Nexus Go SDK

Go SDK for modelling applications to work with the Nexus RPC specification. Client and server implementation not included.

What is Nexus?

Nexus is an RPC protocol for expressing arbitrary duration operations.

A Nexus caller calls a handler. The handler may respond inline (synchronous response) or return a token referencing the ongoing operation (asynchronous response), which the the caller use to cancel the operation. In lieu of a higher level service contract, the caller cannot determine whether an operation is going to resolve synchronously or asynchronously, and should specify a callback URL, which the handler uses to deliver the result of an asynchronous operation when it is ready.

Installation

go get -u github.com/nexus-rpc/sdk-go

Usage

Import

import (
	"github.com/nexus-rpc/sdk-go/nexus"
)

Define an Operation Reference

Operation references can be used in client implementations for type safe invocation without requiring access to a concrete implementation.

var syncOperationRef = nexus.NewOperationReference[MyInput, MyOutput]("sync-example")

Implement a Sync Operation

var syncOperation = nexus.NewSyncOperation("sync-example", func(ctx context.Context, input MyInput, options StartOperationOptions) (MyOutput, error) {
	return MyOutput{Field: "value"}, nil
})

Implement an Async Operation

type myAsyncOperation struct {
	nexus.UnimplementedOperation[MyInput, MyOutput]
}

func (h *myAsyncOperation) Name() string {
	return "example"
}

func (h *myAsyncOperation) Start(ctx context.Context, input MyInput, options nexus.StartOperationOptions) (nexus.HandlerStartOperationResult[MyOutput], error) {
	// alternatively return &nexus.HandlerStartOperationResultSync{Value: MyOutput{}}, nil
	return &nexus.HandlerStartOperationResultAsync{OperationToken: "BASE64_ENCODED_DATA"}, nil
}

func (h *myAsyncOperation) Cancel(ctx context.Context, token string, options nexus.CancelOperationOptions) error {
	fmt.Println("Canceling", h.Name(), "with token:", token)
	return nil
}

Register an Operation implementation with a Service

var service = nexus.NewService("example-service")
svc.MustRegister(operation, &myAsyncOperation{})

Resolve an operation as failed

func (h *myAsyncOperation) Start(ctx context.Context, input MyInput, options nexus.StartOperationOptions) (nexus.HandlerStartOperationResult[MyOutput], error) {
	// Alternatively use NewOperationCanceledError to resolve an operation as canceled.
	return nil, nexus.NewOperationFailedError("do or do not, there is not try")
}

Fail any handler method (Start or Cancel)

Returning an arbitrary error from any of the Operation and OperationHandler methods will result in the error being logged and the request responded to with a generic Internal Server Error and Failure message.

To fail a request with a custom status error type and failure message, return a nexus.HandlerError as the error. The error can either be constructed directly or with the HandlerErrorf helper.

func (h *myAsyncOperation) Start(ctx context.Context, input MyInput, options nexus.StartOperationOptions) (nexus.HandlerStartOperationResult[MyOutput], error) {
	return nil, nexus.HandlerErrorf(nexus.HandlerErrorTypeBadRequest, "invalid input field: %v", input.Field)
}

Failure Structs

nexus exports a Failure struct that is used in both the client and handlers to represent both application level operation failures and framework level HTTP request errors.

Failures typically contain a single Message string but may also convey arbitrary JSONable Details and Metadata.

The Details field is encoded and it is up to the library user to encode to and decode from it.

A failure can be either directly attached to HandlerError and OperationError instances by providing FailureError as the Cause, or indirectly by implementing the FailureConverter interface, which can translate arbitrary user defined errors to Failure instances and back.

Links

Nexus operations can bi-directionally link the caller and handler for tracing the execution path. A caller may provide a set of Link objects via StartOperationOptions that the handler may log or attach to any underlying resources backing the operation. A handler may attach backlinks when responding to a StartOperation request via the a AddHandlerLinks method.

Handler

func (h *myArbitraryLengthOperation) Start(ctx context.Context, input MyInput, options nexus.StartOperationOptions) (nexus.HandlerStartOperationResult[MyOutput], error) {
	output, backlinks, _ := createMyBackingResourceAndAttachCallerLinks(ctx, input, options.Links)
	nexus.AddHandlerLinks(ctx, backlinks)
	return output, nil
}

result, _ := nexus.StartOperation(ctx, client, operation, MyInput{Field: "value"}, nexus.StartOperationOptions{
	Links: []nexus.Link{
		{
			Type: "org.my.MyResource",
			URL:  &url.URL{/* ... */},
		},
	},
})
fmt.Println("got result with backlinks", result.Links)

Middleware

The ServiceRegistry supports middleware registration via the Use method. The registry's handler will invoke every registered middleware in registration order. Typical use cases for middleware include global enforcement of authorization and logging.

Middleware is implemented as a function that takes the current context and the next handler in the invocation chain and returns a new handler to invoke. The function can pass through the given handler or return an error to abort the execution. The registered middleware function has access to common handler information such as the current service, operation, and request headers. To get access to more specific handler method information, such as inputs and operation tokens, wrap the given handler.

Example

type loggingOperation struct {
	nexus.UnimplementedOperation[any, any] // All OperationHandlers must embed this.
	next nexus.OperationHandler[any, any]
}

func (lo *loggingOperation) Start(ctx context.Context, input any, options nexus.StartOperationOptions) (nexus.HandlerStartOperationResult[any], error) {
	log.Println("starting operation", nexus.ExtractHandlerInfo(ctx).Operation)
	return lo.next.Start(ctx, input, options)
}

func (lo *loggingOperation) Cancel(ctx context.Context, token string, options nexus.CancelOperationOptions) error {
	log.Printf("canceling operation", nexus.ExtractHandlerInfo(ctx).Operation)
	return lo.next.Cancel(ctx, token, options)
}

registry.Use(func(ctx context.Context, next nexus.OperationHandler[any, any]) (nexus.OperationHandler[any, any], error) {
	// Optionally call nexus.ExtractHandlerInfo(ctx) here.
	return &loggingOperation{next: next}, nil
})

Contributing

Prerequisites

• Go 1.25
• golangci-lint

Test

go test -v ./...

Lint

golangci-lint run --verbose --timeout 1m --fix=false