Go binary not found when using Dockerfile - docker

Question

I am following Go's Docker instructions. Their example works for me. I am now trying to modify it to run a tcp server:
go get github.com/Kelindar/tcp
Add a Dockerfile:
FROM golang
ADD . /go/src/github.com/Kelindar/tcp
RUN go install github.com/Kelindar/tcp
ENTRYPOINT /go/bin/tcp
EXPOSE 8080
I then build it:
docker build --no-cache -t tcp .
build output:
Sending build context to Docker daemon 322kB
Step 1/5 : FROM golang
---> 9fe4cdc1f173
Step 2/5 : ADD . /go/src/github.com/Kelindar/tcp
---> 10abce658324
Step 3/5 : RUN go install github.com/Kelindar/tcp
---> Running in 59dc47b30474
Removing intermediate container 59dc47b30474
---> 8fab53d2882c
Step 4/5 : ENTRYPOINT /go/bin/tcp
---> Running in 18d4b5befccb
Removing intermediate container 18d4b5befccb
---> 073fdb78a481
Step 5/5 : EXPOSE 8080
---> Running in 8ee2b7bc0cba
Removing intermediate container 8ee2b7bc0cba
---> 8bf9f82d4fef
Successfully built 8bf9f82d4fef
Successfully tagged tcp:latest
Now, I run it:
docker run --name test --rm tcp
I get an error:
/bin/sh: 1: /go/bin/tcp: not found
Not really sure where to go on this.

Answer 1

There are two problems here:
The package github.com/Kelindar/tcp does not contain a main function, thus it can't produce a binary to be executed.
There is no main package, and every go program needs a main package with a main function
Whether you run go build or go install in this repository, you will see that nothing will happen, since your package is actually a library.
Now if you add a cmd/tcp_server folder with a tcp_server.go file like this:
package main
import (
"fmt"
"log"
"net"
"github.com/kelindar/tcp"
)
func main() {
closingChan := make(chan bool)
onAccept := func(c net.Conn) {
// Do something here.
}
l, err := net.Listen("tcp", fmt.Sprintf(":%d", 4242))
if err != nil {
log.Fatalf("Unable to net.Listen: %v", err)
}
server := &tcp.Server{
Closing: closingChan,
OnAccept: onAccept,
}
log.Println("Server ready...")
if err := server.Serve(l); err != nil {
log.Fatalf("Server crashed: %v", err)
}
log.Println("Server stopped")
}
And that you update your Dockerfile to use the command that uses your tcp package:
FROM golang
RUN go get github.com/Kelindar/tcp
RUN go build -o $GOPATH/bin/tcp_server $GOPATH/src/github.com/Kelindar/tcp/cmd/tcp_server/tcp_server.go
ENTRYPOINT tcp_server
EXPOSE 8080
Your server will be working properly within docker:
2019/06/16 05:23:29 Server ready...