context.go

// Copyright 2016-2018 The NATS Authors
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package nats

import (
	"context"
	"reflect"
)

// RequestMsgWithContext takes a context, a subject and payload
// in bytes and request expecting a single response.
func (nc *Conn) RequestMsgWithContext(ctx context.Context, msg *Msg) (*Msg, error) {
	var hdr []byte
	var err error

	if len(msg.Header) > 0 {
		if !nc.info.Headers {
			return nil, ErrHeadersNotSupported
		}

		hdr, err = msg.headerBytes()
		if err != nil {
			return nil, err
		}
	}

	return nc.requestWithContext(ctx, msg.Subject, hdr, msg.Data)
}

// RequestWithContext takes a context, a subject and payload
// in bytes and request expecting a single response.
func (nc *Conn) RequestWithContext(ctx context.Context, subj string, data []byte) (*Msg, error) {
	return nc.requestWithContext(ctx, subj, nil, data)
}

func (nc *Conn) requestWithContext(ctx context.Context, subj string, hdr, data []byte) (*Msg, error) {
	if ctx == nil {
		return nil, ErrInvalidContext
	}
	if nc == nil {
		return nil, ErrInvalidConnection
	}
	// Check whether the context is done already before making
	// the request.
	if ctx.Err() != nil {
		return nil, ctx.Err()
	}

	var m *Msg
	var err error

	// If user wants the old style.
	if nc.useOldRequestStyle() {
		m, err = nc.oldRequestWithContext(ctx, subj, hdr, data)
	} else {
		mch, token, err := nc.createNewRequestAndSend(subj, hdr, data)
		if err != nil {
			return nil, err
		}

		var ok bool

		select {
		case m, ok = <-mch:
			if !ok {
				return nil, ErrConnectionClosed
			}
		case <-ctx.Done():
			nc.mu.Lock()
			delete(nc.respMap, token)
			nc.mu.Unlock()
			return nil, ctx.Err()
		}
	}
	// Check for no responder status.
	if err == nil && len(m.Data) == 0 && m.Header.Get(statusHdr) == noResponders {
		m, err = nil, ErrNoResponders
	}
	return m, err
}

// oldRequestWithContext utilizes inbox and subscription per request.
func (nc *Conn) oldRequestWithContext(ctx context.Context, subj string, hdr, data []byte) (*Msg, error) {
	inbox := nc.newInbox()
	ch := make(chan *Msg, RequestChanLen)

	s, err := nc.subscribe(inbox, _EMPTY_, nil, ch, true, nil)
	if err != nil {
		return nil, err
	}
	s.AutoUnsubscribe(1)
	defer s.Unsubscribe()

	err = nc.publish(subj, inbox, hdr, data)
	if err != nil {
		return nil, err
	}

	return s.NextMsgWithContext(ctx)
}

func (s *Subscription) nextMsgWithContext(ctx context.Context, pullSubInternal, waitIfNoMsg bool) (*Msg, error) {
	if ctx == nil {
		return nil, ErrInvalidContext
	}
	if s == nil {
		return nil, ErrBadSubscription
	}
	if ctx.Err() != nil {
		return nil, ctx.Err()
	}

	s.mu.Lock()
	err := s.validateNextMsgState(pullSubInternal)
	if err != nil {
		s.mu.Unlock()
		return nil, err
	}

	// snapshot
	mch := s.mch
	s.mu.Unlock()

	var ok bool
	var msg *Msg

	// If something is available right away, let's optimize that case.
	select {
	case msg, ok = <-mch:
		if !ok {
			return nil, s.getNextMsgErr()
		}
		if err := s.processNextMsgDelivered(msg); err != nil {
			return nil, err
		} else {
			return msg, nil
		}
	default:
		// If internal and we don't want to wait, signal that there is no
		// message in the internal queue.
		if pullSubInternal && !waitIfNoMsg {
			return nil, errNoMessages
		}
	}

	select {
	case msg, ok = <-mch:
		if !ok {
			return nil, s.getNextMsgErr()
		}
		if err := s.processNextMsgDelivered(msg); err != nil {
			return nil, err
		}
	case <-ctx.Done():
		return nil, ctx.Err()
	}

	return msg, nil
}

// NextMsgWithContext takes a context and returns the next message
// available to a synchronous subscriber, blocking until it is delivered
// or context gets canceled.
func (s *Subscription) NextMsgWithContext(ctx context.Context) (*Msg, error) {
	return s.nextMsgWithContext(ctx, false, true)
}

// FlushWithContext will allow a context to control the duration
// of a Flush() call. This context should be non-nil and should
// have a deadline set. We will return an error if none is present.
func (nc *Conn) FlushWithContext(ctx context.Context) error {
	if nc == nil {
		return ErrInvalidConnection
	}
	if ctx == nil {
		return ErrInvalidContext
	}
	_, ok := ctx.Deadline()
	if !ok {
		return ErrNoDeadlineContext
	}

	nc.mu.Lock()
	if nc.isClosed() {
		nc.mu.Unlock()
		return ErrConnectionClosed
	}
	// Create a buffered channel to prevent chan send to block
	// in processPong()
	ch := make(chan struct{}, 1)
	nc.sendPing(ch)
	nc.mu.Unlock()

	var err error

	select {
	case _, ok := <-ch:
		if !ok {
			err = ErrConnectionClosed
		} else {
			close(ch)
		}
	case <-ctx.Done():
		err = ctx.Err()
	}

	if err != nil {
		nc.removeFlushEntry(ch)
	}

	return err
}

// RequestWithContext will create an Inbox and perform a Request
// using the provided cancellation context with the Inbox reply
// for the data v. A response will be decoded into the vPtrResponse.
func (c *EncodedConn) RequestWithContext(ctx context.Context, subject string, v interface{}, vPtr interface{}) error {
	if ctx == nil {
		return ErrInvalidContext
	}

	b, err := c.Enc.Encode(subject, v)
	if err != nil {
		return err
	}
	m, err := c.Conn.RequestWithContext(ctx, subject, b)
	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)
		if err != nil {
			return err
		}
	}

	return nil
}