Documentation
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Overview ¶
Package rpcreplay supports the capture and replay of gRPC calls. Its main goal is to improve testing. Once you capture the calls of a test that runs against a real service, you have an "automatic mock" that can be replayed against the same test, yielding a unit test that is fast and flake-free.
This package is EXPERIMENTAL and subject to change without notice.
Recording ¶
To record a sequence of gRPC calls to a file, create a Recorder and pass its DialOptions to grpc.Dial:
rec, err := rpcreplay.NewRecorder("service.replay", nil)
if err != nil { ... }
defer func() {
if err := rec.Close(); err != nil { ... }
}()
conn, err := grpc.Dial(serverAddress, rec.DialOptions()...)
It is essential to close the Recorder when the interaction is finished.
There is also a NewRecorderWriter function for capturing to an arbitrary io.Writer.
Replaying ¶
Replaying a captured file looks almost identical: create a Replayer and use its DialOptions. (Since we're reading the file and not writing it, we don't have to be as careful about the error returned from Close).
rep, err := rpcreplay.NewReplayer("service.replay")
if err != nil { ... }
defer rep.Close()
conn, err := grpc.Dial(serverAddress, rep.DialOptions()...)
Initial State ¶
A test might use random or time-sensitive values, for instance to create unique resources for isolation from other tests. The test therefore has initial values, such as the current time, or a random seed, that differ from run to run. You must record this initial state and re-establish it on replay.
To record the initial state, serialize it into a []byte and pass it as the second argument to NewRecorder:
timeNow := time.Now()
b, err := timeNow.MarshalBinary()
if err != nil { ... }
rec, err := rpcreplay.NewRecorder("service.replay", b)
On replay, get the bytes from Replayer.Initial:
rep, err := rpcreplay.NewReplayer("service.replay")
if err != nil { ... }
defer rep.Close()
err = timeNow.UnmarshalBinary(rep.Initial())
if err != nil { ... }
Nondeterminism ¶
A nondeterministic program may invoke RPCs in a different order each time it is run. The order in which RPCs are called during recording may differ from the order during replay.
The replayer matches incoming to recorded requests by method name and request contents, so nondeterminism is only a concern for identical requests that result in different responses. A nondeterministic program whose behavior differs depending on the order of such RPCs probably has a race condition: since both the recorded sequence of RPCs and the sequence during replay are valid orderings, the program should behave the same under both.
Other Replayer Differences ¶
Besides the differences in replay mentioned above, other differences may cause issues for some programs. We list them here.
The Replayer delivers a response to an RPC immediately, without waiting for other incoming RPCs. This can violate causality. For example, in a Pub/Sub program where one goroutine publishes and another subscribes, during replay the Subscribe call may finish before the Publish call begins.
For streaming RPCs, the Replayer delivers the result of Send and Recv calls in the order they were recorded. No attempt is made to match message contents.
At present, this package does not record or replay stream headers and trailers, or the result of the CloseSend method.
Index ¶
Constants ¶
This section is empty.
Variables ¶
This section is empty.
Functions ¶
Types ¶
type Recorder ¶
type Recorder struct {
// contains filtered or unexported fields
}
A Recorder records RPCs for later playback.
func NewRecorder ¶
NewRecorder creates a recorder that writes to filename. The file will also store the initial bytes for retrieval during replay.
You must call Close on the Recorder to ensure that all data is written.
func NewRecorderWriter ¶
NewRecorderWriter creates a recorder that writes to w. The initial bytes will also be written to w for retrieval during replay.
You must call Close on the Recorder to ensure that all data is written.
func (*Recorder) DialOptions ¶
func (r *Recorder) DialOptions() []grpc.DialOption
DialOptions returns the options that must be passed to grpc.Dial to enable recording.
type Replayer ¶
type Replayer struct {
// contains filtered or unexported fields
}
A Replayer replays a set of RPCs saved by a Recorder.
func NewReplayer ¶
NewReplayer creates a Replayer that reads from filename.
func NewReplayerReader ¶
NewReplayerReader creates a Replayer that reads from r.
func (*Replayer) DialOptions ¶
func (r *Replayer) DialOptions() []grpc.DialOption
DialOptions returns the options that must be passed to grpc.Dial to enable replaying.
func (*Replayer) SetLogFunc ¶
SetLogFunc sets a function to be used for debug logging. The function should be safe to be called from multiple goroutines.
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