GoLang的REST路由器方法中的调用对象方法

Question

I have just started development of a REST api with GoLang. I have a class with some methods in the backend. The rest api should call one of the methods of the class and return the json response. I am having problem calling the object method or passing the object by reference. My cods looks like this.

package main

import (
    "time"
    "fmt"
    "log"
    "net/http"
    "github.com/gorilla/mux"
    "./objects")

/*Global Variables*/
var host objects.HostOS  // I have declared this to see if I can have a global variable and later on assign the actual object to that and call that object in the GetStats router method below. 

func main() {
    fmt.Println("Hello World")

    hostConfig := objects.HostConfig{CPUConfig: cpuConfig, MemoryKB: 4096, OSMemoryKB: 1024, OSCompute: 100}

    host := new(objects.HostOS)
    host.Init(hostConfig)

    host.Boot()
    time.Sleep(3 * time.Second)
    process := new(objects.Process)
    process.Init(objects.ProcessConfig{MinThreadCount: 2, MaxThreadCount: 8, ParentOSInstance: host})
    process.Start()

    router := mux.NewRouter().StrictSlash(true)

    router.HandleFunc("/", Index)
    router.HandleFunc("/get_os_stats", GetOSStats)

    log.Fatal(http.ListenAndServe(":8080", router))
    //host.GetStatsJson()
}


func Index(w http.ResponseWriter, r *http.Request) {
    fmt.Fprintln(w, "Welcome!")
}

func GetOSStats(w http.ResponseWriter, r *http.Request) {
    // js, err := host.GetStatsJson()   // This is what I would like to do
    // Ideally I would get the Marshalled json and err and return them. 
    // The object method works fine as I have tested it, I am however unable to call the object method here. 

    fmt.Println("getting json stats")
    host.GetStatsJson()  //This is were I get the server panic issue and the code breaks
    //I would like to access the method of the 'host' object defined in the main() method. 
    fmt.Fprintln(w, "GetOSStats!")
}

I would like to call the method of the object defined in the main() function inside the GetOSStats() method and then return the json output.

When I declare a global variable and then later on assign it in the main function, the GetOSStats() function is still accessing a nil struct.

When I declare the host obj in the main function and try to access it in the GetOSStats() funtion, it throws exception.

I think I have to pass the host obj by reference to the GetOSStats() function while calling it in the main but I am not sure about how to do that. I have tried looking up the documentations and the examples but I couldnot find anything that could help me.

Thanks in advance,

Answer 1

You're redeclaring the host variable locally (this is also called "shadowing")

host := new(objects.HostOS)

instead you should use an assignment operator

host = new(objects.HostOS)