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diff --git a/libbutl/bufstreambuf.hxx b/libbutl/bufstreambuf.hxx
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+// file      : libbutl/bufstreambuf.hxx -*- C++ -*-
+// license   : MIT; see accompanying LICENSE file
+
+#pragma once
+
+#include <cstdint>   // uint64_t
+#include <streambuf>
+
+#include <libbutl/export.hxx>
+
+namespace butl
+{
+  // A buffered streambuf interface that exposes its buffer for direct scan
+  // and provides a notion of logical position. See fdstreambuf for background
+  // and motivation.
+  //
+  class LIBBUTL_SYMEXPORT bufstreambuf: public std::basic_streambuf<char>
+  {
+  public:
+    using base = std::basic_streambuf<char>;
+
+    using int_type = base::int_type;
+    using traits_type = base::traits_type;
+
+    using pos_type = base::pos_type; // std::streampos
+    using off_type = base::off_type; // std::streamoff
+
+  public:
+    explicit
+    bufstreambuf (std::uint64_t pos = 0): off_ (pos) {}
+
+    virtual
+    ~bufstreambuf ();
+
+    // basic_streambuf input interface.
+    //
+  public:
+
+    // Direct access to the get area. Use with caution.
+    //
+    using base::gptr;
+    using base::egptr;
+    using base::gbump;
+
+    // Return the (logical) position of the next byte to be read.
+    //
+    // Note that on Windows when reading in the text mode the logical position
+    // may differ from the physical file descriptor position due to the CRLF
+    // character sequence translation. See the fdstreambuf::seekoff()
+    // implementation for more background on this issue.
+    //
+    std::uint64_t
+    tellg () const {return off_ - (egptr () - gptr ());}
+
+    // basic_streambuf output interface.
+    //
+  public:
+
+    // Return the (logical) position of the next byte to be written.
+    //
+    std::uint64_t
+    tellp () const {return off_ + (pptr () - pbase ());}
+
+  protected:
+    std::uint64_t off_;
+  };
+}