Read max-message-batch-size vendor property for batch sizing

sdk/servicebus/azure-messaging-servicebus/src/main/java/com/azure/messaging/servicebus/ServiceBusSenderAsyncClient.java

@@ -222,6 +222,16 @@ public final class ServiceBusSenderAsyncClient implements AutoCloseable {
      * The default maximum allowable size, in bytes, for a batch to be sent.
      */
     static final int MAX_MESSAGE_LENGTH_BYTES = 256 * 1024;
+    // Temporary workaround: Service Bus enforces a maximum batch payload size of 1 MB that is not
+    // communicated via the AMQP link's max-message-size property. The link reports the per-message
+    // limit (up to 100 MB for Premium partitioned), but the broker rejects batch sends above 1 MB.
+    // This cap is applied only in createMessageBatch(), which is the single enforcement point for
+    // batch size limits. The sendMessages(iterable) and scheduleMessages(iterable) paths use
+    // createMessageBatch() internally and are therefore also capped. Single-message paths
+    // (sendMessage, scheduleMessage) are not capped since individual messages on Premium can
+    // validly exceed 1 MB up to the per-entity limit.
+    // Tracked by: https://github.com/Azure/azure-service-bus/issues/708
+    static final int MAX_BATCH_SIZE_BYTES = 1024 * 1024;
     private static final String TRANSACTION_LINK_NAME = "coordinator";
     private static final ServiceBusMessage END = new ServiceBusMessage(new byte[0]);
     private static final CreateMessageBatchOptions DEFAULT_BATCH_OPTIONS = new CreateMessageBatchOptions();
@@ -463,15 +473,15 @@ public Mono<ServiceBusMessageBatch> createMessageBatch(CreateMessageBatchOptions
         final int maxSize = options.getMaximumSizeInBytes();
 
         return getSendLinkWithRetry("create-batch").flatMap(link -> link.getLinkSize().flatMap(size -> {
-            final int maximumLinkSize = size > 0 ? size : MAX_MESSAGE_LENGTH_BYTES;
+            final int maximumLinkSize = Math.min(size > 0 ? size : MAX_MESSAGE_LENGTH_BYTES, MAX_BATCH_SIZE_BYTES);
             if (maxSize > maximumLinkSize) {
                 return monoError(logger,
                     new IllegalArgumentException(String.format(Locale.US,
-                        "CreateMessageBatchOptions.getMaximumSizeInBytes (%s bytes) is larger than the link size"
-                            + " (%s bytes).",
+                        "CreateMessageBatchOptions.getMaximumSizeInBytes (%s bytes) is larger than the maximum"
+                            + " allowed size (%s bytes).",
                         maxSize, maximumLinkSize)));
             }
-            final int batchSize = maxSize > 0 ? maxSize : maximumLinkSize;
+            final int batchSize = maxSize > 0 ? Math.min(maxSize, maximumLinkSize) : maximumLinkSize;
             return Mono
                 .just(new ServiceBusMessageBatch(isV2, batchSize, link::getErrorContext, tracer, messageSerializer));
         })).onErrorMap(this::mapError);