Sending a message to set of hosts with acknowledgements - go

Question

Function is like:
func Message(worker_ID int, message string, args *Args , reply *int) chan bool {
}
This function resides at host which is called by client when it want to send the message to hosts, hosts are located at different place, so both IP and port required to send message right? which mechanism can be helpful net.dial() or gob or rpc?

Answer 1

If you want something simple then check out net/rpc which wraps gob and networking into a remote procedure call framework which should do what you want.
Server
From the docs a server running over HTTP
type Args struct {
A, B int
}
type Arith int
func (t *Arith) Multiply(args *Args, reply *int) error {
*reply = args.A * args.B
return nil
}
arith := new(Arith)
rpc.Register(arith)
rpc.HandleHTTP()
l, e := net.Listen("tcp", ":1234")
if e != nil {
log.Fatal("listen error:", e)
}
go http.Serve(l, nil)
Client
At this point, clients can see a service "Arith" with method "Arith.Multiply". To invoke one, dial the server then make a call. You can also make asynchronous calls where the result comes back in a channel.
client, err := rpc.DialHTTP("tcp", serverAddress + ":1234")
if err != nil {
log.Fatal("dialing:", err)
}
args := &server.Args{7,8}
var reply int
err = client.Call("Arith.Multiply", args, &reply)
if err != nil {
log.Fatal("arith error:", err)
}
fmt.Printf("Arith: %d*%d=%d", args.A, args.B, reply)
A slight oddity of the framework is that each remote call can have only one input argument and one output argument which means that you need to wrap all your arguments in a struct.

Answer 2

//server.go will provide the interface for communicating and handling hosts
// workerDead(message string), send the message and wait for ack, if no ack means worker dead
package
main
import(
"fmt"
"io"
"net"
"net/http"
"net/rpc"
"path"
"os"
)
type Flag int
type Args struct{
message string
}
func main() {
flag := new(Flag)
rpc.Register(flag)
rpc.HandleHTTP()
err := http.ListenAndServe(":1234", nil) //ListenAndServe starts an HTTP server with a given address and handler.
//The handler is usually nil, which means to use DefaultServeMux.
if err != nil {
fmt.Println(err.Error())
}
}
//Worker counts the number of hosts
func workerCount() int
{
return db.runCommand( { count: 'id' } ) //mongodb command to count the id
}
// Returns an array of the distinct values of field id from all documents in the workers collection
//In mongodb document is analogous to rdbms table and collection is record
func Worker(worker int) []string{
return db.runCommand ({ distinct: 'workers', key: 'id' } ) //mongodb command to get the array of list of
//workers for column id
}
func Message(worker int, message string, args *Args , reply *int) chan bool {
server, err :=rpc.Dial("tcp","192.168.23.12") //Serve Dials here to send message to host, IP address here is of host
if(err!=nil){
log.Fatal("Dialing", err)
}
var reply bool
args:=Args{message};
err = server.Call(args,&reply);
if(err!=nil){
log.Fatal("Dialing", err)
replaceWorker(); // No reply from worker then call to replace worker
}
fmt.Println("Reply from host", reply);
}
return nil
}
//Replace dead worker of particular project with fresh worker
func replaceWorker(worker_id int,project_id int)
{
db.workers.update( //this query updates workers collection with id=worker_id(id of dead worker)
{ _id: worker_id, _project_id: project_id },
{
//$set: { ' ': 'Warner' },
}
)
}