--- /dev/null
+#ifndef CEPH_COMMON_PREBUFFEREDSTREAMBUF_H
+#define CEPH_COMMON_PREBUFFEREDSTREAMBUF_H
+
+#include <streambuf>
+
+/**
+ * streambuf using existing buffer, overflowing into a std::string
+ *
+ * A simple streambuf that uses a preallocated buffer for small
+ * strings, and overflows into a std::string when necessary. If the
+ * preallocated buffer size is chosen well, we can optimize for the
+ * common case and overflow to a slower heap-allocated buffer when
+ * necessary.
+ */
+class PrebufferedStreambuf
+ : public std::basic_streambuf<char, std::basic_string<char>::traits_type>
+{
+ char *m_buf;
+ size_t m_buf_len;
+ std::string m_overflow;
+
+ typedef std::char_traits<char> traits_ty;
+ typedef traits_ty::int_type int_type;
+ typedef traits_ty::pos_type pos_type;
+ typedef traits_ty::off_type off_type;
+
+public:
+ PrebufferedStreambuf(char *buf, size_t len);
+
+ // called when the buffer fills up
+ int_type overflow(int_type c) override;
+
+ // called when we read and need more data
+ int_type underflow() override;
+
+ /// return a string copy (inefficiently)
+ std::string get_str() const;
+
+ // returns current size of content
+ size_t size() const;
+
+ // extracts up to avail chars of content
+ int snprintf(char* dst, size_t avail) const;
+};
+
+#endif