awssnssqs

Documentation

Overview

Package awssnssqs provides an implementation of pubsub that uses AWS SNS (Simple Notification Service) and SQS (Simple Queueing Service).

URLs

For pubsub.OpenTopic and pubsub.OpenSubscription, awssnssqs registers for the schemes "awssns" and "awssqs" respectively. The default URL opener will use an AWS session with the default credentials and configuration; see https://docs.aws.amazon.com/sdk-for-go/api/aws/session/ for more details. To customize the URL opener, or for more details on the URL format, see URLOpener. See https://github.com/eliben/gocdkx/concepts/urls/ for background information.

Message Delivery Semantics

AWS SNS and SQS combine to support at-least-once semantics; applications must call Message.Ack after processing a message, or it will be redelivered. See https://godoc.org/github.com/eliben/gocdkx/pubsub#hdr-At_most_once_and_At_least_once_Delivery for more background.

Escaping

Go CDK supports all UTF-8 strings; to make this work with providers lacking full UTF-8 support, strings must be escaped (during writes) and unescaped (during reads). The following escapes are required for awssnssqs:

• Metadata keys: Characters other than "a-zA-z0-9_-.", and additionally "." when it's at the start of the key or the previous character was ".", are escaped using "__0x<hex>__". These characters were determined by experimentation.
• Metadata values: Escaped using URL encoding.
• Message body: AWS SNS/SQS only supports UTF-8 strings. See the BodyBase64Encoding enum in TopicOptions for strategies on how to send non-UTF-8 message bodies. By default, non-UTF-8 message bodies are base64 encoded.

As

awssnssqs exposes the following types for As:

• Topic: *sns.SNS
• Subscription: *sqs.SQS
• Message: *sqs.Message
• Message.BeforeSend: *sns.PublishInput
• Error: awserror.Error

Example (OpenSubscription)

package main

import (
	"context"
	"log"

	"github.com/eliben/gocdkx/pubsub"
)

func main() {
	// This example is used in https://github.com/eliben/gocdkx/howto/pubsub/subscribe/#sns

	// import _ "github.com/eliben/gocdkx/pubsub/awssnssqs"

	// Variables set up elsewhere:
	ctx := context.Background()

	// OpenSubscription creates a *pubsub.Subscription from a URL.
	// This URL will open the subscription with the URL
	// "https://sqs.us-east-2.amazonaws.com/123456789012/MyQueue".
	subscription, err := pubsub.OpenSubscription(ctx,
		"awssqs://sqs.us-east-2.amazonaws.com/123456789012/"+
			"MyQueue?region=us-east-2")
	if err != nil {
		log.Fatal(err)
	}
	defer subscription.Shutdown(ctx)
}

Example (OpenTopic)

package main

import (
	"context"
	"log"

	"github.com/eliben/gocdkx/pubsub"
)

func main() {
	// This example is used in https://github.com/eliben/gocdkx/howto/pubsub/publish/#sns

	// import _ "github.com/eliben/gocdkx/pubsub/awssnssqs"

	// Variables set up elsewhere:
	ctx := context.Background()

	const topicARN = "arn:aws:sns:us-east-2:123456789012:MyTopic"
	topic, err := pubsub.OpenTopic(ctx, "awssns://"+topicARN+"?region=us-east-2")
	if err != nil {
		log.Fatal(err)
	}
	defer topic.Shutdown(ctx)
}

Index

• Constants
• Variables
• func OpenSubscription(ctx context.Context, sess client.ConfigProvider, qURL string, ...) *pubsub.Subscription
• func OpenTopic(ctx context.Context, sess client.ConfigProvider, topicARN string, ...) *pubsub.Topic
• type BodyBase64Encoding
• type SubscriptionOptions
• type TopicOptions
• type URLOpener
  • func (o *URLOpener) OpenSubscriptionURL(ctx context.Context, u *url.URL) (*pubsub.Subscription, error)
  • func (o *URLOpener) OpenTopicURL(ctx context.Context, u *url.URL) (*pubsub.Topic, error)

Examples

• Package (OpenSubscription)
• Package (OpenTopic)
• OpenSubscription
• OpenTopic

Constants

const SNSScheme = "awssns"

SNSScheme is the URL scheme for pubsub.OpenTopic awssnssqs registers its URLOpeners under on pubsub.DefaultMux.

const SQSScheme = "awssqs"

SQSScheme is the URL scheme for pubsub.OpenSubscription awssnssqs registers its URLOpeners under on pubsub.DefaultMux.

Variables

var Set = wire.NewSet(
	SubscriptionOptions{},
	TopicOptions{},
	URLOpener{},
)

Set holds Wire providers for this package.

Functions

func OpenSubscription

func OpenSubscription(ctx context.Context, sess client.ConfigProvider, qURL string, opts *SubscriptionOptions) *pubsub.Subscription

OpenSubscription opens a subscription based on AWS SQS for the given SQS queue URL. The queue is assumed to be subscribed to some SNS topic, though there is no check for this.

Example

package main

import (
	"context"
	"log"

	"github.com/aws/aws-sdk-go/aws"
	"github.com/aws/aws-sdk-go/aws/session"
	"github.com/eliben/gocdkx/pubsub/awssnssqs"
)

func main() {
	// This example is used in https://github.com/eliben/gocdkx/howto/pubsub/subscribe/#sns-ctor

	// Variables set up elsewhere:
	ctx := context.Background()

	// Establish an AWS session.
	// See https://docs.aws.amazon.com/sdk-for-go/api/aws/session/ for more info.
	// The region must match the region for "MyQueue".
	sess, err := session.NewSession(&aws.Config{
		Region: aws.String("us-east-2"),
	})
	if err != nil {
		log.Fatal(err)
	}

	// Construct a *pubsub.Subscription.
	// https://docs.aws.amazon.com/sdk-for-net/v2/developer-guide/QueueURL.html
	const queueURL = "https://sqs.us-east-2.amazonaws.com/123456789012/MyQueue"
	subscription := awssnssqs.OpenSubscription(ctx, sess, queueURL, nil)
	defer subscription.Shutdown(ctx)
}

func OpenTopic

func OpenTopic(ctx context.Context, sess client.ConfigProvider, topicARN string, opts *TopicOptions) *pubsub.Topic

OpenTopic opens a topic that sends to the SNS topic with the given Amazon Resource Name (ARN).

Example

package main

import (
	"context"
	"log"

	"github.com/aws/aws-sdk-go/aws"
	"github.com/aws/aws-sdk-go/aws/session"
	"github.com/eliben/gocdkx/pubsub/awssnssqs"
)

func main() {
	// This example is used in https://github.com/eliben/gocdkx/howto/pubsub/publish/#sns-ctor

	// Variables set up elsewhere:
	ctx := context.Background()

	// Establish an AWS session.
	// See https://docs.aws.amazon.com/sdk-for-go/api/aws/session/ for more info.
	// The region must match the region for "MyTopic".
	sess, err := session.NewSession(&aws.Config{
		Region: aws.String("us-east-2"),
	})
	if err != nil {
		log.Fatal(err)
	}

	// Create a *pubsub.Topic.
	const topicARN = "arn:aws:sns:us-east-2:123456789012:MyTopic"
	topic := awssnssqs.OpenTopic(ctx, sess, topicARN, nil)
	defer topic.Shutdown(ctx)
}

Types

type BodyBase64Encoding

type BodyBase64Encoding int

BodyBase64Encoding is an enum of strategies for when to base64 message bodies.

const (
	// NonUTF8Only means that message bodies that are valid UTF-8 encodings are
	// sent as-is. Invalid UTF-8 message bodies are base64 encoded, and a
	// MessageAttribute with key "base64encoded" is added to the message.
	// When receiving messages, the "base64encoded" attribute is used to determine
	// whether to base64 decode, and is then filtered out.
	NonUTF8Only BodyBase64Encoding = 0
	// Always means that all message bodies are base64 encoded.
	// A MessageAttribute with key "base64encoded" is added to the message.
	// When receiving messages, the "base64encoded" attribute is used to determine
	// whether to base64 decode, and is then filtered out.
	Always BodyBase64Encoding = 1
	// Never means that message bodies are never base64 encoded. Non-UTF-8
	// bytes in message bodies may be modified by SNS/SQS.
	Never BodyBase64Encoding = 2
)

type SubscriptionOptions

type SubscriptionOptions struct{}

SubscriptionOptions will contain configuration for subscriptions.

type TopicOptions

type TopicOptions struct {
	// BodyBase64Encoding determines when message bodies are base64 encoded.
	// The default is NonUTF8Only.
	BodyBase64Encoding BodyBase64Encoding
}

TopicOptions contains configuration options for topics.

type URLOpener

type URLOpener struct {
	// ConfigProvider configures the connection to AWS.
	ConfigProvider client.ConfigProvider

	// TopicOptions specifies the options to pass to OpenTopic.
	TopicOptions TopicOptions
	// SubscriptionOptions specifies the options to pass to OpenSubscription.
	SubscriptionOptions SubscriptionOptions
}

URLOpener opens AWS SNS/SQS URLs like "awssns://sns-topic-arn" for topics or "awssqs://sqs-queue-url" for subscriptions.

For topics, the URL's host+path is used as the topic Amazon Resource Name (ARN).

For subscriptions, the URL's host+path is prefixed with "https://" to create the queue URL.

See github.com/eliben/gocdkx/aws/ConfigFromURLParams for supported query parameters that affect the default AWS session.

func (*URLOpener) OpenSubscriptionURL

func (o *URLOpener) OpenSubscriptionURL(ctx context.Context, u *url.URL) (*pubsub.Subscription, error)

OpenSubscriptionURL opens a pubsub.Subscription based on u.

func (*URLOpener) OpenTopicURL

func (o *URLOpener) OpenTopicURL(ctx context.Context, u *url.URL) (*pubsub.Topic, error)

OpenTopicURL opens a pubsub.Topic based on u.