Fix execution in silent mode (#407)

* Fix execution in silent mode

Author: anutosh491

src/xinterpreter.cpp

@@ -236,6 +236,45 @@ namespace xcpp
         return "unknown";
     }
 
+    class SilentStreamRedirectRAII
+    {
+    public:
+
+        explicit SilentStreamRedirectRAII(bool silent)
+            : m_silent(silent)
+            , m_old_cout(silent ? std::cout.rdbuf() : nullptr)
+            , m_old_cerr(silent ? std::cerr.rdbuf() : nullptr)
+        {
+            if (m_silent)
+            {
+                std::cout.rdbuf(&m_null);
+                std::cerr.rdbuf(&m_null);
+            }
+        }
+
+        ~SilentStreamRedirectRAII() noexcept
+        {
+            if (m_silent)
+            {
+                std::cout.rdbuf(m_old_cout);
+                std::cerr.rdbuf(m_old_cerr);
+            }
+        }
+
+        SilentStreamRedirectRAII(const SilentStreamRedirectRAII&) = delete;
+        SilentStreamRedirectRAII& operator=(const SilentStreamRedirectRAII&) = delete;
+        SilentStreamRedirectRAII(SilentStreamRedirectRAII&&) = delete;
+        SilentStreamRedirectRAII& operator=(SilentStreamRedirectRAII&&) = delete;
+
+    private:
+
+        bool m_silent;
+        xnull m_null;
+
+        std::streambuf* m_old_cout;
+        std::streambuf* m_old_cerr;
+    };
+
     interpreter::interpreter(int argc, const char* const* argv) :
         xmagics()
         , p_cout_strbuf(nullptr)
@@ -288,16 +327,7 @@ namespace xcpp
 
         // If silent is set to true, temporarily dismiss all std::cerr and
         // std::cout outputs resulting from `process_code`.
-
-        auto cout_strbuf = std::cout.rdbuf();
-        auto cerr_strbuf = std::cerr.rdbuf();
-
-        if (config.silent)
-        {
-            auto null = xnull();
-            std::cout.rdbuf(&null);
-            std::cerr.rdbuf(&null);
-        }
+        SilentStreamRedirectRAII silent_guard(config.silent);
 
         std::string err;
 
@@ -331,13 +361,6 @@ namespace xcpp
         std::cout << std::flush;
         std::cerr << std::flush;
 
-        // Reset non-silent output buffers
-        if (config.silent)
-        {
-            std::cout.rdbuf(cout_strbuf);
-            std::cerr.rdbuf(cerr_strbuf);
-        }
-
         // Depending of error level, publish execution result or execution
         // error, and compose execute_reply message.
         if (errorlevel)

test/test_interpreter.cpp

@@ -1229,3 +1229,41 @@ TEST_SUITE("mime_bundle_repr")
         REQUIRE(res == expected);
     }
 }
+
+#if !defined(__EMSCRIPTEN__)
+// TODO: Currently any test added to this file will fail for the wasm build saying memory access out of bounds.
+TEST_CASE("Silent mode restores std::cout and std::cerr buffers")
+{
+    std::vector<const char*> Args = {};
+    xcpp::interpreter interpreter((int)Args.size(), Args.data());
+
+    auto* cout_before = std::cout.rdbuf();
+    auto* cerr_before = std::cerr.rdbuf();
+
+    xeus::execute_request_config config;
+    config.silent = true;
+    config.store_history = false;
+    config.allow_stdin = false;
+
+    nl::json header = nl::json::object();
+    xeus::xrequest_context::guid_list id = {};
+    xeus::xrequest_context context(header, id);
+
+    std::promise<nl::json> promise;
+    auto callback = [&promise](nl::json result) { promise.set_value(result); };
+
+    std::string code = R"(
+        #include <iostream>
+        std::cout << "hidden stdout\n";
+        std::cerr << "hidden stderr\n";
+    )";
+
+    interpreter.execute_request(context, callback, code, config, nl::json::object());
+
+    auto reply = promise.get_future().get();
+    REQUIRE(reply["status"] == "ok");
+
+    REQUIRE(std::cout.rdbuf() == cout_before);
+    REQUIRE(std::cerr.rdbuf() == cerr_before);
+}
+#endif