TDD: IOHelper.copyStream()

common/src/main/java/com/microsoft/alm/helpers/IOHelper.java

@@ -10,8 +10,12 @@ import java.io.FileInputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.InputStreamReader;
+import java.io.OutputStream;
 
 public class IOHelper {
+
+    static final int BUFFER_SIZE = 4096;
+
     public static void closeQuietly(final Closeable closeable) {
         if (closeable != null) {
             try {
@@ -50,4 +54,13 @@ public class IOHelper {
             IOHelper.closeQuietly(isr);
         }
     }
+
+    public static void copyStream(final InputStream is, final OutputStream os) throws IOException {
+        final byte[] buffer = new byte[BUFFER_SIZE];
+        int bytesRead;
+        while ((bytesRead = is.read(buffer, 0, BUFFER_SIZE)) != -1) {
+            os.write(buffer, 0, bytesRead);
+        }
+        os.flush();
+    }
 }

common/src/test/java/com/microsoft/alm/helpers/IOHelperTest.java

@@ -4,11 +4,70 @@
 package com.microsoft.alm.helpers;
 
 import org.junit.Assert;
+import org.junit.Before;
 import org.junit.Test;
 
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.util.Random;
+
 /**
  * A class to test {@link IOHelper}.
  */
 public class IOHelperTest {
 
+    private static byte[] createRandomByteArray(final int numberOfBytes) {
+        final Random random = new Random(42);
+        final byte[] result = new byte[numberOfBytes];
+        random.nextBytes(result);
+        return result;
+    }
+
+    private static void testCopyStream(final int numberOfBytes) throws IOException {
+        final byte[] input = createRandomByteArray(numberOfBytes);
+        final ByteArrayInputStream bais = new ByteArrayInputStream(input);
+        final ByteArrayOutputStream baos = new ByteArrayOutputStream(numberOfBytes);
+
+        IOHelper.copyStream(bais, baos);
+
+        final byte[] actual = baos.toByteArray();
+        Assert.assertArrayEquals(input, actual);
+        Assert.assertEquals(numberOfBytes, baos.size());
+    }
+
+    @Test
+    public void copyStream_zeroBuffer() throws Exception {
+        testCopyStream(0);
+    }
+
+    @Test
+    public void copyStream_oneByte() throws Exception {
+        testCopyStream(1);
+    }
+
+    @Test
+    public void copyStream_halfSmallerThanBuffer() throws Exception {
+        testCopyStream(IOHelper.BUFFER_SIZE / 2);
+    }
+
+    @Test
+    public void copyStream_justSmallerThanBuffer() throws Exception {
+        testCopyStream(IOHelper.BUFFER_SIZE - 1);
+    }
+
+    @Test
+    public void copyStream_sameAsBuffer() throws Exception {
+        testCopyStream(IOHelper.BUFFER_SIZE);
+    }
+
+    @Test
+    public void copyStream_oneMoreThanBuffer() throws Exception {
+        testCopyStream(IOHelper.BUFFER_SIZE + 1);
+    }
+
+    @Test
+    public void copyStream_twiceMoreThanBuffer() throws Exception {
+        testCopyStream(IOHelper.BUFFER_SIZE * 2);
+    }
 }