passing channel param to a dynamic loaded func in golang - go

Question

I'm new to golang and golang plugins. I'm having trouble passing a chan object to this functions. If I switch to int it works. Not sure what exactly I am missing. Thanks for any help.
dataunit.go
package main
type DataUnit struct {
i int
s string
}
modcounter.go
package main
import (
"fmt"
// "strconv"
)
type module string
//func (m module) RunMod(i int) {
func (m module) RunMod(in <-chan *DataUnit) {
//fmt.Println("Hello Universe " + strconv.Itoa(i))
fmt.Println("Hello Universe ")
n := <-in
fmt.Printf(n.s)
}
var Module module
modmain.go
package main
import (
"fmt"
"os"
"plugin"
)
type DataUnit struct {
i int
s string
}
type Module interface {
//RunMod(i int)
RunMod(in <-chan *DataUnit)
}
func main() {
out := make(chan *DataUnit, 2000)
plug, err := plugin.Open("./modcounter.so")
if err != nil {
fmt.Printf("FATAL (plugin.Open): " + err.Error())
os.Exit(1)
}
symModule, err := plug.Lookup("Module")
if err != nil {
fmt.Printf(err.Error())
os.Exit(1)
}
var module Module
module, ok:= symModule.(Module)
if !ok {
fmt.Println("unexpected type from module symbol")
os.Exit(1)
}
//module.RunMod(5)
module.RunMod(out)
}
go build -buildmode=plugin -o modcounter.so modcounter.go dataunit.go
go build modmain.go dataunit.go
./modmain
unexpected type from module symbol

Answer 1

If you are still learning golang then plugins are definitely not the place to start. I believe plugin support is still experimental and doesn't work on all OS - in 1.10 I believe Darwin was added to previous Linux.
A quick search reveals a pre-existing issue reported similar to yours -looks like it's in go 1.10:
https://github.com/golang/go/issues/24351
You can maybe track through the repository and get a branch or version where this is fixed, but whilst your learning you aren't going to have any confidence in whether problems with this area of functionality are with your code or the plugin system. I recommend therefore sticking to learning go with core language features for now.

Answer 2

In go is possible to pass channels of objects!!
For example, if you to use <-chan http.Header will works fine. The question is that the params must be shared between modules and application. So if you reallocate DataUnit for another package will work.
My test was structured like:
My interface:
//in modmain.go
type Module interface {
RunMod(in <-chan *mydata.DataUnit)
}
My module:
//in modcounter.go
func (m module) RunMod(in <-chan *mydata.DataUnit) {
fmt.Println("Hello Universe ")
n := <-in
fmt.Printf("%v", n.S)
}
My data:
//in dataunit.go
type DataUnit struct {
I int //export field
S string //export field
}
The result:
P.S.: Docker with golang 1.10 was used for tests.
#in Dockerfile
FROM golang:1.10
COPY . /go/
RUN export GOPATH=$GOPATH:/go/
RUN cd /go/src/mydata && go build dataunit.go
RUN cd /go/src/app && go build modmain.go
RUN cd /go/src/app && go build -buildmode=plugin -o modcounter.so modcounter.go
WORKDIR /go/src/app
RUN ls -l
CMD ["/go/src/app/modmain"]