Allow path in URIs passed to newFileSystem (#1470)

* This makes it easier for users who start with a URI describing a full
path to get a FileSystem that can work with that path, since they no
longer have to needlessly remove the path from the URI.

Note that Oracle's description of newFileSystem [1] puts no restriction
on the passed URI.

[1]
https://docs.oracle.com/javase/7/docs/api/java/nio/file/FileSystems.html#newFileSystem(java.net.URI,%20java.util.Map)

google-cloud-contrib/google-cloud-nio/src/main/java/com/google/cloud/storage/contrib/nio/CloudStorageFileSystemProvider.java

@@ -170,14 +170,15 @@ public CloudStorageFileSystem getFileSystem(URI uri) {
   }
 
   /**
-   * Returns Cloud Storage file system, provided a URI with no path, e.g. {@code gs://bucket}.
+   * Returns Cloud Storage file system, provided a URI, e.g. {@code gs://bucket}.
+   * The URI can include a path component (that will be ignored).
    *
    * @param uri bucket and current working directory, e.g. {@code gs://bucket}
    * @param env map of configuration options, whose keys correspond to the method names of
    *     {@link CloudStorageConfiguration.Builder}. However you are not allowed to set the working
    *     directory, as that should be provided in the {@code uri}
-   * @throws IllegalArgumentException if {@code uri} specifies a user, query, fragment, or scheme is
-   *     not {@value CloudStorageFileSystem#URI_SCHEME}
+   * @throws IllegalArgumentException if {@code uri} specifies a port, user, query, or fragment, or
+   *     if scheme is not {@value CloudStorageFileSystem#URI_SCHEME}
    */
   @Override
   public CloudStorageFileSystem newFileSystem(URI uri, Map<String, ?> env) {
@@ -191,11 +192,10 @@ public CloudStorageFileSystem newFileSystem(URI uri, Map<String, ?> env) {
         CloudStorageFileSystem.URI_SCHEME, uri);
     checkArgument(
         uri.getPort() == -1
-            && isNullOrEmpty(uri.getPath())
             && isNullOrEmpty(uri.getQuery())
             && isNullOrEmpty(uri.getFragment())
             && isNullOrEmpty(uri.getUserInfo()),
-        "GCS FileSystem URIs mustn't have: port, userinfo, path, query, or fragment: %s",
+        "GCS FileSystem URIs mustn't have: port, userinfo, query, or fragment: %s",
         uri);
     CloudStorageUtil.checkBucket(uri.getHost());
     initStorage();

google-cloud-contrib/google-cloud-nio/src/test/java/com/google/cloud/storage/contrib/nio/CloudStorageFileSystemProviderTest.java

@@ -54,7 +54,9 @@
 import java.nio.file.OpenOption;
 import java.nio.file.Path;
 import java.nio.file.Paths;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 /**
  * Unit tests for {@link CloudStorageFileSystemProvider}.
@@ -644,6 +646,12 @@ public void testProviderEquals() {
     assertThat(path1.getFileSystem().provider()).isNotEqualTo(path3.getFileSystem().provider());
   }
 
+  @Test
+  public void testNewFileSystem() throws IOException {
+    Map<String,String> env = new HashMap<>();
+    FileSystems.newFileSystem(URI.create("gs://bucket/path/to/file"), env);
+  }
+
   private static CloudStorageConfiguration permitEmptyPathComponents(boolean value) {
     return CloudStorageConfiguration.builder().permitEmptyPathComponents(value).build();
   }