feat: add daily token limit error handling and corresponding test (#16)

Author: hcastc00

apps/gateway/internal/adapters/metering/client.go

@@ -295,6 +295,9 @@ func userFacingMeteringError(method, path string, status int, envelope errorResp
 		if envelope.Error.Code == domain.ErrCodeInsufficientBalance {
 			wantStatus = http.StatusPaymentRequired
 			wantType = domain.ErrTypePermission
+		} else if envelope.Error.Code == domain.ErrCodeDailyTokenLimit {
+			wantStatus = http.StatusTooManyRequests
+			wantType = domain.ErrTypeRateLimit
 		}
 	}
 

apps/gateway/internal/adapters/metering/client_test.go

@@ -263,3 +263,22 @@ func assertInternalMeteringError(t *testing.T, err error) {
 		t.Fatalf("metadata = %#v, want metering dependency", gatewayErr.Metadata)
 	}
 }
+
+func TestClientReserve_MapsDailyTokenLimitWithoutRetry(t *testing.T) {
+	var attempts atomic.Int32
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		attempts.Add(1)
+		w.WriteHeader(http.StatusTooManyRequests)
+		_, _ = w.Write([]byte(`{"error":{"type":"rate_limit_error","code":"daily_token_limit_exceeded","message":"Daily token quota reached"}}`))
+	}))
+	defer server.Close()
+	client := NewClient(server.URL, "token", time.Second)
+	_, err := client.Reserve(context.Background(), testAuth(), domain.EndpointChatCompletions, domain.GenerateRequest{PublicModelID: "model"}, testModel(), "gw-limit")
+	var gatewayErr *domain.GatewayError
+	if !errors.As(err, &gatewayErr) || gatewayErr.HTTPStatus != 429 || gatewayErr.Type != domain.ErrTypeRateLimit || gatewayErr.Code != domain.ErrCodeDailyTokenLimit {
+		t.Fatalf("got %#v, want daily quota 429", err)
+	}
+	if attempts.Load() != 1 {
+		t.Fatalf("quota error retried %d times", attempts.Load())
+	}
+}

pkg/domain/error.go

@@ -11,6 +11,7 @@ const (
 	ErrTypePermission     = "permission_error"
 	ErrTypeProvider       = "provider_error"
 	ErrTypeInternal       = "internal_error"
+	ErrTypeRateLimit      = "rate_limit_error"
 )
 
 // Error codes as defined in the spec.
@@ -33,6 +34,7 @@ const (
 	ErrCodeInvalidField            = "invalid_field"
 	ErrCodeUnknownField            = "unknown_field"
 	ErrCodeInsufficientBalance     = "insufficient_balance"
+	ErrCodeDailyTokenLimit         = "daily_token_limit_exceeded"
 	ErrCodeClientCanceled          = "client_canceled"
 	ErrCodeInternalError           = "internal_error"
 )