Prevent duplicate downloads in DownloadHelper

This change modifies `DownloadHelper` to check if a URL is already
scheduled for download (in pending, running, or paused status) before
enqueuing a new request. If a download for the same URL is found, the
existing download ID is returned, avoiding redundant requests to the
`DownloadManager`.

Bug: 437217681
Test: atest NetworkSecurityUnitTests
Flag: EXEMPT BUGFIX
Change-Id: I64dd5473b4fdb23241f5e2503c65cb64db56617c

networksecurity/service/src/com/android/server/net/ct/DownloadHelper.java

@@ -25,6 +25,7 @@ import android.net.Uri;
 import androidx.annotation.VisibleForTesting;
 
 import com.google.auto.value.AutoValue;
+import java.util.Objects;
 
 /** Class to handle downloads for Certificate Transparency. */
 public class DownloadHelper {
@@ -47,6 +48,10 @@ public class DownloadHelper {
      * @return a downloadId if the request was created successfully, -1 otherwise.
      */
     public long startDownload(String url) {
+        long downloadId = isUrlAlreadyScheduled(url);
+        if (downloadId != -1) {
+            return downloadId;
+        }
         return mDownloadManager.enqueue(
                 new Request(Uri.parse(url))
                         .setAllowedOverRoaming(false)
@@ -54,6 +59,33 @@ public class DownloadHelper {
                         .setRequiresCharging(true));
     }
 
+    private long isUrlAlreadyScheduled(String url) {
+        try (Cursor cursor =
+                mDownloadManager.query(
+                        new Query()
+                                .setFilterByStatus(
+                                        DownloadManager.STATUS_PENDING
+                                                | DownloadManager.STATUS_RUNNING
+                                                | DownloadManager.STATUS_PAUSED))) {
+            if (cursor == null) {
+                return -1;
+            }
+            for (cursor.moveToFirst(); !cursor.isAfterLast(); cursor.moveToNext()) {
+                int idIndex = cursor.getColumnIndex(DownloadManager.COLUMN_ID);
+                int uriIndex = cursor.getColumnIndex(DownloadManager.COLUMN_URI);
+                if (idIndex == -1 || uriIndex == -1) {
+                    continue;
+                }
+                long downloadId = cursor.getLong(idIndex);
+                String uri = cursor.getString(uriIndex);
+                if (Objects.equals(uri, url)) {
+                    return downloadId;
+                }
+            }
+        }
+        return -1;
+    }
+
     /**
      * Returns the status of the provided download id.
      *
@@ -67,7 +99,7 @@ public class DownloadHelper {
                 builder.setStatus(
                         cursor.getInt(cursor.getColumnIndexOrThrow(DownloadManager.COLUMN_STATUS)));
                 builder.setReason(
-                        cursor.getInt(cursor.getColumnIndex(DownloadManager.COLUMN_REASON)));
+                        cursor.getInt(cursor.getColumnIndexOrThrow(DownloadManager.COLUMN_REASON)));
             }
         }
         return builder.build();

networksecurity/tests/unit/src/com/android/server/net/ct/DownloadHelperTest.java

@@ -23,6 +23,7 @@ import static org.mockito.Mockito.when;
 
 import android.app.DownloadManager;
 
+import android.database.MatrixCursor;
 import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
@@ -53,6 +54,21 @@ public class DownloadHelperTest {
         assertThat(mDownloadHelper.startDownload("http://test.org")).isEqualTo(downloadId);
     }
 
+    @Test
+    public void testDownloadHelper_multipleDownloads_doesNotRescheduleDuplicates() {
+        long downloadId1 = 666;
+        String url1 = "http://test1.org";
+        long downloadId2 = 777;
+        String url2 = "http://test2.org";
+        when(mDownloadManager.enqueue(any())).thenReturn(downloadId1, downloadId2);
+
+        assertThat(mDownloadHelper.startDownload(url1)).isEqualTo(downloadId1);
+        mockPendingDownload(downloadId1, url1);
+
+        assertThat(mDownloadHelper.startDownload(url2)).isEqualTo(downloadId2);
+        assertThat(mDownloadHelper.startDownload(url1)).isEqualTo(downloadId1);
+    }
+
     @Test
     public void testDownloadHelper_wrongUri() {
         when(mDownloadManager.enqueue(any())).thenReturn(666L);
@@ -60,4 +76,17 @@ public class DownloadHelperTest {
         assertThrows(
                 IllegalArgumentException.class, () -> mDownloadHelper.startDownload("not_a_uri"));
     }
+
+    private void mockPendingDownload(long downloadId, String url) {
+        MatrixCursor cursor =
+                new MatrixCursor(
+                        new String[] {
+                            DownloadManager.COLUMN_ID,
+                            DownloadManager.COLUMN_URI,
+                            DownloadManager.COLUMN_STATUS
+                        });
+        cursor.addRow(new Object[] {downloadId, url, DownloadManager.STATUS_PENDING});
+
+        when(mDownloadManager.query(any())).thenReturn(cursor);
+    }
 }