packer-cn/vendor/google.golang.org/appengine/README.md

# Go App Engine packages

[![Build Status](https://travis-ci.org/golang/appengine.svg)](https://travis-ci.org/golang/appengine)

This repository supports the Go runtime on *App Engine standard*.
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 [GitHub's issue
tracker](https://github.com/golang/appengine/issues).

## Upgrading an App Engine app to the flexible environment

This package does not work on *App Engine flexible*.

There are many differences between the App Engine standard environment and
the flexible environment.

See the [documentation on upgrading to the flexible environment](https://cloud.google.com/appengine/docs/flexible/go/upgrading).

## 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 from legacy (`import "appengine"`) packages

If you're currently using the bare `appengine` packages
(that is, not these ones, imported via `google.golang.org/appengine`),
then you can use the `aefix` tool to help automate an upgrade to these packages.

Run `go get google.golang.org/appengine/cmd/aefix` to install it.

### 1. 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`.

### 2. 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 there are some 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.ModuleHostname`and `appengine.ModuleName` instead.
* Most of `appengine/file` and parts of `appengine/blobstore` are deprecated.
  Use [Google Cloud Storage](https://godoc.org/cloud.google.com/go/storage) if the
  feature you require is not present in the new
  [blobstore package](https://google.golang.org/appengine/blobstore).
* `appengine/socket` is not required on App Engine flexible environment / Managed VMs.
  Use the standard `net` package instead.

## Key Encode/Decode compatibiltiy to help with datastore library migrations

Key compatibility updates have been added to help customers transition from google.golang.org/appengine/datastore to cloud.google.com/go/datastore.
The `EnableKeyConversion` enables automatic conversion from a key encoded with cloud.google.com/go/datastore to google.golang.org/appengine/datastore key type.

### Enabling key conversion

Enable key conversion by calling `EnableKeyConversion(ctx)` in the `/_ah/start` handler for basic and manual scaling or any handler in automatic scaling.

#### 1. Basic or manual scaling

This start handler will enable key conversion for all handlers in the service.

```
http.HandleFunc("/_ah/start", func(w http.ResponseWriter, r *http.Request) {
    datastore.EnableKeyConversion(appengine.NewContext(r))
})
```

#### 2. Automatic scaling

`/_ah/start` is not supported for automatic scaling and `/_ah/warmup` is not guaranteed to run, so you must call `datastore.EnableKeyConversion(appengine.NewContext(r))`
before you use code that needs key conversion.

You may want to add this to each of your handlers, or introduce middleware where it's called.
`EnableKeyConversion` is safe for concurrent use. Any call to it after the first is ignored.