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// Copyright 2012-2015 Apcera Inc. All rights reserved.
package nats
import (
"errors"
"fmt"
"reflect"
"sync"
"time"
// Default Encoders
. "github.com/nats-io/go-nats/encoders/builtin"
)
// Encoder interface is for all register encoders
type Encoder interface {
Encode(subject string, v interface{}) ([]byte, error)
Decode(subject string, data []byte, vPtr interface{}) error
}
var encMap map[string]Encoder
var encLock sync.Mutex
// Indexe names into the Registered Encoders.
const (
JSON_ENCODER = "json"
GOB_ENCODER = "gob"
DEFAULT_ENCODER = "default"
)
func init() {
encMap = make(map[string]Encoder)
// Register json, gob and default encoder
RegisterEncoder(JSON_ENCODER, &JsonEncoder{})
RegisterEncoder(GOB_ENCODER, &GobEncoder{})
RegisterEncoder(DEFAULT_ENCODER, &DefaultEncoder{})
}
// EncodedConn are the preferred way to interface with NATS. They wrap a bare connection to
// a nats server and have an extendable encoder system that will encode and decode messages
// from raw Go types.
type EncodedConn struct {
Conn *Conn
Enc Encoder
}
// NewEncodedConn will wrap an existing Connection and utilize the appropriate registered
// encoder.
func NewEncodedConn(c *Conn, encType string) (*EncodedConn, error) {
if c == nil {
return nil, errors.New("nats: Nil Connection")
}
if c.IsClosed() {
return nil, ErrConnectionClosed
}
ec := &EncodedConn{Conn: c, Enc: EncoderForType(encType)}
if ec.Enc == nil {
return nil, fmt.Errorf("No encoder registered for '%s'", encType)
}
return ec, nil
}
// RegisterEncoder will register the encType with the given Encoder. Useful for customization.
func RegisterEncoder(encType string, enc Encoder) {
encLock.Lock()
defer encLock.Unlock()
encMap[encType] = enc
}
// EncoderForType will return the registered Encoder for the encType.
func EncoderForType(encType string) Encoder {
encLock.Lock()
defer encLock.Unlock()
return encMap[encType]
}
// Publish publishes the data argument to the given subject. The data argument
// will be encoded using the associated encoder.
func (c *EncodedConn) Publish(subject string, v interface{}) error {
b, err := c.Enc.Encode(subject, v)
if err != nil {
return err
}
return c.Conn.publish(subject, _EMPTY_, b)
}
// PublishRequest will perform a Publish() expecting a response on the
// reply subject. Use Request() for automatically waiting for a response
// inline.
func (c *EncodedConn) PublishRequest(subject, reply string, v interface{}) error {
b, err := c.Enc.Encode(subject, v)
if err != nil {
return err
}
return c.Conn.publish(subject, reply, b)
}
// Request will create an Inbox and perform a Request() call
// with the Inbox reply for the data v. A response will be
// decoded into the vPtrResponse.
func (c *EncodedConn) Request(subject string, v interface{}, vPtr interface{}, timeout time.Duration) error {
b, err := c.Enc.Encode(subject, v)
if err != nil {
return err
}
m, err := c.Conn.Request(subject, b, timeout)
if err != nil {
return err
}
if reflect.TypeOf(vPtr) == emptyMsgType {
mPtr := vPtr.(*Msg)
*mPtr = *m
} else {
err = c.Enc.Decode(m.Subject, m.Data, vPtr)
}
return err
}
// Handler is a specific callback used for Subscribe. It is generalized to
// an interface{}, but we will discover its format and arguments at runtime
// and perform the correct callback, including de-marshalling JSON strings
// back into the appropriate struct based on the signature of the Handler.
//
// Handlers are expected to have one of four signatures.
//
// type person struct {
// Name string `json:"name,omitempty"`
// Age uint `json:"age,omitempty"`
// }
//
// handler := func(m *Msg)
// handler := func(p *person)
// handler := func(subject string, o *obj)
// handler := func(subject, reply string, o *obj)
//
// These forms allow a callback to request a raw Msg ptr, where the processing
// of the message from the wire is untouched. Process a JSON representation
// and demarshal it into the given struct, e.g. person.
// There are also variants where the callback wants either the subject, or the
// subject and the reply subject.
type Handler interface{}
// Dissect the cb Handler's signature
func argInfo(cb Handler) (reflect.Type, int) {
cbType := reflect.TypeOf(cb)
if cbType.Kind() != reflect.Func {
panic("nats: Handler needs to be a func")
}
numArgs := cbType.NumIn()
if numArgs == 0 {
return nil, numArgs
}
return cbType.In(numArgs - 1), numArgs
}
var emptyMsgType = reflect.TypeOf(&Msg{})
// Subscribe will create a subscription on the given subject and process incoming
// messages using the specified Handler. The Handler should be a func that matches
// a signature from the description of Handler from above.
func (c *EncodedConn) Subscribe(subject string, cb Handler) (*Subscription, error) {
return c.subscribe(subject, _EMPTY_, cb)
}
// QueueSubscribe will create a queue subscription on the given subject and process
// incoming messages using the specified Handler. The Handler should be a func that
// matches a signature from the description of Handler from above.
func (c *EncodedConn) QueueSubscribe(subject, queue string, cb Handler) (*Subscription, error) {
return c.subscribe(subject, queue, cb)
}
// Internal implementation that all public functions will use.
func (c *EncodedConn) subscribe(subject, queue string, cb Handler) (*Subscription, error) {
if cb == nil {
return nil, errors.New("nats: Handler required for EncodedConn Subscription")
}
argType, numArgs := argInfo(cb)
if argType == nil {
return nil, errors.New("nats: Handler requires at least one argument")
}
cbValue := reflect.ValueOf(cb)
wantsRaw := (argType == emptyMsgType)
natsCB := func(m *Msg) {
var oV []reflect.Value
if wantsRaw {
oV = []reflect.Value{reflect.ValueOf(m)}
} else {
var oPtr reflect.Value
if argType.Kind() != reflect.Ptr {
oPtr = reflect.New(argType)
} else {
oPtr = reflect.New(argType.Elem())
}
if err := c.Enc.Decode(m.Subject, m.Data, oPtr.Interface()); err != nil {
if c.Conn.Opts.AsyncErrorCB != nil {
c.Conn.ach <- func() {
c.Conn.Opts.AsyncErrorCB(c.Conn, m.Sub, errors.New("nats: Got an error trying to unmarshal: "+err.Error()))
}
}
return
}
if argType.Kind() != reflect.Ptr {
oPtr = reflect.Indirect(oPtr)
}
// Callback Arity
switch numArgs {
case 1:
oV = []reflect.Value{oPtr}
case 2:
subV := reflect.ValueOf(m.Subject)
oV = []reflect.Value{subV, oPtr}
case 3:
subV := reflect.ValueOf(m.Subject)
replyV := reflect.ValueOf(m.Reply)
oV = []reflect.Value{subV, replyV, oPtr}
}
}
cbValue.Call(oV)
}
return c.Conn.subscribe(subject, queue, natsCB, nil)
}
// FlushTimeout allows a Flush operation to have an associated timeout.
func (c *EncodedConn) FlushTimeout(timeout time.Duration) (err error) {
return c.Conn.FlushTimeout(timeout)
}
// Flush will perform a round trip to the server and return when it
// receives the internal reply.
func (c *EncodedConn) Flush() error {
return c.Conn.Flush()
}
// Close will close the connection to the server. This call will release
// all blocking calls, such as Flush(), etc.
func (c *EncodedConn) Close() {
c.Conn.Close()
}
// LastError reports the last error encountered via the Connection.
func (c *EncodedConn) LastError() error {
return c.Conn.err
}