feat: add default stream support for StreamWriter (#744)

* fix: a race condition in test

* .

* .

* fix: allow default stream name to StreamWriter

* .

Author: yirutang

google-cloud-bigquerystorage/src/main/java/com/google/cloud/bigquery/storage/v1beta2/StreamWriter.java

@@ -82,7 +82,7 @@ public class StreamWriter implements AutoCloseable {
   private static final Logger LOG = Logger.getLogger(StreamWriter.class.getName());
 
   private static String streamPatternString =
-      "(projects/[^/]+/datasets/[^/]+/tables/[^/]+)/streams/[^/]+";
+      "(projects/[^/]+/datasets/[^/]+/tables/[^/]+)/(streams/[^/]+|_default)";
 
   private static Pattern streamPattern = Pattern.compile(streamPatternString);
 

google-cloud-bigquerystorage/src/test/java/com/google/cloud/bigquery/storage/v1beta2/StreamWriterTest.java

@@ -58,6 +58,7 @@
 public class StreamWriterTest {
   private static final Logger LOG = Logger.getLogger(StreamWriterTest.class.getName());
   private static final String TEST_STREAM = "projects/p/datasets/d/tables/t/streams/s";
+  private static final String TEST_DEFAULT_STREAM = "projects/p/datasets/d/tables/t/_default";
   private static final ExecutorProvider SINGLE_THREAD_EXECUTOR =
       InstantiatingExecutorProvider.newBuilder().setExecutorThreadCount(1).build();
   private static LocalChannelProvider channelProvider;
@@ -102,6 +103,10 @@ private StreamWriter.Builder getTestStreamWriterBuilder() {
     return getTestStreamWriterBuilder(TEST_STREAM);
   }
 
+  private StreamWriter.Builder getDefaultTestStreamWriterBuilder() {
+    return getTestStreamWriterBuilder(TEST_DEFAULT_STREAM);
+  }
+
   private AppendRowsRequest createAppendRequest(String[] messages, long offset) {
     AppendRowsRequest.Builder requestBuilder = AppendRowsRequest.newBuilder();
     AppendRowsRequest.ProtoData.Builder dataBuilder = AppendRowsRequest.ProtoData.newBuilder();
@@ -143,6 +148,13 @@ public void testTableName() throws Exception {
     }
   }
 
+  @Test
+  public void testDefaultStream() throws Exception {
+    try (StreamWriter writer = getDefaultTestStreamWriterBuilder().build()) {
+      assertEquals("projects/p/datasets/d/tables/t", writer.getTableNameString());
+    }
+  }
+
   @Test
   public void testAppendByDuration() throws Exception {
     StreamWriter writer =