TChannel for Python¶

A Python implementation of TChannel.

Getting Started¶

This guide is current as of version 0.16. See the Upgrade Guide if you’re running an older version.

The code matching this guide is here.

Initial Setup¶

Create a directory called keyvalue to work inside of:

$ mkdir ~/keyvalue
$ cd ~/keyvalue

Inside of this directory we’re also going to create a keyvalue module, which requires an __init__.py and a setup.py at the root:

$ mkdir keyvalue
$ touch keyvalue/__init__.py

Setup a virtual environment for your service and install the tornado and tchannel:

$ virtualenv env
$ source env/bin/activate
$ pip install tchannel thrift tornado

Thrift Interface Definition¶

Create a Thrift file under thrift/service.thrift that defines an interface for your service:

$ mkdir thrift
$ vim thrift/service.thrift
$ cat thrift/service.thrift

exception NotFoundError {
    1: string key,
}

service KeyValue {
    string getValue(
        1: string key,
    ) throws (
        1: NotFoundError notFound,
    )

    void setValue(
        1: string key,
        2: string value,
    )
}

This defines a service named KeyValue with two functions:

getValue: a function which takes one string parameter, and returns a string.
setValue: a void function that takes in two parameters.

Once you have defined your service, generate corresponding Thrift types by running the following:

$ thrift --gen py:new_style,dynamic,slots,utf8strings \
    -out keyvalue thrift/service.thrift

This generates client- and server-side code to interact with your service.

You may want to verify that your thrift code was generated successfully:

$ python -m keyvalue.service.KeyValue

Python Server¶

To serve an application we need to instantiate a TChannel instance, which we will register handlers against. Open up keyvalue/server.py and write something like this:

from __future__ import absolute_import

from tornado import ioloop
from tornado import gen

from service import KeyValue
from tchannel import TChannel


tchannel = TChannel('keyvalue-server')


@tchannel.thrift.register(KeyValue)
def getValue(request):
    pass


@tchannel.thrift.register(KeyValue)
def setValue(request):
    pass


def run():
    tchannel.listen()
    print('Listening on %s' % tchannel.hostport)


if __name__ == '__main__':
    run()
    ioloop.IOLoop.current().start()

Here we have created a TChannel instance and registered two no-op handlers with it. The name of these handlers map directly to the Thrift service we defined earlier.

A TChannel server only has one requirement: a name for itself. By default an ephemeral port will be chosen to listen on (although an explicit port can be provided).

(As your application becomes more complex, you won’t want to put everything in a single file like this. Good code structure is beyond the scope of this guide.)

Let’s make sure this server is in a working state:

python keyvalue/server.py
Listening on localhost:54143
^C

The process should hang until you kill it, since it’s listening for requests to handle. You shouldn’t get any exceptions.

Handlers¶

To implement our service’s endpoints let’s create an in-memory dictionary that our endpoints will manipulate:

values = {}


@tchannel.thrift.register(KeyValue)
def getValue(request):
    key = request.body.key
    value = values.get(key)

    if value is None:
        raise KeyValue.NotFoundError(key)

    return value


@tchannel.thrift.register(KeyValue)
def setValue(request):
    key = request.body.key
    value = request.body.value
    values[key] = value

You can see that the return value of getValue will be coerced into the expected Thrift shape. If we needed to return an additional field, we could accomplish this by returning a dictionary.

This example service doesn’t do any network IO work. If we wanted to take advantage of Tornado’s asynchronous capabilities, we could define our handlers as coroutines and yield to IO operations:

@tchannel.register(KeyValue)
@gen.coroutine
def setValue(request):
    key = request.body.key
    value = request.body.value

    # Simulate some non-blocking IO work.
    yield gen.sleep(1.0)

    values[key] = value

Transport Headers¶

In addition to the call arguments and headers, the request object also provides some additional information about the current request under the request.transport object:

transport.flags: Request flags used by the protocol for fragmentation and streaming.
transport.ttl: The time (in milliseconds) within which the caller expects a response.
transport.headers: Protocol level headers for the request. For more information on transport headers check the Transport Headers section of the protocol document.

Hyperbahn¶

As mentioned earlier, our service is listening on an ephemeral port, so we are going to register it with the Hyperbahn routing mesh. Clients will use this Hyperbahn mesh to determine how to communicate with your service.

Let’s change our run method to advertise our service with a local Hyperbahn instance:

import json
import os

@gen.coroutine
def run():

    tchannel.listen()
    print('Listening on %s' % app.hostport)

    if os.path.exists('/path/to/hyperbahn_hostlist.json'):
        with open('/path/to/hyperbahn_hostlist.json', 'r') as f:
            hyperbahn_hostlist = json.load(f)
        yield tchannel.advertise(routers=hyperbahn_hostlist)

The advertise method takes a seed list of Hyperbahn routers and the name of the service that clients will call into. After advertising, the Hyperbahn will connect to your process and establish peers for service-to-service communication.

Consult the Hyperbahn documentation for instructions on how to start a process locally.

Debugging¶

Let’s spin up the service and make a request to it through Hyperbahn. Python provides tcurl.py script, but we need to use the Node version for now since it has Thrift support.

$ python keyvalue/server.py &
$ tcurl -H /path/to/hyperbahn_host_list.json -t ~/keyvalue/thrift/service.thrift service KeyValue::setValue -3 '{"key": "hello", "value": "world"}'
$ tcurl -H /path/to/hyperbahn_host_list.json -t ~/keyvalue/thrift/service.thrift service KeyValue::getValue -3 '{"key": "hello"}'
$ tcurl -H /path/to/hyperbahn_host_list.json -t ~/keyvalue/thrift/service.thrift service KeyValue::getValue -3 '{"key": "hi"}'

Your service can now be accessed from any language over Hyperbahn + TChannel!

Python Client¶

Let’s make a client call from Python in keyvalue/client.py:

from tornado import gen
from tornado import ioloop
from tchannel import TChannel
from tchannel import thrift_request_builder

from service import KeyValue

KeyValueClient = thrift_request_builder(
    service='keyvalue-server',
    thrift_module=KeyValue,
)

@gen.coroutine
def run():
    app_name = 'keyvalue-client'

    tchannel = TChannel(app_name)
    tchannel.advertise(routers=['127.0.0.1:21300'])

    yield tchannel.thrift(
        KeyValueClient.setValue("foo", "Hello, world!"),
    )

    response = yield tchannel.thrift(
        KeyValueClient.getValue("foo"),
    )

    print response


if __name__ == '__main__':
    ioloop.IOLoop.current().run_sync(run)

Similar to the server case, we initialize a TChannel instance and advertise ourselves on Hyperbahn (to establish how to communicate with keyval-server). After this we create a client class to add TChannel functionality to our generated Thrift code. We then set and retrieve a value from our server.

API Documentation¶

TChannel¶

class tchannel.TChannel(name, hostport=None, process_name=None, known_peers=None, trace=False)[source]¶

Manages connections and requests to other TChannel services.

Usage for a JSON client/server:

tchannel = TChannel(name='foo')

@tchannel.json.register
def handler(request):
    return {'foo': 'bar'}

response = yield tchannel.json(
    service='some-service',
    endpoint='endpoint',
    headers={'req': 'headers'},
    body={'req': 'body'},
)

Variables:	thrift (ThriftArgScheme) – Make Thrift requests over TChannel and register Thrift handlers. json (JsonArgScheme) – Make JSON requests over TChannel and register JSON handlers. raw (RawArgScheme) – Make requests and register handles that pass raw bytes.

__init__(name, hostport=None, process_name=None, known_peers=None, trace=False)[source]¶

Note: In general only one TChannel instance should be used at a time. Multiple TChannel instances are not advisable and could result in undefined behavior.

Parameters:	name (string) – How this application identifies itself. This is the name callers will use to make contact, it is also what your downstream services will see in their metrics. hostport (string) – An optional host/port to serve on, e.g., `"127.0.0.1:5555`. If not provided an ephemeral port will be used. When advertising on Hyperbahn you callers do not need to know your port.

call(*args, **kwargs)[source]¶

Make low-level requests to TChannel services.

Note: Usually you would interact with a higher-level arg scheme like tchannel.schemes.JsonArgScheme or tchannel.schemes.ThriftArgScheme.

advertise(*args, **kwargs)[source]¶

Advertise with Hyperbahn.

After a successful advertisement, Hyperbahn will establish long-lived connections with your application. These connections are used to load balance inbound and outbound requests to other applications on the Hyperbahn network.

Re-advertisement happens periodically after calling this method (every minute). Hyperbahn will eject us from the network if it doesn’t get a re-advertise from us after 5 minutes.

Raises TimeoutError:
Parameters:	routers (list) – A seed list of known Hyperbahn addresses to attempt contact with. Entries should be of the form `"host:port"`. name (string) – The name your application identifies itself as. This is usually unneeded because in the common case it will match the `name` you initialized the `TChannel` instance with. This is the identifier other services will use to make contact with you. timeout – The timeout (in seconds) for the initial advertise attempt. Defaults to 30 seconds. router_file – The host file that contains the routers information. The file should contain a JSON stringified format of the routers parameter. Either routers or router_file should be provided. If both provided, a ValueError will be raised.
Returns:	A future that resolves to the remote server’s response after the first advertise finishes.
	When unable to make our first advertise request to Hyperbahn. Subsequent requests may fail but will be ignored.

class tchannel.Request(body=None, headers=None, transport=None, endpoint=None)[source]¶

A TChannel request.

This is sent by callers and received by registered handlers.

Variables:

body – The payload of this request. The type of this attribute depends on the scheme being used (e.g., JSON, Thrift, etc.).
headers – A dictionary of application headers. This should be a mapping of strings to strings.
transport –
Protocol-level transport headers. These are used for routing over Hyperbahn.

The most useful piece of information here is probably request.transport.caller_name, which is the identity of the application that created this request.

class tchannel.Response(body=None, headers=None, transport=None, status=None)[source]¶

A TChannel response.

This is sent by handlers and received by callers.

Variables:	body – The payload of this response. The type of this attribute depends on the scheme being used (e.g., JSON, Thrift, etc.). headers – A dictionary of application headers. This should be a mapping of strings to strings. transport – Protocol-level transport headers. These are used for routing over Hyperbahn.

class tchannel.context.RequestContext(parent_tracing=None)[source]¶

Tracks the Request currently being handled.

The asynchronous nature of Tornado means that multiple requests can be in-flight at any given moment. It’s often useful to be able to see some information about the request that triggered the current method invocation.

There are two ways to do this:

Pass the tchannel.Request to every method that may need to use it. This is performant but breaks MVC boundaries.
Use RequestContext – in particular get_current_context() – to see this info from any point in your code. This can be “easier” (read: magical).

RequestContext uses Tornado’s StackContext functionality, which hurts throughput. There’s currently no way to disable RequestContext tracking (for cases when you want to pass the tchannel.Request explicity), although it is planned.

Variables:	parent_tracing – Tracing information (trace id, span id) for this request.

tchannel.context.get_current_context()[source]¶

Returns:	The current `RequestContext` for this thread.

Serialization Schemes¶

Thrift¶

class tchannel.schemes.ThriftArgScheme(tchannel)[source]¶

Handler registration and serialization for Thrift.

To register a Thrift handler:

@tchannel.thrift(GeneratedThriftModule)
def method(request):
    print request.body.some_arg

When calling a remote service, generated Thrift types need to be wrapped with thrift_request_builder() to provide TChannel compatibility:

thrift_service = thrift_request_builder(
    service='service-identifier',
    thrift_module=GeneratedThriftModule,
)

response = yield tchannel.thrift(
    thrift_service.method(some_arg='foo'),
)

tchannel.thrift_request_builder(service, thrift_module, hostport=None, thrift_class_name=None)[source]¶

Provide TChannel compatibility with Thrift-generated modules.

The service this creates is meant to be used with TChannel like so:

from tchannel import TChannel, thrift_request_builder
from some_other_service_thrift import some_other_service

tchannel = TChannel('my-service')

some_service = thrift_request_builder(
    service='some-other-service',
    thrift_module=some_other_service
)

resp = tchannel.thrift(
    some_service.fetchPotatoes()
)

Parameters:

service (string) – Name of Thrift service to call. This is used internally for grouping and stats, but also to route requests over Hyperbahn.
thrift_module – The top-level module of the Apache Thrift generated code for the service that will be called.
hostport (string) – When calling the Thrift service directly, and not over Hyperbahn, this ‘host:port’ value should be provided.
thrift_class_name (string) – When the Apache Thrift generated Iface class name does not match thrift_module, then this should be provided.

tchannel.thrift.load(path, service=None, hostport=None, module_name=None)[source]¶

Loads the Thrift file at the specified path.

Note

This functionality is experimental and subject to change. We expect to mark it as stable in a future version.

The file is compiled in-memory and a Python module containing the result is returned. It may be used with TChannel.thrift. For example,

from tchannel import TChannel, thrift

# Load our server's interface definition.
donuts = thrift.load('donuts.thrift')

# We need to specify a service name or hostport because this is a
# downstream service we'll be calling.
coffee = thrift.load('coffee.thrift', 'coffee')

tchannel = TChannel('donuts')

@tchannel.thrift.register(donuts.DonutsService)
@tornado.gen.coroutine
def submitOrder(request):
    args = request.body

    if args.coffee:
        yield tchannel.thrift(
            coffee.CoffeeService.order(args.coffee)
        )

    # ...

The returned module contains, one top-level type for each struct, enum, union, exeption, and service defined in the Thrift file. For each service, the corresponding class contains a classmethod for each function defined in that service that accepts the arguments for that function and returns a ThriftRequest capable of being sent via TChannel.thrift.

Note that the path accepted by load must be either an absolute path or a path relative to the the current directory. If you need to refer to Thrift files relative to the Python module in which load was called, use the __file__ magic variable.

# Given,
#
#   foo/
#     myservice.thrift
#     bar/
#       x.py
#
# Inside foo/bar/x.py,

path = os.path.join(
    os.path.dirname(__file__), '../myservice.thrift'
)

The returned value is a valid Python module. You can install the module by adding it to the sys.modules dictionary. This will allow importing items from this module directly. You can use the __name__ magic variable to make the generated module a submodule of the current module. For example,

# foo/bar.py

import sys
from tchannel import thrift

donuts = = thrift.load('donuts.thrift')
sys.modules[__name__ + '.donuts'] = donuts

This installs the module generated for donuts.thrift as the module foo.bar.donuts. Callers can then import items from that module directly. For example,

# foo/baz.py

from foo.bar.donuts import DonutsService, Order

def baz(tchannel):
    return tchannel.thrift(
        DonutsService.submitOrder(Order(..))
    )

Parameters:

service (str) – Name of the service that the Thrift file represents. This name will be used to route requests through Hyperbahn.
path (str) – Path to the Thrift file. If this is a relative path, it must be relative to the current directory.
hostport (str) – Clients can use this to specify the hostport at which the service can be found. If omitted, TChannel will route the requests through known peers. This value is ignored by servers.
module_name (str) – Name used for the generated Python module. Defaults to the name of the Thrift file.

JSON¶

class tchannel.schemes.JsonArgScheme(tchannel)[source]¶

Semantic params and serialization for json.

__call__(*args, **kwargs)[source]¶

Make JSON TChannel Request.

Parameters:

service (string) – Name of the service to call.
endpoint (string) – Endpoint to call on service.
body (string) – A raw body to provide to the endpoint.
headers (string) – A raw headers block to provide to the endpoint.
timeout (int) – How long to wait (in ms) before raising a TimeoutError - this defaults to tchannel.glossary.DEFAULT_TIMEOUT.
retry_on (string) – What events to retry on - valid values can be found in tchannel.retry.
retry_limit (string) – How many times to retry before
hostport (string) – A ‘host:port’ value to use when making a request directly to a TChannel service, bypassing Hyperbahn.

Return type:

Response

Raw¶

class tchannel.schemes.RawArgScheme(tchannel)[source]¶

Semantic params and serialization for raw.

__call__(service, endpoint, body=None, headers=None, timeout=None, retry_on=None, retry_limit=None, hostport=None, shard_key=None, trace=None)[source]¶

Make a raw TChannel request.

The request’s headers and body are treated as raw bytes and not serialized/deserialized.

Parameters:

service (string) – Name of the service to call.
endpoint (string) – Endpoint to call on service.
body (string) – A raw body to provide to the endpoint.
headers (string) – A raw headers block to provide to the endpoint.
timeout (int) – How long to wait (in ms) before raising a TimeoutError - this defaults to tchannel.glossary.DEFAULT_TIMEOUT.
retry_on (string) – What events to retry on - valid values can be found in tchannel.retry.
retry_limit (string) – How many times to retry before
hostport (string) – A ‘host:port’ value to use when making a request directly to a TChannel service, bypassing Hyperbahn.

Return type:

Response

Exception Handling¶

Errors¶

tchannel.errors.TIMEOUT = 1¶: The request timed out.

tchannel.errors.CANCELED = 2¶: The request was canceled.

tchannel.errors.BUSY = 3¶: The server was busy.

tchannel.errors.BAD_REQUEST = 6¶: The request was bad.

tchannel.errors.NETWORK_ERROR = 7¶: There was a network error when sending the request.

tchannel.errors.UNHEALTHY = 8¶: The server handling the request is unhealthy.

tchannel.errors.FATAL = 255¶: There was a fatal protocol-level error.

exception tchannel.errors.TChannelError(description=None, id=None, tracing=None)[source]¶

Bases: exceptions.Exception

A TChannel-generated exception.

Variables:	code – The error code for this error. See the Specification for a description of these codes.

classmethod from_code(code, **kw)[source]¶

Construct a TChannelError instance from an error code.

This will return the appropriate class type for the given code.

exception tchannel.errors.RetryableError(description=None, id=None, tracing=None)[source]¶

Bases: tchannel.errors.TChannelError

An error where the original request is always safe to retry.

It is always safe to retry a request with this category of errors. The original request was never handled.

exception tchannel.errors.MaybeRetryableError(description=None, id=None, tracing=None)[source]¶

Bases: tchannel.errors.TChannelError

An error where the original request may be safe to retry.

The original request may have reached the intended service. Hence, the request should only be retried if it is known to be idempotent.

exception tchannel.errors.NotRetryableError(description=None, id=None, tracing=None)[source]¶

Bases: tchannel.errors.TChannelError

An error where the original request should not be re-sent.

Something was fundamentally wrong with the request and it should not be retried.

exception tchannel.errors.ReadError(description=None, id=None, tracing=None)[source]¶

Bases: tchannel.errors.FatalProtocolError

Raised when there is an error while reading input.

exception tchannel.errors.InvalidChecksumError(description=None, id=None, tracing=None)[source]¶

Bases: tchannel.errors.FatalProtocolError

Represent invalid checksum type in the message

exception tchannel.errors.NoAvailablePeerError(description=None, id=None, tracing=None)[source]¶

Bases: tchannel.errors.RetryableError

Represents a failure to find any peers for a request.

exception tchannel.errors.AlreadyListeningError(description=None, id=None, tracing=None)[source]¶

Bases: tchannel.errors.FatalProtocolError

Raised when attempting to listen multiple times.

exception tchannel.errors.OneWayNotSupportedError(description=None, id=None, tracing=None)[source]¶

Bases: tchannel.errors.BadRequestError

Raised when a one-way Thrift procedure is called.

exception tchannel.errors.ValueExpectedError(description=None, id=None, tracing=None)[source]¶

Bases: tchannel.errors.BadRequestError

Raised when a non-void Thrift response contains no value.

Retry Behavior¶

These values can be passed as the retry_on behavior to tchannel.TChannel.call().

tchannel.retry.CONNECTION_ERROR = u'c'¶: Retry the request on failures to connect to a remote host. This is the default retry behavior.

tchannel.retry.NEVER = u'n'¶: Never retry the request.

tchannel.retry.TIMEOUT = u't'¶: Retry the request on timeouts waiting for a response.

tchannel.retry.CONNECTION_ERROR_AND_TIMEOUT = u'ct'¶: Retry the request on failures to connect and timeouts after connecting.

tchannel.retry.DEFAULT_RETRY_LIMIT = 4¶: The default number of times to retry a request. This is in addition to the original request.

Synchronous Client¶

class tchannel.sync.TChannel(name, hostport=None, process_name=None, known_peers=None, trace=False, threadloop=None)[source]¶

Make synchronous TChannel requests.

This client does not support incoming requests – it is a uni-directional client only.

The client is implemented on top of the Tornado-based implementation and offloads IO to a thread running an IOLoop next to your process.

Usage mirrors the TChannel class.

tchannel = TChannel(name='my-synchronous-service')

# Advertise with Hyperbahn.
# This returns a future. You may want to block on its result,
# particularly if you want you app to die on unsuccessful
# advertisement.
tchannel.advertise(routers)

# thrift_service is the result of a call to ``thrift_request_builder``
future = tchannel.thrift(
    thrift_service.getItem('foo'),
    timeout=1,  #  1 second
)

result = future.result()

advertise(*args, **kwargs)[source]¶

Advertise with Hyperbahn.

After a successful advertisement, Hyperbahn will establish long-lived connections with your application. These connections are used to load balance inbound and outbound requests to other applications on the Hyperbahn network.

Re-advertisement happens periodically after calling this method (every minute). Hyperbahn will eject us from the network if it doesn’t get a re-advertise from us after 5 minutes.

Raises TimeoutError:
Parameters:	routers (list) – A seed list of known Hyperbahn addresses to attempt contact with. Entries should be of the form `"host:port"`. name (string) – The name your application identifies itself as. This is usually unneeded because in the common case it will match the `name` you initialized the `TChannel` instance with. This is the identifier other services will use to make contact with you. timeout – The timeout (in seconds) for the initial advertise attempt. Defaults to 30 seconds. router_file – The host file that contains the routers information. The file should contain a JSON stringified format of the routers parameter. Either routers or router_file should be provided. If both provided, a ValueError will be raised.
Returns:	A future that resolves to the remote server’s response after the first advertise finishes.
	When unable to make our first advertise request to Hyperbahn. Subsequent requests may fail but will be ignored.

call(*args, **kwargs)[source]¶

Make low-level requests to TChannel services.

Note: Usually you would interact with a higher-level arg scheme like tchannel.schemes.JsonArgScheme or tchannel.schemes.ThriftArgScheme.

Testing¶

VCR¶

tchannel.testing.vcr provides VCR-like functionality for TChannel. Its API is heavily inspired by the vcrpy library.

This allows recording TChannel requests and their responses into YAML files during integration tests and replaying those recorded responses when the tests are run next time.

The simplest way to use this is with the use_cassette() function.

tchannel.testing.vcr.use_cassette(path, record_mode=None, inject=False)[source]¶

Use or create a cassette to record/replay TChannel requests.

This may be used as a context manager or a decorator.

from tchannel.testing import vcr

@pytest.mark.gen_test
@vcr.use_cassette('tests/data/bar.yaml')
def test_bar():
    channel = TChannel('test-client')
    service_client = MyServiceClient(channel)

    yield service_client.myMethod()


def test_bar():
    with vcr.use_cassette('tests/data/bar.yaml', record_mode='none'):
        # ...

Note that when used as a decorator on a coroutine, the use_cassette decorator must be applied BEFORE gen.coroutine or pytest.mark.gen_test.

Parameters:

path – Path to the cassette. If the cassette did not already exist, it will be created. If it existed, its contents will be replayed (depending on the record mode).
record_mode – The record mode dictates whether a cassette is allowed to record or replay interactions. This may be a string specifying the record mode name or an element from the tchannel.testing.vcr.RecordMode object. This parameter defaults to tchannel.testing.vcr.RecordMode.ONCE. See tchannel.testing.vcr.RecordMode for details on supported record modes and how to use them.
inject – If True, when use_cassette is used as a decorator, the cassette object will be injected into the function call as the first argument. Defaults to False.

Configuration¶

Record Modes¶

class tchannel.testing.vcr.RecordMode[source]¶

Record modes dictate how a cassette behaves when interactions are replayed or recorded. The following record modes are supported.

ONCE = 'once'¶: If the YAML file did not exist, record new interactions and save them. If the YAML file already existed, replay existing interactions but disallow any new interactions. This is the default and usually what you want.

NEW_EPISODES = 'new_episodes'¶: Replay existing interactions and allow recording new ones. This is usually undesirable since it reduces predictability in tests.

NONE = 'none'¶: Replay existing interactions and disallow any new interactions. This is a good choice for tests whose behavior is unlikely to change in the near future. It ensures that those tests don’t accidentally start making new requests.

ALL = 'all'¶: Do not replay anything and record all new interactions. Forget all existing interactions. This may be used to record everything anew.

Changelog¶

Changes by Version¶

0.17.2 (2015-09-18)¶

VCR no longer matches on hostport to better support ephemeral ports.
Fixed a bug with thriftrw where registering an endpoint twice could fail.

0.17.1 (2015-09-17)¶

Made “service” optional for thrift.load(). The first argument should be a path, but backwards compatibility is provided for 0.17.0.

0.17.0 (2015-09-14)¶

It is now possible to load Thrift IDL files directly with tchannel.thrift.load. This means that the code generation step using the Apache Thrift compiler can be skipped entirely. Check the API documentation for more details.
Accept host file in advertise: TChannel.advertise() now accepts a parameter, router_file that contains a JSON stringified format of the router list.
Add TChannel.is_listening method to return whether the tchannel instance is listening or not.

0.16.6 (2015-09-14)¶

Fixed a bug where Zipkin traces were not being propagated correctly in services using the tchannel.TChannel API.

0.16.5 (2015-09-09)¶

Actually fix status code being unset in responses when using the Thrift scheme.
Fix request TTLs not being propagated over the wire.

0.16.4 (2015-09-09)¶

Fix bug where status code was not being set correctly on call responses for application errors when using the Thrift scheme.

0.16.3 (2015-09-09)¶

Make TChannel.listen thread-safe and idempotent.

0.16.2 (2015-09-04)¶

Fix retry_limit in TChannel.call not allowing 0 retries.

0.16.1 (2015-08-27)¶

Fixed a bug where the ‘not found’ handler would incorrectly return serialization mismatch errors..
Fixed a bug which prevented VCR support from working with the sync client.
Fixed a bug in VCR that prevented it from recording requests made by the sync client, and requests made with hostport=None.
Made client_for compatible with tchannel.TChannel.
Brought back tchannel.sync.client_for for backwards compatibility.

0.16.0 (2015-08-25)¶

Introduced new server API through methods tchannel.TChannel.thrift.register, tchannel.TChannel.json.register, and tchannel.TChannel.raw.register - when these methods are used, endpoints are passed a tchannel.Request object, and are expected to return a tchannel.Response object or just a response body. The deprecated tchannel.tornado.TChannel.register continues to function how it did before. Note the breaking change to the top-level TChannel on the next line.
Fixed a crash that would occur when forking with an unitialized TChannel instance.
Add hooks property in the tchannel.TChannel class.
BREAKING - tchannel.TChannel.register no longer has the same functionality as tchannel.tornado.TChannel.register, instead it exposes the new server API. See the upgrade guide for details.
BREAKING - remove retry_delay option in the tchannel.tornado.send method.
BREAKING - error types have been reworked significantly. In particular, the all-encompassing ProtocolError has been replaced with more granualar/actionable exceptions. See the upgrade guide for more info.
BREAKING - Remove third proxy argument from the server handler interface.
BREAKING - ZipkinTraceHook is not longer registered by default.
BREAKING - tchannel.sync.client.TChannelSyncClient replaced with tchannel.sync.TChannel.

0.15.2 (2015-08-07)¶

Raise informative and obvious ValueError when anything but a map[string]string is passed as headers to the TChannel.thrift method.
First param, request, in tchannel.thrift method is required.

0.15.1 (2015-08-07)¶

Raise tchannel.errors.ValueExpectedError when calling a non-void Thrift procedure that returns no value.

0.15.0 (2015-08-06)¶

Introduced new top level tchannel.TChannel object, with new request methods call, raw, json, and thrift. This will eventually replace the akward request / send calling pattern.
Introduced tchannel.thrift_request_builder function for creating a request builder to be used with the tchannel.TChannel.thrift function.
Introduced new simplified examples under the examples/simple directory, moved the Guide’s examples to examples/guide, and deleted the remaining examples.
Added ThriftTest.thrift and generated Thrift code to tchannel.testing.data for use with examples and playing around with TChannel.
Fix JSON arg2 (headers) being returned a string instead of a dict.

0.14.0 (2015-08-03)¶

Implement VCR functionality for outgoing requests. Check the documentation for tchannel.testing.vcr for details.
Add support for specifying fallback handlers via TChannel.register by specifying TChannel.fallback as the endpoint.
Fix bug in Response where code expected an object instead of an integer.
Fix bug in Peer.close where a future was expected instead of None.

0.13.0 (2015-07-23)¶

Add support for specifying transport headers for Thrift clients.
Always pass shardKey for TCollector tracing calls. This fixes Zipkin tracing for Thrift clients.

0.12.0 (2015-07-20)¶

Add TChannel.is_listening() to determine if listen has been called.
Calling TChannel.listen() more than once raises a tchannel.errors.AlreadyListeningError.
TChannel.advertise() will now automatically start listening for connections if listen() has not already been called.
Use threadloop==0.4.
Removed print_arg.

0.11.2 (2015-07-20)¶

Fix sync client’s advertise - needed to call listen in thread.

0.11.1 (2015-07-17)¶

Fix sync client using 0.0.0.0 host which gets rejected by Hyperbahn during advertise.

0.11.0 (2015-07-17)¶

Added advertise support to sync client in tchannel.sync.TChannelSyncClient.advertise.
BREAKING - renamed router argument to routers in tchannel.tornado.TChannel.advertise.

0.10.3 (2015-07-13)¶

Support PyPy 2.
Fix bugs in TChannel.advertise.

0.10.2 (2015-07-13)¶

Made TChannel.advertise retry on all exceptions.

0.10.1 (2015-07-10)¶

Previous release was broken with older versions of pip.

0.10.0 (2015-07-10)¶

Add exponential backoff to TChannel.advertise.
Make transport metadata available under request.transport on the server-side.

0.9.1 (2015-07-09)¶

Use threadloop 0.3.* to fix main thread not exiting when tchannel.sync.TChannelSyncClient is used.

0.9.0 (2015-07-07)¶

Allow custom handlers for unrecognized endpoints.
Released tchannel.sync.TChannelSyncClient and tchannel.sync.thrift.client_for.

0.8.5 (2015-06-30)¶

Add port parameter for TChannel.listen.

0.8.4 (2015-06-17)¶

Fix bug where False and False-like values were being treated as None in Thrift servers.

0.8.3 (2015-06-15)¶

Add as attribute to the response header.

0.8.2 (2015-06-11)¶

Fix callable traceflag being propagated to the serializer.
Fix circular imports.
Fix TimeoutError retry logic.

0.8.1 (2015-06-10)¶

Initial release.

Upgrade Guide¶

Migrating to a version of TChannel with breaking changes? This guide documents what broke and how to safely migrate to newer versions.

From 0.15 to 0.16¶

tchannel.TChannel.register no longer mimicks tchannel.tornado.TChannel.register, instead it exposes the new server API like so:

Before:

from tchannel.tornado import TChannel

tchannel = TChannel('my-service-name')

@tchannel.register('endpoint', 'json')
def endpoint(request, response, proxy):
    response.write({'resp': 'body'})

After:

from tchannel import TChannel

tchannel = TChannel('my-service-name')

@tchannel.json.register
def endpoint(request):
    return {'resp': 'body'}

    # Or, if you need to return headers with your response:
    from tchannel import Response
    return Response({'resp': 'body'}, {'header': 'foo'})

TChannelSyncClient has been replaced with tchannel.sync.TChannel. This new synchronous client has been significantly re-worked to more closely match the asynchronous TChannel API. tchannel.sync.thrift.client_for has been removed and tchannel.thrift_request_builder should be used instead (tchannel.thrift.client_for still exists for backwards compatibility but is not recommended). This new API allows specifying headers, timeouts, and retry behavior with Thrift requests.

Before:

from tchannel.sync import TChannelSyncClient
from tchannel.sync.thrift import client_for

from generated.thrift.code import MyThriftService

tchannel_thrift_client = client_for('foo', MyThriftService)

tchannel = TChannelSyncClient(name='bar')

future = tchannel_thrift_client.someMethod(...)

result = future.result()

After:

from tchannel import thrift_request_builder
from tchannel.sync import TChannel
from tchannel.retry import CONNECTION_ERROR_AND_TIMEOUT

from generated.thrift.code import MyThriftService

tchannel_thrift_client = thrift_request_builder(
    service='foo',
    thrift_module=MyThriftService,
)

tchannel = TChannel(name='bar')

future = tchannel.thrift(
    tchannel_thrift_client.someMethod(...)
    headers={'foo': 'bar'},
    retry_on=CONNECTION_ERROR_AND_TIMEOUT,
    timeout=1000,
)

result = future.result()

from tchannel.tornado import TChannel is deprecated.
Removed retry_delay option from tchannel.tornado.peer.PeerClientOperation.send method.

Before: tchannel.tornado.TChannel.request.send(retry_delay=300)

After: no more retry_delay in tchannel.tornado.TChannel.request.send()
If you were catching ProtocolError you will need to catch a more specific type, such as TimeoutError, BadRequestError, NetworkError, UnhealthyError, or UnexpectedError.
If you were catching AdvertiseError, it has been replaced by TimeoutError.
If you were catching BadRequest, it may have been masking checksum errors and fatal streaming errors. These are now raised as FatalProtocolError, but in practice should not need to be handled when interacting with a well-behaved TChannel implementation.
TChannelApplicationError was unused and removed.
Three error types have been introduced to simplify retry handling:
- NotRetryableError (for requests should never be retried),
- RetryableError (for requests that are always safe to retry), and
- MaybeRetryableError (for requests that are safe to retry on idempotent endpoints).

From 0.14 to 0.15¶

No breaking changes.

From 0.13 to 0.14¶

No breaking changes.

From 0.12 to 0.13¶

No breaking changes.

From 0.11 to 0.12¶

Removed print_arg. Use request.get_body() instead.

From 0.10 to 0.11¶

Renamed tchannel.tornado.TChannel.advertise argument router to routers. Since this is a required arg and the first positional arg, only clients who are using as kwarg will break.

Before: tchannel.advertise(router=['localhost:21300'])

After: tchannel.advertise(routers=['localhost:21300'])