fix: json syntax exception

lib/src/main/java/com/nextcloud/android/sso/aidl/ParcelFileDescriptorUtil.java

@@ -16,6 +16,8 @@
 
 public class ParcelFileDescriptorUtil {
 
+    private static final int BUFFER_SIZE = 1024;
+
     private ParcelFileDescriptorUtil() { }
 
     public static ParcelFileDescriptor pipeFrom(InputStream inputStream, IThreadListener listener)
@@ -61,7 +63,7 @@ static class TransferThread extends Thread {
 
         @Override
         public void run() {
-            byte[] buf = new byte[1024];
+            byte[] buf = new byte[BUFFER_SIZE];
             int len;
 
             try {

lib/src/main/java/com/nextcloud/android/sso/api/NextcloudAPI.java

@@ -23,6 +23,7 @@
 import com.nextcloud.android.sso.exceptions.SSOException;
 import com.nextcloud.android.sso.model.SingleSignOnAccount;
 
+import java.io.BufferedReader;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.InputStreamReader;
@@ -37,8 +38,8 @@
 
 public class NextcloudAPI implements AutoCloseable {
 
+    private static final int PEEK_LIMIT = 64;
     private static final String TAG = NextcloudAPI.class.getCanonicalName();
-
     private static final EmptyResponse EMPTY_RESPONSE = new EmptyResponse();
 
     private final NetworkRequest networkRequest;
@@ -127,27 +128,55 @@ public <T> T convertStreamToTargetEntity(InputStream inputStream, Type targetEnt
         ensureTypeNotVoid(targetEntity);
 
         final T result;
-        try (InputStream os = inputStream;
-             Reader targetReader = new InputStreamReader(os)) {
-            if (targetEntity == EmptyResponse.class) {
+
+        try (BufferedReader reader = new BufferedReader(new InputStreamReader(inputStream))) {
+            reader.mark(PEEK_LIMIT);
+            boolean empty = isReaderContainsEmptyResponse(reader);
+            reader.reset();
+
+            if (targetEntity == EmptyResponse.class || empty) {
                 //noinspection unchecked
-                result = (T) EMPTY_RESPONSE;
-            } else {
-                result = gson.fromJson(targetReader, targetEntity);
-                if (result == null) {
-                    if (targetEntity == Object.class) {
-                        //noinspection unchecked
-                        return (T) EMPTY_RESPONSE;
-                    } else {
-                        throw new IllegalStateException("Could not instantiate \"" +
-                                targetEntity + "\", because response was null.");
-                    }
+                return (T) EMPTY_RESPONSE;
+            }
+
+            result = gson.fromJson(reader, targetEntity);
+
+            if (result == null) {
+                if (targetEntity == Object.class) {
+                    //noinspection unchecked
+                    return (T) EMPTY_RESPONSE;
+                } else {
+                    throw new IllegalStateException("Could not instantiate \"" +
+                        targetEntity + "\", because response was null.");
                 }
             }
         }
+
         return result;
     }
 
+    public boolean isReaderContainsEmptyResponse(Reader reader) throws IOException {
+        reader.mark(PEEK_LIMIT);
+        try {
+            int c;
+            int count = 0;
+            while ((c = reader.read()) != -1 && count < PEEK_LIMIT) {
+                if (c != '\u0000' && !Character.isWhitespace(c)) {
+                    // Found meaningful character
+                    return false;
+                }
+                count++;
+            }
+            return true;
+        } finally {
+            try {
+                reader.reset();
+            } catch (Exception e) {
+                // Ignored
+            }
+        }
+    }
+
     /**
      * The InputStreams needs to be closed after reading from it
      *

lib/src/test/java/com/nextcloud/android/sso/api/TestRetrofitAPI.java

@@ -11,9 +11,10 @@
  */
 package com.nextcloud.android.sso.api;
 
-import static junit.framework.TestCase.assertTrue;
 import static junit.framework.TestCase.fail;
+import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNotEquals;
+import static org.junit.Assert.assertTrue;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.ArgumentMatchers.eq;
 import static org.mockito.Mockito.doAnswer;
@@ -34,6 +35,8 @@
 import org.mockito.junit.MockitoRule;
 
 import java.io.IOException;
+import java.io.Reader;
+import java.io.StringReader;
 import java.lang.reflect.Type;
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -75,6 +78,8 @@ public void setUp() throws Exception {
         lenient().when(nextcloudApiMock.getGson()).thenReturn(new GsonBuilder().create());
         lenient().when(nextcloudApiMock.performRequestObservableV2(any(), any())).thenReturn(Observable.empty());
         lenient().when(nextcloudApiMock.performNetworkRequestV2(any())).thenReturn(new com.nextcloud.android.sso.api.Response(null, null));
+        lenient().when(nextcloudApiMock.isReaderContainsEmptyResponse(any()))
+            .thenCallRealMethod();
         mApi = new NextcloudRetrofitApiBuilder(nextcloudApiMock, mApiEndpoint).create(API.class);
     }
 
@@ -538,4 +543,31 @@ public void testEnqueue() throws InterruptedException {
         assertTrue(successful);
     }
 
+    @Test
+    public void testValidJson() throws IOException {
+        String json = "{\"name\": \"value\", \"type\": \"value_2\"}";
+        Reader reader = new StringReader(json);
+        assertFalse(nextcloudApiMock.isReaderContainsEmptyResponse(reader));
+    }
+
+    @Test
+    public void testValidXml() throws IOException {
+        String xml = "<note><to>User</to><from>User2</from></note>";
+        Reader reader = new StringReader(xml);
+        assertFalse(nextcloudApiMock.isReaderContainsEmptyResponse(reader));
+    }
+
+    @Test
+    public void testOnlyNulls() throws IOException {
+        String nulls = "\u0000\u0000\u0000\u0000\u0000   \n\t"; // nulls + whitespace
+        Reader reader = new StringReader(nulls);
+        assertTrue(nextcloudApiMock.isReaderContainsEmptyResponse(reader));
+    }
+
+    @Test
+    public void testWhitespaceOnly() throws IOException {
+        String whitespace = "   \n\t  ";
+        Reader reader = new StringReader(whitespace);
+        assertTrue(nextcloudApiMock.isReaderContainsEmptyResponse(reader));
+    }
 }