Decrease default maximum payload size to 10MiB

The previous setting 10GiB causes a growing memory usage since a buffer
of the upload size will be allocated. This causes OOM exceptions on
mobile phones (see tus/tus-android-client#22).

src/main/java/io/tus/java/client/TusUploader.java

@@ -25,7 +25,7 @@ public class TusUploader {
     private long offset;
     private TusClient client;
     private byte[] buffer;
-    private int requestPayloadSize = 1024 * 1024 * 1024;
+    private int requestPayloadSize = 10 * 1024 * 1024;
     private int bytesRemainingForRequest;
 
     private HttpURLConnection connection;
@@ -116,12 +116,17 @@ public int getChunkSize() {
      * bigger uploads into multiple requests. For example, if you have a resource of 2MB and
      * the payload size set to 1MB, the upload will be transferred by two requests of 1MB each.
      *
-     * The default value for this setting is 1024 * 1024 * 1024 bytes (GiB).
+     * The default value for this setting is 10 * 1024 * 1024 bytes (10 MiB).
      *
-     * Be aware that setting a low maximum payload size (in the megabytes or even less range) will result in decreased
+     * Be aware that setting a low maximum payload size (in the low megabytes or even less range) will result in decreased
      * performance since more requests need to be used for an upload. Each request will come with its overhead in terms
-     * of longer upload times. Furthermore, changing this setting is rarely necessary and is only advised in a situation
-     * when a server cannot deal with streaming request bodies (e.g. some Python frameworks).
+     * of longer upload times.
+     *
+     * Be aware that setting a high maximum payload size may result in a high memory usage since
+     * tus-java-client usually allocates a buffer with the maximum payload size (this buffer is used
+     * to allow retransmission of lost data if necessary). If the client is running on a memory-
+     * constrained device (e.g. mobile app) and the maximum payload size is too high, it might
+     * result in an {@link OutOfMemoryError}.
      *
      * This method must not be called when the uploader has currently an open connection to the
      * remote server. In general, try to set the payload size before invoking {@link #uploadChunk()}

src/test/java/io/tus/java/client/TestTusUploader.java

@@ -171,7 +171,7 @@ public void testSetRequestPayloadSize() throws Exception {
 
         TusUploader uploader = new TusUploader(client, uploadUrl, input, 0);
 
-        assertEquals(uploader.getRequestPayloadSize(), 1024 * 1024 * 1024);
+        assertEquals(uploader.getRequestPayloadSize(), 10 * 1024 * 1024);
         uploader.setRequestPayloadSize(5);
         assertEquals(uploader.getRequestPayloadSize(), 5);