the log wrapper in C/C++ accepts formats

pam-module/include/rust_backend_logging_cpp.h

@@ -0,0 +1,75 @@
+// SPDX-License-Identifier: Apache-2.0
+// C++ stream-style wrappers for Rust logging FFI
+
+#pragma once
+
+// This header expects `rust_backend_ffi.h` to have been included first
+// so that `RustLogLevel` and `rust_log_event_with_level` are available.
+
+#include <sstream>
+#include <string>
+#include <ostream>
+
+class RustLogStream {
+public:
+    explicit RustLogStream(RustLogLevel level) noexcept : level_(level) {}
+
+    // Generic stream insertion
+    template<typename T>
+    RustLogStream& operator<<(const T& v) {
+        try {
+            oss_ << v;
+        } catch (...) {
+            // swallow; avoid exceptions crossing FFI
+        }
+        return *this;
+    }
+
+    // Support manipulators like std::endl
+    RustLogStream& operator<<(std::ostream& (*manip)(std::ostream&)) {
+        try {
+            manip(oss_);
+        } catch (...) {
+        }
+        return *this;
+    }
+
+    // Destructor emits buffered message
+    ~RustLogStream() noexcept {
+        try {
+            const std::string s = oss_.str();
+            if (!s.empty()) {
+                rust_log_event_with_level(s.c_str(), level_);
+            }
+        } catch (...) {
+            // never throw
+        }
+    }
+
+    // Non-copyable
+    RustLogStream(const RustLogStream&) = delete;
+    RustLogStream& operator=(const RustLogStream&) = delete;
+
+    // Movable
+    RustLogStream(RustLogStream&&) = default;
+    RustLogStream& operator=(RustLogStream&&) = default;
+
+private:
+    RustLogLevel level_;
+    std::ostringstream oss_;
+};
+
+// Factories and macros
+inline RustLogStream rust_log_info_stream() { return RustLogStream(RUST_LOG_LEVEL_INFO); }
+inline RustLogStream rust_log_warn_stream() { return RustLogStream(RUST_LOG_LEVEL_WARN); }
+inline RustLogStream rust_log_error_stream() { return RustLogStream(RUST_LOG_LEVEL_ERROR); }
+inline RustLogStream rust_log_debug_stream() { return RustLogStream(RUST_LOG_LEVEL_DEBUG); }
+inline RustLogStream rust_log_trace_stream() { return RustLogStream(RUST_LOG_LEVEL_TRACE); }
+inline RustLogStream rust_log_fatal_stream() { return RustLogStream(RUST_LOG_LEVEL_FATAL); }
+
+#define RUST_COUT() rust_log_info_stream()
+#define RUST_CERR() rust_log_error_stream()
+#define RUST_CDEBUG() rust_log_debug_stream()
+
+// Usage example:
+// RUST_COUT() << "User=" << user << " logged in" << std::endl;