1 files changed, 58 insertions, 0 deletions
diff --git a/src/common/counting_writer.rs b/src/common/counting_writer.rs
new file mode 100644
index 0000000..db13e36
--- /dev/null
+++ b/src/common/counting_writer.rs
@@ -0,0 +1,58 @@
+use std::io::Write;
+use std::io;
+
+
+pub struct CountingWriter<W: Write> {
+    underlying: W,
+    written_bytes: usize,
+}
+
+impl<W: Write> CountingWriter<W> {
+    pub fn wrap(underlying: W) -> CountingWriter<W> {
+        CountingWriter {
+            underlying: underlying,
+            written_bytes: 0,
+        }
+    }
+
+    pub fn written_bytes(&self) -> usize {
+        self.written_bytes
+    }
+
+    pub fn finish(mut self) -> io::Result<(W, usize)> {
+        self.flush()?;
+        Ok((self.underlying, self.written_bytes))
+    }
+}
+
+impl<W: Write> Write for CountingWriter<W> {
+    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
+        let written_size = self.underlying.write(buf)?;
+        self.written_bytes += written_size;
+        Ok(written_size)
+    }
+
+    fn flush(&mut self) -> io::Result<()> {
+        self.underlying.flush()
+    }
+}
+
+
+
+#[cfg(test)]
+mod test {
+
+    use super::CountingWriter;
+    use std::io::Write;
+
+    #[test]
+    fn test_counting_writer() {
+        let buffer: Vec<u8> = vec![];
+        let mut counting_writer = CountingWriter::wrap(buffer);
+        let bytes = (0u8..10u8).collect::<Vec<u8>>();
+        counting_writer.write_all(&bytes).unwrap();
+        let (w, len): (Vec<u8>, usize) = counting_writer.finish().unwrap();
+        assert_eq!(len, 10);
+        assert_eq!(w.len(), 10);
+    }
+}