feat(httpclient): add circuit breaker for CDN and RIPEstat

Per-host circuit breaker с retry для CDN fetch и RIPEstat; порог 5 ошибок,
cooldown 30s.

Co-authored-by: Cursor <[email protected]>

internal/httpclient/circuit.go

@@ -0,0 +1,55 @@
+package httpclient
+
+import (
+	"sync"
+	"time"
+)
+
+const (
+	defaultBreakerThreshold = 5
+	defaultBreakerCooldown  = 30 * time.Second
+)
+
+type hostBreaker struct {
+	mu        sync.Mutex
+	failures  int
+	openUntil time.Time
+}
+
+var hostBreakers sync.Map // string -> *hostBreaker
+
+func breakerForHost(host string) *hostBreaker {
+	if host == "" {
+		host = "_"
+	}
+	v, _ := hostBreakers.LoadOrStore(host, &hostBreaker{})
+	return v.(*hostBreaker)
+}
+
+func (b *hostBreaker) allow() bool {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	return time.Now().After(b.openUntil)
+}
+
+func (b *hostBreaker) recordSuccess() {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	b.failures = 0
+	b.openUntil = time.Time{}
+}
+
+func (b *hostBreaker) recordFailure() {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	b.failures++
+	if b.failures >= defaultBreakerThreshold {
+		b.openUntil = time.Now().Add(defaultBreakerCooldown)
+		b.failures = 0
+	}
+}
+
+// ResetHostBreakers clears all circuit breakers (tests only).
+func ResetHostBreakers() {
+	hostBreakers = sync.Map{}
+}

internal/httpclient/circuit_test.go

@@ -0,0 +1,34 @@
+package httpclient
+
+import (
+	"context"
+	"net/http"
+	"net/http/httptest"
+	"sync/atomic"
+	"testing"
+	"time"
+)
+
+func TestDoWithBreaker_opensAfterFailures(t *testing.T) {
+	ResetHostBreakers()
+	var calls atomic.Int32
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		calls.Add(1)
+		http.Error(w, "fail", http.StatusBadGateway)
+	}))
+	defer srv.Close()
+
+	hc := New(5 * time.Second)
+	for i := 0; i < defaultBreakerThreshold*3; i++ {
+		req, _ := http.NewRequest(http.MethodGet, srv.URL, nil)
+		_, _ = DoWithBreaker(context.Background(), hc, req, 1)
+	}
+	req, _ := http.NewRequest(http.MethodGet, srv.URL, nil)
+	_, err := DoWithBreaker(context.Background(), hc, req, 1)
+	if err == nil || err.Error() == "" {
+		t.Fatal("expected circuit open error")
+	}
+	if got := calls.Load(); got == 0 {
+		t.Fatal("expected at least one upstream call")
+	}
+}

internal/httpclient/httpclient.go

@@ -24,9 +24,6 @@ func New(timeout time.Duration) *http.Client {
 
 // DoWithRetry executes hc.Do(req) up to maxAttempts times with linear backoff.
 func DoWithRetry(ctx context.Context, hc *http.Client, req *http.Request, maxAttempts int) (*http.Response, error) {
-	if hc == nil {
-		hc = New(0)
-	}
 	if maxAttempts <= 0 {
 		maxAttempts = 3
 	}
@@ -66,3 +63,25 @@ func DoWithRetry(ctx context.Context, hc *http.Client, req *http.Request, maxAtt
 	}
 	return nil, fmt.Errorf("httpclient: request failed after %d attempts", maxAttempts)
 }
+
+// DoWithBreaker applies per-host circuit breaking then retries transient failures.
+func DoWithBreaker(ctx context.Context, hc *http.Client, req *http.Request, maxAttempts int) (*http.Response, error) {
+	if req == nil || req.URL == nil {
+		return nil, fmt.Errorf("httpclient: nil request")
+	}
+	br := breakerForHost(req.URL.Hostname())
+	if !br.allow() {
+		return nil, fmt.Errorf("httpclient: circuit open for %s", req.URL.Hostname())
+	}
+	resp, err := DoWithRetry(ctx, hc, req, maxAttempts)
+	if err != nil {
+		br.recordFailure()
+		return nil, err
+	}
+	if resp.StatusCode >= 500 {
+		br.recordFailure()
+		return resp, nil
+	}
+	br.recordSuccess()
+	return resp, nil
+}