Added an option for a sockstreambuf to automatically flush its output

buffers before performing any network reads.

dlib/sockstreambuf/sockstreambuf.cpp

@@ -109,6 +109,15 @@ namespace dlib
         // copy the putback characters into the putback end of the in_buffer
         std::memmove(in_buffer+(max_putback-num_put_back), gptr()-num_put_back, num_put_back);
 
+        if (flushes_output_on_read())
+        {
+            if (flush_out_buffer() == EOF)
+            {
+                // an error occurred
+                return EOF;
+            }
+        }
+
         int num = con.read(in_buffer+max_putback, in_buffer_size-max_putback);
         if (num <= 0)
         {

dlib/sockstreambuf/sockstreambuf.h

@@ -40,7 +40,8 @@ namespace dlib
         ) :
             con(*con_),
             out_buffer(0),
-            in_buffer(0)
+            in_buffer(0),
+            autoflush(false)
         {
             init();
         }
@@ -50,7 +51,8 @@ namespace dlib
         ) :
             con(*con_),
             out_buffer(0),
-            in_buffer(0)
+            in_buffer(0),
+            autoflush(false)
         {
             init();
         }
@@ -66,6 +68,20 @@ namespace dlib
         connection* get_connection (
         ) { return &con; }
 
+        void flush_output_on_read()
+        {
+            autoflush = true;
+        }
+
+        bool flushes_output_on_read() const
+        {
+            return autoflush;
+        }
+
+        void do_not_flush_output_on_read()
+        {
+            autoflush = false;
+        }
 
     protected:
 
@@ -140,6 +156,7 @@ namespace dlib
         static const std::streamsize in_buffer_size = 10000;
         char* out_buffer;
         char* in_buffer;
+        bool autoflush;
     
     };
 

dlib/sockstreambuf/sockstreambuf_abstract.h

@@ -53,6 +53,7 @@ namespace dlib
                 - con == a valid connection object
             ensures
                 - *this will read from and write to con
+                - #flushes_output_on_read() == false
             throws
                 - std::bad_alloc
         !*/
@@ -65,6 +66,7 @@ namespace dlib
                 - con == a valid connection object
             ensures
                 - *this will read from and write to con
+                - #flushes_output_on_read() == false
             throws
                 - std::bad_alloc
         !*/
@@ -88,6 +90,28 @@ namespace dlib
                   reads from and writes to
         !*/
 
+        void flush_output_on_read (
+        );
+        /*!
+            ensures
+                - #flushes_output_on_read() == true
+        !*/
+
+        bool flushes_output_on_read (
+        ) const;
+        /*!
+            ensures
+                - This function returns true if this object will flush its output buffer
+                  to the network socket before performing any network read.   
+        !*/
+
+        void do_not_flush_output_on_read (
+        );
+        /*!
+            ensures
+                - #flushes_output_on_read() == false
+        !*/
+
     };
 
 // ---------------------------------------------------------------------------------------- 

dlib/sockstreambuf/sockstreambuf_unbuffered.h

@@ -17,9 +17,14 @@ namespace dlib
     {
         /*!
             WHAT THIS OBJECT REPRESENTS
-                This is an implementation of the interface defined in sockstreambuf_abstract.h
-                except that it doesn't do any kind of buffering at all.  It just writes
-                data directly to a connection.
+                This is an implementation of the interface defined in
+                sockstreambuf_abstract.h except that it doesn't do any kind of buffering at
+                all.  It just writes data directly to a connection.  However, note that we
+                don't implement the flushes_output_on_read() routine as this object always
+                flushes immediately (since it isn't buffers.  Moreover, it should be
+                pointed out that this object is deprecated and only present for backwards
+                compatibility with previous versions of dlib.  So you really should use the
+                sockstreambuf object instead.  
 
             INITIAL VALUE
                 con == a connection