fix: do not cause a failure when encountering no bindings (#1177)

Thank you for opening a Pull Request! Before submitting your PR, there are a few things you can do to make sure it goes smoothly: - [x] Make sure to open an issue as a [bug/issue](https://github.com/googleapis/java-storage/issues/new/choose) before writing your code! That way we can discuss the change, evaluate designs, and agree on the general idea - [x] Ensure the tests and linter pass - [x] Appropriate docs were updated (if necessary) Fixes #1175 ☕️

Author: frankyn

google-cloud-storage/src/main/java/com/google/cloud/storage/PolicyHelper.java

@@ -34,8 +34,8 @@ class PolicyHelper {
  static Policy convertFromApiPolicy(com.google.api.services.storage.model.Policy apiPolicy) {
  Policy.Builder policyBuilder = Policy.newBuilder();
  List<Bindings> bindings = apiPolicy.getBindings();
+ ImmutableList.Builder<Binding> coreBindings = ImmutableList.builder();
  if (null != bindings && !bindings.isEmpty()) {
- ImmutableList.Builder<Binding> coreBindings = ImmutableList.builder();
  for (Bindings binding : bindings) {
  Binding.Builder bindingBuilder = Binding.newBuilder();
  bindingBuilder.setRole(binding.getRole());
@@ -49,10 +49,8 @@ static Policy convertFromApiPolicy(com.google.api.services.storage.model.Policy
  }
  coreBindings.add(bindingBuilder.build());
  }
- policyBuilder.setBindings(coreBindings.build());
- } else {
- throw new IllegalStateException("Missing required bindings.");
  }
+ policyBuilder.setBindings(coreBindings.build());
  return policyBuilder.setEtag(apiPolicy.getEtag()).setVersion(apiPolicy.getVersion()).build();
  }
 

google-cloud-storage/src/main/java/com/google/cloud/storage/Storage.java

@@ -3540,6 +3540,11 @@ HmacKeyMetadata updateHmacKeyState(
  /**
  * Gets the IAM policy for the provided bucket.
  *
+ * <p>It's possible for bindings to be empty and instead have permissions inherited through
+ * Project or Organization IAM Policies. To prevent corrupting policies when you update an IAM
+ * policy with {@code Storage.setIamPolicy}, the ETAG value is used to perform optimistic
+ * concurrency.
+ *
  * <p>Example of getting the IAM policy for a bucket.
  *
  * <pre>{@code
@@ -3556,6 +3561,9 @@ HmacKeyMetadata updateHmacKeyState(
  /**
  * Updates the IAM policy on the specified bucket.
  *
+ * <p>To prevent corrupting policies when you update an IAM policy with {@code
+ * Storage.setIamPolicy}, the ETAG value is used to perform optimistic concurrency.
+ *
  * <p>Example of updating the IAM policy on a bucket.
  *
  * <pre>{@code

google-cloud-storage/src/test/java/com/google/cloud/storage/PolicyHelperTest.java

@@ -65,11 +65,15 @@ public void testEquivalence() {
  assertTrue(new ApiPolicyMatcher(apiPolicy).matches(actualApiPolicy));
  }
 
- @Test(expected = IllegalStateException.class)
+ @Test
  public void testApiPolicyWithoutBinding() {
  List<Bindings> bindings = null;
  com.google.api.services.storage.model.Policy apiPolicy =
- new com.google.api.services.storage.model.Policy().setBindings(bindings).setEtag(ETAG);
- PolicyHelper.convertFromApiPolicy(apiPolicy);
+ new com.google.api.services.storage.model.Policy()
+ .setBindings(bindings)
+ .setEtag(ETAG)
+ .setVersion(1);
+ Policy policy = PolicyHelper.convertFromApiPolicy(apiPolicy);
+ assertEquals(policy.getBindings().size(), 0);
  }
 }