smartproxy/readme.hints.md

SmartProxy Development Hints

Byte Tracking and Metrics

Throughput Drift Issue (Fixed)

Problem: Throughput numbers were gradually increasing over time for long-lived connections.

Root Cause: The byRoute() and byIP() methods were dividing cumulative total bytes (since connection start) by the window duration, causing rates to appear higher as connections aged:

• Hour 1: 1GB total / 60s = 17 MB/s ✓
• Hour 2: 2GB total / 60s = 34 MB/s ✗ (appears doubled!)
• Hour 3: 3GB total / 60s = 50 MB/s ✗ (keeps rising!)

Solution: Implemented dedicated ThroughputTracker instances for each route and IP address:

• Each route and IP gets its own throughput tracker with per-second sampling
• Samples are taken every second and stored in a circular buffer
• Rate calculations use actual samples within the requested window
• Default window is now 1 second for real-time accuracy

What Gets Counted (Network Interface Throughput)

The byte tracking is designed to match network interface throughput (what Unifi/network monitoring tools show):

Counted bytes include:

• All application data
• TLS handshakes and protocol overhead
• TLS record headers and encryption padding
• HTTP headers and protocol data
• WebSocket frames and protocol overhead
• TLS alerts sent to clients

NOT counted:

• PROXY protocol headers (sent to backend, not client)
• TCP/IP headers (handled by OS, not visible at application layer)

Byte direction:

• bytesReceived: All bytes received FROM the client on the incoming connection
• bytesSent: All bytes sent TO the client on the incoming connection
• Backend connections are separate and not mixed with client metrics

Double Counting Issue (Fixed)

Problem: Initial data chunks were being counted twice in the byte tracking:

1. Once when stored in pendingData in setupDirectConnection()
2. Again when the data flowed through bidirectional forwarding

Solution: Removed the byte counting when storing initial chunks. Bytes are now only counted when they actually flow through the setupBidirectionalForwarding() callbacks.

HttpProxy Metrics (Fixed)

Problem: HttpProxy forwarding was updating connection record byte counts but not calling metricsCollector.recordBytes(), resulting in missing throughput data.

Solution: Added metricsCollector.recordBytes() calls to the HttpProxy bidirectional forwarding callbacks.

Metrics Architecture

The metrics system has multiple layers:

1. Connection Records (record.bytesReceived/bytesSent): Track total bytes per connection
2. Global ThroughputTracker: Accumulates bytes between samples for overall rate calculations
3. Per-Route ThroughputTrackers: Dedicated tracker for each route with per-second sampling
4. Per-IP ThroughputTrackers: Dedicated tracker for each IP with per-second sampling
5. connectionByteTrackers: Track cumulative bytes and metadata for active connections

Key features:

• All throughput trackers sample every second (1Hz)
• Each tracker maintains a circular buffer of samples (default: 1 hour retention)
• Rate calculations are accurate for any requested window (default: 1 second)
• All byte counting happens exactly once at the data flow point
• Unused route/IP trackers are automatically cleaned up when connections close

Understanding "High" Byte Counts

If byte counts seem high compared to actual application data, remember:

• TLS handshakes can be 1-5KB depending on cipher suites and certificates
• Each TLS record has 5 bytes of header overhead
• TLS encryption adds 16-48 bytes of padding/MAC per record
• HTTP/2 has additional framing overhead
• WebSocket has frame headers (2-14 bytes per message)

This overhead is real network traffic and should be counted for accurate throughput metrics.

Byte Counting Paths

There are two mutually exclusive paths for connections:

1. Direct forwarding (route-connection-handler.ts):

   • Used for TCP passthrough, TLS passthrough, and direct connections
   • Bytes counted in setupBidirectionalForwarding callbacks
   • Initial chunk NOT counted separately (flows through bidirectional forwarding)

2. HttpProxy forwarding (http-proxy-bridge.ts):

   • Used for TLS termination (terminate, terminate-and-reencrypt)
   • Initial chunk counted when written to proxy
   • All subsequent bytes counted in setupBidirectionalForwarding callbacks
   • This is the ONLY counting point for these connections

Byte Counting Audit (2025-01-06)

A comprehensive audit was performed to verify byte counting accuracy:

Audit Results:

• ✅ No double counting detected in any connection flow
• ✅ Each byte counted exactly once in each direction
• ✅ Connection records and metrics updated consistently
• ✅ PROXY protocol headers correctly excluded from client metrics
• ✅ NFTables forwarded connections correctly not counted (kernel handles)

Key Implementation Points:

• All byte counting happens in only 2 files: route-connection-handler.ts and http-proxy-bridge.ts
• Both use the same pattern: increment record.bytesReceived/Sent AND call metricsCollector.recordBytes()
• Initial chunks handled correctly: stored but not counted until forwarded
• TLS alerts counted as sent bytes (correct - they are sent to client)

For full audit details, see readme.byte-counting-audit.md

Connection Cleanup

Zombie Connection Detection

The connection manager performs comprehensive zombie detection every 10 seconds:

• Full zombies: Both incoming and outgoing sockets destroyed but connection not cleaned up
• Half zombies: One socket destroyed, grace period expired (5 minutes for TLS, 30 seconds for non-TLS)
• Stuck connections: Data received but none sent back after threshold (5 minutes for TLS, 60 seconds for non-TLS)

Cleanup Queue

Connections are cleaned up through a batched queue system:

• Batch size: 100 connections
• Processing triggered immediately when batch size reached
• Otherwise processed after 100ms delay
• Prevents overwhelming the system during mass disconnections

Keep-Alive Handling

Keep-alive connections receive special treatment based on keepAliveTreatment setting:

• standard: Normal timeout applies
• extended: Timeout multiplied by keepAliveInactivityMultiplier (default 6x)
• immortal: No timeout, connections persist indefinitely

PROXY Protocol

The system supports both receiving and sending PROXY protocol:

• Receiving: Automatically detected from trusted proxy IPs (configured in proxyIPs)
• Sending: Enabled per-route or globally via sendProxyProtocol setting
• Real client IP is preserved and used for all connection tracking and security checks

Metrics and Throughput Calculation

The metrics system tracks throughput using per-second sampling:

1. Byte Recording: Bytes are recorded as data flows through connections
2. Sampling: Every second, accumulated bytes are stored as a sample
3. Rate Calculation: Throughput is calculated by summing bytes over a time window
4. Per-Route/IP Tracking: Separate ThroughputTracker instances for each route and IP

Key implementation details:

• Bytes are recorded in the bidirectional forwarding callbacks
• The instant() method returns throughput over the last 1 second
• The recent() method returns throughput over the last 10 seconds
• Custom windows can be specified for different averaging periods

Throughput Spikes Issue

There's a fundamental difference between application-layer and network-layer throughput:

Application Layer (what we measure):

• Bytes are recorded when delivered to/from the application
• Large chunks can arrive "instantly" due to kernel/Node.js buffering
• Shows spikes when buffers are flushed (e.g., 20MB in 1 second = 160 Mbit/s)

Network Layer (what Unifi shows):

• Actual packet flow through the network interface
• Limited by physical network speed (e.g., 20 Mbit/s)
• Data transfers over time, not in bursts

The spikes occur because:

1. Data flows over network at 20 Mbit/s (takes 8 seconds for 20MB)
2. Kernel/Node.js buffers this incoming data
3. When buffer is flushed, application receives large chunk at once
4. We record entire chunk in current second, creating artificial spike

Potential Solutions:

1. Use longer window for "instant" measurements (e.g., 5 seconds instead of 1)
2. Track socket write backpressure to estimate actual network flow
3. Implement bandwidth estimation based on connection duration
4. Accept that application-layer != network-layer throughput

Connection Limiting

Per-IP Connection Limits

• SmartProxy tracks connections per IP address in the SecurityManager
• Default limit is 100 connections per IP (configurable via maxConnectionsPerIP)
• Connection rate limiting is also enforced (default 300 connections/minute per IP)
• HttpProxy has been enhanced to also enforce per-IP limits when forwarding from SmartProxy

Route-Level Connection Limits

• Routes can define security.maxConnections to limit connections per route
• ConnectionManager tracks connections by route ID using a separate Map
• Limits are enforced in RouteConnectionHandler before forwarding
• Connection is tracked when route is matched: trackConnectionByRoute(routeId, connectionId)

HttpProxy Integration

• When SmartProxy forwards to HttpProxy for TLS termination, it sends a CLIENT_IP:<ip>\r\n header
• HttpProxy parses this header to track the real client IP, not the localhost IP
• This ensures per-IP limits are enforced even for forwarded connections
• The header is parsed in the connection handler before any data processing

Memory Optimization

• Periodic cleanup runs every 60 seconds to remove:
  • IPs with no active connections
  • Expired rate limit timestamps (older than 1 minute)
• Prevents memory accumulation from many unique IPs over time
• Cleanup is automatic and runs in background with unref() to not keep process alive

Connection Cleanup Queue

• Cleanup queue processes connections in batches to prevent overwhelming the system
• Race condition prevention using isProcessingCleanup flag
• Try-finally block ensures flag is always reset even if errors occur
• New connections added during processing are queued for next batch

Important Implementation Notes

• Always use NodeJS.Timeout type instead of NodeJS.Timer for interval/timeout references
• IPv4/IPv6 normalization is handled (e.g., ::ffff:127.0.0.1 and 127.0.0.1 are treated as the same IP)
• Connection limits are checked before route matching to prevent DoS attacks
• SharedSecurityManager supports checking route-level limits via optional parameter

Log Deduplication

To reduce log spam during high-traffic scenarios or attacks, SmartProxy implements log deduplication for repetitive events:

How It Works

• Similar log events are batched and aggregated over a 5-second window
• Instead of logging each event individually, a summary is emitted
• Events are grouped by type and deduplicated by key (e.g., IP address, reason)

Deduplicated Event Types

1. Connection Rejections (connection-rejected):

   • Groups by rejection reason (global-limit, route-limit, etc.)
   • Example: "Rejected 150 connections (reasons: global-limit: 100, route-limit: 50)"

2. IP Rejections (ip-rejected):

   • Groups by IP address
   • Shows top offenders with rejection counts and reasons
   • Example: "Rejected 500 connections from 10 IPs (top offenders: 192.168.1.100 (200x, rate-limit), ...)"

3. Connection Cleanups (connection-cleanup):

   • Groups by cleanup reason (normal, timeout, error, zombie, etc.)
   • Example: "Cleaned up 250 connections (reasons: normal: 200, timeout: 30, error: 20)"

4. IP Tracking Cleanup (ip-cleanup):

   • Summarizes periodic IP cleanup operations
   • Example: "IP tracking cleanup: removed 50 entries across 5 cleanup cycles"

Configuration

• Default flush interval: 5 seconds
• Maximum batch size: 100 events (triggers immediate flush)
• Global periodic flush: Every 10 seconds (ensures logs are emitted regularly)
• Process exit handling: Logs are flushed on SIGINT/SIGTERM

Benefits

• Reduces log volume during attacks or high traffic
• Provides better overview of patterns (e.g., which IPs are attacking)
• Improves log readability and analysis
• Prevents log storage overflow
• Maintains detailed information in aggregated form

Log Output Examples

Instead of hundreds of individual logs:

Connection rejected
Connection rejected
Connection rejected
... (repeated 500 times)

You'll see:

[SUMMARY] Rejected 500 connections from 10 IPs in 5s (top offenders: 192.168.1.100 (200x, rate-limit), 10.0.0.1 (150x, per-ip-limit))

Instead of:

Connection terminated: ::ffff:127.0.0.1 (client_closed). Active: 266
Connection terminated: ::ffff:127.0.0.1 (client_closed). Active: 265
... (repeated 266 times)

You'll see:

[SUMMARY] 266 HttpProxy connections terminated in 5s (reasons: client_closed: 266, activeConnections: 0)

Rapid Event Handling

• During attacks or high-volume scenarios, logs are flushed more frequently
• If 50+ events occur within 1 second, immediate flush is triggered
• Prevents memory buildup during flooding attacks
• Maintains real-time visibility during incidents