add comments for lab1

libsponge/stream_reassembler.cc

@@ -21,37 +21,41 @@ StreamReassembler::StreamReassembler(const size_t capacity)
 //! possibly out-of-order, from the logical stream, and assembles any newly
 //! contiguous substrings and writes them into the output stream in order.
 void StreamReassembler::push_substring(const string &data, const size_t index, const bool eof) {
-    DUMMY_CODE(data, index, eof);
+    auto _unread = _unassem - _output.buffer_size();
-    _unread = _unassem - _output.buffer_size();
     _aux_buffer.resize(_capacity - _output.buffer_size(), '\0');
     _aux_buffer_valid.resize(_aux_buffer.size(), false);
+    // resize to spare space for incoming bytes
 
     if (eof) {
         _eof = index + data.size();
+        // record first, in case eof packet arrives ahead of non-eof ones
     }
     auto start = std::max(index, _unassem);
     auto end = std::min(index + data.size(), _unread + _capacity);
+    // it is possible that index < _unassem (overlap with packets that have already been pushed into bytestream)
     for (auto i = start; i < end; ++i) {
         _aux_buffer[i - _unassem] = data[i - index];
         if (!_aux_buffer_valid[i - _unassem]) {
             _aux_buffer_valid[i - _unassem] = true;
             _unassem_count++;
+            // calculate unassembled bytes, this only counts valid bytes
         }
     }
     std::string wr_data;
     while (!_aux_buffer_valid.empty() && _aux_buffer_valid.front()) {
+        // watch out for fetching front from an empty queue
         wr_data.push_back(_aux_buffer.front());
         _aux_buffer.pop_front();
-        _aux_buffer_valid.pop_front();
+        _aux_buffer_valid.pop_front(); // remember to pop assistent queue
         ++_unassem;
         --_unassem_count;
     }
-    if (_unassem == _eof) {
-        _output.end_input();
-    }
     if (wr_data.size()) {
         _output.write(wr_data);
     }
+    if (_unassem == _eof) {
+        _output.end_input(); // stream approached to eof
+    }
 }
 
 size_t StreamReassembler::unassembled_bytes() const { return _unassem_count; }

libsponge/stream_reassembler.hh

@@ -15,12 +15,11 @@ class StreamReassembler {
 
     ByteStream _output;  //!< The reassembled in-order byte stream
     size_t _capacity{};  //!< The maximum number of bytes
-    size_t _unread{};    //!< The index (in the stream) of the first unread byte
     size_t _unassem{};   //!< The index (in the stream) of the first unassembled byte
-    size_t _unassem_count{};
+    size_t _unassem_count{}; //!< Keep the number of unassembled bytes
     std::deque<char> _aux_buffer;        //!< auxiliary storage, initially allocated _capacity bytes
     std::deque<bool> _aux_buffer_valid;  //!< indicate whether the bit in _aux_buffer is filled with a valid byte
-    size_t _eof{static_cast<size_t>(-1)};
+    size_t _eof{static_cast<size_t>(-1)}; //!< indicate the eof byte's index in stream
 
   public:
     //! \brief Construct a `StreamReassembler` that will store up to `capacity` bytes.