natsdotnet/differences.md

Go vs .NET NATS Server: Functionality Differences

Excludes clustering/routes, gateways, leaf nodes, and JetStream. Generated 2026-02-22 by comparing golang/nats-server/server/ against src/NATS.Server/.

---

1. Core Server Lifecycle

Server Initialization

Feature	Go	.NET	Notes
NKey generation (server identity)	Y	Y	Ed25519 key pair via NATS.NKeys at startup
System account setup	Y	Y	$SYS account with InternalEventSystem, event publishing, request-reply services
Config file validation on startup	Y	Y	Full config parsing with error collection via ConfigProcessor
PID file writing	Y	Y	Written on startup, deleted on shutdown
Profiling HTTP endpoint (/debug/pprof)	Y	Stub	ProfPort option exists but endpoint not implemented
Ports file output	Y	Y	JSON ports file written to PortsFileDir on startup

Accept Loop

Feature	Go	.NET	Notes
Exponential backoff on accept errors	Y	Y	.NET backs off from 10ms to 1s on repeated failures
Config reload lock during client creation	Y	N	Go holds reloadMu around createClient
Goroutine/task tracking (WaitGroup)	Y	Y	Interlocked counter + drain with 10s timeout on shutdown
Callback-based error handling	Y	N	Go uses errFunc callback pattern
Random/ephemeral port (port=0)	Y	Y	Port resolved after Bind+Listen, stored in _options.Port

Shutdown

Feature	Go	.NET	Notes
Graceful shutdown with WaitForShutdown()	Y	Y	Idempotent CAS-guarded ShutdownAsync() + blocking WaitForShutdown()
Close reason tracking per connection	Y	Y	37-value ClosedState enum, CAS-based first-writer-wins MarkClosed()
Lame duck mode (stop new, drain existing)	Y	Y	LameDuckShutdownAsync() with grace period + stagger-close with jitter
Wait for accept loop completion	Y	Y	TaskCompletionSource signaled in accept loop finally
Flush pending data before close	Y	Y	FlushAndCloseAsync() with best-effort flush, skip-flush for error conditions

Signal Handling

Signal	Go	.NET	Notes
SIGINT (Ctrl+C)	Y	Y	Both handle graceful shutdown
SIGTERM	Y	Y	PosixSignalRegistration triggers ShutdownAsync()
SIGUSR1 (reopen logs)	Y	Y	SIGUSR1 handler calls ReOpenLogFile
SIGUSR2 (lame duck mode)	Y	Y	Triggers LameDuckShutdownAsync()
SIGHUP (config reload)	Y	Y	Re-parses config, diffs options, applies reloadable subset; CLI flags preserved
Windows Service integration	Y	Y	--service flag with Microsoft.Extensions.Hosting.WindowsServices

---

2. Client / Connection Handling

Concurrency Model

Feature	Go	.NET	Notes
Separate read + write loops	Y	Y	Channel-based RunWriteLoopAsync with QueueOutbound()
Write coalescing / batch flush	Y	Y	Write loop drains all channel items before single FlushAsync
Dynamic buffer sizing (512B-64KB)	Y	N	.NET delegates to System.IO.Pipelines
Output buffer pooling (3-tier)	Y	N	Go pools at 512B, 4KB, 64KB

Connection Types

Type	Go	.NET	Notes
CLIENT	Y	Y
ROUTER	Y	N	Excluded per scope
GATEWAY	Y	N	Excluded per scope
LEAF	Y	N	Excluded per scope
SYSTEM (internal)	Y	Y	InternalClient + InternalEventSystem with Channel-based send/receive loops
JETSTREAM (internal)	Y	N
ACCOUNT (internal)	Y	Y	Lazy per-account InternalClient with import/export subscription support
WebSocket clients	Y	N
MQTT clients	Y	N

Client Features

Feature	Go	.NET	Notes
Echo suppression (echo: false)	Y	Y	.NET checks echo in delivery path (NatsServer.cs:234,253)
Verbose mode (+OK responses)	Y	Y	Sends +OK after CONNECT, SUB, UNSUB, PUB when verbose:true
No-responders validation	Y	Y	CONNECT rejects no_responders without headers; 503 HMSG on no match
Slow consumer detection	Y	Y	Pending bytes threshold (64MB) + write deadline timeout (10s)
Write deadline / timeout policies	Y	Y	WriteDeadline option with CancellationTokenSource.CancelAfter on flush
RTT measurement	Y	Y	_rttStartTicks/Rtt property, computed on PONG receipt
Per-client trace mode	Y	Y	SetTraceMode() toggles parser logger dynamically via ClientFlags.TraceMode
Detailed close reason tracking	Y	Y	37-value ClosedState enum with CAS-based MarkClosed()
Connection state flags (16 flags)	Y	Y	7-flag ClientFlagHolder with Interlocked.Or/And

Slow Consumer Handling

Go implements a sophisticated slow consumer detection system:

• Tracks pendingBytes per client output buffer
• If pending exceeds maxPending, enters stall mode (2-5ms waits)
• Total stall capped at 10ms per read cycle
• Closes with SlowConsumerPendingBytes or SlowConsumerWriteDeadline
• Sets isSlowConsumer flag for monitoring

.NET now implements pending bytes tracking and write deadline enforcement via Channel<ReadOnlyMemory<byte>>. Key differences from Go: no stall/retry mode (immediate close on threshold exceeded), write deadline via CancellationTokenSource.CancelAfter instead of SetWriteDeadline. IsSlowConsumer flag and server-level SlowConsumerCount stats are tracked for monitoring.

Stats Tracking

Feature	Go	.NET	Notes
Per-connection atomic stats	Y	Y	.NET uses Interlocked for stats access
Per-read-cycle stat batching	Y	Y	Local accumulators flushed via Interlocked.Add per read cycle
Per-account stats	Y	Y	Interlocked counters for InMsgs/OutMsgs/InBytes/OutBytes per Account
Slow consumer counters	Y	Y	SlowConsumers and SlowConsumerClients incremented on detection

---

3. Protocol Parsing

Parser Architecture

Aspect	Go	.NET
Approach	Byte-by-byte state machine (74 states)	Two-phase: line extraction + command dispatch
Case handling	Per-state character checks	Bit-mask lowercase normalization (| 0x20)
Buffer strategy	Jump-ahead optimization for payloads	Direct size-based reads via Pipe
Split-buffer handling	argBuf accumulation with scratch buffer	State variables (_awaitingPayload, etc.)
Error model	Inline error sending + error return	Exception-based (ProtocolViolationException)
CRLF in payload	Included in message buffer	Excluded by design

Protocol Operations

Operation	Go	.NET	Notes
PUB	Y	Y
HPUB (headers)	Y	Y
SUB	Y	Y
UNSUB	Y	Y
CONNECT	Y	Y
INFO	Y	Y
PING / PONG	Y	Y
MSG / HMSG	Y	Y
+OK / -ERR	Y	Y
RS+/RS-/RMSG (routes)	Y	N	Excluded per scope
A+/A- (accounts)	Y	N	Excluded per scope
LS+/LS-/LMSG (leaf)	Y	N	Excluded per scope

Protocol Parsing Gaps

Feature	Go	.NET	Notes
Multi-client-type command routing	Y	N	Go checks c.kind to allow/reject commands
Protocol tracing in parser	Y	Y	TraceInOp() logs <<- OP arg at LogLevel.Trace via optional ILogger
Subject mapping (input→output)	Y	Y	Compiled SubjectTransform engine with 9 function tokens; wired into ProcessMessage
MIME header parsing	Y	Y	NatsHeaderParser.Parse() — status line + key-value headers from ReadOnlySpan<byte>
Message trace event initialization	Y	N

Protocol Writing

Aspect	Go	.NET	Notes
INFO serialization	Once at startup	Once at startup	Cached at startup; nonce connections serialize per-connection
MSG/HMSG construction	Direct buffer write	Span-based buffer write	int.TryFormat + CopyTo into rented buffer, no string allocations
Pre-encoded constants	Y	Y	Both pre-encode PING/PONG/OK

---

4. Subscriptions & Subject Matching

Trie Implementation

Feature	Go	.NET	Notes
Basic trie with */> wildcards	Y	Y	Core matching identical
Queue group support	Y	Y
Result caching (1024 max)	Y	Y	Same limits
plist optimization (>256 subs)	Y	N	Go converts high-fanout nodes to array
Async cache sweep (background)	Y	N	.NET sweeps inline under write lock
Atomic generation ID for invalidation	Y	Y	Interlocked.Increment on insert/remove; cached results store generation
Cache eviction strategy	Random	First-N	Semantic difference minimal

SubList Features

Feature	Go	.NET	Notes
Stats() — comprehensive statistics	Y	Y	Matches, cache hits, inserts, removes tracked via Interlocked
HasInterest() — fast bool check	Y	Y	Walks trie without allocating result list
NumInterest() — fast count	Y	Y	Counts plain + queue subs without allocation
ReverseMatch() — pattern→literal query	Y	Y	Finds subscriptions whose wildcards match a literal subject
RemoveBatch() — efficient bulk removal	Y	Y	Single generation increment for batch; increments _removes per sub
All() — enumerate all subscriptions	Y	Y	Recursive trie walk returning all subscriptions
Notification system (interest changes)	Y	N
Local/remote subscription filtering	Y	N
Queue weight expansion (remote subs)	Y	N
MatchBytes() — zero-copy byte API	Y	N

Subject Validation

Feature	Go	.NET	Notes
Basic validation (empty tokens, wildcards)	Y	Y
Literal subject check	Y	Y
UTF-8/null rune validation	Y	Y	IsValidSubject(string, bool checkRunes) rejects null bytes
Collision detection (SubjectsCollide)	Y	Y	Token-by-token wildcard comparison; O(n) via upfront Split
Token utilities (tokenAt, numTokens)	Y	Y	TokenAt returns ReadOnlySpan<char>; NumTokens counts separators
Stack-allocated token buffer	Y	N	Go uses [32]string{} on stack

Subscription Lifecycle

Feature	Go	.NET	Notes
Per-account subscription limit	Y	Y	Account.IncrementSubscriptions() returns false when MaxSubscriptions exceeded
Auto-unsubscribe on max messages	Y	Y	Enforced at delivery; sub removed from trie + client dict when exhausted
Subscription routing propagation	Y	N	For clusters
Queue weight (qw) field	Y	N	For remote queue load balancing

---

5. Authentication & Authorization

Auth Mechanisms

Mechanism	Go	.NET	Notes
Username/password	Y	Y
Token	Y	Y
NKeys (Ed25519)	Y	Y	.NET has framework but integration is basic
JWT validation	Y	Y	NatsJwt decode/verify, JwtAuthenticator with account resolution + revocation
Bcrypt password hashing	Y	Y	.NET supports bcrypt ($2* prefix) with constant-time fallback
TLS certificate mapping	Y	Y	X500DistinguishedName with full DN match and CN fallback
Custom auth interface	Y	N
External auth callout	Y	N
Proxy authentication	Y	N
Bearer tokens	Y	Y	UserClaims.BearerToken skips nonce signature verification
User revocation tracking	Y	Y	Per-account ConcurrentDictionary with wildcard (*) revocation support

Account System

Feature	Go	.NET	Notes
Per-account SubList isolation	Y	Y
Multi-account user resolution	Y	Y	AccountConfig per account in NatsOptions.Accounts; GetOrCreateAccount wires limits
Account exports/imports	Y	Y	ServiceImport/StreamImport with ExportAuth, subject transforms, response routing
Per-account connection limits	Y	Y	Account.AddClient() returns false when MaxConnections exceeded
Per-account subscription limits	Y	Y	Account.IncrementSubscriptions() enforced in ProcessSub()
Account JetStream limits	Y	N	Excluded per scope

Permissions

Feature	Go	.NET	Notes
Publish allow list	Y	Y
Subscribe allow list	Y	Y
Publish deny list	Y	Y	Full enforcement with LRU-cached results
Subscribe deny list	Y	Y	Queue-aware deny checking in IsSubscribeAllowed
Message-level deny filtering	Y	Y	IsDeliveryAllowed() checked before MSG send; auto-unsub cleanup on deny
Permission caching (128 entries)	Y	Y	PermissionLruCache — Dictionary+LinkedList LRU, matching Go's maxPermCacheSize
Response permissions (reply tracking)	Y	Y	ResponseTracker with configurable TTL + max messages; not LRU-cached
Auth expiry enforcement	Y	Y	Task.Delay timer closes client when JWT/auth expires
Permission templates (JWT)	Y	Y	PermissionTemplates.Expand() — 6 functions with cartesian product for multi-value tags

---

6. Configuration

CLI Flags

Flag	Go	.NET	Notes
-p/--port	Y	Y
-a/--addr	Y	Y
-n/--name (ServerName)	Y	Y
-m/--http_port (monitoring)	Y	Y
-c (config file)	Y	Y	Full config parsing: lexer → parser → processor; CLI args override config
-D/-V/-DV (debug/trace)	Y	Y	-D/--debug for debug, -V/-T/--trace for trace, -DV for both
--tlscert/--tlskey/--tlscacert	Y	Y
--tlsverify	Y	Y
--http_base_path	Y	Y
--https_port	Y	Y

Configuration System

Feature	Go	.NET	Notes
Config file parsing	Y	Y	Custom NATS conf lexer/parser ported from Go; supports includes, variables, blocks
Hot reload (SIGHUP)	Y	Y	Reloads logging, auth, limits, TLS certs on SIGHUP; rejects non-reloadable changes
Config change detection	Y	Y	SHA256 digest comparison; InCmdLine tracks CLI flag precedence
~450 option fields	Y	~72	.NET covers core + all single-server options; cluster/JetStream keys silently ignored

Missing Options Categories

• Logging options — file logging, rotation, syslog, debug/trace, color, timestamps, per-subsystem log control all implemented
• Advanced limits (MaxSubs, MaxSubTokens, MaxPending, WriteDeadline) — MaxSubs, MaxSubTokens implemented; MaxPending/WriteDeadline already existed
• Tags/metadata — Tags dictionary implemented in NatsOptions
• OCSP configuration — OcspConfig with 4 modes (Auto/Always/Must/Never), peer verification, and stapling
• WebSocket/MQTT options
• Operator mode / account resolver — JwtAuthenticator + IAccountResolver + MemAccountResolver with trusted keys

---

7. Monitoring

HTTP Endpoints

Endpoint	Go	.NET	Notes
/healthz	Y	Y
/varz	Y	Y
/connz	Y	Y
/ (root listing)	Y	Y
/routez	Y	Stub	Returns empty response
/gatewayz	Y	Stub	Returns empty response
/leafz	Y	Stub	Returns empty response
/subz / /subscriptionsz	Y	Y	Account filtering, test subject filtering, pagination, and subscription details
/accountz	Y	Stub	Returns empty response
/accstatz	Y	Stub	Returns empty response
/jsz	Y	Stub	Returns empty response

Varz Response

Field Category	Go	.NET	Notes
Identity (ID, Name, Version)	Y	Y
Network (Host, Port, URLs)	Y	Y
Security (AuthRequired, TLS)	Y	Y
Limits (MaxConn, MaxPayload)	Y	Y
Timing (Start, Now, Uptime)	Y	Y
Runtime (Mem, CPU, Cores)	Y	Y
Connections (current, total)	Y	Y
Messages (in/out msgs/bytes)	Y	Y
SlowConsumer breakdown	Y	N	Go tracks per connection type
Cluster/Gateway/Leaf blocks	Y	N	Excluded per scope
JetStream block	Y	N	Excluded per scope
TLS cert expiry info	Y	Y	TlsCertNotAfter loaded via X509CertificateLoader in /varz

Connz Response

Feature	Go	.NET	Notes
Filtering by CID, user, account	Y	Partial
Sorting (11 options)	Y	Y	All options including ByStop, ByReason, ByRtt
State filtering (open/closed/all)	Y	Y	`state=open
Closed connection tracking	Y	Y	ConcurrentQueue<ClosedClient> capped at 10,000 entries
Pagination (offset, limit)	Y	Y
Subscription detail mode	Y	N
TLS peer certificate info	Y	N
JWT/IssuerKey/Tags fields	Y	N
MQTT client ID filtering	Y	N
Proxy info	Y	N

---

8. TLS

TLS Modes

Mode	Go	.NET	Notes
No TLS	Y	Y
INFO-first (default NATS)	Y	Y
TLS-first (before INFO)	Y	Y
Mixed/Fallback	Y	Y
TLS-required	Y	Y

TLS Features

Feature	Go	.NET	Notes
PEM cert/key loading	Y	Y
CA chain validation	Y	Y
Mutual TLS (client certs)	Y	Y
Certificate pinning (SHA256 SPKI)	Y	Y
TLS handshake timeout	Y	Y
TLS rate limiting	Y	Y	Rate enforcement with refill; unit tests cover rate limiting and refill
First-byte peeking (0x16 detection)	Y	Y
Cert subject→user mapping	Y	Y	X500DistinguishedName with full DN match and CN fallback
OCSP stapling	Y	Y	SslStreamCertificateContext.Create with offline:false for runtime OCSP fetch
Min TLS version control	Y	Y

---

9. Logging

Feature	Go	.NET	Notes
Structured logging	Partial	Y	.NET uses Serilog with ILogger
File logging with rotation	Y	Y	-l/--log_file flag + LogSizeLimit/LogMaxFiles via Serilog.Sinks.File
Syslog (local and remote)	Y	Y	--syslog and --remote_syslog flags via Serilog.Sinks.SyslogMessages
Log reopening (SIGUSR1)	Y	Y	SIGUSR1 handler calls ReOpenLogFile callback
Trace mode (protocol-level)	Y	Y	-V/-T/--trace flags; parser TraceInOp() logs at Trace level
Debug mode	Y	Y	-D/--debug flag lowers Serilog minimum to Debug
Per-subsystem log control	Y	Y	--log_level_override ns=level CLI flag with Serilog MinimumLevel.Override
Color output on TTY	Y	Y	Auto-detected via Console.IsOutputRedirected, uses AnsiConsoleTheme.Code
Timestamp format control	Y	Y	--logtime and --logtime_utc flags

---

10. Ping/Pong & Keepalive

Feature	Go	.NET	Notes
Server-initiated PING	Y	Y
Configurable interval	Y	Y	PingInterval option
Max pings out	Y	Y	MaxPingsOut option
Stale connection close	Y	Y
RTT-based first PING delay	Y	Y	Skips PING until FirstPongSent or 2s elapsed
RTT tracking	Y	Y	_rttStartTicks/Rtt property, computed on PONG receipt
Stale connection stats	Y	Y	StaleConnectionStats model, exposed in /varz

---

Summary: Critical Gaps for Production Use

Resolved Since Initial Audit

The following items from the original gap list have been implemented:

• Slow consumer detection — pending bytes threshold (64MB) with write deadline enforcement
• Write coalescing / batch flush — channel-based write loop drains all items before single flush
• Verbose mode — +OK responses for CONNECT, SUB, UNSUB, PUB when verbose:true
• Permission deny enforcement at delivery — IsDeliveryAllowed + auto-unsub cleanup
• No-responders validation — CONNECT rejects no_responders without headers; 503 HMSG on no match
• File logging with rotation — Serilog.Sinks.File with rolling file support
• TLS certificate mapping — X500DistinguishedName with full DN match and CN fallback
• Protocol tracing — -V/-T flag enables trace-level logging; -D for debug
• Subscription statistics — Stats(), HasInterest(), NumInterest(), etc.
• Per-account limits — connection + subscription limits via AccountConfig
• Reply subject tracking — ResponseTracker with TTL + max messages
• JWT authentication — JwtAuthenticator with decode/verify, account resolution, revocation, permission templates
• OCSP support — peer verification via X509RevocationMode.Online, stapling via SslStreamCertificateContext
• Subject mapping — compiled SubjectTransform engine with 9 function tokens, wired into message delivery
• Windows Service integration — --service flag with Microsoft.Extensions.Hosting.WindowsServices
• Per-subsystem log control — --log_level_override CLI flag with Serilog overrides
• Per-client trace mode — SetTraceMode() with dynamic parser logger toggling
• Per-account stats — Interlocked counters for InMsgs/OutMsgs/InBytes/OutBytes
• TLS cert expiry in /varz — TlsCertNotAfter populated via X509CertificateLoader
• Permission templates — PermissionTemplates.Expand() with 6 functions and cartesian product
• Bearer tokens — UserClaims.BearerToken skips nonce verification
• User revocation — per-account tracking with wildcard (*) revocation
• Config file parsing — custom lexer/parser ported from Go; supports includes, variables, nested blocks, size suffixes
• Hot reload (SIGHUP) — re-parses config, diffs changes, validates reloadable set, applies with CLI precedence
• SYSTEM client type — InternalClient with InternalEventSystem, Channel-based send/receive loops, event publishing
• ACCOUNT client type — lazy per-account InternalClient with import/export subscription support
• System event publishing — connect/disconnect advisories, server stats, shutdown/lame-duck events, auth errors
• System request-reply services — $SYS.REQ.SERVER.*.VARZ/CONNZ/SUBSZ/HEALTHZ/IDZ/STATSZ with ping wildcards
• Account exports/imports — service and stream imports with ExportAuth, subject transforms, response routing, latency tracking

Remaining Lower Priority

1. Dynamic buffer sizing — delegated to Pipe, less optimized for long-lived connections