How can I create cloud context.Context from appengine.Context

Question

I can't figure out how to call cloud.WithContext and google.DefaultClient if I have appengine.Context and not context.Context.

There are (old) "appengine" and (new) "google.golang.org/appengine" packages. The first one brings custom appengine.Context when second one comes with context.Context from "golang.org/x/net/context"

The whole google.golang.org/cloud expects context.Context only.

I would be happy to move to using new "google.golang.org/appengine", but I've stuck with runtime.RunInBackground that have not been ported yet. From https://github.com/golang/appengine:

appengine/aetest, appengine/cloudsql and appengine/runtime have not been ported yet.

What I could write if appengine/runtime have been ported already:

import (
    "golang.org/x/net/context"

    "google.golang.org/appengine"
    "google.golang.org/appengine/runtime"
    "google.golang.org/cloud"
    "google.golang.org/cloud/storage"
)

func handler(w http.ResponseWriter, r *http.Request) {
    c := appengine.NewContext(r)
    runtime.RunInBackground(c, func(ctx context.Context) {
        hc, _ := google.DefaultClient(ctx, storage.ScopeFullControl)
        cc := cloud.WithContext(ctx, appengine.AppID(ctx), hc)
        …
   })
}

but there is no "google.golang.org/appengine/runtime" yet. So I have

runtime.RunInBackground(c, func(ctx appengine.Context) {

Answer 1

At the moment there is no way to get cloud context.Context from (old) appengine.Context.

Solution for Managed VM

A month ago BackgroundContext() method was added to google.golang.org/appengine (available for Managed VM only). This allows start goroutine and get cloud context.Context without passing it into.

Solution for classic Appengine

There is no solution at the moment.

Answer 2

Do this:

func getCloudContext(appengineContext context.Context) context.Context {
    hc := &http.Client{
        Transport: &oauth2.Transport{
            Source: google.AppEngineTokenSource(appengineContext, storage.ScopeFullControl),
            Base:   &urlfetch.Transport{Context: appengineContext},
        },
    }

    return cloud.NewContext(appengine.AppID(appengineContext), hc)
}

Or if passing the credentials through the dev server isn't working, you can also use explicit credentials:

func getCloudContext(aeCtx context.Context) (context.Context, error) {
    data, err := ioutil.ReadFile("/path/to/credentials.json")
    if err != nil {
        return nil, err
    }

    conf, err := google.JWTConfigFromJSON(
        data,
        storage.ScopeFullControl,
    )
    if err != nil {
        return nil, err
    }

    tokenSource := conf.TokenSource(aeCtx)

    hc := &http.Client{
        Transport: &oauth2.Transport{
            Source: tokenSource,
            Base:   &urlfetch.Transport{Context: aeCtx},
        },
    }

    return cloud.NewContext(appengine.AppID(aeCtx), hc), nil
}