client_hooks.go

// Copyright 2018 Twitch Interactive, Inc.  All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License"). You may not
// use this file except in compliance with the License. A copy of the License is
// located at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// or in the "license" file accompanying this file. This file is distributed on
// an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
// express or implied. See the License for the specific language governing
// permissions and limitations under the License.
package twirp

import (
	"context"
	"net/http"
)

// ClientOption is a functional option for extending a Twirp client.
type ClientOption func(*ClientOptions)

// ClientOptions encapsulate the configurable parameters on a Twirp client.
type ClientOptions struct {
	hooks *ClientHooks
}

// ClientHooks is a container for callbacks that can instrument a
// Twirp-generated client. These callbacks all accept a context and some return
// a context. They can use this to add to the context, appending values or
// deadlines to it.
//
// The RequestPrepared hook is special because it can return errors. If it
// returns non-nil error, handling for that request will be stopped at that
// point. The Error hook will then be triggered.
//
// The RequestPrepaared hook will always be called first and will be called for
// each outgoing request from the Twirp client. The last hook to be called
// will either be Error or ResponseReceived, so be sure to handle both cases in
// your hooks.
type ClientHooks struct {
	// RequestPrepared is called as soon as a request has been created and before it has been sent
	// to the Twirp server.
	RequestPrepared func(context.Context, *http.Request) (context.Context, error)

	// ResponseReceived is called after a request has finished sending. Since this
	// is terminal, the context is not returned. ResponseReceived will not be
	// called in the case of an error being returned from the request.
	ResponseReceived func(context.Context)

	// Error hook is called whenever an error occurs during the sending of a
	// request. The Error is passed as an argument to the hook.
	Error func(context.Context, Error)
}

// WithClientHooks sets the *ClientHooks for a Twirp client which chains the
// callbacks in each of the constituent hooks passed in. Each hook function will
// be called in the order of the ClientHooks values passed in.

// For the erroring hook, RequestPrepared, any returned errors prevent
// processing by later hooks.
func WithClientHooks(hooks ...*ClientHooks) ClientOption {
	return func(o *ClientOptions) {
		o.hooks = chainClientHooks(hooks...)
	}
}

func (o *ClientOptions) Hooks() *ClientHooks {
	return o.hooks
}

func chainClientHooks(hooks ...*ClientHooks) *ClientHooks {
	if len(hooks) == 0 {
		return nil
	}
	if len(hooks) == 1 {
		return hooks[0]
	}
	return &ClientHooks{
		RequestPrepared: func(ctx context.Context, req *http.Request) (context.Context, error) {
			for _, h := range hooks {
				if h != nil && h.RequestPrepared != nil {
					var err error
					ctx, err = h.RequestPrepared(ctx, req)
					if err != nil {
						return ctx, err
					}
				}
			}
			return ctx, nil
		},
		ResponseReceived: func(ctx context.Context) {
			for _, h := range hooks {
				if h != nil && h.ResponseReceived != nil {
					h.ResponseReceived(ctx)
				}
			}
		},
		Error: func(ctx context.Context, twerr Error) {
			for _, h := range hooks {
				if h != nil && h.Error != nil {
					h.Error(ctx, twerr)
				}
			}
		},
	}
}