fix(zarinhub): limit upstream response size

backend/internal/zarinhub/client.go

@@ -13,6 +13,8 @@ import (
 	"card-to-iban/internal/service"
 )
 
+const maxResponseBodySize = 1 << 20
+
 type Client struct {
 	httpClient  *http.Client
 	endpointURL string
@@ -95,7 +97,9 @@ func (c *Client) Convert(
 		UpstreamHTTPStatus: resp.StatusCode,
 	}
 
-	body, err := io.ReadAll(resp.Body)
+	body, err := io.ReadAll(
+		io.LimitReader(resp.Body, maxResponseBodySize+1),
+	)
 	if err != nil {
 		return result,
 			fmt.Errorf(
@@ -105,6 +109,14 @@ func (c *Client) Convert(
 			)
 	}
 
+	if len(body) > maxResponseBodySize {
+		return result,
+			fmt.Errorf(
+				"%w: response body is too large",
+				ErrInvalidResponse,
+			)
+	}
+
 	result.RawResponse = body
 
 	switch {

backend/internal/zarinhub/client_test.go

@@ -381,3 +381,36 @@ func TestClientReturnsTimeout(t *testing.T) {
 		)
 	}
 }
+
+func TestClientRejectsOversizedResponse(t *testing.T) {
+	server := httptest.NewServer(
+		http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			w.WriteHeader(http.StatusOK)
+
+			body := make([]byte, maxResponseBodySize+1)
+			for index := range body {
+				body[index] = 'x'
+			}
+
+			if _, err := w.Write(body); err != nil {
+				t.Errorf("write response: %v", err)
+			}
+		}),
+	)
+	defer server.Close()
+
+	client := NewClient(
+		&http.Client{Timeout: time.Second},
+		server.URL,
+		"test-token",
+	)
+
+	_, err := client.Convert(
+		context.Background(),
+		"6037997512345678",
+	)
+
+	if !errors.Is(err, ErrInvalidResponse) {
+		t.Fatalf("error = %v, want ErrInvalidResponse", err)
+	}
+}