Package (v2.0.5)

Package appengine provides basic functionality for Google App Engine.

For more information on how to write Go apps for Google App Engine, see:



var Middleware func(http.Handler) http.Handler = internal.Middleware

Middleware wraps an http handler so that it can make GAE API calls


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. "").

func BackgroundContext (deprecated)

func BackgroundContext() context.Context

BackgroundContext returns a context not associated with a request.

Deprecated: App Engine no longer has a special background context. Just use context.Background().

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. ""). This is suitable for use in constructing URLs.

func InstanceID

func InstanceID() string

InstanceID returns a mostly-unique identifier for this instance.

func IsAppEngine

func IsAppEngine() bool

IsAppEngine reports whether the App Engine app is running on App Engine, in either the standard or flexible environment.

func IsDevAppServer

func IsDevAppServer() bool

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

func IsFlex

func IsFlex() bool

IsFlex reports whether the App Engine app is running in the flexible environment.

func IsOverQuota

func IsOverQuota(err error) bool

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

func IsSecondGen

func IsSecondGen() bool

IsSecondGen reports whether the App Engine app is running on the second generation runtimes (>= Go 1.11).

func IsStandard

func IsStandard() bool

IsStandard reports whether the App Engine app is running in the standard environment. This includes both the first generation runtimes (<= Go 1.9) and the second generation runtimes (>= Go 1.11).

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 an app running in App Engine.

On App Engine Flexible 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 for details on how to do your own health checking.

On App Engine Standard it ensures the server has started and is prepared to receive requests.

Main never returns.

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

package main

import (

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

func 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

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.


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 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 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 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 []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