Documentation ¶
Overview ¶
Package gae provides a fakable wrapped interface for the appengine SDK's APIs. This means that it's possible to mock all of the supported appengine APIs for testing (or potentially implement a different backend for them).
Features ¶
gae currently provides interfaces for:
- Datastore
- Memcache
- TaskQueue
- Info (e.g. Namespace, AppID, etc.)
Additional features include:
- true service interfaces (not package-level functions)
- methods don't need explicit context passed to them, increasing readability.
- service filters allow for composition of functionality. For example:
- transparent memcaching of datastore access
- transparent transaction buffering
- statistics-gathering shims
- deterministic and probabalistic API failure simulation
- transparent retries
- truly parallel in-memory testing implementation. No more need for dev_appserver.py subprocesses :).
- Separate service and user-facing interfaces
- Allows easier filter and service implementation while retaining the benefits of a user-friendly interface.
Package Organization ¶
The gae library is organized into several subpackages:
- service/* supported service definitions
- impl/* implementations of the services
- filter/* extra filter functionality for the services, agnostic to the underlying implementation.
Service Definitions ¶
A service defintion lives under the `service` subfolder, and defines the user-facing interface for a service. Each service has a few common types and functions. Common types are:
service.Interface - the main user-friendly service interface. service.RawInterface - the internal service interface used by service and filter implementations. Note that some services like Info don't distinguish between the service interface and the user interface. This interface is typically a bit lower level than Interface and lacks convenience methods. service.Testable - any additional methods that a 'testing' implementation should provide. This can be accessed via the Testable method on RawInterface. If the current implementation is not testable, it will return nil. This is only meant to be accessed when testing. service.RawFactory - a function returning a RawInterface service.RawFilter - a function returning a new RawInterface based on the previous filtered interface. Filters chain together to allow behavioral service features without needing to agument the underlying service implementations directly.
And common functions are:
service.GetRaw - Retrieve the current, filtered RawInterface implementation from the context. This is less frequently used, but can be useful if you want to avoid some of the overhead of the user-friendly Interface, which can do sometimes-unnecessary amounts of reflection or allocation. The RawInterface and Interface for a service are fully interchangable and usage of them can be freely mixed in an application. service.AddRawFilters - adds one or more RawFilters to the context. service.SetRawFactory - adds a RawFactory to the context service.SetRaw - adds an implementation of RawInterface to the context (shorthand for SetRawFactory, useful for testing)
Implementations ¶
The impl subdirectory contains a couple different service implementations, depending on your needs.
'prod' is the production (e.g. real appengine-backed) implementation. It calls through to the original appengine SDK.
'memory' is a truly parallel in-memory testing implementation. It should be functionally the same as the production appengine services, implementing many of the real-world quirks of the actual services. It also implements the services' Testable interface, for those services which define those interfaces.
'dummy' provides a bunch of implementations of the various RawInterfaces. These implementations just panic with an appropriate message, depending on which API method was called. They're useful to embed in filter or service implementations as stubs while you're implementing the filter.
Filters ¶
Each service also supports "filters". Filters are proxy objects which have the same interface as the service they're filtering, and pass data through to the previous filter in the stack. Conceptually, a filtered version of, for example, the Datastore, could look like:
User code <count filter (counts how many times each API is called by the user)> <dscache filter (attempts to use memcache as a cache for datastore)> <count filter (counts how many times each API is actually hit)> memory datastore.RawInterface implementation
Filters may or may not have state, it's up to the filter itself. In the case of the count filter, it returns its state from the Filter<Service> method, and the state can be observed to see how many times each API was invoked. Since filters stack, we can compare counts from rawCount versus userCount to see how many calls to the actual real datastore went through, vs. how many went to memcache, for example.
Note that Filters apply only to the service.RawInterface. All implementations of service.Interface boil down to calls to service.RawInterface methods, but it's possible that bad calls to the service.Interface methods could return an error before ever reaching the filters or service implementation.
Example ¶
package main import ( "fmt" "net/http" "net/http/httptest" "go.chromium.org/gae/impl/memory" "go.chromium.org/gae/impl/prod" "go.chromium.org/gae/service/datastore" "golang.org/x/net/context" ) func main() { // This is suitable for use in tests. c := memory.Use(context.Background()) w := httptest.NewRecorder() _, err := http.NewRequest("GET", "/doesntmatter", nil) if err != nil { panic(err) } innerHandler(c, w) fmt.Printf(string(w.Body.Bytes())) } // This is what you would use in production. func handler(w http.ResponseWriter, r *http.Request) { c := context.Background() c = prod.Use(c, r) // add production filters, etc. here innerHandler(c, w) } type CoolStruct struct { ID string `gae:"$id"` Value string } func innerHandler(c context.Context, w http.ResponseWriter) { obj := &CoolStruct{ID: "struct-id", Value: "hello"} if err := datastore.Put(c, obj); err != nil { http.Error(w, err.Error(), http.StatusInternalServerError) } fmt.Fprintf(w, "I wrote: %s", datastore.KeyForObj(c, obj)) }
Output: I wrote: dev~app::/CoolStruct,"struct-id"
Directories ¶
Path | Synopsis |
---|---|
filter
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count
Package count contains 'counter' filters for all the gae services.
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Package count contains 'counter' filters for all the gae services. |
dscache
Package dscache provides a transparent cache for RawDatastore which is backed by Memcache.
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Package dscache provides a transparent cache for RawDatastore which is backed by Memcache. |
featureBreaker
Package featureBreaker contains filters for dynamically disabling/breaking API features at test-time.
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Package featureBreaker contains filters for dynamically disabling/breaking API features at test-time. |
featureBreaker/flaky
Package flaky can be used to emulate flaky GAE errors that happen randomly with some probability.
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Package flaky can be used to emulate flaky GAE errors that happen randomly with some probability. |
readonly
Package readonly implements a filter that enforces read-only accesses to services.
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Package readonly implements a filter that enforces read-only accesses to services. |
txnBuf
Package txnBuf contains a transaction buffer filter for the datastore service.
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Package txnBuf contains a transaction buffer filter for the datastore service. |
txndefer
Package txndefer implements a filter that calls best-effort callbacks on successful transaction commits.
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Package txndefer implements a filter that calls best-effort callbacks on successful transaction commits. |
impl
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cloud
Package cloud provides an implementation of services based on regular Cloud APIs and works from anywhere (not necessarily from AppEngine).
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Package cloud provides an implementation of services based on regular Cloud APIs and works from anywhere (not necessarily from AppEngine). |
dummy
Package dummy provides panicking dummy implementations of all service Interfaces.
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Package dummy provides panicking dummy implementations of all service Interfaces. |
memory
Package memory provides an implementation of infra/gae/libs/wrapper which backs to local memory ONLY.
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Package memory provides an implementation of infra/gae/libs/wrapper which backs to local memory ONLY. |
prod
Package prod provides an implementation of services/* which backs to AppEngine Classic (Go version <=1.11).
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Package prod provides an implementation of services/* which backs to AppEngine Classic (Go version <=1.11). |
prod/constraints
Package constraints contains production datastore constraints.
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Package constraints contains production datastore constraints. |
service
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blobstore
Package blobstore is a PLACEHOLDER for the blobstore implementation.
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Package blobstore is a PLACEHOLDER for the blobstore implementation. |
datastore/dumper
Package dumper implements a very VERY dumb datastore-dumping debugging aid.
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Package dumper implements a very VERY dumb datastore-dumping debugging aid. |
datastore/internal/protos/datastore
Package datastore is a generated protocol buffer package.
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Package datastore is a generated protocol buffer package. |
datastore/meta
Package meta contains some methods for interacting with GAE's metadata APIs.
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Package meta contains some methods for interacting with GAE's metadata APIs. |
datastore/serialize
Package serialize provides methods for reading and writing concatenable, bytewise-sortable forms of the datatypes defined in the datastore package.
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Package serialize provides methods for reading and writing concatenable, bytewise-sortable forms of the datatypes defined in the datastore package. |
info/support
Package support provides Info-related support functionality.
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Package support provides Info-related support functionality. |
logging
Package logging is simply documentation :) In order to use logging, please import and use the "go.chromium.org/luci/common/logging" package.
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Package logging is simply documentation :) In order to use logging, please import and use the "go.chromium.org/luci/common/logging" package. |
urlfetch
Package urlfetch provides a way for an application to get http.RoundTripper that can make outbound HTTP requests.
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Package urlfetch provides a way for an application to get http.RoundTripper that can make outbound HTTP requests. |
tools
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