gax-go: github.com/googleapis/gax-go/v2 Index | Examples | Files

package gax

import "github.com/googleapis/gax-go/v2"

Package gax contains a set of modules which aid the development of APIs for clients and servers based on gRPC and Google API conventions.

Application code will rarely need to use this library directly. However, code generated automatically from API definition files can use it to simplify code generation and to provide more convenient and idiomatic API surfaces.

Index

Examples

Package Files

call_option.go gax.go header.go invoke.go

Constants

const Version = "2.0.5"

Version specifies the gax-go version being used.

func Invoke Uses

func Invoke(ctx context.Context, call APICall, opts ...CallOption) error

Invoke calls the given APICall, performing retries as specified by opts, if any.

func Sleep Uses

func Sleep(ctx context.Context, d time.Duration) error

Sleep is similar to time.Sleep, but it can be interrupted by ctx.Done() closing. If interrupted, Sleep returns ctx.Err().

func XGoogHeader Uses

func XGoogHeader(keyval ...string) string

XGoogHeader is for use by the Google Cloud Libraries only.

XGoogHeader formats key-value pairs. The resulting string is suitable for x-goog-api-client header.

type APICall Uses

type APICall func(context.Context, CallSettings) error

APICall is a user defined call stub.

type Backoff Uses

type Backoff struct {
    // Initial is the initial value of the retry period, defaults to 1 second.
    Initial time.Duration

    // Max is the maximum value of the retry period, defaults to 30 seconds.
    Max time.Duration

    // Multiplier is the factor by which the retry period increases.
    // It should be greater than 1 and defaults to 2.
    Multiplier float64
    // contains filtered or unexported fields
}

Backoff implements exponential backoff. The wait time between retries is a random value between 0 and the "retry period" - the time between retries. The retry period starts at Initial and increases by the factor of Multiplier every retry, but is capped at Max.

Note: MaxNumRetries / RPCDeadline is specifically not provided. These should be built on top of Backoff.

Code:

ctx := context.Background()

bo := gax.Backoff{
    Initial:    time.Second,
    Max:        time.Minute, // Maximum amount of time between retries.
    Multiplier: 2,
}

performHTTPCallWithRetry := func(ctx context.Context, doHTTPCall func(ctx context.Context) (*http.Response, error)) (*http.Response, error) {
    for {
        resp, err := doHTTPCall(ctx)
        if err != nil {
            // Retry 503 UNAVAILABLE.
            if resp.StatusCode == http.StatusServiceUnavailable {
                if err := gax.Sleep(ctx, bo.Pause()); err != nil {
                    return nil, err
                }
                continue
            }
            return nil, err
        }
        return resp, err
    }
}

// It's recommended to set deadlines on HTTP calls and around retrying. This
// is also usually preferred over setting some fixed number of retries: one
// advantage this has is that backoff settings can be changed independently
// of the deadline, whereas with a fixed number of retries the deadline
// would be a constantly-shifting goalpost.
ctxWithTimeout, cancel := context.WithDeadline(ctx, time.Now().Add(5*time.Minute))
defer cancel()

resp, err := performHTTPCallWithRetry(ctxWithTimeout, func(ctx context.Context) (*http.Response, error) {
    req, err := http.NewRequestWithContext(ctx, "some-method", "example.com", nil)
    if err != nil {
        return nil, err
    }
    return http.DefaultClient.Do(req)
})
if err != nil {
    // TODO: handle err
}
_ = resp // TODO: use resp if err is nil

func (*Backoff) Pause Uses

func (bo *Backoff) Pause() time.Duration

Pause returns the next time.Duration that the caller should use to backoff.

type CallOption Uses

type CallOption interface {
    // Resolve applies the option by modifying cs.
    Resolve(cs *CallSettings)
}

CallOption is an option used by Invoke to control behaviors of RPC calls. CallOption works by modifying relevant fields of CallSettings.

func WithGRPCOptions Uses

func WithGRPCOptions(opt ...grpc.CallOption) CallOption

WithGRPCOptions allows passing gRPC call options during client creation.

func WithRetry Uses

func WithRetry(fn func() Retryer) CallOption

WithRetry sets CallSettings.Retry to fn.

type CallSettings Uses

type CallSettings struct {
    // Retry returns a Retryer to be used to control retry logic of a method call.
    // If Retry is nil or the returned Retryer is nil, the call will not be retried.
    Retry func() Retryer

    // CallOptions to be forwarded to GRPC.
    GRPC []grpc.CallOption
}

CallSettings allow fine-grained control over how calls are made.

type Retryer Uses

type Retryer interface {
    // Retry reports whether a request should be retriedand how long to pause before retrying
    // if the previous attempt returned with err. Invoke never calls Retry with nil error.
    Retry(err error) (pause time.Duration, shouldRetry bool)
}

Retryer is used by Invoke to determine retry behavior.

func OnCodes Uses

func OnCodes(cc []codes.Code, bo Backoff) Retryer

OnCodes returns a Retryer that retries if and only if the previous attempt returns a GRPC error whose error code is stored in cc. Pause times between retries are specified by bo.

bo is only used for its parameters; each Retryer has its own copy.

Code:

ctx := context.Background()
c := &fakeClient{}

// UNKNOWN and UNAVAILABLE are typically safe to retry for idempotent RPCs.
retryer := gax.OnCodes([]codes.Code{codes.Unknown, codes.Unavailable}, gax.Backoff{
    Initial:    time.Second,
    Max:        32 * time.Second,
    Multiplier: 2,
})

performSomeRPCWithRetry := func(ctx context.Context) (*fakeResponse, error) {
    for {
        resp, err := c.PerformSomeRPC(ctx)
        if err != nil {
            if delay, shouldRetry := retryer.Retry(err); shouldRetry {
                if err := gax.Sleep(ctx, delay); err != nil {
                    return nil, err
                }
                continue
            }
            return nil, err
        }
        return resp, err
    }
}

// It's recommended to set deadlines on RPCs and around retrying. This is
// also usually preferred over setting some fixed number of retries: one
// advantage this has is that backoff settings can be changed independently
// of the deadline, whereas with a fixed number of retries the deadline
// would be a constantly-shifting goalpost.
ctxWithTimeout, cancel := context.WithDeadline(ctx, time.Now().Add(5*time.Minute))
defer cancel()

resp, err := performSomeRPCWithRetry(ctxWithTimeout)
if err != nil {
    // TODO: handle err
}
_ = resp // TODO: use resp if err is nil

Package gax imports 8 packages (graph) and is imported by 97 packages. Updated 2019-10-18. Refresh now. Tools for package owners.