Go App Engine packages

This repository supports the Go runtime on App Engine, including both the standard App Engine and the “App Engine flexible environment” (formerly known as “Managed VMs”). It provides APIs for interacting with App Engine services. Its canonical import path is google.golang.org/appengine.

See https://cloud.google.com/appengine/docs/go/ for more information.

File issue reports and feature requests on the Google App Engine issue tracker.

Directory structure

The top level directory of this repository is the appengine package. It contains the basic APIs (e.g. appengine.NewContext) that apply across APIs. Specific API packages are in subdirectories (e.g. datastore).

There is an internal subdirectory that contains service protocol buffers, plus packages required for connectivity to make API calls. App Engine apps should not directly import any package under internal.

Updating a Go App Engine app

This section describes how to update a traditional Go App Engine app to use these packages.

1. Update YAML files (App Engine flexible environment / Managed VMs only)

The app.yaml file (and YAML files for modules) should have these new lines added:

vm: true

See https://cloud.google.com/appengine/docs/go/modules/#Go_Instance_scaling_and_class for details.

2. Update import paths

The import paths for App Engine packages are now fully qualified, based at google.golang.org/appengine. You will need to update your code to use import paths starting with that; for instance, code importing appengine/datastore will now need to import google.golang.org/appengine/datastore. You can do that manually, or by running this command to recursively update all Go source files in the current directory: (may require GNU sed)

sed -i '/"appengine/{s,"appengine,"google.golang.org/appengine,;s,appengine_,appengine/,}' \
  $(find . -name '*.go')

3. Update code using deprecated, removed or modified APIs

Most App Engine services are available with exactly the same API. A few APIs were cleaned up, and some are not available yet. This list summarises the differences:

appengine.Context has been replaced with the Context type from golang.org/x/net/context.
Logging methods that were on appengine.Context are now functions in google.golang.org/appengine/log.
appengine.Timeout has been removed. Use context.WithTimeout instead.
appengine.Datacenter now takes a context.Context argument.
datastore.PropertyLoadSaver has been simplified to use slices in place of channels.
delay.Call now returns an error.
search.FieldLoadSaver now handles document metadata.
urlfetch.Transport no longer has a Deadline field; set a deadline on the context.Context instead.
aetest no longer declares its own Context type, and uses the standard one instead.
taskqueue.QueueStats no longer takes a maxTasks argument. That argument has been deprecated and unused for a long time.
appengine.BackendHostname and appengine.BackendInstance were for the deprecated backends feature. Use appengine.ModuleHostnameand appengine.ModuleName instead.
Most of appengine/file and parts of appengine/blobstore are deprecated. Use Google Cloud Storage instead.
appengine/socket is not required on App Engine flexible environment / Managed VMs. Use the standard net package instead.