Fix reading from Blob stream not returning -1 when end of stream (#1902)

* c4stream_read return zero not -1 when end of stream.
* Fixed BlobInputStream to return -1 when the number of bytes is zero.

#1900

Author: pasin

android/CouchbaseLite/src/androidTest/java/com/couchbase/lite/BlobTest.java

@@ -17,12 +17,16 @@
 //
 package com.couchbase.lite;
 
+import android.os.Debug;
+import android.util.Log;
+
 import com.couchbase.lite.utils.IOUtils;
 
 import org.junit.Rule;
 import org.junit.Test;
 import org.junit.rules.TemporaryFolder;
 
+import java.io.ByteArrayOutputStream;
 import java.io.File;
 import java.io.FileOutputStream;
 import java.io.IOException;
@@ -261,6 +265,36 @@ public void testBlobReadFunctions() throws Exception {
         }
     }
 
+    @Test
+    public void testReadBlobStream() throws Exception {
+        byte[] bytes;
+        InputStream is = getAsset("attachment.png");
+        try {
+            bytes = IOUtils.toByteArray(is);
+        } finally {
+            is.close();
+        }
+
+        Blob blob = new Blob("image/png", bytes);
+        MutableDocument mDoc = new MutableDocument("doc1");
+        mDoc.setBlob("blob", blob);
+        Document doc = save(mDoc);
+
+        Blob savedBlob = doc.getBlob("blob");
+        assertNotNull(savedBlob);
+        assertEquals("image/png", savedBlob.getContentType());
+
+        int len = 0;
+        final byte[] buffer = new byte[1024];
+        ByteArrayOutputStream out = new ByteArrayOutputStream();
+        InputStream inputStream = savedBlob.getContentStream();
+        while ((len = inputStream.read(buffer)) != -1) {
+            out.write(buffer, 0, len);
+        }
+        byte[] readBytes = out.toByteArray();
+        assertTrue(Arrays.equals(bytes, readBytes));
+    }
+
     @Test
     public void testBlobConstructorsWithEmptyArgs() throws Exception {
         byte[] bytes;

shared/src/main/java/com/couchbase/lite/Blob.java

@@ -535,7 +535,7 @@ public int read(byte[] b) throws IOException {
             try {
                 byte[] bytes = readStream.read(b.length);
                 System.arraycopy(bytes, 0, b, 0, bytes.length);
-                if (bytes.length >= 0)
+                if (bytes.length > 0)
                     return bytes.length;
                 else
                     return -1;
@@ -549,7 +549,7 @@ public int read(byte[] b, int off, int len) throws IOException {
             try {
                 byte[] bytes = readStream.read(len);
                 System.arraycopy(bytes, 0, b, off, bytes.length);
-                if (bytes.length >= 0)
+                if (bytes.length > 0)
                     return bytes.length;
                 else
                     return -1;