Start with com.twitter.finagle.
Start with com.twitter.finagle.
Finagle is an extensible RPC system.
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.
Package exp contains experimental code.
Package exp contains experimental code. This can be removed or stabilized (moved elsewhere) at any time.
This package implements client side load balancing algorithms.
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).
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.
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.
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.
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:
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.
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
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 peerDesired signals that TLS is preferred but not required by this peerRequired 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.
Package netty4 implements the bottom finagle primitives: com.twitter.finagle.Server and a client transport in terms of the netty4 event loop.
Package netty4 implements the bottom finagle primitives: com.twitter.finagle.Server and a client transport in terms of the netty4 event loop.
Defines common com.twitter.finagle.Stack.Param's shared between finagle clients and servers.
Defines common com.twitter.finagle.Stack.Param's shared between finagle clients and servers.
Please use the new interface, com.twitter.finagle.Thrift, for constructing Thrift clients and servers.
Please use the new interface, com.twitter.finagle.Thrift, for constructing Thrift clients and servers.
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.
This object contains utility functions for adding and removing weight metadata for com.twitter.finagle.Address.
This object contains utility functions for adding and removing weight metadata for com.twitter.finagle.Address.
These weights are consumed by a com.twitter.finagle.factory.TrafficDistributor.