From 6a15c8431f8fbf078003a8f000f21e1968cb7da8 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Wed, 25 Nov 2015 12:50:09 +0200
Subject: Implement ofdstream

---
 butl/fdstream     | 50 ++++++++++++++++++++++++++++++----------
 butl/fdstream.cxx | 68 +++++++++++++++++++++++++++++++++++++++++++++++++++----
 2 files changed, 102 insertions(+), 16 deletions(-)

diff --git a/butl/fdstream b/butl/fdstream
index 01a19b7..2814d4b 100644
--- a/butl/fdstream
+++ b/butl/fdstream
@@ -6,18 +6,19 @@
 #define BUTL_FDSTREAM
 
 #include <istream>
+#include <ostream>
 
 namespace butl
 {
-  // An input stream that is initialized with a file descriptor
-  // rather than a file name.
+  // An iostream that is initialized with a file descriptor rather than
+  // a file name.
   //
   // Notes and limitations:
   //
   // - char only
-  // - input only
+  // - input or output but not both
   // - no support for put back
-  // - throws std::system_error in case of a read() error
+  // - throws std::system_error in case of a read()/write() error
   // - not movable, though can be easily supported
   //
   class fdbuf: public std::basic_streambuf<char>
@@ -35,17 +36,18 @@ namespace butl
     close ();
 
     void
-    open (int fd) {close (); fd_ = fd; setg (buf_, buf_, buf_);}
+    open (int fd);
 
     bool
     is_open () const {return fd_ != -1;}
 
-    // basic_streambuf input interface.
-    //
   public:
     using int_type = std::basic_streambuf<char>::int_type;
     using traits_type = std::basic_streambuf<char>::traits_type;
 
+    // basic_streambuf input interface.
+    //
+  public:
     virtual std::streamsize
     showmanyc ();
 
@@ -56,26 +58,50 @@ namespace butl
     bool
     load ();
 
+    // basic_streambuf output interface.
+    //
+  public:
+    virtual int_type
+    overflow (int_type);
+
+    virtual int
+    sync ();
+
+  private:
+    bool
+    save ();
+
   private:
     int fd_ = -1;
     char buf_[2048];
   };
 
-  class ifdstream_base
+  class fdstream_base
   {
   protected:
-    ifdstream_base () = default;
-    ifdstream_base (int fd): buf_ (fd) {}
+    fdstream_base () = default;
+    fdstream_base (int fd): buf_ (fd) {}
 
   protected:
     fdbuf buf_;
   };
 
-  class ifdstream: ifdstream_base, public std::istream
+  class ifdstream: fdstream_base, public std::istream
   {
   public:
     ifdstream (): std::istream (&buf_) {}
-    ifdstream (int fd): ifdstream_base (fd), std::istream (&buf_) {}
+    ifdstream (int fd): fdstream_base (fd), std::istream (&buf_) {}
+
+    void close () {buf_.close ();}
+    void open (int fd) {buf_.open (fd);}
+    bool is_open () const {return buf_.is_open ();}
+  };
+
+  class ofdstream: fdstream_base, public std::ostream
+  {
+  public:
+    ofdstream (): std::ostream (&buf_) {}
+    ofdstream (int fd): fdstream_base (fd), std::ostream (&buf_) {}
 
     void close () {buf_.close ();}
     void open (int fd) {buf_.open (fd);}
diff --git a/butl/fdstream.cxx b/butl/fdstream.cxx
index 6d7532a..0386f49 100644
--- a/butl/fdstream.cxx
+++ b/butl/fdstream.cxx
@@ -5,9 +5,9 @@
 #include <butl/fdstream>
 
 #ifndef _WIN32
-#  include <unistd.h>    // close, read
+#  include <unistd.h>    // close(), read(), write()
 #else
-#  include <io.h>        // _close, _read
+#  include <io.h>        // _close(), _read(), _write()
 #endif
 
 #include <system_error>
@@ -20,9 +20,18 @@ namespace butl
   ~fdbuf () {close ();}
 
   void fdbuf::
+  open (int fd)
+  {
+    close ();
+    fd_ = fd;
+    setg (buf_, buf_, buf_);
+    setp (buf_, buf_ + sizeof (buf_) - 1); // Keep space for overflow's char.
+  }
+
+  void fdbuf::
   close ()
   {
-    if (fd_ != -1)
+    if (is_open ())
     {
 #ifndef _WIN32
       ::close (fd_);
@@ -42,7 +51,7 @@ namespace butl
   fdbuf::int_type fdbuf::
   underflow ()
   {
-    int_type r = traits_type::eof ();
+    int_type r (traits_type::eof ());
 
     if (is_open ())
     {
@@ -68,4 +77,55 @@ namespace butl
     setg (buf_, buf_, buf_ + n);
     return n != 0;
   }
+
+  fdbuf::int_type fdbuf::
+  overflow (int_type c)
+  {
+    int_type r (traits_type::eof ());
+
+    if (is_open () && c != traits_type::eof ())
+    {
+      // Store last character in the space we reserved in open(). Note
+      // that pbump() doesn't do any checks.
+      //
+      *pptr () = traits_type::to_char_type (c);
+      pbump (1);
+
+      if (save ())
+        r = c;
+    }
+
+    return r;
+  }
+
+  int fdbuf::
+  sync ()
+  {
+    return is_open () && save () ? 0 : -1;
+  }
+
+  bool fdbuf::
+  save ()
+  {
+    size_t n (pptr () - pbase ());
+
+    if (n != 0)
+    {
+#ifndef _WIN32
+      ssize_t m (::write (fd_, buf_, n));
+#else
+      int m (_write (fd_, buf_, static_cast<unsigned int> (sizeof (buf_))));
+#endif
+
+      if (m == -1)
+        throw system_error (errno, system_category ());
+
+      if (n != static_cast<size_t> (m))
+        return false;
+
+      setp (buf_, buf_ + sizeof (buf_) - 1);
+    }
+
+    return true;
+  }
 }
-- 
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