ceph/src/common/PrebufferedStreambuf.h

   1 #ifndef CEPH_COMMON_PREBUFFEREDSTREAMBUF_H
   2 #define CEPH_COMMON_PREBUFFEREDSTREAMBUF_H
   3
   4 #include <streambuf>
   5
   6 /**
   7  * streambuf using existing buffer, overflowing into a std::string
   8  *
   9  * A simple streambuf that uses a preallocated buffer for small
  10  * strings, and overflows into a std::string when necessary.  If the
  11  * preallocated buffer size is chosen well, we can optimize for the
  12  * common case and overflow to a slower heap-allocated buffer when
  13  * necessary.
  14  */
  15 class PrebufferedStreambuf
  16   : public std::basic_streambuf<char, std::basic_string<char>::traits_type>
  17 {
  18   char *m_buf;
  19   size_t m_buf_len;
  20   std::string m_overflow;
  21
  22   typedef std::char_traits<char> traits_ty;
  23   typedef traits_ty::int_type int_type;
  24   typedef traits_ty::pos_type pos_type;
  25   typedef traits_ty::off_type off_type;
  26
  27 public:
  28   PrebufferedStreambuf(char *buf, size_t len);
  29
  30   // called when the buffer fills up
  31   int_type overflow(int_type c) override;
  32
  33   // called when we read and need more data
  34   int_type underflow() override;
  35
  36   /// return a string copy (inefficiently)
  37   std::string get_str() const;
  38
  39   // returns current size of content
  40   size_t size() const;
  41
  42   // extracts up to avail chars of content
  43   int snprintf(char* dst, size_t avail) const;
  44 };
  45
  46 #endif