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server.go
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server.go
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package commandbusnats
import (
"context"
"github.com/go-gulfstream/gulfstream/pkg/stream"
"github.com/go-gulfstream/gulfstream/pkg/command"
"github.com/nats-io/nats.go"
)
const errKey = "_e"
type ServerRequestFunc func(h nats.Header, c *command.Command)
type ServerResponseFunc func(h nats.Header, r *command.Reply)
type ContextFunc func(ctx context.Context) context.Context
type ServerErrorHandler func(msg *nats.Msg, err error)
type Server struct {
subject string
mutator stream.CommandSinker
commandCodec command.Encoding
requestFunc []ServerRequestFunc
responseFunc []ServerResponseFunc
contextFunc []ContextFunc
errorHandler []ServerErrorHandler
}
func NewServer(
subject string,
mutator stream.CommandSinker,
opts ...ServerOption,
) *Server {
srv := &Server{
subject: toSubj(subject),
mutator: mutator,
}
for _, opt := range opts {
opt(srv)
}
return srv
}
type ServerOption func(*Server)
func WithServerCodec(c command.Encoding) ServerOption {
return func(srv *Server) {
srv.commandCodec = c
}
}
func WithServerRequestFunc(fn ServerRequestFunc) ServerOption {
return func(srv *Server) {
srv.requestFunc = append(srv.requestFunc, fn)
}
}
func WithServerResponseFunc(fn ServerResponseFunc) ServerOption {
return func(srv *Server) {
srv.responseFunc = append(srv.responseFunc, fn)
}
}
func WithServerContextFunc(fn ContextFunc) ServerOption {
return func(srv *Server) {
srv.contextFunc = append(srv.contextFunc, fn)
}
}
func WithServerErrorHandler(fn ServerErrorHandler) ServerOption {
return func(srv *Server) {
srv.errorHandler = append(srv.errorHandler, fn)
}
}
func (s *Server) Listen(conn *nats.Conn) error {
if _, err := conn.QueueSubscribe(s.subject, s.subject, func(msg *nats.Msg) {
rawReply := s.handleMsg(msg)
if err := msg.Respond(rawReply); err != nil {
s.handleError(msg, err)
}
}); err != nil {
return err
}
if err := conn.Flush(); err != nil {
return err
}
return conn.LastError()
}
func (s *Server) handleMsg(msg *nats.Msg) []byte {
ctx, cancel := context.WithCancel(context.Background())
defer cancel()
for _, ctxFunc := range s.contextFunc {
ctx = ctxFunc(ctx)
}
if msg.Header == nil {
msg.Header = nats.Header{}
}
cmd, err := s.decodeCommand(msg.Data)
if err != nil {
return s.writeError(msg, err)
}
for _, reqFunc := range s.requestFunc {
reqFunc(msg.Header, cmd)
}
reply, err := s.mutator.CommandSink(ctx, cmd)
if err != nil {
return s.writeError(msg, err)
}
for _, respFunc := range s.responseFunc {
respFunc(msg.Header, reply)
}
rawReply, err := reply.MarshalBinary()
if err != nil {
return s.writeError(msg, err)
}
msg.Header.Del(errKey)
return rawReply
}
func (s *Server) handleError(msg *nats.Msg, err error) {
for _, errFunc := range s.errorHandler {
errFunc(msg, err)
}
}
func (s *Server) writeError(msg *nats.Msg, err error) []byte {
s.handleError(msg, err)
msg.Header.Set(errKey, errKey)
return []byte(err.Error())
}
func (s *Server) decodeCommand(data []byte) (*command.Command, error) {
if s.commandCodec != nil {
return s.commandCodec.Decode(data)
} else {
return command.Decode(data)
}
}