NullPointerException from SnsInterceptor when publishing an SNS batch without a topic ARN

v1 と v2 の SnsInterceptor の batch パスと、既存の「SNS message to phone number doesn't leak exception」テストを調査します。aws-java-sns-1.0 と aws-java-sns-2.0 のテストタスクを実行します。topic ARN を含まない batch リクエストが agent NPE をスローするのではなく、SDK の検証エラーに到達すれば完了です。

Tracer Version(s)

1.66.0

Java Version(s)

25.0.2

JVM Vendor

Eclipse Adoptium / Temurin

Bug Report

SnsInterceptor derives the DSM topic name from the topic ARN. The single-publish path handles a missing ARN, because a publish to a phone number has neither topicArn nor targetArn:

String snsTopicArn = request.topicArn();
if (null == snsTopicArn) {
  snsTopicArn = request.targetArn();
  if (null == snsTopicArn) {
    return context.request();
  }
}

The batch path dereferences it straight away:

String snsTopicArn = request.topicArn();
String snsTopicName = snsTopicArn.substring(snsTopicArn.lastIndexOf(':') + 1);

PublishBatchRequest builds without a topic ARN, and the interceptor runs before marshalling, so a request that the SDK would have rejected with a validation error instead dies with an NPE thrown from the agent. Neither SDK wraps exceptions from modifyRequest (v2) or beforeMarshalling (v1), so it reaches the caller as-is:

java.lang.NullPointerException: Cannot invoke "String.lastIndexOf(int)" because "snsTopicArn" is null
	at datadog.trace.instrumentation.aws.v2.sns.SnsInterceptor.modifyRequest

Both the v1 and v2 interceptors have it. I checked the other ARN parsing in the aws-java modules while I was there: AwsSdkClientDecorator guards it in v1 (if (null != topicArn)) and uses Optional.map in v2, so these two batch branches were the only unguarded ones.

Fix is up as #12457. It skips the injection and leaves the request alone, matching what the single-publish path already does. Tests mirror the existing SNS message to phone number doesn't leak exception case, and the aws-java-sns-1.0 and aws-java-sns-2.0 test tasks pass.

Filing this as an issue as well so it can be triaged and labelled. I can't set the inst:/type: labels on the PR myself.

Expected Behavior

A batch publish without a topic ARN should fail the way the SDK would fail it on its own, with a validation error. The agent should not turn it into an NPE.

Reproduction Code

SnsClient client = SnsClient.builder()
    .endpointOverride(URI.create("http://localhost:4566"))
    .region(Region.US_EAST_1)
    .build();

client.publishBatch(PublishBatchRequest.builder()
    .publishBatchRequestEntries(
        PublishBatchRequestEntry.builder().id("1").message("hello").build())
    .build());

With the agent attached this throws NullPointerException from SnsInterceptor. Without it, the SDK reports the missing topic.