feat: Update SQS message size limit from 256 KB to 1 MB (#136)

* Fix typo in documentation

* feat: Update SQS message size limit from 256 KB to 1 MB

AWS increased the SQS message size limit from 256 KB to 1 MB on Aug 4, 2025.
This commit updates our code to reflect this change:

- MAX_MESSAGE_LENGTH constant updated from 262144 to 1048576 bytes
- Documentation updated to reference 1 MB instead of 256 KB
- Tests adjusted to work with the new limit
- Added xfail for localstack tests as ElasticMQ still uses the old limit

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

---------

Co-authored-by: Claude <noreply@anthropic.com>

Author: Schnouki

README.md

@@ -108,7 +108,7 @@ When batching is enabled:
 
 - tasks are added to SQS by batches of 10, reducing the number of AWS operations
 - it is not possible to get the task `MessageId`, as it is not known until the batch is sent
-- care has to be taken about message size, as SQS limits both the individual message size and the maximum total payload size to 256 kB.
+- care has to be taken about message size, as SQS limits both the individual message size and the maximum total payload size to 1 MB.
 
 ## Batch Reads
 
@@ -507,7 +507,7 @@ Localstack tests should perform faster than testing against AWS, and besides, th
 Run [ElasticMQ](https://github.com/softwaremill/elasticmq) and make sure that the SQS endpoint is available by the address localhost:4566:
 
 ```bash
-uv run -p 4566:9324 --rm -it softwaremill/elasticmq-native
+docker run -p 4566:9324 --rm -it softwaremill/elasticmq-native
 ```
 
 Then run

sqs_workers/queue.py

@@ -28,7 +28,7 @@
 
 DEFAULT_MESSAGE_GROUP_ID = "default"
 SEND_BATCH_SIZE = 10
-MAX_MESSAGE_LENGTH = 262144  # 256 KiB
+MAX_MESSAGE_LENGTH = 1048576  # 1 MiB (since Aug 4, 2025)
 
 if TYPE_CHECKING:
     from collections.abc import Generator, Iterable

tests/test_sqs.py

@@ -4,6 +4,7 @@
 import time
 
 import botocore
+import localstack_client.session
 import pytest
 
 from sqs_workers import (
@@ -157,17 +158,19 @@ def test_batch_should_keep_messages_until_overflow(sqs, queue_name):
     assert len(queue.get_raw_messages(0)) == 1
 
 
-def test_batch_flush_on_large_messages(sqs, queue_name):
+def test_batch_flush_on_large_messages(sqs_session, sqs, queue_name):
+    if isinstance(sqs_session, localstack_client.session.Session):
+        pytest.xfail("ElasticMQ still has the old 256 KiB message limit")
+
     queue = sqs.queue(queue_name)
     say_hello_task = queue.connect_processor("say_hello", say_hello)
 
-    # 256KiB is our message limit
+    # 1 MiB is our message limit
     with say_hello_task.batch():
         # no messages after 9 tasks
         for n in range(9):
-            # each message is approx 32427 Bytes
-            say_hello_task.delay(username=f"Homer {n} 🍩" * 1_000_000)
-        # first 9 items is ~283651 Bytes so flush is triggered
+            say_hello_task.delay(username=f"Homer {n} 🍩" * 4_000_000)
+        # first 9 items is ~1.1 MiB so flush is triggered
         # and we walk back 1 item
         assert len(queue.get_raw_messages(0)) == 8
 
@@ -182,11 +185,11 @@ def test_batch_fails_on_a_giant_message(sqs_session, sqs, queue_name):
     queue = sqs.queue(queue_name)
     say_hello_task = queue.connect_processor("say_hello", say_hello)
 
-    # 262144 Bytes is our message limit
+    # 1 MiB is our message limit
     with say_hello_task.batch():
         with pytest.raises(botocore.exceptions.ClientError) as excinfo:
-            # message ~264087 bytes long
-            say_hello_task.delay(username="Homer 🍩" * 10_150_000)
+            # message exceeds 1 MiB limit
+            say_hello_task.delay(username="Homer 🍩" * 40_600_000)
         assert "MessageTooLong" in str(excinfo.value)