Release Notes¶

0.9.3¶

Make compatible in Python 3.9 by addressing deprecation issues.

0.9.2¶

Consistent error message in py2 and py3 for error in Timestamp decode

0.9.1¶

Fix issues in KATCPReply __repr__ in py3

0.9.0¶

Add asyncio compatible ioloop to ioloop manager.

0.8.0¶

Added bulk sensor sampling feature.

0.7.2¶

Support for handling generator expressions in Discrete type.
Fix handling of strings and bytes in get_sensor in testutils.
Allow strings or bytes for assert_request_fails and test_assert_request_succeeds function arguments.
Handle str type correctly (‘easier’) in testutils.get_sensor for python 2 and python 3.
Allow bytes and strings in test_sensor_list comparison of sensors.
Correct handling of floats test_sensor_list.
black formatting on certain test files.

0.7.1¶

All params in future_get_sensor are now cast to byte strings.
Added tests to test_fake_clients.py and test_inspecting_client.py.
Ensure testutils method casts expected requests to byte strings.

0.7.0¶

Added Python 3 compatibility.

See also CHANGELOG.md for more details on changes.

Important changes for Python 3 compatibility¶

General notes¶

The package is now compatible with both Python 2 and 3. The goals of the migration were:

Do not change the public API.
Do not break existing functionality for Python 2.
Ease migration of packages using katcp to Python 3.

Despite these goals, some of the stricter type checking that has been added may force minor updates in existing code. E.g., using integer for the options of a discrete sensor is no longer allowed.

Asynchronous code is still using tornado in the same Python 2 way. The new Python 3.5 async and await keywords are not used. The tornado version is also pinned to older versions that support both Python 2 and 3. The 5.x versions also support Python 2, but they are avoided as some significant changes result in test failures.

The Python future package was used for the compatibility layer. The use of the newstr and newbytes compatibility types was avoided, to reduce confusion. I.e., from builtins import str, bytes is not done.

Docstrings¶

In docstrings the interpretation of parameter and return types described as “str” has changed slightly. In Python 2 the str type is a byte string, while in Python 3, str is a unicode string. The str type is referred to as the “native” string type. In code, native literal strings would have no prefix, for example: "native string", as opposed to explicit byte strings, b"byte string", and explicit unicode strings, u"unicode string". In the docstrings “bytes” means a byte string is expected (or returned), “str” means a native string, and “str or bytes” means either type.

Changes to types¶

As part of the Python 3 compatibility update, note the following:

katcp.Message. - arguments and mid attributes will be forced to byte strings in all Python versions. This is to match what is sent on the wire (serialised byte stream). - name: is expected to be a native string. - repr(): the result will differ slightly in Python 3 - the arguments will be shown as quoted byte strings. E.g., Python 2: "<Message reply ok (123, zzz)>", vs. Python 3: "<Message reply ok (b'123', b'zzz')>". In all versions, arguments longer than 1000 characters are now truncated.
katcp.Sensor. - name, description, units, params (for discrete sensors): __init__ can take byte strings or native strings, but attributes will be coerced to native strings. - set_formatted, parse_value: only accept byte strings (stricter checking). - The float and strict_timestamp sensor values are now encoded using repr() instead of "%.15g". This means that more significant digits are transmitted on the wire (16 to 17, instead of 15), and the client will be able to reconstruct the exact some floating point value.

Non-ASCII and UTF-8¶

Prior to these changes, all strings were byte strings, so there was no encoding required. Arbitrary bytes could be used for message parameters and string sensor values. After these changes, strings sensors and Str types are considered “text”. In Python 3, UTF-8 encoding will be used when changing between byte strings and unicode strings for “text”. This has the following effects:

katcp.Message - the arguments are always using byte strings, so arbitrary bytes can still be sent and received using this class directly.
katcp.Sensor - Values for string and discrete sensor types cannot be arbitrary byte strings in Python 3 - they need to be UTF-8 compatible.
kattypes.Str, kattypes.Discrete, kattypes.DiscreteMulti - These types is still used in request and reply decorators. - For sending messages, they accept any type of object, but UTF-8 encoding is used if values are not already byte strings. - When decoding received messages, “native” strings are returned.

Keep in mind that a Python 2 server may be communicating with a Python 3 client, so sticking to ASCII is safest. If you are sure both client and server are on Python 3 (or understand the encoding the same), then UTF-8 could be used. That is also the encoding option used by the aiokatcp package.

Performance degradation¶

Adding the compatibility results in more checks and conversions. From some basic benchmarking, there appears to be up to 20% performance degradation when instantiating message objects.

Benchmark, in ipython:

import random, katcp

args_groups = []
for i in range(1000):
    args_groups.append((random.randint(0, 1) == 1,
                        random.randint(0, 1000),
                        random.random(),
                        str(random.random())))

def benchmark():
    for args in args_groups:
        tx_msg = katcp.Message.reply('foo', *args)
        serialised = bytes(tx_msg)
        parser = katcp.MessageParser()
        rx_msg = parser.parse(serialised)
        assert tx_msg == rx_msg


%timeit benchmark()

Old Py2: 10 loops, best of 3: 23.4 ms per loop
New Py2: 10 loops, best of 3: 29.9 ms per loop
New Py3: 25.1 ms ± 86.8 µs per loop (mean ± std. dev. of 7 runs, 10 loops each)

0.6.4¶

Fix some client memory leaks, and add until_stopped methods.
Increase server MAX_QUEUE_SIZE to handle more clients.
Use correct ioloop for client AsyncEvent objects.

See also CHANGELOG.md for more details on changes.

Important API changes¶

Stopping KATCP clients¶

When stopping KATCP client classes that use a managed ioloop (i.e., create their own in a new thread), the traditional semantics are to call stop() followed by join() from another thread. This is unchanged. In the case of an unmanaged ioloop (i.e., an existing ioloop instance is provided to the client), we typically stop from the same thread, and calling join() does nothing. For the case of unmanaged ioloops, a new method, until_stopped(), has been added. It returns a future that resolves when the client has stopped. The caller can yield on this future to be sure that the client has completed all its coroutines. Using this new method is not required. If the ioloop will keep running, the stopped client’s coroutines will eventually exit. However, it is useful in some cases, e.g., to verify correct clean up in unit tests.

The new method is available on katcp.DeviceClient and derived classes, on katcp.inspecting_client.InspectingClientAsync, and on the high-level clients katcp.KATCPClientResource and katcp.KATCPClientResourceContainer.

An additional change is that the inspecting client now sends a state update (indicating that it is disconnected and not synced) when stopping. This means high-level clients that were waiting on until_not_synced when the client was stopped will now be notified. Previously, this was not the case.

0.6.3¶

Put docs on readthedocs.
Better error handling for messages with non-ASCII characters (invalid).
Increase container sync time to better support large containers.
Limit tornado version to <5.
Allow sampling strategy to be removed from cache.
Improve error messages for DeviceMetaClass assertions.
Increase server’s message queue length handle more simultaneous client connections.
Improve Jenkins pipeline configuration.
Add information on how to contribute to the project.

See also CHANGELOG.md for more details on changes.

0.6.2¶

Various bug fixes
Docstring and code style improvements
Bumped the tornado dependency to at least 4.3
Added the ability to let ClientGroup wait for a quorum of clients
Added default request-timeout-hint implementation to server.py
Moved IOLoopThreadWrapper to ioloop_manager.py, a more sensible location
Added a random-exponential retry backoff process

See also CHANGELOG.md for more details on changes.

0.6.1¶

Various bug fixes
Improvements to testing utilities
Improvements to various docstrings
Use katversion to determine version string on install
Better dependency management using setup.py with setuptools
Fixed a memory leak when using KATCPResourceContainer

See also CHANGELOG.md for more details on changes.

0.6.0¶

Major change: Use the tornado event loop and async socket routines.

See also CHANGELOG.md for more details on changes.

Important API changes¶

Tornado based event loop(s)¶

While the networking stack and event loops have been re-implemented using Tornado, this change should be largely invisible to existing users of the library. All client and server classes now expose an ioloop attribute that is the tornado.ioloop.IOLoop instance being used. Unless new server or client classes are used or default settings are changed, the thread-safety and concurrency semantics of 0.5.x versions should be retained. User code that made use of non-public interfaces may run into trouble.

High level auto-inspecting KATCP client APIs added¶

The high level client API inspects a KATCP device server and present requests as method calls and sensors as objects. See Using the high-level client API.

Sensor observer API¶

The katcp.Sensor sensor observer API has been changed to pass the sensor reading in the observer.update() callback, preventing potential lost updates due to race conditions. This is a backwards incompatible change. Whereas before observers were called as observer.update(sensor), they are now called as observer.update(sensor, reading), where reading is an instance of katcp.core.Reading.

Sample Strategy callback API¶

Sensor strategies now call back with the sensor object and raw Python datatype values rather than the sensor name and KATCP formatted values. The sensor classes have also grown a katcp.Sensor.format_reading() method that can be used to do KATCP-version specific formatting of the sensor reading.

0.5.5¶

Various cleanups (logging, docstrings, base request set, minor refactoring)
Improvements to testing utilities
Convenience utility functions in katcp.version, katcp.client, katcp.testutils.

0.5.4¶

Change event-rate strategy to always send an update if the sensor has changed and shortest-period has passed.
Add differential-rate strategy.

0.5.3¶

Add convert_seconds() method to katcp client classes that converts seconds into the device timestamp format.

0.5.2¶

Fix memory leak in sample reactor, other minor fixes.

0.5.1¶

Minor bugfixes and stability improvements

0.5.0¶

First stable release supporting (a subset of) KATCP v5. No updates apart from documentation since 0.5.0a0; please refer to the 0.5.0a release notes below.

0.5.0a0¶

First alpha release supporting (a subset of) KATCP v5. The KATCP v5 spec brings a number of backward incompatible changes, and hence requires care. This library implements support for both KATCP v5 and for the older dialect. Some API changes have also been made, mainly in aid of fool-proof support of the Message ID feature of KATCP v5. The changes do, however, also eliminate a category of potential bugs for older versions of the spec.

Important API changes¶

CallbackClient.request()¶

Renamed request() to callback_request() to be more consistent with superclass API.

Sending replies and informs in server request handlers¶

The function signature used for request handler methods in previous versions of this library were request_requestname(self, sock, msg), where sock is a raw python socket object and msg is a katcp Message object. The sock object was never used directly by the request handler, but was passed to methods on the server to send inform or reply messages.

Before:

class MyServer(DeviceServer):
    def request_echo(self, sock, msg):
        self.inform(sock, Message.inform('echo', len(msg.arguments)))
        return Message.reply('echo', 'ok', *msg.arguments)

The old method requires the name of the request to be repeated several times, inviting error and cluttering code. The user is also required to instantiate katcp Message object each time a reply is made. The new method passes a request-bound connection object that knows to what request it is replying, and that automatically constructs Message objects.

Now:

class MyServer(DeviceServer):
    def request_echo(self, req, msg):
        req.inform(len(msg.arguments)))
        return req.make_reply('ok', *msg.arguments)

A req.reply() method with the same signature as req.make_reply() is also available for asyncronous reply handlers, and req.reply_with_message() which takes a Message instance rather than message arguments. These methods replace the use of DeviceServer.reply().

The request object also contains the katcp request Message object (req.msg), and the equivalent of a socket object (req.client_connection). See the next section for a description of client_connection.

Using the server methods with a req object in place of sock will still work as before, but will log deprecation warnings.

Connection abstraction¶

Previously, the server classes internally used each connection’s low-level sock object as an identifier for the connection. In the interest of abstracting out the transport backend, the sock object has been replaced by a ClientConnectionTCP object. This object is passed to all server handler functions (apart from request handlers) instead of the sock object. The connection object be used in the same places where sock was previously used. It also defines inform(), reply_inform() and reply() methods for sending Message objects to a client.

Backwards incompatible KATCP V5 changes¶

Timestamps¶

Excerpted from NRF-KAT7-6.0-IFCE-002-Rev5.pdf:

All core messages involving time (i.e. timestamp or period specifications) have changed from using milliseconds to seconds. This provides consistency with SI units. Note also that from version five timestamps should always be specified in UTC time.

Message Identifiers (mid)¶

Excerpted from NRF-KAT7-6.0-IFCE-002-Rev5.pdf:

Message identifiers were introduced in version 5 of the protocol to allow replies to be uniquely associated with a particular request. If a client sends a request with a message identifier the server must include the same identifier in the reply. Message identifiers are limited to integers in the range 1 to 231 − 1 inclusive. It is the client’s job to construct suitable identifiers – a server should not assume that these are unique. Clients that need to determine whether a server supports message identifiers should examine the #version-connect message returned by the server when the client connects (see Section 4). If no #version-connect message is received the client may assume message identifiers are not supported.

also:

If the request contained a message id each inform that forms part of the response should be marked with the original message id.

Support for message IDs is optional. A properly implemented server should never use mids in replies unless the client request has an mid. Similarly, a client should be able to detect whether a server supports MIDs by checking the #version-connect informs sent by the server, or by doing a !version-list request. Furthermore, a KATCP v5 server should never send #build-state or #version informs.

Server KATCP Version Auto-detection¶

The DeviceClient client uses the presence of #build-state or #version informs as a heuristic to detect pre-v5 servers, and the presence of #version-connect informs to detect v5+ servers. If mixed messages are received the client gives up auto-detection and disconnects. In this case preset_protocol_flags() can be used to configure the client before calling start().

Level of KATCP support in this release¶

This release implements the majority of the KATCP v5 spec; excluded parts are:

Support for optional warning/error range meta-information on sensors.
Differential-rate sensor strategy.