在Google App Engine上从main.go传递出去后，上下文值发生了变化

There's a problem where I don't know why a context.Context was changed once I pass it to a different package on Google App Engine.

The following code works fine when running on App Engine:

package main

import (
    "net/http"
    "log"

    "google.golang.org/appengine"
)

func main() {
    http.HandleFunc("/", myHandler)

    appengine.Main()
}

func myHandler(w http.ResponseWriter, r *http.Request) {
    ctx := r.Context()
    account, err := appengine.ServiceAccount(ctx)
    if err != nil {
        log.Println("[myHandler] error:", err)
    } else {
        log.Println("[myHandler] ServiceAccount:", account)
    }   

    w.Write([]byte("ok"))
}

I could retrieve the ServiceAccount successfully when accessing /, and everything was good.

However, when I passed the context from main.go to another package, the function call didn't work. The following was added to main.go:

import (
    // other stuff
    "github.com/adlerhsieh/q_context/handlers"
)

func main() {
    http.HandleFunc("/", myHandler)

    appengine.Main()
}

func myHandler(w http.ResponseWriter, r *http.Request) {
    ctx := r.Context()
    account, err := appengine.ServiceAccount(ctx)
    if err != nil {
        log.Println("[myHandler] error:", err)
    } else {
        log.Println("[myHandler] ServiceAccount:", account)
    }   

    handlers.AnotherFunc(ctx) // <--- added this

    w.Write([]byte("ok"))
}

Another package:

package handlers

import (
    "log"
    "context"

    "google.golang.org/appengine"
)

func AnotherFunc(ctx context.Context) {
    account, err := appengine.ServiceAccount(ctx)
    if err != nil {
        log.Println("[AnotherFunc] error:", err)
    } else {
        log.Println("[AnotherFunc] ServiceAccount:", account)
    }
}

When I ran it on App Engine, the log said:

2019/09/04 09:36:30 [myHandler] ServiceAccount: myaccount@gmail.com
2019/09/04 09:36:30 [AnotherFunc] error: not an App Engine context

The function calls are the same, but just in different packages. I dug in the package itself and found that it uses the key here (which leads to here) to setup the context. And here to check whether that value was setup properly. However, that value seem to be modified/changed so that the second function call couldn't get it. Even if I omitted the first function call and went straight to the second one, it still has the same error.

Any idea why context object was modified when passing to another package?

The following is my app.yaml:

runtime: go111
service: default
instance_class: F1
automatic_scaling:
  min_idle_instances: 0
  max_idle_instances: automatic
  min_pending_latency: automatic
  max_pending_latency: automatic
  max_concurrent_requests: 30

handlers:
- url: /.*
  script: auto
  login: admin

nobuild_files:
- vendor

env_variables:
  ENV: 'dev'
  GO111MODULE: 'off'

Here is the GitHub repo link.

Thank you!