Probe for optimal network buffer size.

We want to match the underlying system socket buffer.
Filling this buffer minimizes the number of syscalls we do.
Larger would be a waste.

Also changed parser to use enums that more closely match the NATS
message types.

src/server/Server.zig

@@ -4,6 +4,7 @@ const ArrayList = std.ArrayList;
 const AutoHashMapUnmanaged = std.AutoHashMapUnmanaged;
 
 const Io = std.Io;
+const Dir = Io.Dir;
 const Group = Io.Group;
 const IpAddress = std.Io.net.IpAddress;
 const Mutex = Io.Mutex;
@@ -21,6 +22,7 @@ pub const Subscription = struct {
     subject: []const u8,
     client_id: usize,
     sid: []const u8,
+    queue: *Queue(Message),
 
     fn deinit(self: Subscription, alloc: Allocator) void {
         alloc.free(self.subject);
@@ -63,13 +65,24 @@ pub fn start(server: *Server, io: Io, gpa: Allocator) !void {
     var client_group: Group = .init;
     defer client_group.cancel(io);
 
+    const read_buffer_size, const write_buffer_size = getBufferSizes(io);
+    log.debug("read buf: {d} write buf: {d}", .{ read_buffer_size, write_buffer_size });
+
     var id: usize = 0;
     while (true) : (id +%= 1) {
         if (server.clients.contains(id)) continue;
         log.debug("Accepting next client", .{});
         const stream = try tcp_server.accept(io);
         log.debug("Accepted connection {d}", .{id});
-        _ = client_group.concurrent(io, handleConnectionInfallible, .{ server, gpa, io, id, stream }) catch {
+        _ = client_group.concurrent(io, handleConnectionInfallible, .{
+            server,
+            gpa,
+            io,
+            id,
+            stream,
+            read_buffer_size,
+            write_buffer_size,
+        }) catch {
             log.err("Could not start concurrent handler for {d}", .{id});
             stream.close(io);
         };
@@ -96,13 +109,29 @@ fn removeClient(server: *Server, io: Io, allocator: Allocator, id: usize) void {
     }
 }
 
-fn handleConnectionInfallible(server: *Server, server_allocator: Allocator, io: Io, id: usize, stream: Stream) void {
-    handleConnection(server, server_allocator, io, id, stream) catch |err| {
+fn handleConnectionInfallible(
+    server: *Server,
+    server_allocator: Allocator,
+    io: Io,
+    id: usize,
+    stream: Stream,
+    r_buf_size: usize,
+    w_buf_size: usize,
+) void {
+    handleConnection(server, server_allocator, io, id, stream, r_buf_size, w_buf_size) catch |err| {
         log.err("Failed processing client {d}: {any}", .{ id, err });
     };
 }
 
-fn handleConnection(server: *Server, server_allocator: Allocator, io: Io, id: usize, stream: Stream) !void {
+fn handleConnection(
+    server: *Server,
+    server_allocator: Allocator,
+    io: Io,
+    id: usize,
+    stream: Stream,
+    r_buf_size: usize,
+    w_buf_size: usize,
+) !void {
     defer stream.close(io);
 
     // TODO: use a client allocator for things that should only live for as long as the client?
@@ -111,26 +140,27 @@ fn handleConnection(server: *Server, server_allocator: Allocator, io: Io, id: us
     // messages when done processing them (usually outside the client process, ie: publish).
 
     // Set up client writer
-    // TODO: how many bytes can fit in a network write syscall? cat /proc/sys/net/core/wmem_max
-    var w_buffer: [212992]u8 = undefined;
-    var writer = stream.writer(io, &w_buffer);
+    const w_buffer: []u8 = try server_allocator.alloc(u8, w_buf_size);
+    defer server_allocator.free(w_buffer);
+    var writer = stream.writer(io, w_buffer);
     const out = &writer.interface;
 
     // Set up client reader
-    // TODO: how many bytes can fit in a network read syscall? cat /proc/sys/net/core/rmem_max
-    var r_buffer: [212992]u8 = undefined;
-    var reader = stream.reader(io, &r_buffer);
+    const r_buffer: []u8 = try server_allocator.alloc(u8, r_buf_size);
+    defer server_allocator.free(r_buffer);
+    var reader = stream.reader(io, r_buffer);
     const in = &reader.interface;
 
     // Set up buffer queue
-    var qbuf: [r_buffer.len / @sizeOf(Message)]Message = undefined;
-    var queue: Queue(Message) = .init(&qbuf);
+    const qbuf: []Message = try server_allocator.alloc(Message, r_buffer.len / @sizeOf(Message));
+    defer server_allocator.free(qbuf);
+    var queue: Queue(Message) = .init(qbuf);
     defer {
         queue.close(io);
         while (queue.getOne(io)) |msg| {
             switch (msg) {
-                .msg => |m| m.deinit(server_allocator),
-                .hmsg => |h| h.deinit(server_allocator),
+                .MSG => |m| m.deinit(server_allocator),
+                .HMSG => |h| h.deinit(server_allocator),
                 else => {},
             }
         } else |_| {}
@@ -144,7 +174,7 @@ fn handleConnection(server: *Server, server_allocator: Allocator, io: Io, id: us
     defer server.removeClient(io, server_allocator, id);
 
     // Do initial handshake with client
-    try queue.putOne(io, .{ .info = server.info });
+    try queue.putOne(io, .{ .INFO = server.info });
 
     var client_task = try io.concurrent(Client.start, .{ &client, io, server_allocator });
     defer client_task.cancel(io) catch {};
@@ -152,27 +182,28 @@ fn handleConnection(server: *Server, server_allocator: Allocator, io: Io, id: us
     // Messages are owned by the server after they are received from the client
     while (client.next(server_allocator)) |msg| {
         switch (msg) {
-            .ping => {
+            .PING => {
                 // Respond to ping with pong.
-                try client.send(io, .pong);
+                try client.send(io, .PONG);
             },
-            .@"pub", .hpub => {
+            .PUB, .HPUB => {
+                @branchHint(.likely);
                 defer switch (msg) {
-                    .@"pub" => |pb| pb.deinit(server_allocator),
-                    .hpub => |hp| hp.deinit(server_allocator),
+                    .PUB => |pb| pb.deinit(server_allocator),
+                    .HPUB => |hp| hp.deinit(server_allocator),
                     else => unreachable,
                 };
                 try server.publishMessage(io, server_allocator, &client, msg);
             },
-            .sub => |sub| {
+            .SUB => |sub| {
                 defer sub.deinit(server_allocator);
-                try server.subscribe(io, server_allocator, id, sub);
+                try server.subscribe(io, server_allocator, id, &queue, sub);
             },
-            .unsub => |unsub| {
+            .UNSUB => |unsub| {
                 defer unsub.deinit(server_allocator);
                 try server.unsubscribe(io, server_allocator, id, unsub);
             },
-            .connect => |connect| {
+            .CONNECT => |connect| {
                 if (client.connect) |*current| {
                     current.deinit(server_allocator);
                 }
@@ -227,53 +258,46 @@ test subjectMatches {
 }
 
 fn publishMessage(server: *Server, io: Io, alloc: Allocator, source_client: *Client, msg: Message) !void {
-    errdefer {
-        if (source_client.connect) |c| {
-            if (c.verbose) {
-                source_client.send(io, .{ .@"-err" = "Slow Consumer" }) catch {};
-            }
+    defer if (source_client.connect) |c| {
+        if (c.verbose) {
+            source_client.send(io, .@"+OK") catch {};
         }
-    }
+    };
+
     const subject = switch (msg) {
-        .@"pub" => |pb| pb.subject,
-        .hpub => |hp| hp.@"pub".subject,
+        .PUB => |pb| pb.subject,
+        .HPUB => |hp| hp.@"pub".subject,
         else => unreachable,
     };
     try server.subs_lock.lock(io);
     defer server.subs_lock.unlock(io);
     for (server.subscriptions.items) |subscription| {
         if (subjectMatches(subscription.subject, subject)) {
-            const client = server.clients.get(subscription.client_id) orelse {
-                log.debug("Trying to publish to a client that no longer exists: {d}\n", .{subscription.client_id});
-                continue;
-            };
-
             switch (msg) {
-                .@"pub" => |pb| client.send(io, .{
-                    .msg = try pb.toMsg(alloc, subscription.sid),
-                }) catch |err| switch (err) {
-                    error.Canceled => return err,
-                    else => {},
+                .PUB => |pb| {
+                    try subscription.queue.putOne(io, .{
+                        .MSG = try pb.toMsg(alloc, subscription.sid),
+                    });
                 },
-                .hpub => |hp| client.send(io, .{ .hmsg = try hp.toHMsg(
-                    alloc,
-                    subscription.sid,
-                ) }) catch |err| switch (err) {
-                    error.Canceled => return err,
-                    else => {},
+                .HPUB => |hp| {
+                    try subscription.queue.putOne(io, .{
+                        .HMSG = try hp.toHMsg(alloc, subscription.sid),
+                    });
                 },
                 else => unreachable,
             }
         }
     }
-    if (source_client.connect) |c| {
-        if (c.verbose) {
-            source_client.send(io, .@"+ok") catch {};
-        }
-    }
 }
 
-fn subscribe(server: *Server, io: Io, gpa: Allocator, id: usize, msg: Message.Sub) !void {
+fn subscribe(
+    server: *Server,
+    io: Io,
+    gpa: Allocator,
+    id: usize,
+    queue: *Queue(Message),
+    msg: Message.Sub,
+) !void {
     try server.subs_lock.lock(io);
     defer server.subs_lock.unlock(io);
     const subject = try gpa.dupe(u8, msg.subject);
@@ -284,10 +308,17 @@ fn subscribe(server: *Server, io: Io, gpa: Allocator, id: usize, msg: Message.Su
         .subject = subject,
         .client_id = id,
         .sid = sid,
+        .queue = queue,
     });
 }
 
-fn unsubscribe(server: *Server, io: Io, gpa: Allocator, id: usize, msg: Message.Unsub) !void {
+fn unsubscribe(
+    server: *Server,
+    io: Io,
+    gpa: Allocator,
+    id: usize,
+    msg: Message.Unsub,
+) !void {
     try server.subs_lock.lock(io);
     defer server.subs_lock.unlock(io);
     const len = server.subscriptions.items.len;
@@ -301,5 +332,36 @@ fn unsubscribe(server: *Server, io: Io, gpa: Allocator, id: usize, msg: Message.
     }
 }
 
+const parseUnsigned = std.fmt.parseUnsigned;
+
+fn getBufferSizes(io: Io) struct { usize, usize } {
+    const default_size = 4 * 1024;
+    const default = .{ default_size, default_size };
+
+    const dir = Dir.openDirAbsolute(io, "/proc/sys/net/core", .{}) catch {
+        log.err("couldn't open /proc/sys/net/core", .{});
+        return default;
+    };
+
+    var buf: [64]u8 = undefined;
+
+    const rmem_max = readBufferSize(io, dir, "rmem_max", &buf, default_size);
+    const wmem_max = readBufferSize(io, dir, "wmem_max", &buf, default_size);
+
+    return .{ rmem_max, wmem_max };
+}
+
+fn readBufferSize(io: Io, dir: anytype, filename: []const u8, buf: []u8, default: usize) usize {
+    const bytes = dir.readFile(io, filename, buf) catch |err| {
+        log.err("couldn't open {s}: {any}", .{ filename, err });
+        return default;
+    };
+
+    return parseUnsigned(usize, bytes[0 .. bytes.len - 1], 10) catch |err| {
+        log.err("couldn't parse {s}: {any}", .{ bytes[0 .. bytes.len - 1], err });
+        return default;
+    };
+}
+
 pub const default_id = "server-id-123";
 pub const default_name = "Zits Server";