Comment 1:

Drive by comment, have you run your server program under the go race detector?

Comment 2:

Labels changed: added repo-main, release-none.

Comment 3 by HongF.Yue:

I rebuild and run server code in -race flag, and edit rpc server code as below:
----------------------------------------
//rpc server
package main
import (
    "fmt"
    "net"
    "net/rpc"
    "os"
)
type Args struct {
    A int
}
type Rsp struct {
    A int
}
type Echoer int
var isFirst = true
func (t *Echoer) Echo(args *Args, reply *Rsp) error {
    if isFirst {
        reply.A = args.A
        isFirst = false
    } else {
        reply.A = 0
    }
    fmt.Println("reply-----", reply.A)
    return nil
}
func main() {
    echoer := new(Echoer)
    rpc.Register(echoer)
    tcpAddr, err := net.ResolveTCPAddr("tcp", ":1234")
    checkError(err)
    listener, err := net.ListenTCP("tcp", tcpAddr)
    checkError(err)
    conn, err := listener.Accept()
    checkError(err)
    rpc.ServeConn(conn)
}
func checkError(err error) {
    if err != nil {
        fmt.Println("Fatal error ", err.Error())
        os.Exit(1)
    }
}
----------------------------------
The output of both client and server have nothing different from original. And sending
Ctrl-C to client, server exit with no warning or error. 
The Processor of this server is only one, I don't think this problem is related to
concurrent or race condition. Maybe some strange behavior of gob codec (zero value) is
the answer.

Running to the same issue here. When reply value is 0(for int type), it seems that the decoder just overlook this field.

A simpler way to reproduce is,
let "rsp := {A:3}" and let the function make "reply.A = 0", you can see what happens.

I also found that in rpc client code, when I move var rsp Rsp to inner of for loop, everything goes well.

Still have the same issue with Go 1.7.1. When will this be fixed?

This is because net/rpc use encoding/gob as default codec. And if a field has the zero value for its type, it is omitted from the transmission. So you should start with a clean, zeroed item before decoding.
See https://golang.org/pkg/encoding/gob/#hdr-Encoding_Details and #21929

func main() {
    if len(os.Args) != 2 {
        fmt.Println("Usage: ", os.Args[0], "server:port")
        os.Exit(1)
    }
    service := os.Args[1]
    client, err := rpc.Dial("tcp", service)
    if err != nil {
        log.Fatal("dialing:", err)
    }
    args := Args{3}
    //  var rsp Rsp
    for {
        var rsp Rsp // make it clean
        err = client.Call("Echoer.Echo", args, &rsp)
        if err != nil {
            log.Fatal("arith error:", err)
        }
        fmt.Printf("Echoer: A=%d\n", rsp.A)
        time.Sleep(time.Second * 2)
    }
}

Just got bit by this bug. I wanted to use a pointer in a struct to differentiate between the value existing vs. the value being the zero value, but gob doesn't support this use case correctly.

Reading through the spec of gob encoding, this shouldn't be the intended behaviour.

If a field has the zero value for its type (except for arrays; see above), it is omitted from the transmission.

The zero value for *T is nil, not the zero value of T.

I recently discovered that the JSON encoding omitempty option behaves correctly with respect to pointers and nil vs. zero values. So there is precedent for this behaviour to be fixed.

https://pkg.go.dev/encoding/json#Marshal

The "omitempty" option specifies that the field should be omitted from the encoding if the field has an empty value, defined as false, 0, a nil pointer, a nil interface value, and any empty array, slice, map, or string.

A non-nil pointer to a boolean that is false still gets encoded as false for JSON even with omitempty.

I believe this is working as expected for encoding/gob.