messaging

package
v0.9.0-rc17 Latest Latest
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 Go to latest Published: Mar 30, 2015 License: MIT Imports: 20 Imported by: 0

Documentation

Overview

Package messaging implements a distributed, raft-backed messaging system.

Basics

The broker writes every configuration change and data insert and replicates those changes to data nodes across the cluster. These changes are segmented into multiple topics so that they can be parallelized. Configuration changes are placed in a single "config" topic that is replicated to all data nodes. Each shard's data is placed in its own topic so that it can be parallized across the cluster.

Index

Constants

View Source 
const (
	// DefaultReconnectTimeout is the default time to wait between when a broker
	// stream disconnects and another connection is retried.
	DefaultReconnectTimeout = 1000 * time.Millisecond

	// DefaultPingInterval is the default time to wait between checks to the broker.
	DefaultPingInterval = 1000 * time.Millisecond
)
View Source 
const BrokerMessageType = 0x8000

BrokerMessageType is a flag set on broker messages to prevent them from being passed through to topics.

View Source 
const DefaultMaxSegmentSize = 10 * 1024 * 1024 // 10MB

DefaultMaxSegmentSize is the largest a segment can get before starting a new segment.

View Source 
const DefaultPollInterval = 100 * time.Millisecond

DefaultPollInterval is the default amount of time a topic reader will wait between checks for new segments or new data on an existing segment. This only occurs when the reader is at the end of all the data.

View Source 
const (
	SetTopicMaxIndexMessageType = BrokerMessageType | MessageType(0x00)
)

Variables

View Source 
var (
	// ErrPathRequired is returned when opening a broker without a path.
	ErrPathRequired = errors.New("path required")

	// ErrPathRequired is returned when opening a broker without a connection address.
	ErrConnectionAddressRequired = errors.New("connection address required")

	// ErrClosed is returned when closing a broker that's already closed.
	ErrClosed = errors.New("broker already closed")

	// ErrSubscribed is returned when a stream is already subscribed to a topic.
	ErrSubscribed = errors.New("already subscribed")

	// ErrTopicExists is returned when creating a duplicate topic.
	ErrTopicExists = errors.New("topic already exists")

	// ErrReplicaExists is returned when creating a duplicate replica.
	ErrReplicaExists = errors.New("replica already exists")

	// ErrReplicaNotFound is returned when referencing a replica that doesn't exist.
	ErrReplicaNotFound = errors.New("replica not found")

	// ErrReplicaIDRequired is returned when creating a replica without an id.
	ErrReplicaIDRequired = errors.New("replica id required")

	// ErrClientOpen is returned when opening an already open client.
	ErrClientOpen = errors.New("client already open")

	// ErrClientClosed is returned when closing an already closed client.
	ErrClientClosed = errors.New("client closed")

	// ErrConnOpen is returned when opening an already open connection.
	ErrConnOpen = errors.New("connection already open")

	// ErrConnClosed is returned when closing an already closed connection.
	ErrConnClosed = errors.New("connection closed")

	// ErrConnCannotReuse is returned when opening a previously closed connection.
	ErrConnCannotReuse = errors.New("cannot reuse connection")

	// ErrMessageTypeRequired is returned publishing a message without a type.
	ErrMessageTypeRequired = errors.New("message type required")

	// ErrTopicRequired is returned publishing a message without a topic ID.
	ErrTopicRequired = errors.New("topic required")

	// ErrNoLeader is returned when a leader cannot be reached.
	ErrNoLeader = errors.New("no leader")

	// ErrIndexRequired is returned when making a call without a valid index.
	ErrIndexRequired = errors.New("index required")

	// ErrTopicOpen is returned when opening an already open topic.
	ErrTopicOpen = errors.New("topic already open")

	// ErrSegmentReclaimed is returned when requesting a segment that has been deleted.
	ErrSegmentReclaimed = errors.New("segment reclaimed")

	// ErrStaleWrite is returned when writing a message with an old index to a topic.
	ErrStaleWrite = errors.New("stale write")

	// ErrReaderClosed is returned when reading from a closed topic reader.
	ErrReaderClosed = errors.New("reader closed")

	// ErrMessageDataRequired is returned when publishing a message without data.
	ErrMessageDataRequired = errors.New("message data required")
)

Functions

func CopyFlush 

func CopyFlush(dst io.Writer, src io.Reader) (written int64, err error)

CopyFlush copies from src to dst until EOF or an error occurs. Each write is proceeded by a flush, if the writer implements http.Flusher.

This implementation is copied from io.Copy().

func ReadSegmentMaxIndex 

func ReadSegmentMaxIndex(path string) (uint64, error)

ReadSegmentMaxIndex returns the highest index recorded in a segment.

Types

type Broker 

type Broker struct {

	// Log is the distributed raft log that commands are applied to.
	Log interface {
		URL() url.URL
		URLs() []url.URL
		Leader() (uint64, url.URL)
		IsLeader() bool
		ClusterID() uint64
		Apply(data []byte) (index uint64, err error)
	}

	Logger *log.Logger
	// contains filtered or unexported fields
}

Broker represents distributed messaging system segmented into topics. Each topic represents a linear series of events.

func NewBroker 

func NewBroker() *Broker

NewBroker returns a new instance of a Broker with default values.

func (*Broker) Apply 

func (b *Broker) Apply(m *Message) error

Apply executes a message against the broker.

func (*Broker) Close 

func (b *Broker) Close() error

Close closes the broker and all topics.

func (*Broker) ClusterID 

func (b *Broker) ClusterID() uint64

ClusterID returns the identifier for the cluster.

func (*Broker) Index 

func (b *Broker) Index() uint64

Index returns the highest index seen by the broker across all topics. Returns 0 if the broker is closed.

func (*Broker) IsLeader 

func (b *Broker) IsLeader() bool

IsLeader returns true if the broker is the current cluster leader.

func (*Broker) LeaderURL 

func (b *Broker) LeaderURL() url.URL

LeaderURL returns the URL to the leader broker.

func (*Broker) Open 

func (b *Broker) Open(path string) error

Open initializes the log. The broker then must be initialized or join a cluster before it can be used.

func (*Broker) Path 

func (b *Broker) Path() string

Path returns the path used when opening the broker. Returns empty string if the broker is not open.

func (*Broker) Publish 

func (b *Broker) Publish(m *Message) (uint64, error)

Publish writes a message. Returns the index of the message. Otherwise returns an error.

func (*Broker) ReadFrom 

func (b *Broker) ReadFrom(r io.Reader) (int64, error)

ReadFrom reads a broker snapshot from r.

func (*Broker) SetMaxIndex 

func (b *Broker) SetMaxIndex(index uint64) error

SetMaxIndex sets the highest index applied by the broker. This is only used for internal log messages. Topics may have a higher index.

func (*Broker) SetTopicMaxIndex 

func (b *Broker) SetTopicMaxIndex(topicID, index uint64) error

SetTopicMaxIndex updates the highest replicated index for a topic. If a higher index is already set on the topic then the call is ignored. This index is only held in memory and is used for topic segment reclamation.

func (*Broker) Topic 

func (b *Broker) Topic(id uint64) *Topic

Topic returns a topic on a broker by id. Returns nil if the topic doesn't exist or the broker is closed.

func (*Broker) TopicPath 

func (b *Broker) TopicPath(id uint64) string

TopicPath returns the file path to a topic's data. Returns a blank string if the broker is closed.

func (*Broker) TopicReader 

func (b *Broker) TopicReader(topicID, index uint64, streaming bool) io.ReadCloser

TopicReader returns a new topic reader for a topic starting from a given index.

func (*Broker) URL 

func (b *Broker) URL() url.URL

URL returns the URL of the broker.

func (*Broker) URLs 

func (b *Broker) URLs() []url.URL

URLs returns a list of all broker URLs in the cluster.

func (*Broker) WriteTo 

func (b *Broker) WriteTo(w io.Writer) (int64, error)

WriteTo writes a snapshot of the broker to w.

type Client 

type Client struct {

	// The amount of time to wait before reconnecting to a broker stream.
	ReconnectTimeout time.Duration

	// The amount of time between pings to verify the broker is alive.
	PingInterval time.Duration

	// The logging interface used by the client for out-of-band errors.
	Logger *log.Logger
	// contains filtered or unexported fields
}

Client represents a client for the broker's HTTP API.

func NewClient 

func NewClient() *Client

NewClient returns a new instance of Client with defaults set.

func (*Client) Close 

func (c *Client) Close() error

Close disconnects the client from the broker cluster.

func (*Client) Conn 

func (c *Client) Conn(topicID uint64) *Conn

Conn returns a connection to the broker for a given topic.

func (*Client) Open 

func (c *Client) Open(path string) error

Open opens the client and reads the configuration from the specified path.

func (*Client) Ping 

func (c *Client) Ping() error

Ping sends a request to the current broker to check if it is alive. If the broker is down then a new URL is tried.

func (*Client) Publish 

func (c *Client) Publish(m *Message) (uint64, error)

Publish sends a message to the broker and returns an index or error.

func (*Client) SetURL 

func (c *Client) SetURL(u url.URL)

SetURL sets the current URL to connect to for the client and its connections.

func (*Client) SetURLs 

func (c *Client) SetURLs(a []url.URL)

SetURLs sets a list of possible URLs to connect to for the client and its connections.

func (*Client) URL 

func (c *Client) URL() url.URL

URL returns the current broker leader's URL.

func (*Client) URLs 

func (c *Client) URLs() []url.URL

URLs returns a list of possible broker URLs to connect to.

type ClientConfig 

type ClientConfig struct {
	URLs []url.URL
}

ClientConfig represents the configuration that must be persisted across restarts.

func (ClientConfig) MarshalJSON 

func (c ClientConfig) MarshalJSON() ([]byte, error)

func (*ClientConfig) UnmarshalJSON 

func (c *ClientConfig) UnmarshalJSON(b []byte) error

type Conn 

type Conn struct {

	// The amount of time to wait before reconnecting to a broker stream.
	ReconnectTimeout time.Duration

	// The logging interface used by the connection for out-of-band errors.
	Logger *log.Logger
	// contains filtered or unexported fields
}

Conn represents a stream over the client for a single topic.

func NewConn 

func NewConn(topicID uint64) *Conn

NewConn returns a new connection to the broker for a topic.

func (*Conn) C 

func (c *Conn) C() <-chan *Message

C returns streaming channel for the connection.

func (*Conn) Close 

func (c *Conn) Close() error

Close closes a connection.

func (*Conn) Heartbeat 

func (c *Conn) Heartbeat() error

Heartbeat sends a heartbeat back to the broker with the client's index.

func (*Conn) Index 

func (c *Conn) Index() uint64

Index returns the highest index replicated to the caller.

func (*Conn) Open 

func (c *Conn) Open(index uint64, streaming bool) error

Open opens a streaming connection to the broker.

func (*Conn) SetIndex 

func (c *Conn) SetIndex(index uint64)

SetIndex sets the highest index replicated to the caller.

func (*Conn) SetURL 

func (c *Conn) SetURL(u url.URL)

SetURL sets the current URL of the connection.

func (*Conn) Streaming 

func (c *Conn) Streaming() bool

Streaming returns true if the connection streams messages continuously.

func (*Conn) TopicID 

func (c *Conn) TopicID() uint64

TopicID returns the connection's topic id.

func (*Conn) URL 

func (c *Conn) URL() url.URL

URL returns the current URL of the connection.

type Handler 

type Handler struct {
	Broker interface {
		URLs() []url.URL
		IsLeader() bool
		LeaderURL() url.URL
		TopicReader(topicID, index uint64, streaming bool) io.ReadCloser
		Publish(m *Message) (uint64, error)
		SetTopicMaxIndex(topicID, index uint64) error
	}

	RaftHandler http.Handler
}

Handler represents an HTTP handler by the broker.

func (*Handler) ServeHTTP 

func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request)

ServeHTTP serves an HTTP request.

type Message 

type Message struct {
	Type    MessageType
	TopicID uint64
	Index   uint64
	Data    []byte
}

Message represents a single item in a topic.

func UnmarshalMessage 

func UnmarshalMessage(data []byte) (*Message, error)

UnmarshalMessage decodes a byte slice into a message.

func (*Message) MarshalBinary 

func (m *Message) MarshalBinary() ([]byte, error)

MarshalBinary returns a binary representation of the message. This implements encoding.BinaryMarshaler. An error cannot be returned.

func (*Message) UnmarshalBinary 

func (m *Message) UnmarshalBinary(b []byte) error

UnmarshalBinary reads a message from a binary encoded slice. This implements encoding.BinaryUnmarshaler.

func (*Message) WriteTo 

func (m *Message) WriteTo(w io.Writer) (n int64, err error)

WriteTo encodes and writes the message to a writer. Implements io.WriterTo.

type MessageDecoder 

type MessageDecoder struct {
	// contains filtered or unexported fields
}

MessageDecoder decodes messages from a reader.

func NewMessageDecoder 

func NewMessageDecoder(r io.Reader) *MessageDecoder

NewMessageDecoder returns a new instance of the MessageDecoder.

func (*MessageDecoder) Decode 

func (dec *MessageDecoder) Decode(m *Message) error

Decode reads a message from the decoder's reader.

type MessageType 

type MessageType uint16

MessageType represents the type of message.

type RaftFSM 

type RaftFSM struct {
	Broker interface {
		io.WriterTo
		io.ReaderFrom

		Apply(m *Message) error
		Index() uint64
		SetMaxIndex(uint64) error
	}
}

RaftFSM is a wrapper struct around the broker that implements the raft.FSM interface. It will panic for any errors that occur during Apply.

func (*RaftFSM) Apply 

func (fsm *RaftFSM) Apply(e *raft.LogEntry) error

Apply applies a raft command to the broker.

func (*RaftFSM) Index 

func (fsm *RaftFSM) Index() uint64

func (*RaftFSM) ReadFrom 

func (fsm *RaftFSM) ReadFrom(r io.Reader) (n int64, err error)

func (*RaftFSM) WriteTo 

func (fsm *RaftFSM) WriteTo(w io.Writer) (n int64, err error)

type Segment 

type Segment struct {
	Index uint64 // starting index of the segment and name
	Path  string // path to the segment file.
}

Segment represents a contiguous section of a topic log.

func ReadSegmentByIndex 

func ReadSegmentByIndex(path string, index uint64) (*Segment, error)

ReadSegmentByIndex returns the segment that contains a given index.

func (*Segment) Size 

func (s *Segment) Size() (int64, error)

Size returns the file size of the segment.

type Segments 

type Segments []*Segment

Segments represents a list of segments sorted by index.

func ReadSegments 

func ReadSegments(path string) (Segments, error)

ReadSegments reads all segments from a directory path.

func (Segments) Last 

func (a Segments) Last() *Segment

Last returns the last segment in the slice. Returns nil if there are no segments.

func (Segments) Len 

func (a Segments) Len() int

func (Segments) Less 

func (a Segments) Less(i, j int) bool

func (Segments) Swap 

func (a Segments) Swap(i, j int)

type Topic 

type Topic struct {

	// The largest a segment can get before splitting into a new segment.
	MaxSegmentSize int64
	// contains filtered or unexported fields
}

topic represents a single named queue of messages. Each topic is identified by a unique path.

Topics write their entries to segmented log files which contain a contiguous range of entries.

func NewTopic 

func NewTopic(id uint64, path string) *Topic

NewTopic returns a new instance of Topic.

func (*Topic) Close 

func (t *Topic) Close() error

Close closes the topic and segment writer.

func (*Topic) ID 

func (t *Topic) ID() uint64

ID returns the topic identifier.

func (*Topic) Index 

func (t *Topic) Index() uint64

Index returns the highest replicated index for the topic.

func (*Topic) Open 

func (t *Topic) Open() error

Open opens a topic for writing.

func (*Topic) Path 

func (t *Topic) Path() string

Path returns the topic path.

func (*Topic) ReadIndex 

func (t *Topic) ReadIndex() (uint64, error)

ReadIndex reads the highest available index for a topic from disk.

func (*Topic) SegmentPath 

func (t *Topic) SegmentPath(index uint64) string

SegmentPath returns the path to a segment starting with a given log index.

func (*Topic) WriteMessage 

func (t *Topic) WriteMessage(m *Message) error

WriteMessage writes a message to the end of the topic.

type TopicReader 

type TopicReader struct {

	// The time between file system polling to check for new segments.
	PollInterval time.Duration
	// contains filtered or unexported fields
}

TopicReader reads data on a single topic from a given index.

func NewTopicReader 

func NewTopicReader(path string, index uint64, streaming bool) *TopicReader

NewTopicReader returns a new instance of TopicReader that reads segments from a path starting from a given index.

func (*TopicReader) Close 

func (r *TopicReader) Close() error

Close closes the reader.

func (*TopicReader) File 

func (r *TopicReader) File() (*os.File, error)

File returns the current segment file handle. Returns nil when there is no more data left.

func (*TopicReader) Read 

func (r *TopicReader) Read(p []byte) (int, error)

Read reads the next bytes from the reader into the buffer.

type Topics 

type Topics []*Topic

Topics represents a list of topics sorted by id.

func ReadTopics 

func ReadTopics(path string) (Topics, error)

ReadTopics reads all topics from a directory path.

func (Topics) Len 

func (a Topics) Len() int

func (Topics) Less 

func (a Topics) Less(i, j int) bool

func (Topics) Swap 

func (a Topics) Swap(i, j int)

Source Files

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