diff --git a/src/main/php/io/streams/StreamTransfer.class.php b/src/main/php/io/streams/StreamTransfer.class.php
index b2b8d03b7..6d5926265 100755
--- a/src/main/php/io/streams/StreamTransfer.class.php
+++ b/src/main/php/io/streams/StreamTransfer.class.php
@@ -41,21 +41,26 @@ public function __construct(InputStream $in, OutputStream $out) {
   public function transferAll() {
     $r= 0;
     while ($this->in->available()) {
-      $r+= $this->out->write($this->in->read());
+      $chunk= $this->in->read();
+      $this->out->write($chunk);
+      $r+= strlen($chunk);
     }
     return $r;
   }
 
   /**
    * Transmit all available input from in, yielding control after each chunk.
+   * Uses default chunk size of 8192 bytes.
    *
+   * @param  int $size
    * @return iterable
    * @throws io.IOException
    */
-  public function transmit() {
+  public function transmit($size= 8192) {
     while ($this->in->available()) {
-      $this->out->write($this->in->read());
-      yield;
+      $chunk= $this->in->read($size);
+      $this->out->write($chunk);
+      yield strlen($chunk);
     }
   }
 
@@ -71,15 +76,15 @@ public function close() {
     try {
       $this->in->close();
     } catch (IOException $e) {
-      $errors.= 'Could not close input stream: '.$e->getMessage().', ';
+      $errors.= ', Could not close input stream: '.$e->getMessage();
     }
     try {
       $this->out->close();
     } catch (IOException $e) {
-      $errors.= 'Could not close output stream: '.$e->getMessage().', ';
+      $errors.= ', Could not close output stream: '.$e->getMessage();
     }
     if ($errors) {
-      throw new IOException(rtrim($errors, ', '));
+      throw new IOException(substr($errors, 2));
     }
   }
 
diff --git a/src/test/php/io/unittest/StreamTransferTest.class.php b/src/test/php/io/unittest/StreamTransferTest.class.php
index 9ad36754e..b97a1c065 100755
--- a/src/test/php/io/unittest/StreamTransferTest.class.php
+++ b/src/test/php/io/unittest/StreamTransferTest.class.php
@@ -2,7 +2,7 @@
 
 use io\IOException;
 use io\streams\{InputStream, MemoryInputStream, MemoryOutputStream, OutputStream, StreamTransfer};
-use test\{Assert, Test};
+use test\{Assert, Test, Values};
 
 class StreamTransferTest {
 
@@ -49,9 +49,10 @@ public function transfer_all() {
     $out= new MemoryOutputStream();
 
     $s= new StreamTransfer(new MemoryInputStream('Hello'), $out);
-    $s->transferAll();
+    $size= $s->transferAll();
 
     Assert::equals('Hello', $out->bytes());
+    Assert::equals(5, $size);
   }
 
   #[Test]
@@ -64,6 +65,21 @@ public function transmit() {
     Assert::equals('Hello', $out->bytes());
   }
 
+  #[Test, Values([[0, []], [1, [1]], [1024, [1024]], [1025, [1024, 1]], [2077, [1024, 1024, 29]]])]
+  public function transmit_chunks($length, $chunks) {
+    $out= new MemoryOutputStream();
+    $data= str_repeat('*', $length);
+
+    $s= new StreamTransfer(new MemoryInputStream($data), $out);
+    $transmitted= [];
+    foreach ($s->transmit(1024) as $yield) {
+      $transmitted[]= $yield;
+    }
+
+    Assert::equals($data, $out->bytes());
+    Assert::equals($chunks, $transmitted);
+  }
+
   #[Test]
   public function nothing_available_after_transfer() {
     $in= new MemoryInputStream('Hello');