Harden binary stream overlapping writes

src/foundation/binary_stream.cpp

@@ -1,7 +1,28 @@
 #include "foundation/binary_stream.h"
 
+#include <cstdint>
+
 namespace pp::foundation {
 
+namespace {
+
+[[nodiscard]] bool overlaps_backing_storage(
+    const std::vector<std::byte>& backing,
+    std::span<const std::byte> bytes) noexcept
+{
+    if (backing.empty() || bytes.empty()) {
+        return false;
+    }
+
+    const auto backing_begin = reinterpret_cast<std::uintptr_t>(backing.data());
+    const auto backing_end = backing_begin + backing.size();
+    const auto bytes_begin = reinterpret_cast<std::uintptr_t>(bytes.data());
+    const auto bytes_end = bytes_begin + bytes.size();
+    return bytes_begin < backing_end && backing_begin < bytes_end;
+}
+
+}
+
 ByteReader::ByteReader(std::span<const std::byte> bytes) noexcept
     : bytes_(bytes)
 {
@@ -135,6 +156,12 @@ Status ByteWriter::write_bytes(std::span<const std::byte> bytes)
         return Status::invalid_argument("writer has no backing storage");
     }
 
+    if (overlaps_backing_storage(*bytes_, bytes)) {
+        const std::vector<std::byte> copy(bytes.begin(), bytes.end());
+        bytes_->insert(bytes_->end(), copy.begin(), copy.end());
+        return Status::success();
+    }
+
     bytes_->insert(bytes_->end(), bytes.begin(), bytes.end());
     return Status::success();
 }