Add support for querying position in fdbuf

2 files changed, 22 insertions, 2 deletions

diff --git a/libbutl/fdstream.cxx b/libbutl/fdstream.cxx
index 292324a..daa344f 100644
--- a/libbutl/fdstream.cxx
+++ b/libbutl/fdstream.cxx
@@ -145,7 +145,7 @@ namespace butl
 
     setg (buf_, buf_, buf_);
     setp (buf_, buf_ + sizeof (buf_) - 1); // Keep space for overflow's char.
-
+    off_ = 0; // @@ Strictly speaking, need to query, can be at end.
     fd_ = move (fd);
   }
 
@@ -177,6 +177,8 @@ namespace butl
         return -1;
 
       setg (buf_, buf_, buf_ + n);
+      off_ += n;
+
       return n;
     }
 #endif
@@ -223,6 +225,7 @@ namespace butl
       throw_ios_failure (errno);
 
     setg (buf_, buf_, buf_ + n);
+    off_ += n;
     return n != 0;
   }
 
@@ -295,6 +298,8 @@ namespace butl
       if (m == -1)
         throw_ios_failure (errno);
 
+      off_ += m;
+
       if (n != static_cast<size_t> (m))
         return false;
 
@@ -352,6 +357,7 @@ namespace butl
       throw_ios_failure (errno);
 
     size_t m (static_cast<size_t> (r));
+    off_ += m;
 
     // If the buffered data wasn't fully written then move the unwritten part
     // to the beginning of the buffer.
@@ -395,6 +401,7 @@ namespace butl
       throw_ios_failure (errno);
 
     size_t m (static_cast<size_t> (r));
+    off_ += m;
 
     // If the buffered data wasn't fully written then move the unwritten part
     // to the beginning of the buffer.
@@ -430,6 +437,8 @@ namespace butl
     if (r == -1)
       throw_ios_failure (errno);
 
+    off_ += r;
+
     return an + r;
 #endif
   }
diff --git a/libbutl/fdstream.hxx b/libbutl/fdstream.hxx
index 771d242..27530e2 100644
--- a/libbutl/fdstream.hxx
+++ b/libbutl/fdstream.hxx
@@ -10,7 +10,7 @@
 #include <istream>
 #include <ostream>
 #include <utility> // move()
-#include <cstdint> // uint16_t
+#include <cstdint> // uint16_t, uint64_t
 
 #include <libbutl/export.hxx>
 
@@ -143,6 +143,11 @@ namespace butl
     using base::egptr;
     using base::gbump;
 
+    // Return the (logical) position of the next byte to be read.
+    //
+    uint64_t
+    tellg () const {return off_ - (egptr () - gptr ());}
+
   private:
     bool
     load ();
@@ -159,12 +164,18 @@ namespace butl
     virtual std::streamsize
     xsputn (const char_type*, std::streamsize);
 
+    // Return the (logical) position of the next byte to be written.
+    //
+    uint64_t
+    tellp () const {return off_ + (pptr () - buf_);}
+
   private:
     bool
     save ();
 
   private:
     auto_fd fd_;
+    uint64_t off_;
     char buf_[8192];
     bool non_blocking_ = false;
   };