appengine

README

Go App Engine packages

This repository supports the Go runtime on App Engine, including both classic App Engine and 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 (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 Managed VMs. Use the standard net package instead.

Documentation

Overview

Package appengine provides basic functionality for Google App Engine.

For more information on how to write Go apps for Google App Engine, see: https://cloud.google.com/appengine/docs/go/

Index

• func APICall(ctx context.Context, service, method string, in, out proto.Message) error
• func AccessToken(c context.Context, scopes ...string) (token string, expiry time.Time, err error)
• func AppID(c context.Context) string
• func BackgroundContext() context.Context
• func Datacenter(c context.Context) string
• func DefaultVersionHostname(c context.Context) string
• func InstanceID() string
• func IsDevAppServer() bool
• func IsOverQuota(err error) bool
• func IsTimeoutError(err error) bool
• func Main()
• func ModuleHostname(c context.Context, module, version, instance string) (string, error)
• func ModuleName(c context.Context) string
• func Namespace(c context.Context, namespace string) (context.Context, error)
• func NewContext(req *http.Request) context.Context
• func RequestID(c context.Context) string
• func ServerSoftware() string
• func ServiceAccount(c context.Context) (string, error)
• func SignBytes(c context.Context, bytes []byte) (keyName string, signature []byte, err error)
• func VersionID(c context.Context) string
• func WithAPICallFunc(ctx context.Context, f APICallFunc) context.Context
• func WithContext(parent context.Context, req *http.Request) context.Context
• type APICallFunc
• type BlobKey
• type Certificate
  • func PublicCertificates(c context.Context) ([]Certificate, error)
• type GeoPoint
  • func (g GeoPoint) Valid() bool
• type MultiError
  • func (m MultiError) Error() string

Functions

func APICall

func APICall(ctx context.Context, service, method string, in, out proto.Message) error

APICall performs an API call.

This is not intended for general use; it is exported for use in conjunction with WithAPICallFunc.

func AccessToken

func AccessToken(c context.Context, scopes ...string) (token string, expiry time.Time, err error)

AccessToken generates an OAuth2 access token for the specified scopes on behalf of service account of this application. This token will expire after the returned time.

func AppID

func AppID(c context.Context) string

AppID returns the application ID for the current application. The string will be a plain application ID (e.g. "appid"), with a domain prefix for custom domain deployments (e.g. "example.com:appid").

func BackgroundContext

func BackgroundContext() context.Context

BackgroundContext returns a context not associated with a request. This should only be used when not servicing a request. This only works on Managed VMs.

func Datacenter

func Datacenter(c context.Context) string

Datacenter returns an identifier for the datacenter that the instance is running in.

func DefaultVersionHostname

func DefaultVersionHostname(c context.Context) string

DefaultVersionHostname returns the standard hostname of the default version of the current application (e.g. "my-app.appspot.com"). This is suitable for use in constructing URLs.

func InstanceID

func InstanceID() string

InstanceID returns a mostly-unique identifier for this instance.

func IsDevAppServer

func IsDevAppServer() bool

IsDevAppServer reports whether the App Engine app is running in the development App Server.

func IsOverQuota

func IsOverQuota(err error) bool

IsOverQuota reports whether err represents an API call failure due to insufficient available quota.

func IsTimeoutError

func IsTimeoutError(err error) bool

IsTimeoutError reports whether err is a timeout error.

func Main

func Main()

Main is the principal entry point for a Managed VMs app. It installs a trivial health checker if one isn't already registered, and starts listening on port 8080 (overridden by the $PORT environment variable).

See https://cloud.google.com/appengine/docs/managed-vms/custom-runtimes#health_check_requests for details on how to do your own health checking.

Main never returns.

Main is designed so that the app's main package looks like this:

package main

import (
        "google.golang.org/appengine"

        _ "myapp/package0"
        _ "myapp/package1"
)

func main() {
        appengine.Main()
}

The "myapp/packageX" packages are expected to register HTTP handlers in their init functions.

func ModuleHostname

func ModuleHostname(c context.Context, module, version, instance string) (string, error)

ModuleHostname returns a hostname of a module instance. If module is the empty string, it refers to the module of the current instance. If version is empty, it refers to the version of the current instance if valid, or the default version of the module of the current instance. If instance is empty, ModuleHostname returns the load-balancing hostname.

func ModuleName

func ModuleName(c context.Context) string

ModuleName returns the module name of the current instance.

func Namespace

func Namespace(c context.Context, namespace string) (context.Context, error)

Namespace returns a replacement context that operates within the given namespace.

func NewContext

func NewContext(req *http.Request) context.Context

NewContext returns a context for an in-flight HTTP request. This function is cheap.

func RequestID

func RequestID(c context.Context) string

RequestID returns a string that uniquely identifies the request.

func ServerSoftware

func ServerSoftware() string

ServerSoftware returns the App Engine release version. In production, it looks like "Google App Engine/X.Y.Z". In the development appserver, it looks like "Development/X.Y".

func ServiceAccount

func ServiceAccount(c context.Context) (string, error)

ServiceAccount returns a string representing the service account name, in the form of an email address (typically app_id@appspot.gserviceaccount.com).

func SignBytes

func SignBytes(c context.Context, bytes []byte) (keyName string, signature []byte, err error)

SignBytes signs bytes using a private key unique to your application.

func VersionID

func VersionID(c context.Context) string

VersionID returns the version ID for the current application. It will be of the form "X.Y", where X is specified in app.yaml, and Y is a number generated when each version of the app is uploaded. It does not include a module name.

func WithAPICallFunc

func WithAPICallFunc(ctx context.Context, f APICallFunc) context.Context

WithAPICallFunc returns a copy of the parent context that will cause API calls to invoke f instead of their normal operation.

This is intended for advanced users only.

func WithContext

func WithContext(parent context.Context, req *http.Request) context.Context

WithContext returns a copy of the parent context and associates it with an in-flight HTTP request. This function is cheap.

Types

type APICallFunc

type APICallFunc func(ctx context.Context, service, method string, in, out proto.Message) error

APICallFunc defines a function type for handling an API call. See WithCallOverride.

type BlobKey

type BlobKey string

BlobKey is a key for a blobstore blob.

Conceptually, this type belongs in the blobstore package, but it lives in the appengine package to avoid a circular dependency: blobstore depends on datastore, and datastore needs to refer to the BlobKey type.

type Certificate

type Certificate struct {
	KeyName string
	Data    []byte // PEM-encoded X.509 certificate
}

Certificate represents a public certificate for the app.

func PublicCertificates

func PublicCertificates(c context.Context) ([]Certificate, error)

PublicCertificates retrieves the public certificates for the app. They can be used to verify a signature returned by SignBytes.

type GeoPoint

type GeoPoint struct {
	Lat, Lng float64
}

GeoPoint represents a location as latitude/longitude in degrees.

func (GeoPoint) Valid

func (g GeoPoint) Valid() bool

Valid returns whether a GeoPoint is within [-90, 90] latitude and [-180, 180] longitude.

type MultiError

type MultiError []error

MultiError is returned by batch operations when there are errors with particular elements. Errors will be in a one-to-one correspondence with the input elements; successful elements will have a nil entry.

func (MultiError) Error

func (m MultiError) Error() string