[BUG] autobahn flatbuffers support requires nonexisting `autobahn.flatbuffers`

[mgorny]

Bug Description

Summary: autobahn flatbuffers serializer expects autobahn.flatbuffers which doesn't exist

Expected Behavior:
Working flatbuffers serializer. Or tests passing.

Actual Behavior:

autobahn-python/src/autobahn/wamp/serializer.py

Lines 1034 to 1041 in 60f226c

	_HAS_FLATBUFFERS = False
	try:
	from autobahn import flatbuffers # noqa
	from autobahn.wamp import message_fbs
	except ImportError:
	pass
	else:
	_HAS_FLATBUFFERS = True

expects autobahn.flatbuffers. However, there is no such module. There is autobahn.wamp.flatbuffers package but it isn't installed correctly either (it only installs .fbs files). As a result, the test suite is failing:

===============================================================================
[ERROR]
Traceback (most recent call last):
  File "/usr/lib/python3.11/unittest/case.py", line 57, in testPartExecutor
    yield
  File "/usr/lib/python3.11/unittest/case.py", line 623, in run
    self._callTestMethod(testMethod)
  File "/usr/lib/python3.11/unittest/case.py", line 579, in _callTestMethod
    if method() is not None:
  File "/tmp/portage/dev-python/autobahn-25.12.1/work/autobahn-25.12.1-python3_11/install/usr/lib/python3.11/site-packages/autobahn/wam
p/test/test_wamp_serializer.py", line 264, in test_basic
    ser = serializer.FlatBuffersSerializer()
builtins.AttributeError: module 'autobahn.wamp.serializer' has no attribute 'FlatBuffersSerializer'

autobahn.wamp.test.test_wamp_serializer.TestFlatBuffersSerializer.test_basic

Reproduction Steps

1. pip install autobahn
2. python -c 'import autobahn.wamp.serializer; print(autobahn.wamp.serializer._HAS_FLATBUFFERS)'

Environment

• Package: autobahn-python
• Version: 25.12.1
• Python Version: n/a
• Operating System: n/a
• Framework: n/a

Additional Context

n/a

Checklist

• I have searched existing issues to avoid duplicates
• I have provided a minimal reproducible example
• I have included version information
• I have included error messages/logs

[sjlongland]

Looks like there is a autobahn.flatbuffers module, but it's excluded:

https://github.com/crossbario/autobahn-python/blob/master/pyproject.toml#L270

[oberstet]

yes, true, this isn't right yet - autobahn-python will follow what zlmdb will do, which is to properly bundle upstream flatbuffers - both in native wheels (flatc) as well as in sdists to build from source. why & how? latest flatbuffers upstream, and flatc fully in sync with run-time flatbuffers reflection. please see my comment here: #1816 (comment)

[oberstet]

fixed via #1822

[oberstet]

Update: FlatBuffers vendoring verification implemented ✅

We've now implemented comprehensive verification for the vendored FlatBuffers in autobahn-python (and zlmdb). Here's what's in place:

Smoke Tests for Package Verification

Every wheel and sdist build is now verified via scripts/smoke_test_flatc.py which runs three required tests:

1. test_import_flatbuffers() - Verifies autobahn.flatbuffers imports correctly and reports its version
2. test_flatc_binary() - Verifies the bundled flatc compiler:
   - Binary exists and is executable
   - flatc --version returns expected output
   - flatc version matches the vendored runtime version (e.g., both are 25.9.23)
3. test_reflection_files() - Verifies reflection.fbs and reflection.bfbs are present

These tests run in CI for both wheel installs (just test-wheel-install) and sdist installs (just test-sdist-install).

Cross-Project Version Synchronization

For applications using both autobahn (data-in-transit) and zlmdb (data-at-rest) with FlatBuffers serialization (like Crossbar.io), we've added a runtime check:

import autobahn

Raises RuntimeError if versions differ

version = autobahn.check_zlmdb_flatbuffers_version_in_sync()
print(f"FlatBuffers version: {version}") # e.g., (25, 9, 23, 2, "95053e6a")

This ensures both libraries use compatible FlatBuffers runtimes, preventing subtle serialization issues when sending database records as WAMP payloads.

Version Function

Both autobahn.flatbuffers and zlmdb.flatbuffers now expose a version() function:

from autobahn import flatbuffers
print(flatbuffers.version()) # (25, 9, 23, 2, "95053e6a")

Returns: (major, minor, patch, local_version, commit_hash)

Shared Test Infrastructure

The smoke test module (scripts/smoke_test_flatc.py) is shared across WAMP ecosystem projects via wamp-cicd, ensuring consistent verification.

---

This will be released in v25.12.2 (pending CI green + tag push).