first pass at channels

docs/API.md

@@ -406,11 +406,19 @@ The 'private' parameter of a P2P topic is defined by each participant individual
 
 ### Group Topics
 
-Group topics represent communication channels between multiple users. The name of a group topic is `grp` followed by a string of characters from base64 URL-encoding set. No other assumptions can be made about internal structure or length of the group name.
+Group topic represents a communication channel between multiple users. The name of a group topic is `grp` or `chn` followed by a string of characters from base64 URL-encoding set. No other assumptions can be made about internal structure or length of the group name.
 
-A group topic is created by sending a `{sub}` message with the topic field set to string `new` optionally followed by any characters, e.g. `new` or `newAbC123` are equivalent. Tinode will respond with a `{ctrl}` message with the name of the newly created topic, i.e. `{sub topic="new"}` is replied with `{ctrl topic="grpmiKBkQVXnm3P"}`. If topic creation fails, the error is reported on the original topic name, i.e. `new` or `newAbC123`. The user who created the topic becomes topic owner. Ownership can be transferred to another user with a `{set}` message but one user must remain the owner at all times.
+Group topics support limited number of subscribers (controlled by a `max_subscriber_count` parameter in configuration file) with access permissions of each subscriber managed individually. Group topics may also be enabled to support any number of read-only users - `readers`. All `readers` have the same access permissions. Group topics with enabled `readers` are called `channels`.
 
-A user joining or leaving the topic generates a `{pres}` message to all other users who are currently in the joined state with the topic.
+A group topic is created by sending a `{sub}` message with the topic field set to string `new` or `nch` optionally followed by any characters, e.g. `new` or `newAbC123` are equivalent. Tinode will respond with a `{ctrl}` message with the name of the newly created topic, i.e. `{sub topic="new"}` is replied with `{ctrl topic="grpmiKBkQVXnm3P"}`. If topic creation fails, the error is reported on the original topic name, i.e. `new` or `newAbC123`. The user who created the topic becomes topic owner. Ownership can be transferred to another user with a `{set}` message but one user must remain the owner at all times.
+
+A `channel` topic is different from the non-channel group topic in the following ways:
+
+ * Channel-enabled topic is created by sending `{sub topic="nch"}`. Sending `{sub topic="new"}` will create a group topic without enabling channel functionality.
+ * Sending `{sub topic="chnAbC123"}` will create a `reader` subscription to a channel. A non-channel topic will reject such subscription request.
+ * When searching for topics using [`fnd`](#fnd-and-tags-finding-users-and-topics), channels will show addresses with `chn` prefixes, non-channel topic will show with `grp` prefixes.
+ * Default permissions for a channel and non-channel group topics are different: channel group topic grants no permissions at all.
+ * A subscriber joining or leaving the topic generates a `{pres}` message to all other subscribers who are currently in the joined state with the topic and have appropriate permissions. Reader joining or leaving the channel generates no `{pres}` message.
 
 ### `sys` Topic
 

server/init_topic.go

@@ -33,14 +33,14 @@ func topicInit(t *Topic, join *sessionJoin, h *Hub) {
 		// Request to load an existing or create a new p2p topic, then attach to it.
 		err = initTopicP2P(t, join)
 	case strings.HasPrefix(t.xoriginal, "new"):
-		// Processing request to create a new group topic or a channel.
-		err = initTopicNewGrp(t, join)
-	case strings.HasPrefix(t.xoriginal, "grp"):
-		// Load existing group topic.
-		err = initTopicGrpChn(t, join, false)
-	case strings.HasPrefix(t.xoriginal, "chn"):
-		// Load existing channel.
-		err = initTopicGrpChn(t, join, true)
+		// Processing request to create a new group topic.
+		err = initTopicNewGrp(t, join, false)
+	case strings.HasPrefix(t.xoriginal, "nch"):
+		// Processing request to create a new channel.
+		err = initTopicNewGrp(t, join, true)
+	case strings.HasPrefix(t.xoriginal, "grp") || strings.HasPrefix(t.xoriginal, "chn"):
+		// Load existing group topic (or channel).
+		err = initTopicGrp(t, join)
 	case t.xoriginal == "sys":
 		// Initialize system topic.
 		err = initTopicSys(t, join)
@@ -477,7 +477,7 @@ func initTopicP2P(t *Topic, sreg *sessionJoin) error {
 }
 
 // Create a new group topic
-func initTopicNewGrp(t *Topic, sreg *sessionJoin) error {
+func initTopicNewGrp(t *Topic, sreg *sessionJoin, isChan bool) error {
 	timestamp := types.TimeNow()
 	pktsub := sreg.pkt.Sub
 
@@ -486,8 +486,14 @@ func initTopicNewGrp(t *Topic, sreg *sessionJoin) error {
 	// Generic topics have parameters stored in the topic object
 	t.owner = types.ParseUserId(sreg.pkt.AsUser)
 
-	t.accessAuth = getDefaultAccess(t.cat, true)
-	t.accessAnon = getDefaultAccess(t.cat, false)
+	if isChan {
+		// The channel is not accessible by default.
+		t.accessAuth = types.ModeNone
+		t.accessAnon = types.ModeNone
+	} else {
+		t.accessAuth = getDefaultAccess(t.cat, true)
+		t.accessAnon = getDefaultAccess(t.cat, false)
+	}
 
 	// Owner/creator gets full access to the topic. Owner may change the default modeWant through 'set'.
 	userData := perUserData{
@@ -562,6 +568,7 @@ func initTopicNewGrp(t *Topic, sreg *sessionJoin) error {
 		ObjHeader: types.ObjHeader{Id: sreg.pkt.RcptTo, CreatedAt: timestamp},
 		Access:    types.DefaultAccess{Auth: t.accessAuth, Anon: t.accessAnon},
 		Tags:      tags,
+		UseBt:     isChan,
 		Public:    t.public}
 
 	// store.Topics.Create will add a subscription record for the topic creator
@@ -578,14 +585,10 @@ func initTopicNewGrp(t *Topic, sreg *sessionJoin) error {
 	return nil
 }
 
-// Initialize existing group topic. There is a race condition
-// when two users attempt to load the same topic at the same time.
-func initTopicGrpChn(t *Topic, sreg *sessionJoin, isChan bool) error {
-	if isChan {
-		t.cat = types.TopicCatChn
-	} else {
-		t.cat = types.TopicCatGrp
-	}
+// Initialize existing group topic. There is a race condition when two users attempt to load
+// the same topic at the same time. It's prevented at hub level.
+func initTopicGrp(t *Topic, sreg *sessionJoin) error {
+	t.cat = types.TopicCatGrp
 
 	// TODO(gene): check and validate topic name
 	stopic, err := store.Topics.Get(t.name)
@@ -599,6 +602,8 @@ func initTopicGrpChn(t *Topic, sreg *sessionJoin, isChan bool) error {
 		return err
 	}
 
+	t.isChan = stopic.UseBt
+
 	// t.owner is set by loadSubscriptions
 
 	t.accessAuth = stopic.Access.Auth

server/session.go

@@ -451,8 +451,8 @@ func (s *Session) dispatch(msg *ClientComMessage) {
 
 // Request to subscribe to a topic
 func (s *Session) subscribe(msg *ClientComMessage) {
-	if strings.HasPrefix(msg.Original, "new") {
-		// Request to create a new named topic.
+	if strings.HasPrefix(msg.Original, "new") || strings.HasPrefix(msg.Original, "nch") {
+		// Request to create a new group topic.
 		// If we are in a cluster, make sure the new topic belongs to the current node.
 		msg.RcptTo = globals.cluster.genLocalTopicName()
 	} else {
@@ -1069,6 +1069,8 @@ func (s *Session) expandTopicName(msg *ClientComMessage) (string, *ServerComMess
 			return "", ErrPermissionDenied(msg.Id, msg.Original, msg.timestamp)
 		}
 		routeTo = uid1.P2PName(uid2)
+	} else if strings.HasPrefix(msg.Original, "chn") {
+		routeTo = strings.Replace(msg.Original, "chn", "grp", 1)
 	} else {
 		routeTo = msg.Original
 	}

server/store/types/types.go

@@ -1189,8 +1189,6 @@ const (
 	TopicCatGrp
 	// TopicCatSys is a constant indicating a system topic.
 	TopicCatSys
-	// TopicCatChn is a constant indicating a channel.
-	TopicCatChn
 )
 
 // GetTopicCat given topic name returns topic category.
@@ -1200,14 +1198,12 @@ func GetTopicCat(name string) TopicCat {
 		return TopicCatMe
 	case "p2p":
 		return TopicCatP2P
-	case "grp":
+	case "grp", "chn":
 		return TopicCatGrp
 	case "fnd":
 		return TopicCatFnd
 	case "sys":
 		return TopicCatSys
-	case "chn":
-		return TopicCatChn
 	default:
 		panic("invalid topic type for name '" + name + "'")
 	}

server/topic.go

@@ -32,6 +32,9 @@ type Topic struct {
 	// Topic category
 	cat types.TopicCat
 
+	// Channel functionality is enabled for the group topic.
+	isChan bool
+
 	// If isProxy == true, the actual topic is hosted by another cluster member.
 	// The topic should:
 	// 1. forward all messages to master