initial commit

.gitignore

@@ -0,0 +1,2 @@
+*~
+bin

LICENSE

@@ -0,0 +1,28 @@
+Copyright (c) 2021, City and County of San Francisco, acting by and through its
+Airport Commission ("City"). All rights reserved.
+
+The City and County of San Francisco, acting by and through its Airport
+Commission, created and operates the SFO Museum.
+
+Redistribution and use in source and binary forms, with or without modification,
+are permitted provided that the following conditions are met:
+
+1.  Redistributions of source code must retain the above copyright notice, this
+    list of conditions and the following disclaimer.
+2.  Redistributions in binary form must reproduce the above copyright notice,
+    this list of conditions and the following disclaimer in the documentation
+    and/or other materials provided with the distribution.
+3.  Neither the name of the City nor the names of its contributors may be used
+    to endorse or promote products derived from this software without specific
+    prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR
+ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

README.md

@@ -0,0 +1,17 @@
+# go-pubsub
+
+Go package to provide a common interface for abstract publish and subscribe operations.
+
+## Important
+
+Ideally this package would/could be replaced by the [GoCloud pubsub package](https://gocloud.dev/howto/pubsub/) but it does not support Redis.
+
+## Documentation
+
+Documentation is incomplete at this time.
+
+## See also
+
+* https://gocloud.dev/howto/pubsub/
+* https://github.com/google/go-cloud/issues/1368
+* https://github.com/go-redis/redis/v8

doc.go

@@ -0,0 +1,5 @@
+// Package pubsub provides a common interface for abstract publish and subscribe operations.
+// Ideally this package would/could be replaced by the GoCloud pubsub package but it does not support Redis...
+// https://gocloud.dev/howto/pubsub/
+// https://github.com/google/go-cloud/issues/1368
+package pubsub

go.mod

@@ -0,0 +1,8 @@
+module github.com/sfomuseum/go-pubsub
+
+go 1.16
+
+require (
+	github.com/aaronland/go-roster v0.0.2
+	github.com/go-redis/redis/v8 v8.9.0
+)

go.sum

@@ -0,0 +1,84 @@
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publisher/channels.go

@@ -0,0 +1,33 @@
+package publisher
+
+// https://eli.thegreenplace.net/2020/pubsub-using-channels-in-go/
+
+import (
+	"context"
+	_ "log"
+)
+
+type ChannelPublisher struct {
+	Publisher
+	channel chan string
+}
+
+func NewChannelPublisherWithChannel(ctx context.Context, ch chan string) (Publisher, error) {
+
+	pub := &ChannelPublisher{
+		channel: ch,
+	}
+
+	return pub, nil
+}
+
+func (pub *ChannelPublisher) Publish(ctx context.Context, msg string) error {
+
+	// Add timeout here...
+	pub.channel <- msg
+	return nil
+}
+
+func (pub *ChannelPublisher) Close() error {
+	return nil
+}

publisher/publisher.go

@@ -0,0 +1,87 @@
+// package publisher provides a common interface for publish operations.
+package publisher
+
+import (
+	"context"
+	"fmt"
+	"github.com/aaronland/go-roster"
+	"net/url"
+	"sort"
+	"strings"
+)
+
+type Publisher interface {
+	Publish(context.Context, string) error
+	Close() error
+}
+
+type PublisherInitializeFunc func(ctx context.Context, uri string) (Publisher, error)
+
+var publishers roster.Roster
+
+func ensurePublisherRoster() error {
+
+	if publishers == nil {
+
+		r, err := roster.NewDefaultRoster()
+
+		if err != nil {
+			return err
+		}
+
+		publishers = r
+	}
+
+	return nil
+}
+
+func RegisterPublisher(ctx context.Context, scheme string, f PublisherInitializeFunc) error {
+
+	err := ensurePublisherRoster()
+
+	if err != nil {
+		return err
+	}
+
+	return publishers.Register(ctx, scheme, f)
+}
+
+func Schemes() []string {
+
+	ctx := context.Background()
+	schemes := []string{}
+
+	err := ensurePublisherRoster()
+
+	if err != nil {
+		return schemes
+	}
+
+	for _, dr := range publishers.Drivers(ctx) {
+		scheme := fmt.Sprintf("%s://", strings.ToLower(dr))
+		schemes = append(schemes, scheme)
+	}
+
+	sort.Strings(schemes)
+	return schemes
+}
+
+func NewPublisher(ctx context.Context, uri string) (Publisher, error) {
+
+	u, err := url.Parse(uri)
+
+	if err != nil {
+		return nil, err
+	}
+
+	scheme := u.Scheme
+
+	i, err := publishers.Driver(ctx, scheme)
+
+	if err != nil {
+		return nil, err
+	}
+
+	f := i.(PublisherInitializeFunc)
+	return f(ctx, uri)
+}

publisher/redis.go

@@ -0,0 +1,64 @@
+package publisher
+
+import (
+	"context"
+	"fmt"
+	"github.com/go-redis/redis/v8"
+	"net/url"
+)
+
+type RedisPublisher struct {
+	Publisher
+	redis_client  *redis.Client
+	redis_channel string
+}
+
+func init() {
+	ctx := context.Background()
+	RegisterPublisher(ctx, "redis", NewRedisPublisher)
+}
+
+func NewRedisPublisher(ctx context.Context, uri string) (Publisher, error) {
+
+	u, err := url.Parse(uri)
+
+	if err != nil {
+		return nil, err
+	}
+
+	q := u.Query()
+
+	host := q.Get("host")
+	port := q.Get("port")
+	channel := q.Get("channel")
+
+	endpoint := fmt.Sprintf("%s:%s", host, port)
+
+	client := redis.NewClient(&redis.Options{
+		Addr: endpoint,
+	})
+
+	p := &RedisPublisher{
+		redis_client:  client,
+		redis_channel: channel,
+	}
+
+	return p, nil
+}
+
+func (p *RedisPublisher) Publish(ctx context.Context, msg string) error {
+
+	select {
+	case <-ctx.Done():
+		return nil
+	default:
+		// pass
+	}
+
+	cmd := p.redis_client.Publish(ctx, p.redis_channel, msg)
+	return cmd.Err()
+}
+
+func (p *RedisPublisher) Close() error {
+	return p.redis_client.Close()
+}

subscriber/channel.go

@@ -0,0 +1,37 @@
+package subscriber
+
+import (
+	"context"
+)
+
+type ChannelSubscriber struct {
+	Subscriber
+	channel chan string
+}
+
+func NewChannelSubscriberWithChannel(ctx context.Context, ch chan string) (Subscriber, error) {
+
+	sub := &ChannelSubscriber{
+		channel: ch,
+	}
+
+	return sub, nil
+}
+
+func (sub *ChannelSubscriber) Listen(ctx context.Context, messages_ch chan string) error {
+
+	for {
+		select {
+		case <-ctx.Done():
+			return nil
+		case msg := <-sub.channel:
+			messages_ch <- msg
+		}
+	}
+
+	return nil
+}
+
+func (sub *ChannelSubscriber) Close() error {
+	return nil
+}