GetObjectRequest should support final bytes as a Range header value

Fixes aws#1551

Author: omalley

aws-java-sdk-s3/src/main/java/com/amazonaws/services/s3/AmazonS3Client.java

@@ -1461,7 +1461,11 @@ public S3Object getObject(GetObjectRequest getObjectRequest)
         // Range
         long[] range = getObjectRequest.getRange();
         if (range != null) {
-            request.addHeader(Headers.RANGE, "bytes=" + Long.toString(range[0]) + "-" + Long.toString(range[1]));
+            if (range[0] < 0) {
+                request.addHeader(Headers.RANGE, "bytes=" + Long.toString(range[0]));
+            } else {
+                request.addHeader(Headers.RANGE, "bytes=" + Long.toString(range[0]) + "-" + Long.toString(range[1]));
+            }
         }
 
         populateRequesterPaysHeader(request, getObjectRequest.isRequesterPays());

aws-java-sdk-s3/src/main/java/com/amazonaws/services/s3/model/GetObjectRequest.java

@@ -474,7 +474,10 @@ public void setRange(long start, long end) {
      * <p>
      * The first byte in an object has
      * position 0; as an example, the object is of 10 bytes in length, the last
-     * 4 bytes can be downloaded by specifying the start range as 6.
+     * 4 bytes can be downloaded by specifying the start range as 6. Positions
+     * may also be specified as a negative number counting from the end of the
+     * object. Therefore, start = -4 will get the last four bytes of the
+     * object regardless of its length.
      * </p>
      * <p>
      * If no byte range is specified, this request downloads the entire
@@ -534,7 +537,10 @@ public GetObjectRequest withRange(long start, long end) {
      * <p>
      * The first byte in an object has
      * position 0; as an example, the object is of 10 bytes in length, the last
-     * 4 bytes can be downloaded by specifying the start range as 6.
+     * 4 bytes can be downloaded by specifying the start range as 6. Positions
+     * may also be specified as a negative number counting from the end of the
+     * object. Therefore, start = -4 will get the last four bytes of the
+     * object regardless of its length.
      * </p>
      * <p>
      * If no byte range is specified, this request downloads the entire