diff --git a/phpseclib/Net/SFTP.php b/phpseclib/Net/SFTP.php
index a2034550..ce7605b9 100644
--- a/phpseclib/Net/SFTP.php
+++ b/phpseclib/Net/SFTP.php
@@ -72,6 +72,11 @@ class SFTP extends SSH2
     */
     // this value isn't really used anymore but i'm keeping it reserved for historical reasons
     const SOURCE_STRING = 2;
+    /**
+     * Reads data from callback:
+     * function callback($length) returns string to proceed, null for EOF
+     */
+    const SOURCE_CALLBACK = 16;
     /**
      * Resumes an upload
     */
@@ -1718,6 +1723,8 @@ class SFTP extends SSH2
      * contain as many bytes as filename.ext does on your local filesystem.  If your filename.ext is 1MB then that is how
      * large $remote_file will be, as well.
      *
+     * Setting $mode to self::SOURCE_CALLBACK will use $data as callback function, which gets only one parameter -- number of bytes to return, and returns a string if there is some data or null if there is no more data
+     *
      * If $data is a resource then it'll be used as a resource instead.
      *
      * Currently, only binary mode is supported.  As such, if the line endings need to be adjusted, you will need to take
@@ -1798,7 +1805,15 @@ class SFTP extends SSH2
         }
 
         // http://tools.ietf.org/html/draft-ietf-secsh-filexfer-13#section-8.2.3
+        $callback = false;
         switch (true) {
+            case $mode & self::SOURCE_CALLBACK;
+                if (!is_callable($data)) {
+                    user_error("\$data should be is_callable() if you specify SOURCE_CALLBACK flag");
+                }
+                $callback = $data;
+                // do nothing
+                break;
             case is_resource($data):
                 $mode = $mode & ~self::SOURCE_LOCAL_FILE;
                 $fp = $data;
@@ -1825,6 +1840,8 @@ class SFTP extends SSH2
             } else {
                 fseek($fp, $offset);
             }
+        } elseif ($callback) {
+            $size = 0;
         } else {
             $size = strlen($data);
         }
@@ -1836,8 +1853,15 @@ class SFTP extends SSH2
         // make the SFTP packet be exactly 4096 bytes by including the bytes in the NET_SFTP_WRITE packets "header"
         $sftp_packet_size-= strlen($handle) + 25;
         $i = 0;
-        while ($sent < $size) {
-            $temp = isset($fp) ? fread($fp, $sftp_packet_size) : substr($data, $sent, $sftp_packet_size);
+        while ($callback || $sent < $size) {
+            if ($callback) {
+                $temp = call_user_func($callback, $sftp_packet_size);
+                if (is_null($temp)) {
+                    break;
+                }
+            } else {
+                $temp = isset($fp) ? fread($fp, $sftp_packet_size) : substr($data, $sent, $sftp_packet_size);
+            }
             $subtemp = $offset + $sent;
             $packet = pack('Na*N3a*', strlen($handle), $handle, $subtemp / 4294967296, $subtemp, strlen($temp), $temp);
             if (!$this->_send_sftp_packet(NET_SFTP_WRITE, $packet)) {
diff --git a/tests/Functional/Net/SFTPUserStoryTest.php b/tests/Functional/Net/SFTPUserStoryTest.php
index 1b7e1f71..3f989ed2 100644
--- a/tests/Functional/Net/SFTPUserStoryTest.php
+++ b/tests/Functional/Net/SFTPUserStoryTest.php
@@ -13,6 +13,7 @@ class Functional_Net_SFTPUserStoryTest extends PhpseclibFunctionalTestCase
     static protected $scratchDir;
     static protected $exampleData;
     static protected $exampleDataLength;
+    static protected $buffer;
 
     static public function setUpBeforeClass()
     {
@@ -159,6 +160,41 @@ class Functional_Net_SFTPUserStoryTest extends PhpseclibFunctionalTestCase
         return $sftp;
     }
 
+
+    static function callback($length)
+    {
+        $r = substr(self::$buffer, 0, $length);
+        self::$buffer = substr(self::$buffer, $length);
+        if (strlen($r)) return $r;
+        return null;
+    }
+
+    /**
+    * @depends testStatOnDir
+    */
+    public function testPutSizeGetFileCallback($sftp)
+    {
+        self::$buffer =  self::$exampleData;
+        $this->assertTrue(
+            $sftp->put('file1.txt', array(__CLASS__, 'callback'), $sftp::SOURCE_CALLBACK),
+            'Failed asserting that example data could be successfully put().'
+        );
+
+        $this->assertSame(
+            self::$exampleDataLength,
+            $sftp->size('file1.txt'),
+            'Failed asserting that put example data has the expected length'
+        );
+
+        $this->assertSame(
+            self::$exampleData,
+            $sftp->get('file1.txt'),
+            'Failed asserting that get() returns expected example data.'
+        );
+
+        return $sftp;
+    }
+
     /**
      * @depends testPutSizeGetFile
      */