races {
		request.Races[i] = rest.InitRace{RaceName: raceName(i)}
	}
	return request
}

func raceName(i int) string {
	return fmt.Sprintf("Race_%02d", i)
}