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// Copyright 2012, 2013 Canonical Ltd.
// Licensed under the AGPLv3, see LICENCE file for details.
package rpc
import (
"errors"
"strings"
)
var ErrShutdown = errors.New("connection is shut down")
// Call represents an active RPC.
type Call struct {
Request
Params interface{}
Response interface{}
Error error
Done chan *Call
}
// RequestError represents an error returned from an RPC request.
type RequestError struct {
Message string
Code string
}
func (e *RequestError) Error() string {
m := "request error: " + e.Message
if e.Code != "" {
m += " (" + e.Code + ")"
}
return m
}
func (e *RequestError) ErrorCode() string {
return e.Code
}
func (conn *Conn) send(call *Call) {
conn.sending.Lock()
defer conn.sending.Unlock()
// Register this call.
conn.mutex.Lock()
if conn.dead == nil {
panic("rpc: call made when connection not started")
}
if conn.closing || conn.shutdown {
call.Error = ErrShutdown
conn.mutex.Unlock()
call.done()
return
}
conn.reqId++
reqId := conn.reqId
conn.clientPending[reqId] = call
conn.mutex.Unlock()
// Encode and send the request.
hdr := &Header{
RequestId: reqId,
Request: call.Request,
}
params := call.Params
if params == nil {
params = struct{}{}
}
if conn.notifier != nil {
conn.notifier.ClientRequest(hdr, params)
}
if err := conn.codec.WriteMessage(hdr, params); err != nil {
conn.mutex.Lock()
call = conn.clientPending[reqId]
delete(conn.clientPending, reqId)
conn.mutex.Unlock()
if call != nil {
call.Error = err
call.done()
}
}
}
func (conn *Conn) handleResponse(hdr *Header) error {
reqId := hdr.RequestId
conn.mutex.Lock()
call := conn.clientPending[reqId]
delete(conn.clientPending, reqId)
conn.mutex.Unlock()
var err error
switch {
case call == nil:
// We've got no pending call. That usually means that
// WriteHeader partially failed, and call was already
// removed; response is a server telling us about an
// error reading request body. We should still attempt
// to read error body, but there's no one to give it to.
if conn.notifier != nil {
conn.notifier.ClientReply(Request{}, hdr, nil)
}
err = conn.readBody(nil, false)
case hdr.Error != "":
// Report rpcreflect.NoSuchMethodError with CodeNotImplemented.
if strings.HasPrefix(hdr.Error, "no such request ") && hdr.ErrorCode == "" {
hdr.ErrorCode = CodeNotImplemented
}
// We've got an error response. Give this to the request;
// any subsequent requests will get the ReadResponseBody
// error if there is one.
call.Error = &RequestError{
Message: hdr.Error,
Code: hdr.ErrorCode,
}
err = conn.readBody(nil, false)
if conn.notifier != nil {
conn.notifier.ClientReply(call.Request, hdr, nil)
}
call.done()
default:
err = conn.readBody(call.Response, false)
if conn.notifier != nil {
conn.notifier.ClientReply(call.Request, hdr, call.Response)
}
call.done()
}
return err
}
func (call *Call) done() {
select {
case call.Done <- call:
// ok
default:
// We don't want to block here. It is the caller's responsibility to make
// sure the channel has enough buffer space. See comment in Go().
logger.Errorf("discarding Call reply due to insufficient Done chan capacity")
}
}
// Call invokes the named action on the object of the given type with
// the given id. The returned values will be stored in response, which
// should be a pointer. If the action fails remotely, the returned
// error will be of type RequestError. The params value may be nil if
// no parameters are provided; the response value may be nil to indicate
// that any result should be discarded.
func (conn *Conn) Call(req Request, params, response interface{}) error {
call := <-conn.Go(req, params, response, make(chan *Call, 1)).Done
return call.Error
}
// Go invokes the request asynchronously. It returns the Call structure representing
// the invocation. The done channel will signal when the call is complete by returning
// the same Call object. If done is nil, Go will allocate a new channel.
// If non-nil, done must be buffered or Go will deliberately panic.
func (conn *Conn) Go(req Request, args, response interface{}, done chan *Call) *Call {
if done == nil {
done = make(chan *Call, 1)
} else {
// If caller passes done != nil, it must arrange that
// done has enough buffer for the number of simultaneous
// RPCs that will be using that channel. If the channel
// is totally unbuffered, it's best not to run at all.
if cap(done) == 0 {
panic("launchpad.net/juju-core/rpc: done channel is unbuffered")
}
}
call := &Call{
Request: req,
Params: args,
Response: response,
Done: done,
}
conn.send(call)
return call
}
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