Q:

What is the correct way to send binary data using protocol buffers? 

After using the protogen tool, I have a message type for sending messages:
type File struct {
    Info string `protobuf:"bytes,1,opt,name=info,json=info" json:"info,omitempty"`
    BytesValues []byte  `protobuf:"bytes,2,opt,name=bytes_values,json=bytesValues,proto3" json:"bytes_values,omitempty"`
}

I am trying to send some binary data using the BytesValues field like so:
filePath := filepath. Join("test", "myfile.bin")

f, _ := ioutil. ReadFile(filePath) // error return value ignored for brevity

msg := File{BytesValues: f}

body, _ := proto. Marshal(msg) // encode

The server seems to have problems decoding the message I am sending to it.  Is this the correct way to send binary data using a []byte field with protocol buffers? 

A:

In my case, the problem was actually the server not reading the raw bytes from the correct field. 
The correct way to send raw bytes is to just set the bytes to the field.  There is no need to encode the bytes in any way because protocol buffers is a binary format. 
filePath := filepath. Join("test", "myfile.bin")

f, _ := ioutil. ReadFile(filePath) // error return value ignored for brevity

msg := File{BytesValues: f}

body, _ := proto. Marshal(msg) // encode

