Support queue groups

src/server/Server.zig

@@ -26,6 +26,7 @@ pub const Subscription = struct {
     subject: []const u8,
     client_id: usize,
     sid: []const u8,
+    queue_group: ?[]const u8,
     queue: *Queue(Msgs),
     // used to alloc messages in the queue
     alloc: Allocator,
@@ -33,6 +34,7 @@ pub const Subscription = struct {
     fn deinit(self: Subscription, alloc: Allocator) void {
         alloc.free(self.subject);
         alloc.free(self.sid);
+        if (self.queue_group) |g| alloc.free(g);
     }
 };
 
@@ -201,12 +203,12 @@ fn handleConnection(
             .PUB => |pb| {
                 @branchHint(.likely);
                 defer pb.deinit(server_allocator);
-                try server.publishMessage(io, &client, msg);
+                try server.publishMessage(io, server_allocator, &client, msg);
             },
             .HPUB => |hp| {
                 @branchHint(.likely);
                 defer hp.deinit(server_allocator);
-                try server.publishMessage(io, &client, msg);
+                try server.publishMessage(io, server_allocator, &client, msg);
             },
             .SUB => |sub| {
                 defer sub.deinit(server_allocator);
@@ -270,7 +272,13 @@ test subjectMatches {
     try expect(subjectMatches("foo.>", "foo.bar.baz"));
 }
 
-fn publishMessage(server: *Server, io: Io, source_client: *Client, msg: Message) !void {
+fn publishMessage(
+    server: *Server,
+    io: Io,
+    alloc: Allocator,
+    source_client: *Client,
+    msg: Message,
+) !void {
     defer if (source_client.connect) |c| {
         if (c.verbose) {
             source_client.send(io, .@"+OK") catch {};
@@ -284,8 +292,26 @@ fn publishMessage(server: *Server, io: Io, source_client: *Client, msg: Message)
     };
     try server.subs_lock.lock(io);
     defer server.subs_lock.unlock(io);
-    for (server.subscriptions.items) |subscription| {
+    var published_queue_groups: ArrayList([]const u8) = .empty;
+    defer published_queue_groups.deinit(alloc);
+    var published_queue_sub_idxs: ArrayList(usize) = .empty;
+    defer published_queue_sub_idxs.deinit(alloc);
+
+    subs: for (0..server.subscriptions.items.len) |i| {
+        const subscription = server.subscriptions.items[i];
         if (subjectMatches(subscription.subject, subject)) {
+            if (subscription.queue_group) |sg| {
+                for (published_queue_groups.items) |g| {
+                    if (eql(u8, g, sg)) {
+                        continue :subs;
+                    }
+                }
+                // Don't republish to the same queue
+                try published_queue_groups.append(alloc, sg);
+                // Move this index to the end of the subscription list,
+                // to prioritize other subscriptions in the queue next time.
+                try published_queue_sub_idxs.append(alloc, i);
+            }
             switch (msg) {
                 .PUB => |pb| {
                     try subscription.queue.putOne(io, .{
@@ -301,6 +327,11 @@ fn publishMessage(server: *Server, io: Io, source_client: *Client, msg: Message)
             }
         }
     }
+
+    for (0..published_queue_sub_idxs.items.len) |from_end| {
+        const i = published_queue_sub_idxs.items.len - from_end - 1;
+        server.subscriptions.appendAssumeCapacity(server.subscriptions.orderedRemove(i));
+    }
 }
 
 fn subscribe(
@@ -317,10 +348,13 @@ fn subscribe(
     errdefer gpa.free(subject);
     const sid = try gpa.dupe(u8, msg.sid);
     errdefer gpa.free(sid);
+    const queue_group = if (msg.queue_group) |q| try gpa.dupe(u8, q) else null;
+    errdefer if (queue_group) |q| gpa.free(q);
     try server.subscriptions.append(gpa, .{
         .subject = subject,
         .client_id = id,
         .sid = sid,
+        .queue_group = queue_group,
         .queue = client.msg_queue,
         .alloc = client.alloc,
     });