Remote API for Go

The Go SDK includes the appengine/remote_api package that lets you transparently access App Engine services from any Go application. For example, you can use Remote API to access a production datastore from an app running on your local machine. You can also use Remote API to access the datastore of one App Engine app from a different App Engine app.

Enabling Remote API

First, add the remote_api url handler to your app.yaml as follows:

- url: /_ah/remote_api
  script: _go_app
  login: admin

This maps the URL /_ah/remote_api to your Go app. Access to this URL is restricted to administrators for the application.

Then import the appengine/remote_api package in one of your project's packages. Add this line to any of your .go source files:

import _ "appengine/remote_api"

During program initialization, the remote_api package registers itself as an endpoint with the /_ah/remote_api path. The underscore in the import declaration means "import this package, but we won't use it directly." (Without the underscore you would receive an "imported but not used" error message on compilation.)

Finally, update your app:

goapp deploy <app-directory>

Using the Remote API in a Local Client

The Remote API can be used to write local applications that use App Engine services and access datastore. It is important to note that using the Remote API will incur quota usage on the application you are accessing. Other limitations of the Remote API are discussed in the Remote API article.

Before beginning, make sure the Remote API is enabled in your App Engine application. The local application can use the Remote API by creating a context with remote_api.NewRemoteContext , and using that in place of the regular App Engine context in all API calls.

package demo

import (
        "net/http"
        "time"

        "appengine/datastore"
        "appengine/remote_api"
)

// GuestbookCount returns the number of guestbook entries from the last week
// stored in the datastore of the app at the given host.
func GuestbookCount(host string, client *http.Client) (int, err) {
        c, err := remote_api.NewRemoteContext(host, client)
        if err != nil {
                return 0, err
        }

        q := datastore.NewQuery("Greeting").
                Filter("Date >=", time.Now().AddDate(0, 0, -7))
        return q.Count(c)
}

You need to provide the hostname of your server and a http.Client in the call to NewRemoteContext . The provided http.Client is responsible for passing the required authetication information in each request. See the demos/remote_api directory within the SDK for a complete example.

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