Packages

package root

Definition Classes: root

package com

Definition Classes: root

package twitter

Start with com.twitter.finagle.

Definition Classes: com

package finagle

Finagle is an extensible RPC system.

Services are represented by class com.twitter.finagle.Service. Clients make use of com.twitter.finagle.Service objects while servers implement them.

Finagle contains a number of protocol implementations; each of these implement Client and/or com.twitter.finagle.Server. For example, Finagle's HTTP implementation, com.twitter.finagle.Http (in package finagle-http), exposes both.

Thus a simple HTTP server is built like this:

import com.twitter.finagle.{Http, Service}
import com.twitter.finagle.http.{Request, Response}
import com.twitter.util.{Await, Future}

val service = new Service[Request, Response] {
  def apply(req: Request): Future[Response] =
    Future.value(Response())
}
val server = Http.server.serve(":8080", service)
Await.ready(server)

We first define a service to which requests are dispatched. In this case, the service returns immediately with a HTTP 200 OK response, and with no content.

This service is then served via the Http protocol on TCP port 8080. Finally we wait for the server to stop serving.

We can now query our web server:

% curl -D - localhost:8080
HTTP/1.1 200 OK

Building an HTTP client is also simple. (Note that type annotations are added for illustration.)

import com.twitter.finagle.{Http, Service}
import com.twitter.finagle.http.{Request, Response}
import com.twitter.util.{Future, Return, Throw}

val client: Service[Request, Response] = Http.client.newService("localhost:8080")
val f: Future[Response] = client(Request()).respond {
  case Return(rep) =>
    printf("Got HTTP response %s\n", rep)
  case Throw(exc) =>
    printf("Got error %s\n", exc)
}

Http.client.newService("localhost:8080") constructs a new com.twitter.finagle.Service instance connected to localhost TCP port 8080. We then issue a HTTP/1.1 GET request to URI "/". The service returns a com.twitter.util.Future representing the result of the operation. We listen to this future, printing an appropriate message when the response arrives.

The Finagle homepage contains useful documentation and resources for using Finagle.

Definition Classes: twitter

package addr

Definition Classes: finagle

package builder

Definition Classes: finagle

package client

Definition Classes: finagle

package context

Definition Classes: finagle

package core

Definition Classes: finagle

package dispatch

Definition Classes: finagle

package exp

Package exp contains experimental code.

Package exp contains experimental code. This can be removed or stabilized (moved elsewhere) at any time.

Definition Classes: finagle

package factory

Definition Classes: finagle

package filter

Definition Classes: finagle

AbstractDarkTrafficFilter

ClientExceptionTracingFilter

DarkTrafficFilter

DtabStatsFilter

ExceptionSourceFilter

ForwardingWarmUpFilter

RequestSemaphoreFilter

ToggleAwareSimpleFilter

restrictWorkQueueFiberZone

package http

Definition Classes: finagle

package http2

Definition Classes: finagle

package liveness

Definition Classes: finagle

package loadbalancer

This package implements client side load balancing algorithms.

As an end-user, see the Balancers API to create instances which can be used to configure a Finagle client with various load balancing strategies.

As an implementor, each algorithm gets its own subdirectory and is exposed via the Balancers object. Several convenient traits are provided which factor out common behavior and can be mixed in (i.e. Balancer, DistributorT, NodeT, and Updating).

Definition Classes: finagle

package logging

Definition Classes: finagle

package memcached

Definition Classes: finagle

package mux

Package mux implements a generic RPC multiplexer with a rich protocol.

Package mux implements a generic RPC multiplexer with a rich protocol. Mux is itself encoding independent, so it is meant to use as the transport for other RPC systems (eg. thrift). In OSI terminology, it is a pure session layer.

In the below description, all numeric values are unsigned and in big-endian byte order. The schema size:4 body:10 defines the field size to be 4 bytes, followed by 10 bytes of the field body. The schema key~4 defines the field key to be defined by 4 bytes interpreted as the size of the field, followed by that many bytes comprising the field itself--it is shorthand for keysize:4 key:keysize. Groups are denoted by parenthesis; * denotes repetition of the previous schema 0 or more times, while {n} indicates repetition exactly n times. Unspecified sizes consume the rest of the frame: they may be specified only as the last field in the message.

All strings in Mux are Utf-8 encoded, and are never null-terminated.

Message framing

Messages in mux are framed with a 4-byte big-endian size header, followed by 1 byte describing the message type and a 3-byte tag; or, diagrammatically: size:4 type:1 tag:3. The remainder of the frame (size-4 bytes) contains the body. Its format depends on the message type, documented below.

Tag 0 designates a "marker" T message that expects no reply. Some messages may be split into an ordered sequence of fragments. Tag MSB=0 denotes the last message in such a sequence, making the tag namespace 23 bits. The tag is otherwise arbitrary, and is chosen by the sender of the T message.

Currently, only Tdispatch and Rdispatch messages may be split into an ordered sequence of fragments. TdispatchError message ends a Tdispatch sequence and an Rerr ends an Rdispatch sequence.

Message types, interpreted as a two's complement, 1-byte integer are numbered as follows: positive numbers are T-messages; their negative complement is the corresponding R message. T-messages greater than 63 (correspondingly R-messages smaller than -63) are session messages. The message number -128 is reserved for Rerr. All other messages are application messages. Middle boxes may forward application messages indiscriminately. Because of an early implementation bug, two aliases exist: 127 is Rerr, and -62 is Tdiscarded.

The protocol is full duplex: both the server and client may send T messages initiating an exchange.

Exchanges

Messages are designated as "T messages" or "R messages", T and R being stand-ins for transmit and receive. A T message initiates an exchange and is assigned a free tag by the sender. A reply is either an R message of the same type (Rx replies to Tx for some x), or an Rerr, indicating a session layer error. R messages are matched to their T messages by tag, and the reply concludes the exchange and frees the tag for future use. Implementations should reuse small tag numbers.

Messages

size:4 Tinit:1 tag:3 version:2 (key~4 value~4)* reinitializes a session. Clients typically send this at the beginning of the session. When doing so, the sender may issue no more T messages until the corresponding size:4 Rinit:1 tag:3 version:2 (key~4 value~4)* has been received. After the Rinit was received, all connection state has been reset (outstanding tags are invalidated) and the stream is resumed according to the newly negotiated parameters. Prior to the first Tinit, the session operates at version 1. Rinit's version field is the accepted version of the session (which may be lower than the one requested by Tinit).

size:4 Treq:1 tag:3 n:1 (key:1 value~1){n} body: initiates the request described by its body. The request body is delivered to the application. The request header contains a number of key-value pairs that describe request metadata.

Keys for Treq messages are as follows:

traceid: a 24-byte value describing the full Dapper trace id assigned by the client. The value's format is spanid:8 parentid:8 traceid:8.

2. traceflag: a bitmask describing trace flags. Currently, the only defined flag is bit 0 which enables "debug mode", asking the server to force trace sampling.

size:4 Tdispatch:1 tag:3 nctx:2 (ckey~2 cval~2){nc} dst~2 nd:2 (from~2 to~2){nd} body: implements destination dispatch. Tdispatch messages carry a set of keyed request contexts, followed by a logical destination encoded as a UTF-8 string. A delegation table follows describing rewrite rules that apply to this request.

size:4 Rreq:1 tag:3 status:1 body: replies to a request. Status codes are as follows: 0=OK; the body contains the reply. 1=ERROR; the body contains a string describing the error. 2=NACK; a negative acknowledgment, the body contains a string describing the reason.

size:4 Rdispatch:1 tag:3 status:1 nctx:2 (key~2 value~2){nctx} body: replies to a Tdispatch request. Status codes are as in Rreq. Replies can include request contexts. MuxFailure flags are currently sent via Rdispatch contexts under the "MuxFailure" key. See the MuxFailure flags section below.

size:4 Rerr:1 tag:3 why: indicates that the corresponding T message produced an error. Rerr is specifically for server errors: the server failed to interpret or act on the message. The body carries a string describing the error.

size:4 Tdrain:1 tag:3 is a request sent by the server telling the client to stop sending new requests. A client acknowledges this with an Rdrain message.

size:4 Tping:1 tag:3 is sent by either party to check the liveness of its peer; these should be responded to immediately with a Rping message.

size:4 Tdiscarded:1 tag:3 discard_tag:3 why: is a marker message and therefore has a tag value of 0. discard_tag indicates the tag of the Tdispatch to be discarded by the client. This can be used as a hint for early termination. Why is a string describing why the request was discarded. Note that it does *not* free the server from the obligation of replying to the original Treq.

size:4 Tlease:1 tag:3 unit:1 howmuch:8 is a marker message indicating that a lease has been issued for howmuch units. As a marker message, its tag value must be 0. Unit '0' is reserved for duration in milliseconds. Whenever a lease has not been issued, a client can assume it holds an indefinite lease. Adhering to the lease is optional, but the server may reject requests or provide degraded service should the lease expire. This is used by servers to implement features like garbage collection avoidance.

MuxFailure Flags

Failure flags are read and written as an 8 byte integer. Unrecognized flags will be ignored silently, but should all be considered reserved for future use.

Flag Value Meaning Restartable 1 << 0 Request is safe to re-issue Rejected 1 << 1 Request was rejected/Nacked by the server NonRetryable 1 << 2 Request should not be retried

Security

TLS is supported via three mechanisms: - Explicit and exclusive TLS. This pathway involves requiring the establishment of TLS immediately after establishing the socket connection. This is configured by adding TLS configuration to the client or server and not configuring opportunistic TLS or TLS snooping (see below).

- Negotiated Opportunistic TLS. This pathway involves starting the connection as cleartext and the client and server subsequently negotiate a TLS level via the handshake. Based on that handshake the connection is either left as cleartext or upgraded to TLS. This is configured by adding TLS configuration and also configuring an opportunistic TLS level but not configuring TLS snooping.

In this pathway there are three configuration options:

Off signals that TLS is not supported by this peer
Desired signals that TLS is preferred but not required by this peer
Required signals that this peer will only allow the session to continue over TLS

- TLS snooping. This pathway allows a server to use TLS either by performing a TLS handshake immediately after the socket is established or by starting the session as cleartext or using the negotiated pathway described above. If the session is started as a TLS session the headers that drive the opportunistic TLS pathway are ignored.

Note that the server may still require TLS but leaves the option to start TLS immediately after establishing the socket or starting cleartext and requiring TLS via the opportunistic TLS pathway described above.

Definition Classes: finagle

package mysql

Definition Classes: finagle

package namer

Definition Classes: finagle

package naming

Definition Classes: finagle

package netty4

Package netty4 implements the bottom finagle primitives: com.twitter.finagle.Server and a client transport in terms of the netty4 event loop.

Definition Classes: finagle

package offload

Definition Classes: finagle

package param

Defines common com.twitter.finagle.Stack.Param's shared between finagle clients and servers.

Definition Classes: finagle

package partitioning

Definition Classes: finagle

package pool

Definition Classes: finagle

package postgresql

Definition Classes: finagle

package pushsession

Definition Classes: finagle

package redis

Definition Classes: finagle

package scribe

Definition Classes: finagle

package server

Definition Classes: finagle

package serverset2

Definition Classes: finagle

package service

Definition Classes: finagle

package ssl

Definition Classes: finagle

package stats

Definition Classes: finagle

package thrift

Please use the new interface, com.twitter.finagle.Thrift, for constructing Thrift clients and servers.

Deprecation

Please use the new interface, com.twitter.finagle.Thrift, for constructing Thrift clients and servers.

Thrift codecs

We provide client and server protocol support for the framed protocol. The public implementations are defined on the Thrift object:

The type of the server codec is Service[Array[Byte], Array[Byte]] and the client codecs are Service[ThriftClientRequest, Array[Byte]]. The service provided is that of a "transport" of thrift messages (requests and replies) according to the protocol chosen. This is why the client codecs need to have access to a thrift ProtocolFactory.

These transports are used by the services produced by the finagle thrift codegenerator.

val service: Service[ThriftClientRequest, Array[Byte]] = ClientBuilder()
  .hosts("foobar.com:123")
  .stack(Thrift.client)
  .build()

// Wrap the raw Thrift transport in a Client decorator. The client
// provides a convenient procedural interface for accessing the Thrift
// server.
val client = new Hello.ServiceToClient(service, protocolFactory)

In this example, Hello is the thrift interface, and the inner class ServiceToClient is provided by the finagle thrift code generator.

Definition Classes: finagle

package thriftmux

Definition Classes: finagle

package toggle

Definition Classes: finagle

package tracing

Definition Classes: finagle

package transport

Definition Classes: finagle

package tunable

Definition Classes: finagle

package util

Definition Classes: finagle

package zipkin

Definition Classes: finagle

package zookeeper

Definition Classes: finagle

com.twitter.finagle

filter

package filter

Ordering

Alphabetic

Visibility

Public
Protected

Type Members

trait AbstractDarkTrafficFilter extends AnyRef
class ClientExceptionTracingFilter[Req, Rep] extends SimpleFilter[Req, Rep]
Reports error and exception annotations when a span completes.
class DarkTrafficFilter[Req, Rep] extends SimpleFilter[Req, Rep] with AbstractDarkTrafficFilter
Forwards dark traffic to the given service when the given function returns true for a request.
class DtabStatsFilter[Req, Rep] extends SimpleFilter[Req, Rep]
Adds three stats:
Adds three stats:
- dtab/size, a default stat that tracks the size of both Dtab.limited and Dtab.local for all requests with a non-empty Dtab
- dtab/local/size, a debug stat which tracks just the size of Dtab.local for all requests with a non-empty Dtab
- dtab/limited/size, a debug stat which tracks just the size of Dtab.limited for all requests with a non-empty Dtab
class ExceptionSourceFilter[Req, Rep] extends SimpleFilter[Req, Rep]
A com.twitter.finagle.Filter that sources exceptions.
A com.twitter.finagle.Filter that sources exceptions. The serviceName and appId fields of any com.twitter.finagle.SourcedException thrown by the underlying com.twitter.finagle.Service is set to the serviceName and appId arguments of this filter.
abstract class ForwardingWarmUpFilter[Req, Rep] extends SimpleFilter[Req, Rep]
A filter that forwards thrift requests to a specified service.
A filter that forwards thrift requests to a specified service. It enables a smooth start of processing the requests by slowly increasing the percentage of requests that are being processed and lowering the amount of requests that are being forwarded.
trait LogFormatter[-Req, Rep] extends AnyRef
trait LoggingFilter[Req, Rep] extends SimpleFilter[Req, Rep]
A com.twitter.finagle.Filter that logs all requests according to formatter.
class MaskCancelFilter[Req, Rep] extends SimpleFilter[Req, Rep]
A com.twitter.finagle.Filter that prevents cancellations from propagating to any subsequent Services.
A com.twitter.finagle.Filter that prevents cancellations from propagating to any subsequent Services. i.e. when Future.raise is invoked on the result of this filter's apply method, the interrupt will not be propagated to the service. This is useful for lightweight protocols for which finishing a request is preferable to closing and reestablishing a connection.
class MkJvmFilter extends AnyRef
Given a com.twitter.util.Jvm, use apply to create a Filter to trace garbage collection events.
class MonitorFilter[Req, Rep] extends SimpleFilter[Req, Rep]
A com.twitter.finagle.Filter that handles exceptions (incl.
A com.twitter.finagle.Filter that handles exceptions (incl. raw) thrown by the subsequent com.twitter.finagle.Service. Exceptions are handled according to the argument com.twitter.util.Monitor.
class NackAdmissionFilter[Req, Rep] extends SimpleFilter[Req, Rep]
This filter probabilistically drops requests if the nack rate exceeds the nackRateThreshold.
This filter probabilistically drops requests if the nack rate exceeds the nackRateThreshold. In the case that most or all of the cluster which the client is speaking to is overloaded, this will help the cluster cool off.
The implementation of this filter is heavily inspired by Chapter 21, section "Client-Side Throttling" of O'Reilly's "Site Reliability Engineering: How Google Runs Production Systems", by Beyer, Jones, Petoff, and Murphy, 1e.
NOTE: Here is a brief summary of the configurable params.
A configuration with a nackRateThreshold of N% and a window of duration W roughly translates as, "start dropping some requests to the cluster when the nack rate averages at least N% over a window of duration W."
Here are some examples of situations with param values chosen to make the filter useful:
- Owners of Service A examine their service's nack rate over several days and find that it is almost always under 10% and rarely above 1% (e.g., during traffic spikes) or 5% (e.g., during a data center outage). They do not want to preemptively drop requests unless the cluster sees an extreme overload situation so they choose a nack rate threshold of 20%. And in such a situation they want the filter to act relatively quickly, so they choose a window of 30 seconds.
- Owners of Service B observe that excess load typically causes peak nack rates of around 25% for up to 60 seconds. They want to be aggressive about avoiding cluster overload and don’t mind dropping some innocent requests during mild load so they choose a window of 10 seconds and a threshold of 0.15 (= 15%).
class PayloadSizeFilter[Req, Rep] extends SimpleFilter[Req, Rep]
A filter that exports two histograms to a given StatsReceiver.
A filter that exports two histograms to a given StatsReceiver.
1. "request_payload_bytes" - a distribution of request payload sizes in bytes 2. "response_payload_bytes" - a distribution of response payload sizes in bytes
The sizes are also traced using the binary annotations clnt/request_payload_bytes and clnt/response_payload_bytes on the client side, and srv/request_payload_bytes and srv/response_payload_bytes. on the server.
class RequestMeterFilter[Req, Rep] extends SimpleFilter[Req, Rep]
A com.twitter.finagle.Filter that rate limits requests to a fixed rate over time by using the com.twitter.concurrent.AsyncMeter implementation.
A com.twitter.finagle.Filter that rate limits requests to a fixed rate over time by using the com.twitter.concurrent.AsyncMeter implementation. It can be used for slowing down access to throttled resources. Requests that cannot be enqueued to await a permit are failed immediately with a com.twitter.finagle.Failure that signals that the work was never done, so it's safe to reenqueue.
NOTE: If you're just trying not to be overwhelmed, you almost certainly want to use com.twitter.finagle.filter.RequestSemaphoreFilter instead, because RequestMeterFilter doesn't work well with "real" resources that are sometimes faster or slower (like a service that you're depending on that sometimes slows when it takes bursty traffic). This is better for resources that are artificially bounded, like a rate-limited API.
class RequestSemaphoreFilter[Req, Rep] extends SimpleFilter[Req, Rep]
A com.twitter.finagle.Filter that restricts request concurrency according to the given com.twitter.concurrent.AsyncSemaphore.
A com.twitter.finagle.Filter that restricts request concurrency according to the given com.twitter.concurrent.AsyncSemaphore. Requests that are unable to acquire a permit are failed immediately with a com.twitter.finagle.Failure that signals a restartable or idempotent process.
class ToggleAwareSimpleFilter[Req, Rep] extends SimpleFilter[Req, Rep]
Simple filter which calls the underlying filter if the toggle is enabled or passes the call through

Value Members

object AbstractDarkTrafficFilter
object DarkTrafficFilter
object DtabStatsFilter
object ExceptionSourceFilter
object MaskCancelFilter
object NackAdmissionFilter
object OffloadFilter
These modules introduce async-boundary into the future chain, effectively shifting continuations off of IO threads (into a given FuturePool).
These modules introduce async-boundary into the future chain, effectively shifting continuations off of IO threads (into a given FuturePool).
This filter can be enabled by default through the flag com.twitter.finagle.offload.numWorkers.
object PayloadSizeFilter
object RequestLogger
object RequestSemaphoreFilter
object restrictWorkQueueFiberZone extends GlobalFlag[Boolean]

Packages

Message framing

Exchanges

Messages

MuxFailure Flags

Security

Deprecation

Thrift codecs

filter

package filter

Type Members

Value Members

Ungrouped

filter